Detect more startup config errors on Cortex M (#832)

Verify that the application has correctly installed PendSV
and SVCall handlers. The application can choose to
disable these checks by setting configCHECK_HANDLER_INSTALLATION
to 0 in their FreeRTOSConfig.h.

include/FreeRTOS.h

@@ -365,6 +365,17 @@
     #define configPRECONDITION_DEFINED    1
 #endif
 
+#ifndef configCHECK_HANDLER_INSTALLATION
+    #define configCHECK_HANDLER_INSTALLATION    1
+#else
+
+/* The application has explicitly defined configCHECK_HANDLER_INSTALLATION
+ * to 1. The checks requires configASSERT() to be defined. */
+    #if ( ( configCHECK_HANDLER_INSTALLATION == 1 ) && ( configASSERT_DEFINED == 0 ) )
+        #error You must define configASSERT() when configCHECK_HANDLER_INSTALLATION is 1.
+    #endif
+#endif
+
 #ifndef portMEMORY_BARRIER
     #define portMEMORY_BARRIER()
 #endif

portable/ARMv8M/non_secure/port.c

@@ -80,6 +80,12 @@
 #endif
 /*-----------------------------------------------------------*/
 
+/**
+ * @brief Prototype of all Interrupt Service Routines (ISRs).
+ */
+typedef void ( * portISR_t )( void );
+/*-----------------------------------------------------------*/
+
 /**
  * @brief Constants required to manipulate the NVIC.
  */
@@ -101,10 +107,18 @@
 /**
  * @brief Constants required to manipulate the SCB.
  */
-#define portSCB_SYS_HANDLER_CTRL_STATE_REG    ( *( volatile uint32_t * ) 0xe000ed24 )
+#define portSCB_VTOR_REG                      ( *( ( portISR_t ** ) 0xe000ed08 ) )
+#define portSCB_SYS_HANDLER_CTRL_STATE_REG    ( *( ( volatile uint32_t * ) 0xe000ed24 ) )
 #define portSCB_MEM_FAULT_ENABLE_BIT          ( 1UL << 16UL )
 /*-----------------------------------------------------------*/
 
+/**
+ * @brief Constants used to check the installation of the FreeRTOS interrupt handlers.
+ */
+#define portVECTOR_INDEX_SVC       ( 11 )
+#define portVECTOR_INDEX_PENDSV    ( 14 )
+/*-----------------------------------------------------------*/
+
 /**
  * @brief Constants required to check the validity of an interrupt priority.
  */
@@ -1598,22 +1612,52 @@ void vPortSVCHandler_C( uint32_t * pulCallerStackAddress ) /* PRIVILEGED_FUNCTIO
 
 BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
 {
+    /* An application can install FreeRTOS interrupt handlers in one of the
+     * folllowing ways:
+     * 1. Direct Routing - Install the functions SVC_Handler and PendSV_Handler
+     *    for SVCall and PendSV interrupts respectively.
+     * 2. Indirect Routing - Install separate handlers for SVCall and PendSV
+     *    interrupts and route program control from those handlers to
+     *    SVC_Handler and PendSV_Handler functions.
+     *
+     * Applications that use Indirect Routing must set
+     * configCHECK_HANDLER_INSTALLATION to 0 in their FreeRTOSConfig.h. Direct
+     * routing, which is validated here when configCHECK_HANDLER_INSTALLATION
+     * is 1, should be preferred when possible. */
+    #if ( configCHECK_HANDLER_INSTALLATION == 1 )
+    {
+        const portISR_t * const pxVectorTable = portSCB_VTOR_REG;
+
+        /* Validate that the application has correctly installed the FreeRTOS
+         * handlers for SVCall and PendSV interrupts. We do not check the
+         * installation of the SysTick handler because the application may
+         * choose to drive the RTOS tick using a timer other than the SysTick
+         * timer by overriding the weak function vPortSetupTimerInterrupt().
+         *
+         * Assertion failures here indicate incorrect installation of the
+         * FreeRTOS handlers. For help installing the FreeRTOS handlers, see
+         * https://www.FreeRTOS.org/FAQHelp.html.
+         *
+         * Systems with a configurable address for the interrupt vector table
+         * can also encounter assertion failures or even system faults here if
+         * VTOR is not set correctly to point to the application's vector table. */
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_SVC ] == SVC_Handler );
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_PENDSV ] == PendSV_Handler );
+    }
+    #endif /* configCHECK_HANDLER_INSTALLATION */
+
     #if ( ( configASSERT_DEFINED == 1 ) && ( portHAS_ARMV8M_MAIN_EXTENSION == 1 ) )
     {
-        volatile uint32_t ulOriginalPriority;
         volatile uint32_t ulImplementedPrioBits = 0;
         volatile uint8_t ucMaxPriorityValue;
 
         /* Determine the maximum priority from which ISR safe FreeRTOS API
-         * functions can be called.  ISR safe functions are those that end in
+         * functions can be called. ISR safe functions are those that end in
-         * "FromISR".  FreeRTOS maintains separate thread and ISR API functions to
+         * "FromISR". FreeRTOS maintains separate thread and ISR API functions to
          * ensure interrupt entry is as fast and simple as possible.
          *
-         * Save the interrupt priority value that is about to be clobbered. */
+         * First, determine the number of priority bits available. Write to all
-        ulOriginalPriority = portNVIC_SHPR2_REG;
+         * possible bits in the priority setting for SVCall. */
-
-        /* Determine the number of priority bits available.  First write to all
-         * possible bits. */
         portNVIC_SHPR2_REG = 0xFF000000;
 
         /* Read the value back to see how many bits stuck. */
@@ -1636,7 +1680,6 @@ BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
 
         /* Calculate the maximum acceptable priority group value for the number
          * of bits read back. */
-
         while( ( ucMaxPriorityValue & portTOP_BIT_OF_BYTE ) == portTOP_BIT_OF_BYTE )
         {
             ulImplementedPrioBits++;
@@ -1674,16 +1717,14 @@ BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
          * register. */
         ulMaxPRIGROUPValue <<= portPRIGROUP_SHIFT;
         ulMaxPRIGROUPValue &= portPRIORITY_GROUP_MASK;
-
-        /* Restore the clobbered interrupt priority register to its original
-         * value. */
-        portNVIC_SHPR2_REG = ulOriginalPriority;
     }
     #endif /* #if ( ( configASSERT_DEFINED == 1 ) && ( portHAS_ARMV8M_MAIN_EXTENSION == 1 ) ) */
 
-    /* Make PendSV, CallSV and SysTick the same priority as the kernel. */
+    /* Make PendSV and SysTick the lowest priority interrupts, and make SVCall
+     * the highest priority. */
     portNVIC_SHPR3_REG |= portNVIC_PENDSV_PRI;
     portNVIC_SHPR3_REG |= portNVIC_SYSTICK_PRI;
+    portNVIC_SHPR2_REG = 0;
 
     #if ( configENABLE_MPU == 1 )
     {

portable/GCC/ARM_CM0/port.c

@@ -34,6 +34,9 @@
 #include "FreeRTOS.h"
 #include "task.h"
 
+/* Prototype of all Interrupt Service Routines (ISRs). */
+typedef void ( * portISR_t )( void );
+
 /* Constants required to manipulate the NVIC. */
 #define portNVIC_SYSTICK_CTRL_REG             ( *( ( volatile uint32_t * ) 0xe000e010 ) )
 #define portNVIC_SYSTICK_LOAD_REG             ( *( ( volatile uint32_t * ) 0xe000e014 ) )
@@ -51,6 +54,10 @@
 #define portNVIC_PENDSV_PRI                   ( portMIN_INTERRUPT_PRIORITY << 16UL )
 #define portNVIC_SYSTICK_PRI                  ( portMIN_INTERRUPT_PRIORITY << 24UL )
 
+/* Constants used to check the installation of the FreeRTOS interrupt handlers. */
+#define portSCB_VTOR_REG                      ( *( ( portISR_t ** ) 0xe000ed08 ) )
+#define portVECTOR_INDEX_PENDSV               ( 14 )
+
 /* Constants required to set up the initial stack. */
 #define portINITIAL_XPSR                      ( 0x01000000 )
 
@@ -200,20 +207,20 @@ void vPortSVCHandler( void )
 
 void vPortStartFirstTask( void )
 {
-    /* The MSP stack is not reset as, unlike on M3/4 parts, there is no vector
+    /* Don't reset the MSP stack as is done on CM3/4 devices. The vector table
-     * table offset register that can be used to locate the initial stack value.
+     * in some CM0 devices cannot be modified and thus may not hold the
-     * Not all M0 parts have the application vector table at address 0. */
+     * application's initial MSP value. */
     __asm volatile (
         "   .syntax unified             \n"
         "   ldr  r2, pxCurrentTCBConst2 \n"     /* Obtain location of pxCurrentTCB. */
         "   ldr  r3, [r2]               \n"
         "   ldr  r0, [r3]               \n"     /* The first item in pxCurrentTCB is the task top of stack. */
-        "   adds r0, #32                    \n" /* Discard everything up to r0. */
+        "   adds r0, #32                \n"     /* Discard everything up to r0. */
-        "   msr  psp, r0                    \n" /* This is now the new top of stack to use in the task. */
+        "   msr  psp, r0                \n"     /* This is now the new top of stack to use in the task. */
         "   movs r0, #2                 \n"     /* Switch to the psp stack. */
-        "   msr  CONTROL, r0                \n"
+        "   msr  CONTROL, r0            \n"
         "   isb                         \n"
-        "   pop  {r0-r5}                    \n" /* Pop the registers that are saved automatically. */
+        "   pop  {r0-r5}                \n"     /* Pop the registers that are saved automatically. */
         "   mov  lr, r5                 \n"     /* lr is now in r5. */
         "   pop  {r3}                   \n"     /* Return address is now in r3. */
         "   pop  {r2}                   \n"     /* Pop and discard XPSR. */
@@ -231,7 +238,42 @@ void vPortStartFirstTask( void )
  */
 BaseType_t xPortStartScheduler( void )
 {
-    /* Make PendSV, CallSV and SysTick the same priority as the kernel. */
+    /* An application can install FreeRTOS interrupt handlers in one of the
+     * folllowing ways:
+     * 1. Direct Routing - Install the function xPortPendSVHandler for PendSV
+     *    interrupt.
+     * 2. Indirect Routing - Install separate handler for PendSV interrupt and
+     *    route program control from that handler to xPortPendSVHandler function.
+     *
+     * Applications that use Indirect Routing must set
+     * configCHECK_HANDLER_INSTALLATION to 0 in their FreeRTOSConfig.h. Direct
+     * routing, which is validated here when configCHECK_HANDLER_INSTALLATION
+     * is 1, should be preferred when possible. */
+    #if ( configCHECK_HANDLER_INSTALLATION == 1 )
+    {
+        /* Point pxVectorTable to the interrupt vector table. Systems without
+         * a VTOR register provide the value zero in the VTOR register and
+         * the vector table itself is located at the address 0x00000000. */
+        const portISR_t * const pxVectorTable = portSCB_VTOR_REG;
+
+        /* Validate that the application has correctly installed the FreeRTOS
+         * handler for PendSV interrupt. We do not check the installation of the
+         * SysTick handler because the application may choose to drive the RTOS
+         * tick using a timer other than the SysTick timer by overriding the
+         * weak function vPortSetupTimerInterrupt().
+         *
+         * Assertion failures here indicate incorrect installation of the
+         * FreeRTOS handler. For help installing the FreeRTOS handler, see
+         * https://www.FreeRTOS.org/FAQHelp.html.
+         *
+         * Systems with a configurable address for the interrupt vector table
+         * can also encounter assertion failures or even system faults here if
+         * VTOR is not set correctly to point to the application's vector table. */
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_PENDSV ] == xPortPendSVHandler );
+    }
+    #endif /* configCHECK_HANDLER_INSTALLATION */
+
+    /* Make PendSV and SysTick the lowest priority interrupts. */
     portNVIC_SHPR3_REG |= portNVIC_PENDSV_PRI;
     portNVIC_SHPR3_REG |= portNVIC_SYSTICK_PRI;
 

portable/GCC/ARM_CM23/non_secure/port.c

@@ -80,6 +80,12 @@
 #endif
 /*-----------------------------------------------------------*/
 
+/**
+ * @brief Prototype of all Interrupt Service Routines (ISRs).
+ */
+typedef void ( * portISR_t )( void );
+/*-----------------------------------------------------------*/
+
 /**
  * @brief Constants required to manipulate the NVIC.
  */
@@ -101,10 +107,18 @@
 /**
  * @brief Constants required to manipulate the SCB.
  */
-#define portSCB_SYS_HANDLER_CTRL_STATE_REG    ( *( volatile uint32_t * ) 0xe000ed24 )
+#define portSCB_VTOR_REG                      ( *( ( portISR_t ** ) 0xe000ed08 ) )
+#define portSCB_SYS_HANDLER_CTRL_STATE_REG    ( *( ( volatile uint32_t * ) 0xe000ed24 ) )
 #define portSCB_MEM_FAULT_ENABLE_BIT          ( 1UL << 16UL )
 /*-----------------------------------------------------------*/
 
+/**
+ * @brief Constants used to check the installation of the FreeRTOS interrupt handlers.
+ */
+#define portVECTOR_INDEX_SVC       ( 11 )
+#define portVECTOR_INDEX_PENDSV    ( 14 )
+/*-----------------------------------------------------------*/
+
 /**
  * @brief Constants required to check the validity of an interrupt priority.
  */
@@ -1598,22 +1612,52 @@ void vPortSVCHandler_C( uint32_t * pulCallerStackAddress ) /* PRIVILEGED_FUNCTIO
 
 BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
 {
+    /* An application can install FreeRTOS interrupt handlers in one of the
+     * folllowing ways:
+     * 1. Direct Routing - Install the functions SVC_Handler and PendSV_Handler
+     *    for SVCall and PendSV interrupts respectively.
+     * 2. Indirect Routing - Install separate handlers for SVCall and PendSV
+     *    interrupts and route program control from those handlers to
+     *    SVC_Handler and PendSV_Handler functions.
+     *
+     * Applications that use Indirect Routing must set
+     * configCHECK_HANDLER_INSTALLATION to 0 in their FreeRTOSConfig.h. Direct
+     * routing, which is validated here when configCHECK_HANDLER_INSTALLATION
+     * is 1, should be preferred when possible. */
+    #if ( configCHECK_HANDLER_INSTALLATION == 1 )
+    {
+        const portISR_t * const pxVectorTable = portSCB_VTOR_REG;
+
+        /* Validate that the application has correctly installed the FreeRTOS
+         * handlers for SVCall and PendSV interrupts. We do not check the
+         * installation of the SysTick handler because the application may
+         * choose to drive the RTOS tick using a timer other than the SysTick
+         * timer by overriding the weak function vPortSetupTimerInterrupt().
+         *
+         * Assertion failures here indicate incorrect installation of the
+         * FreeRTOS handlers. For help installing the FreeRTOS handlers, see
+         * https://www.FreeRTOS.org/FAQHelp.html.
+         *
+         * Systems with a configurable address for the interrupt vector table
+         * can also encounter assertion failures or even system faults here if
+         * VTOR is not set correctly to point to the application's vector table. */
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_SVC ] == SVC_Handler );
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_PENDSV ] == PendSV_Handler );
+    }
+    #endif /* configCHECK_HANDLER_INSTALLATION */
+
     #if ( ( configASSERT_DEFINED == 1 ) && ( portHAS_ARMV8M_MAIN_EXTENSION == 1 ) )
     {
-        volatile uint32_t ulOriginalPriority;
         volatile uint32_t ulImplementedPrioBits = 0;
         volatile uint8_t ucMaxPriorityValue;
 
         /* Determine the maximum priority from which ISR safe FreeRTOS API
-         * functions can be called.  ISR safe functions are those that end in
+         * functions can be called. ISR safe functions are those that end in
-         * "FromISR".  FreeRTOS maintains separate thread and ISR API functions to
+         * "FromISR". FreeRTOS maintains separate thread and ISR API functions to
          * ensure interrupt entry is as fast and simple as possible.
          *
-         * Save the interrupt priority value that is about to be clobbered. */
+         * First, determine the number of priority bits available. Write to all
-        ulOriginalPriority = portNVIC_SHPR2_REG;
+         * possible bits in the priority setting for SVCall. */
-
-        /* Determine the number of priority bits available.  First write to all
-         * possible bits. */
         portNVIC_SHPR2_REG = 0xFF000000;
 
         /* Read the value back to see how many bits stuck. */
@@ -1636,7 +1680,6 @@ BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
 
         /* Calculate the maximum acceptable priority group value for the number
          * of bits read back. */
-
         while( ( ucMaxPriorityValue & portTOP_BIT_OF_BYTE ) == portTOP_BIT_OF_BYTE )
         {
             ulImplementedPrioBits++;
@@ -1674,16 +1717,14 @@ BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
          * register. */
         ulMaxPRIGROUPValue <<= portPRIGROUP_SHIFT;
         ulMaxPRIGROUPValue &= portPRIORITY_GROUP_MASK;
-
-        /* Restore the clobbered interrupt priority register to its original
-         * value. */
-        portNVIC_SHPR2_REG = ulOriginalPriority;
     }
     #endif /* #if ( ( configASSERT_DEFINED == 1 ) && ( portHAS_ARMV8M_MAIN_EXTENSION == 1 ) ) */
 
-    /* Make PendSV, CallSV and SysTick the same priority as the kernel. */
+    /* Make PendSV and SysTick the lowest priority interrupts, and make SVCall
+     * the highest priority. */
     portNVIC_SHPR3_REG |= portNVIC_PENDSV_PRI;
     portNVIC_SHPR3_REG |= portNVIC_SYSTICK_PRI;
+    portNVIC_SHPR2_REG = 0;
 
     #if ( configENABLE_MPU == 1 )
     {

portable/GCC/ARM_CM23_NTZ/non_secure/port.c

@@ -80,6 +80,12 @@
 #endif
 /*-----------------------------------------------------------*/
 
+/**
+ * @brief Prototype of all Interrupt Service Routines (ISRs).
+ */
+typedef void ( * portISR_t )( void );
+/*-----------------------------------------------------------*/
+
 /**
  * @brief Constants required to manipulate the NVIC.
  */
@@ -101,10 +107,18 @@
 /**
  * @brief Constants required to manipulate the SCB.
  */
-#define portSCB_SYS_HANDLER_CTRL_STATE_REG    ( *( volatile uint32_t * ) 0xe000ed24 )
+#define portSCB_VTOR_REG                      ( *( ( portISR_t ** ) 0xe000ed08 ) )
+#define portSCB_SYS_HANDLER_CTRL_STATE_REG    ( *( ( volatile uint32_t * ) 0xe000ed24 ) )
 #define portSCB_MEM_FAULT_ENABLE_BIT          ( 1UL << 16UL )
 /*-----------------------------------------------------------*/
 
+/**
+ * @brief Constants used to check the installation of the FreeRTOS interrupt handlers.
+ */
+#define portVECTOR_INDEX_SVC       ( 11 )
+#define portVECTOR_INDEX_PENDSV    ( 14 )
+/*-----------------------------------------------------------*/
+
 /**
  * @brief Constants required to check the validity of an interrupt priority.
  */
@@ -1598,22 +1612,52 @@ void vPortSVCHandler_C( uint32_t * pulCallerStackAddress ) /* PRIVILEGED_FUNCTIO
 
 BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
 {
+    /* An application can install FreeRTOS interrupt handlers in one of the
+     * folllowing ways:
+     * 1. Direct Routing - Install the functions SVC_Handler and PendSV_Handler
+     *    for SVCall and PendSV interrupts respectively.
+     * 2. Indirect Routing - Install separate handlers for SVCall and PendSV
+     *    interrupts and route program control from those handlers to
+     *    SVC_Handler and PendSV_Handler functions.
+     *
+     * Applications that use Indirect Routing must set
+     * configCHECK_HANDLER_INSTALLATION to 0 in their FreeRTOSConfig.h. Direct
+     * routing, which is validated here when configCHECK_HANDLER_INSTALLATION
+     * is 1, should be preferred when possible. */
+    #if ( configCHECK_HANDLER_INSTALLATION == 1 )
+    {
+        const portISR_t * const pxVectorTable = portSCB_VTOR_REG;
+
+        /* Validate that the application has correctly installed the FreeRTOS
+         * handlers for SVCall and PendSV interrupts. We do not check the
+         * installation of the SysTick handler because the application may
+         * choose to drive the RTOS tick using a timer other than the SysTick
+         * timer by overriding the weak function vPortSetupTimerInterrupt().
+         *
+         * Assertion failures here indicate incorrect installation of the
+         * FreeRTOS handlers. For help installing the FreeRTOS handlers, see
+         * https://www.FreeRTOS.org/FAQHelp.html.
+         *
+         * Systems with a configurable address for the interrupt vector table
+         * can also encounter assertion failures or even system faults here if
+         * VTOR is not set correctly to point to the application's vector table. */
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_SVC ] == SVC_Handler );
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_PENDSV ] == PendSV_Handler );
+    }
+    #endif /* configCHECK_HANDLER_INSTALLATION */
+
     #if ( ( configASSERT_DEFINED == 1 ) && ( portHAS_ARMV8M_MAIN_EXTENSION == 1 ) )
     {
-        volatile uint32_t ulOriginalPriority;
         volatile uint32_t ulImplementedPrioBits = 0;
         volatile uint8_t ucMaxPriorityValue;
 
         /* Determine the maximum priority from which ISR safe FreeRTOS API
-         * functions can be called.  ISR safe functions are those that end in
+         * functions can be called. ISR safe functions are those that end in
-         * "FromISR".  FreeRTOS maintains separate thread and ISR API functions to
+         * "FromISR". FreeRTOS maintains separate thread and ISR API functions to
          * ensure interrupt entry is as fast and simple as possible.
          *
-         * Save the interrupt priority value that is about to be clobbered. */
+         * First, determine the number of priority bits available. Write to all
-        ulOriginalPriority = portNVIC_SHPR2_REG;
+         * possible bits in the priority setting for SVCall. */
-
-        /* Determine the number of priority bits available.  First write to all
-         * possible bits. */
         portNVIC_SHPR2_REG = 0xFF000000;
 
         /* Read the value back to see how many bits stuck. */
@@ -1636,7 +1680,6 @@ BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
 
         /* Calculate the maximum acceptable priority group value for the number
          * of bits read back. */
-
         while( ( ucMaxPriorityValue & portTOP_BIT_OF_BYTE ) == portTOP_BIT_OF_BYTE )
         {
             ulImplementedPrioBits++;
@@ -1674,16 +1717,14 @@ BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
          * register. */
         ulMaxPRIGROUPValue <<= portPRIGROUP_SHIFT;
         ulMaxPRIGROUPValue &= portPRIORITY_GROUP_MASK;
-
-        /* Restore the clobbered interrupt priority register to its original
-         * value. */
-        portNVIC_SHPR2_REG = ulOriginalPriority;
     }
     #endif /* #if ( ( configASSERT_DEFINED == 1 ) && ( portHAS_ARMV8M_MAIN_EXTENSION == 1 ) ) */
 
-    /* Make PendSV, CallSV and SysTick the same priority as the kernel. */
+    /* Make PendSV and SysTick the lowest priority interrupts, and make SVCall
+     * the highest priority. */
     portNVIC_SHPR3_REG |= portNVIC_PENDSV_PRI;
     portNVIC_SHPR3_REG |= portNVIC_SYSTICK_PRI;
+    portNVIC_SHPR2_REG = 0;
 
     #if ( configENABLE_MPU == 1 )
     {

portable/GCC/ARM_CM3/port.c

@@ -34,10 +34,14 @@
 #include "FreeRTOS.h"
 #include "task.h"
 
+/* Prototype of all Interrupt Service Routines (ISRs). */
+typedef void ( * portISR_t )( void );
+
 /* Constants required to manipulate the core.  Registers first... */
 #define portNVIC_SYSTICK_CTRL_REG             ( *( ( volatile uint32_t * ) 0xe000e010 ) )
 #define portNVIC_SYSTICK_LOAD_REG             ( *( ( volatile uint32_t * ) 0xe000e014 ) )
 #define portNVIC_SYSTICK_CURRENT_VALUE_REG    ( *( ( volatile uint32_t * ) 0xe000e018 ) )
+#define portNVIC_SHPR2_REG                    ( *( ( volatile uint32_t * ) 0xe000ed1c ) )
 #define portNVIC_SHPR3_REG                    ( *( ( volatile uint32_t * ) 0xe000ed20 ) )
 /* ...then bits in the registers. */
 #define portNVIC_SYSTICK_CLK_BIT              ( 1UL << 2UL )
@@ -52,6 +56,11 @@
 #define portNVIC_PENDSV_PRI                   ( ( ( uint32_t ) portMIN_INTERRUPT_PRIORITY ) << 16UL )
 #define portNVIC_SYSTICK_PRI                  ( ( ( uint32_t ) portMIN_INTERRUPT_PRIORITY ) << 24UL )
 
+/* Constants used to check the installation of the FreeRTOS interrupt handlers. */
+#define portSCB_VTOR_REG                      ( *( ( portISR_t ** ) 0xE000ED08 ) )
+#define portVECTOR_INDEX_SVC                  ( 11 )
+#define portVECTOR_INDEX_PENDSV               ( 14 )
+
 /* Constants required to check the validity of an interrupt priority. */
 #define portFIRST_USER_INTERRUPT_NUMBER       ( 16 )
 #define portNVIC_IP_REGISTERS_OFFSET_16       ( 0xE000E3F0 )
@@ -259,6 +268,40 @@ static void prvPortStartFirstTask( void )
  */
 BaseType_t xPortStartScheduler( void )
 {
+    /* An application can install FreeRTOS interrupt handlers in one of the
+     * folllowing ways:
+     * 1. Direct Routing - Install the functions vPortSVCHandler and
+     *    xPortPendSVHandler for SVCall and PendSV interrupts respectively.
+     * 2. Indirect Routing - Install separate handlers for SVCall and PendSV
+     *    interrupts and route program control from those handlers to
+     *    vPortSVCHandler and xPortPendSVHandler functions.
+     *
+     * Applications that use Indirect Routing must set
+     * configCHECK_HANDLER_INSTALLATION to 0 in their FreeRTOSConfig.h. Direct
+     * routing, which is validated here when configCHECK_HANDLER_INSTALLATION
+     * is 1, should be preferred when possible. */
+    #if ( configCHECK_HANDLER_INSTALLATION == 1 )
+    {
+        const portISR_t * const pxVectorTable = portSCB_VTOR_REG;
+
+        /* Validate that the application has correctly installed the FreeRTOS
+         * handlers for SVCall and PendSV interrupts. We do not check the
+         * installation of the SysTick handler because the application may
+         * choose to drive the RTOS tick using a timer other than the SysTick
+         * timer by overriding the weak function vPortSetupTimerInterrupt().
+         *
+         * Assertion failures here indicate incorrect installation of the
+         * FreeRTOS handlers. For help installing the FreeRTOS handlers, see
+         * https://www.FreeRTOS.org/FAQHelp.html.
+         *
+         * Systems with a configurable address for the interrupt vector table
+         * can also encounter assertion failures or even system faults here if
+         * VTOR is not set correctly to point to the application's vector table. */
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_SVC ] == vPortSVCHandler );
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_PENDSV ] == xPortPendSVHandler );
+    }
+    #endif /* configCHECK_HANDLER_INSTALLATION */
+
     #if ( configASSERT_DEFINED == 1 )
     {
         volatile uint8_t ucOriginalPriority;
@@ -343,9 +386,11 @@ BaseType_t xPortStartScheduler( void )
     }
     #endif /* configASSERT_DEFINED */
 
-    /* Make PendSV and SysTick the lowest priority interrupts. */
+    /* Make PendSV and SysTick the lowest priority interrupts, and make SVCall
+     * the highest priority. */
     portNVIC_SHPR3_REG |= portNVIC_PENDSV_PRI;
     portNVIC_SHPR3_REG |= portNVIC_SYSTICK_PRI;
+    portNVIC_SHPR2_REG = 0;
 
     /* Start the timer that generates the tick ISR.  Interrupts are disabled
      * here already. */

portable/GCC/ARM_CM33/non_secure/port.c

@@ -80,6 +80,12 @@
 #endif
 /*-----------------------------------------------------------*/
 
+/**
+ * @brief Prototype of all Interrupt Service Routines (ISRs).
+ */
+typedef void ( * portISR_t )( void );
+/*-----------------------------------------------------------*/
+
 /**
  * @brief Constants required to manipulate the NVIC.
  */
@@ -101,10 +107,18 @@
 /**
  * @brief Constants required to manipulate the SCB.
  */
-#define portSCB_SYS_HANDLER_CTRL_STATE_REG    ( *( volatile uint32_t * ) 0xe000ed24 )
+#define portSCB_VTOR_REG                      ( *( ( portISR_t ** ) 0xe000ed08 ) )
+#define portSCB_SYS_HANDLER_CTRL_STATE_REG    ( *( ( volatile uint32_t * ) 0xe000ed24 ) )
 #define portSCB_MEM_FAULT_ENABLE_BIT          ( 1UL << 16UL )
 /*-----------------------------------------------------------*/
 
+/**
+ * @brief Constants used to check the installation of the FreeRTOS interrupt handlers.
+ */
+#define portVECTOR_INDEX_SVC       ( 11 )
+#define portVECTOR_INDEX_PENDSV    ( 14 )
+/*-----------------------------------------------------------*/
+
 /**
  * @brief Constants required to check the validity of an interrupt priority.
  */
@@ -1598,22 +1612,52 @@ void vPortSVCHandler_C( uint32_t * pulCallerStackAddress ) /* PRIVILEGED_FUNCTIO
 
 BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
 {
+    /* An application can install FreeRTOS interrupt handlers in one of the
+     * folllowing ways:
+     * 1. Direct Routing - Install the functions SVC_Handler and PendSV_Handler
+     *    for SVCall and PendSV interrupts respectively.
+     * 2. Indirect Routing - Install separate handlers for SVCall and PendSV
+     *    interrupts and route program control from those handlers to
+     *    SVC_Handler and PendSV_Handler functions.
+     *
+     * Applications that use Indirect Routing must set
+     * configCHECK_HANDLER_INSTALLATION to 0 in their FreeRTOSConfig.h. Direct
+     * routing, which is validated here when configCHECK_HANDLER_INSTALLATION
+     * is 1, should be preferred when possible. */
+    #if ( configCHECK_HANDLER_INSTALLATION == 1 )
+    {
+        const portISR_t * const pxVectorTable = portSCB_VTOR_REG;
+
+        /* Validate that the application has correctly installed the FreeRTOS
+         * handlers for SVCall and PendSV interrupts. We do not check the
+         * installation of the SysTick handler because the application may
+         * choose to drive the RTOS tick using a timer other than the SysTick
+         * timer by overriding the weak function vPortSetupTimerInterrupt().
+         *
+         * Assertion failures here indicate incorrect installation of the
+         * FreeRTOS handlers. For help installing the FreeRTOS handlers, see
+         * https://www.FreeRTOS.org/FAQHelp.html.
+         *
+         * Systems with a configurable address for the interrupt vector table
+         * can also encounter assertion failures or even system faults here if
+         * VTOR is not set correctly to point to the application's vector table. */
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_SVC ] == SVC_Handler );
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_PENDSV ] == PendSV_Handler );
+    }
+    #endif /* configCHECK_HANDLER_INSTALLATION */
+
     #if ( ( configASSERT_DEFINED == 1 ) && ( portHAS_ARMV8M_MAIN_EXTENSION == 1 ) )
     {
-        volatile uint32_t ulOriginalPriority;
         volatile uint32_t ulImplementedPrioBits = 0;
         volatile uint8_t ucMaxPriorityValue;
 
         /* Determine the maximum priority from which ISR safe FreeRTOS API
-         * functions can be called.  ISR safe functions are those that end in
+         * functions can be called. ISR safe functions are those that end in
-         * "FromISR".  FreeRTOS maintains separate thread and ISR API functions to
+         * "FromISR". FreeRTOS maintains separate thread and ISR API functions to
          * ensure interrupt entry is as fast and simple as possible.
          *
-         * Save the interrupt priority value that is about to be clobbered. */
+         * First, determine the number of priority bits available. Write to all
-        ulOriginalPriority = portNVIC_SHPR2_REG;
+         * possible bits in the priority setting for SVCall. */
-
-        /* Determine the number of priority bits available.  First write to all
-         * possible bits. */
         portNVIC_SHPR2_REG = 0xFF000000;
 
         /* Read the value back to see how many bits stuck. */
@@ -1636,7 +1680,6 @@ BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
 
         /* Calculate the maximum acceptable priority group value for the number
          * of bits read back. */
-
         while( ( ucMaxPriorityValue & portTOP_BIT_OF_BYTE ) == portTOP_BIT_OF_BYTE )
         {
             ulImplementedPrioBits++;
@@ -1674,16 +1717,14 @@ BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
          * register. */
         ulMaxPRIGROUPValue <<= portPRIGROUP_SHIFT;
         ulMaxPRIGROUPValue &= portPRIORITY_GROUP_MASK;
-
-        /* Restore the clobbered interrupt priority register to its original
-         * value. */
-        portNVIC_SHPR2_REG = ulOriginalPriority;
     }
     #endif /* #if ( ( configASSERT_DEFINED == 1 ) && ( portHAS_ARMV8M_MAIN_EXTENSION == 1 ) ) */
 
-    /* Make PendSV, CallSV and SysTick the same priority as the kernel. */
+    /* Make PendSV and SysTick the lowest priority interrupts, and make SVCall
+     * the highest priority. */
     portNVIC_SHPR3_REG |= portNVIC_PENDSV_PRI;
     portNVIC_SHPR3_REG |= portNVIC_SYSTICK_PRI;
+    portNVIC_SHPR2_REG = 0;
 
     #if ( configENABLE_MPU == 1 )
     {

portable/GCC/ARM_CM33_NTZ/non_secure/port.c

@@ -80,6 +80,12 @@
 #endif
 /*-----------------------------------------------------------*/
 
+/**
+ * @brief Prototype of all Interrupt Service Routines (ISRs).
+ */
+typedef void ( * portISR_t )( void );
+/*-----------------------------------------------------------*/
+
 /**
  * @brief Constants required to manipulate the NVIC.
  */
@@ -101,10 +107,18 @@
 /**
  * @brief Constants required to manipulate the SCB.
  */
-#define portSCB_SYS_HANDLER_CTRL_STATE_REG    ( *( volatile uint32_t * ) 0xe000ed24 )
+#define portSCB_VTOR_REG                      ( *( ( portISR_t ** ) 0xe000ed08 ) )
+#define portSCB_SYS_HANDLER_CTRL_STATE_REG    ( *( ( volatile uint32_t * ) 0xe000ed24 ) )
 #define portSCB_MEM_FAULT_ENABLE_BIT          ( 1UL << 16UL )
 /*-----------------------------------------------------------*/
 
+/**
+ * @brief Constants used to check the installation of the FreeRTOS interrupt handlers.
+ */
+#define portVECTOR_INDEX_SVC       ( 11 )
+#define portVECTOR_INDEX_PENDSV    ( 14 )
+/*-----------------------------------------------------------*/
+
 /**
  * @brief Constants required to check the validity of an interrupt priority.
  */
@@ -1598,22 +1612,52 @@ void vPortSVCHandler_C( uint32_t * pulCallerStackAddress ) /* PRIVILEGED_FUNCTIO
 
 BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
 {
+    /* An application can install FreeRTOS interrupt handlers in one of the
+     * folllowing ways:
+     * 1. Direct Routing - Install the functions SVC_Handler and PendSV_Handler
+     *    for SVCall and PendSV interrupts respectively.
+     * 2. Indirect Routing - Install separate handlers for SVCall and PendSV
+     *    interrupts and route program control from those handlers to
+     *    SVC_Handler and PendSV_Handler functions.
+     *
+     * Applications that use Indirect Routing must set
+     * configCHECK_HANDLER_INSTALLATION to 0 in their FreeRTOSConfig.h. Direct
+     * routing, which is validated here when configCHECK_HANDLER_INSTALLATION
+     * is 1, should be preferred when possible. */
+    #if ( configCHECK_HANDLER_INSTALLATION == 1 )
+    {
+        const portISR_t * const pxVectorTable = portSCB_VTOR_REG;
+
+        /* Validate that the application has correctly installed the FreeRTOS
+         * handlers for SVCall and PendSV interrupts. We do not check the
+         * installation of the SysTick handler because the application may
+         * choose to drive the RTOS tick using a timer other than the SysTick
+         * timer by overriding the weak function vPortSetupTimerInterrupt().
+         *
+         * Assertion failures here indicate incorrect installation of the
+         * FreeRTOS handlers. For help installing the FreeRTOS handlers, see
+         * https://www.FreeRTOS.org/FAQHelp.html.
+         *
+         * Systems with a configurable address for the interrupt vector table
+         * can also encounter assertion failures or even system faults here if
+         * VTOR is not set correctly to point to the application's vector table. */
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_SVC ] == SVC_Handler );
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_PENDSV ] == PendSV_Handler );
+    }
+    #endif /* configCHECK_HANDLER_INSTALLATION */
+
     #if ( ( configASSERT_DEFINED == 1 ) && ( portHAS_ARMV8M_MAIN_EXTENSION == 1 ) )
     {
-        volatile uint32_t ulOriginalPriority;
         volatile uint32_t ulImplementedPrioBits = 0;
         volatile uint8_t ucMaxPriorityValue;
 
         /* Determine the maximum priority from which ISR safe FreeRTOS API
-         * functions can be called.  ISR safe functions are those that end in
+         * functions can be called. ISR safe functions are those that end in
-         * "FromISR".  FreeRTOS maintains separate thread and ISR API functions to
+         * "FromISR". FreeRTOS maintains separate thread and ISR API functions to
          * ensure interrupt entry is as fast and simple as possible.
          *
-         * Save the interrupt priority value that is about to be clobbered. */
+         * First, determine the number of priority bits available. Write to all
-        ulOriginalPriority = portNVIC_SHPR2_REG;
+         * possible bits in the priority setting for SVCall. */
-
-        /* Determine the number of priority bits available.  First write to all
-         * possible bits. */
         portNVIC_SHPR2_REG = 0xFF000000;
 
         /* Read the value back to see how many bits stuck. */
@@ -1636,7 +1680,6 @@ BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
 
         /* Calculate the maximum acceptable priority group value for the number
          * of bits read back. */
-
         while( ( ucMaxPriorityValue & portTOP_BIT_OF_BYTE ) == portTOP_BIT_OF_BYTE )
         {
             ulImplementedPrioBits++;
@@ -1674,16 +1717,14 @@ BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
          * register. */
         ulMaxPRIGROUPValue <<= portPRIGROUP_SHIFT;
         ulMaxPRIGROUPValue &= portPRIORITY_GROUP_MASK;
-
-        /* Restore the clobbered interrupt priority register to its original
-         * value. */
-        portNVIC_SHPR2_REG = ulOriginalPriority;
     }
     #endif /* #if ( ( configASSERT_DEFINED == 1 ) && ( portHAS_ARMV8M_MAIN_EXTENSION == 1 ) ) */
 
-    /* Make PendSV, CallSV and SysTick the same priority as the kernel. */
+    /* Make PendSV and SysTick the lowest priority interrupts, and make SVCall
+     * the highest priority. */
     portNVIC_SHPR3_REG |= portNVIC_PENDSV_PRI;
     portNVIC_SHPR3_REG |= portNVIC_SYSTICK_PRI;
+    portNVIC_SHPR2_REG = 0;
 
     #if ( configENABLE_MPU == 1 )
     {

portable/GCC/ARM_CM35P/non_secure/port.c

@@ -80,6 +80,12 @@
 #endif
 /*-----------------------------------------------------------*/
 
+/**
+ * @brief Prototype of all Interrupt Service Routines (ISRs).
+ */
+typedef void ( * portISR_t )( void );
+/*-----------------------------------------------------------*/
+
 /**
  * @brief Constants required to manipulate the NVIC.
  */
@@ -101,10 +107,18 @@
 /**
  * @brief Constants required to manipulate the SCB.
  */
-#define portSCB_SYS_HANDLER_CTRL_STATE_REG    ( *( volatile uint32_t * ) 0xe000ed24 )
+#define portSCB_VTOR_REG                      ( *( ( portISR_t ** ) 0xe000ed08 ) )
+#define portSCB_SYS_HANDLER_CTRL_STATE_REG    ( *( ( volatile uint32_t * ) 0xe000ed24 ) )
 #define portSCB_MEM_FAULT_ENABLE_BIT          ( 1UL << 16UL )
 /*-----------------------------------------------------------*/
 
+/**
+ * @brief Constants used to check the installation of the FreeRTOS interrupt handlers.
+ */
+#define portVECTOR_INDEX_SVC       ( 11 )
+#define portVECTOR_INDEX_PENDSV    ( 14 )
+/*-----------------------------------------------------------*/
+
 /**
  * @brief Constants required to check the validity of an interrupt priority.
  */
@@ -1598,22 +1612,52 @@ void vPortSVCHandler_C( uint32_t * pulCallerStackAddress ) /* PRIVILEGED_FUNCTIO
 
 BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
 {
+    /* An application can install FreeRTOS interrupt handlers in one of the
+     * folllowing ways:
+     * 1. Direct Routing - Install the functions SVC_Handler and PendSV_Handler
+     *    for SVCall and PendSV interrupts respectively.
+     * 2. Indirect Routing - Install separate handlers for SVCall and PendSV
+     *    interrupts and route program control from those handlers to
+     *    SVC_Handler and PendSV_Handler functions.
+     *
+     * Applications that use Indirect Routing must set
+     * configCHECK_HANDLER_INSTALLATION to 0 in their FreeRTOSConfig.h. Direct
+     * routing, which is validated here when configCHECK_HANDLER_INSTALLATION
+     * is 1, should be preferred when possible. */
+    #if ( configCHECK_HANDLER_INSTALLATION == 1 )
+    {
+        const portISR_t * const pxVectorTable = portSCB_VTOR_REG;
+
+        /* Validate that the application has correctly installed the FreeRTOS
+         * handlers for SVCall and PendSV interrupts. We do not check the
+         * installation of the SysTick handler because the application may
+         * choose to drive the RTOS tick using a timer other than the SysTick
+         * timer by overriding the weak function vPortSetupTimerInterrupt().
+         *
+         * Assertion failures here indicate incorrect installation of the
+         * FreeRTOS handlers. For help installing the FreeRTOS handlers, see
+         * https://www.FreeRTOS.org/FAQHelp.html.
+         *
+         * Systems with a configurable address for the interrupt vector table
+         * can also encounter assertion failures or even system faults here if
+         * VTOR is not set correctly to point to the application's vector table. */
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_SVC ] == SVC_Handler );
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_PENDSV ] == PendSV_Handler );
+    }
+    #endif /* configCHECK_HANDLER_INSTALLATION */
+
     #if ( ( configASSERT_DEFINED == 1 ) && ( portHAS_ARMV8M_MAIN_EXTENSION == 1 ) )
     {
-        volatile uint32_t ulOriginalPriority;
         volatile uint32_t ulImplementedPrioBits = 0;
         volatile uint8_t ucMaxPriorityValue;
 
         /* Determine the maximum priority from which ISR safe FreeRTOS API
-         * functions can be called.  ISR safe functions are those that end in
+         * functions can be called. ISR safe functions are those that end in
-         * "FromISR".  FreeRTOS maintains separate thread and ISR API functions to
+         * "FromISR". FreeRTOS maintains separate thread and ISR API functions to
          * ensure interrupt entry is as fast and simple as possible.
          *
-         * Save the interrupt priority value that is about to be clobbered. */
+         * First, determine the number of priority bits available. Write to all
-        ulOriginalPriority = portNVIC_SHPR2_REG;
+         * possible bits in the priority setting for SVCall. */
-
-        /* Determine the number of priority bits available.  First write to all
-         * possible bits. */
         portNVIC_SHPR2_REG = 0xFF000000;
 
         /* Read the value back to see how many bits stuck. */
@@ -1636,7 +1680,6 @@ BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
 
         /* Calculate the maximum acceptable priority group value for the number
          * of bits read back. */
-
         while( ( ucMaxPriorityValue & portTOP_BIT_OF_BYTE ) == portTOP_BIT_OF_BYTE )
         {
             ulImplementedPrioBits++;
@@ -1674,16 +1717,14 @@ BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
          * register. */
         ulMaxPRIGROUPValue <<= portPRIGROUP_SHIFT;
         ulMaxPRIGROUPValue &= portPRIORITY_GROUP_MASK;
-
-        /* Restore the clobbered interrupt priority register to its original
-         * value. */
-        portNVIC_SHPR2_REG = ulOriginalPriority;
     }
     #endif /* #if ( ( configASSERT_DEFINED == 1 ) && ( portHAS_ARMV8M_MAIN_EXTENSION == 1 ) ) */
 
-    /* Make PendSV, CallSV and SysTick the same priority as the kernel. */
+    /* Make PendSV and SysTick the lowest priority interrupts, and make SVCall
+     * the highest priority. */
     portNVIC_SHPR3_REG |= portNVIC_PENDSV_PRI;
     portNVIC_SHPR3_REG |= portNVIC_SYSTICK_PRI;
+    portNVIC_SHPR2_REG = 0;
 
     #if ( configENABLE_MPU == 1 )
     {

portable/GCC/ARM_CM35P_NTZ/non_secure/port.c

@@ -80,6 +80,12 @@
 #endif
 /*-----------------------------------------------------------*/
 
+/**
+ * @brief Prototype of all Interrupt Service Routines (ISRs).
+ */
+typedef void ( * portISR_t )( void );
+/*-----------------------------------------------------------*/
+
 /**
  * @brief Constants required to manipulate the NVIC.
  */
@@ -101,10 +107,18 @@
 /**
  * @brief Constants required to manipulate the SCB.
  */
-#define portSCB_SYS_HANDLER_CTRL_STATE_REG    ( *( volatile uint32_t * ) 0xe000ed24 )
+#define portSCB_VTOR_REG                      ( *( ( portISR_t ** ) 0xe000ed08 ) )
+#define portSCB_SYS_HANDLER_CTRL_STATE_REG    ( *( ( volatile uint32_t * ) 0xe000ed24 ) )
 #define portSCB_MEM_FAULT_ENABLE_BIT          ( 1UL << 16UL )
 /*-----------------------------------------------------------*/
 
+/**
+ * @brief Constants used to check the installation of the FreeRTOS interrupt handlers.
+ */
+#define portVECTOR_INDEX_SVC       ( 11 )
+#define portVECTOR_INDEX_PENDSV    ( 14 )
+/*-----------------------------------------------------------*/
+
 /**
  * @brief Constants required to check the validity of an interrupt priority.
  */
@@ -1598,22 +1612,52 @@ void vPortSVCHandler_C( uint32_t * pulCallerStackAddress ) /* PRIVILEGED_FUNCTIO
 
 BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
 {
+    /* An application can install FreeRTOS interrupt handlers in one of the
+     * folllowing ways:
+     * 1. Direct Routing - Install the functions SVC_Handler and PendSV_Handler
+     *    for SVCall and PendSV interrupts respectively.
+     * 2. Indirect Routing - Install separate handlers for SVCall and PendSV
+     *    interrupts and route program control from those handlers to
+     *    SVC_Handler and PendSV_Handler functions.
+     *
+     * Applications that use Indirect Routing must set
+     * configCHECK_HANDLER_INSTALLATION to 0 in their FreeRTOSConfig.h. Direct
+     * routing, which is validated here when configCHECK_HANDLER_INSTALLATION
+     * is 1, should be preferred when possible. */
+    #if ( configCHECK_HANDLER_INSTALLATION == 1 )
+    {
+        const portISR_t * const pxVectorTable = portSCB_VTOR_REG;
+
+        /* Validate that the application has correctly installed the FreeRTOS
+         * handlers for SVCall and PendSV interrupts. We do not check the
+         * installation of the SysTick handler because the application may
+         * choose to drive the RTOS tick using a timer other than the SysTick
+         * timer by overriding the weak function vPortSetupTimerInterrupt().
+         *
+         * Assertion failures here indicate incorrect installation of the
+         * FreeRTOS handlers. For help installing the FreeRTOS handlers, see
+         * https://www.FreeRTOS.org/FAQHelp.html.
+         *
+         * Systems with a configurable address for the interrupt vector table
+         * can also encounter assertion failures or even system faults here if
+         * VTOR is not set correctly to point to the application's vector table. */
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_SVC ] == SVC_Handler );
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_PENDSV ] == PendSV_Handler );
+    }
+    #endif /* configCHECK_HANDLER_INSTALLATION */
+
     #if ( ( configASSERT_DEFINED == 1 ) && ( portHAS_ARMV8M_MAIN_EXTENSION == 1 ) )
     {
-        volatile uint32_t ulOriginalPriority;
         volatile uint32_t ulImplementedPrioBits = 0;
         volatile uint8_t ucMaxPriorityValue;
 
         /* Determine the maximum priority from which ISR safe FreeRTOS API
-         * functions can be called.  ISR safe functions are those that end in
+         * functions can be called. ISR safe functions are those that end in
-         * "FromISR".  FreeRTOS maintains separate thread and ISR API functions to
+         * "FromISR". FreeRTOS maintains separate thread and ISR API functions to
          * ensure interrupt entry is as fast and simple as possible.
          *
-         * Save the interrupt priority value that is about to be clobbered. */
+         * First, determine the number of priority bits available. Write to all
-        ulOriginalPriority = portNVIC_SHPR2_REG;
+         * possible bits in the priority setting for SVCall. */
-
-        /* Determine the number of priority bits available.  First write to all
-         * possible bits. */
         portNVIC_SHPR2_REG = 0xFF000000;
 
         /* Read the value back to see how many bits stuck. */
@@ -1636,7 +1680,6 @@ BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
 
         /* Calculate the maximum acceptable priority group value for the number
          * of bits read back. */
-
         while( ( ucMaxPriorityValue & portTOP_BIT_OF_BYTE ) == portTOP_BIT_OF_BYTE )
         {
             ulImplementedPrioBits++;
@@ -1674,16 +1717,14 @@ BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
          * register. */
         ulMaxPRIGROUPValue <<= portPRIGROUP_SHIFT;
         ulMaxPRIGROUPValue &= portPRIORITY_GROUP_MASK;
-
-        /* Restore the clobbered interrupt priority register to its original
-         * value. */
-        portNVIC_SHPR2_REG = ulOriginalPriority;
     }
     #endif /* #if ( ( configASSERT_DEFINED == 1 ) && ( portHAS_ARMV8M_MAIN_EXTENSION == 1 ) ) */
 
-    /* Make PendSV, CallSV and SysTick the same priority as the kernel. */
+    /* Make PendSV and SysTick the lowest priority interrupts, and make SVCall
+     * the highest priority. */
     portNVIC_SHPR3_REG |= portNVIC_PENDSV_PRI;
     portNVIC_SHPR3_REG |= portNVIC_SYSTICK_PRI;
+    portNVIC_SHPR2_REG = 0;
 
     #if ( configENABLE_MPU == 1 )
     {

portable/GCC/ARM_CM3_MPU/port.c

@@ -58,6 +58,9 @@
     #define configALLOW_UNPRIVILEGED_CRITICAL_SECTIONS    1
 #endif
 
+/* Prototype of all Interrupt Service Routines (ISRs). */
+typedef void ( * portISR_t )( void );
+
 /* Constants required to access and manipulate the NVIC. */
 #define portNVIC_SYSTICK_CTRL_REG                 ( *( ( volatile uint32_t * ) 0xe000e010 ) )
 #define portNVIC_SYSTICK_LOAD_REG                 ( *( ( volatile uint32_t * ) 0xe000e014 ) )
@@ -87,7 +90,6 @@
 #define portMIN_INTERRUPT_PRIORITY                ( 255UL )
 #define portNVIC_PENDSV_PRI                       ( ( ( uint32_t ) portMIN_INTERRUPT_PRIORITY ) << 16UL )
 #define portNVIC_SYSTICK_PRI                      ( ( ( uint32_t ) portMIN_INTERRUPT_PRIORITY ) << 24UL )
-#define portNVIC_SVC_PRI                          ( ( ( uint32_t ) configMAX_SYSCALL_INTERRUPT_PRIORITY - 1UL ) << 24UL )
 
 /* Constants required to set up the initial stack. */
 #define portINITIAL_XPSR                          ( 0x01000000 )
@@ -95,6 +97,11 @@
 #define portINITIAL_CONTROL_IF_UNPRIVILEGED       ( 0x03 )
 #define portINITIAL_CONTROL_IF_PRIVILEGED         ( 0x02 )
 
+/* Constants used to check the installation of the FreeRTOS interrupt handlers. */
+#define portSCB_VTOR_REG                          ( *( ( portISR_t ** ) 0xE000ED08 ) )
+#define portVECTOR_INDEX_SVC                      ( 11 )
+#define portVECTOR_INDEX_PENDSV                   ( 14 )
+
 /* Constants required to check the validity of an interrupt priority. */
 #define portFIRST_USER_INTERRUPT_NUMBER           ( 16 )
 #define portNVIC_IP_REGISTERS_OFFSET_16           ( 0xE000E3F0 )
@@ -414,7 +421,6 @@ void vSVCHandler_C( uint32_t * pulParam ) /* PRIVILEGED_FUNCTION */
     switch( ucSVCNumber )
     {
         case portSVC_START_SCHEDULER:
-            portNVIC_SHPR2_REG |= portNVIC_SVC_PRI;
             prvRestoreContextOfFirstTask();
             break;
 
@@ -737,6 +743,40 @@ static void prvRestoreContextOfFirstTask( void )
  */
 BaseType_t xPortStartScheduler( void )
 {
+    /* An application can install FreeRTOS interrupt handlers in one of the
+     * folllowing ways:
+     * 1. Direct Routing - Install the functions vPortSVCHandler and
+     *    xPortPendSVHandler for SVCall and PendSV interrupts respectively.
+     * 2. Indirect Routing - Install separate handlers for SVCall and PendSV
+     *    interrupts and route program control from those handlers to
+     *    vPortSVCHandler and xPortPendSVHandler functions.
+     *
+     * Applications that use Indirect Routing must set
+     * configCHECK_HANDLER_INSTALLATION to 0 in their FreeRTOSConfig.h. Direct
+     * routing, which is validated here when configCHECK_HANDLER_INSTALLATION
+     * is 1, should be preferred when possible. */
+    #if ( configCHECK_HANDLER_INSTALLATION == 1 )
+    {
+        const portISR_t * const pxVectorTable = portSCB_VTOR_REG;
+
+        /* Validate that the application has correctly installed the FreeRTOS
+         * handlers for SVCall and PendSV interrupts. We do not check the
+         * installation of the SysTick handler because the application may
+         * choose to drive the RTOS tick using a timer other than the SysTick
+         * timer by overriding the weak function vPortSetupTimerInterrupt().
+         *
+         * Assertion failures here indicate incorrect installation of the
+         * FreeRTOS handlers. For help installing the FreeRTOS handlers, see
+         * https://www.FreeRTOS.org/FAQHelp.html.
+         *
+         * Systems with a configurable address for the interrupt vector table
+         * can also encounter assertion failures or even system faults here if
+         * VTOR is not set correctly to point to the application's vector table. */
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_SVC ] == vPortSVCHandler );
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_PENDSV ] == xPortPendSVHandler );
+    }
+    #endif /* configCHECK_HANDLER_INSTALLATION */
+
     #if ( configASSERT_DEFINED == 1 )
     {
         volatile uint8_t ucOriginalPriority;
@@ -821,11 +861,12 @@ BaseType_t xPortStartScheduler( void )
     }
     #endif /* configASSERT_DEFINED */
 
-    /* Make PendSV and SysTick the same priority as the kernel, and the SVC
+    /* Make PendSV and SysTick the lowest priority interrupts, and make SVCall
-     * handler higher priority so it can be used to exit a critical section (where
+     * the highest priority. */
-     * lower priorities are masked). */
     portNVIC_SHPR3_REG |= portNVIC_PENDSV_PRI;
     portNVIC_SHPR3_REG |= portNVIC_SYSTICK_PRI;
+    portNVIC_SHPR2_REG = 0;
+
 
     /* Configure the regions in the MPU that are common to all tasks. */
     prvSetupMPU();

portable/GCC/ARM_CM4F/port.c

@@ -38,10 +38,14 @@
     #error This port can only be used when the project options are configured to enable hardware floating point support.
 #endif
 
+/* Prototype of all Interrupt Service Routines (ISRs). */
+typedef void ( * portISR_t )( void );
+
 /* Constants required to manipulate the core.  Registers first... */
 #define portNVIC_SYSTICK_CTRL_REG             ( *( ( volatile uint32_t * ) 0xe000e010 ) )
 #define portNVIC_SYSTICK_LOAD_REG             ( *( ( volatile uint32_t * ) 0xe000e014 ) )
 #define portNVIC_SYSTICK_CURRENT_VALUE_REG    ( *( ( volatile uint32_t * ) 0xe000e018 ) )
+#define portNVIC_SHPR2_REG                    ( *( ( volatile uint32_t * ) 0xe000ed1c ) )
 #define portNVIC_SHPR3_REG                    ( *( ( volatile uint32_t * ) 0xe000ed20 ) )
 /* ...then bits in the registers. */
 #define portNVIC_SYSTICK_CLK_BIT              ( 1UL << 2UL )
@@ -62,6 +66,11 @@
 #define portNVIC_PENDSV_PRI                   ( ( ( uint32_t ) portMIN_INTERRUPT_PRIORITY ) << 16UL )
 #define portNVIC_SYSTICK_PRI                  ( ( ( uint32_t ) portMIN_INTERRUPT_PRIORITY ) << 24UL )
 
+/* Constants used to check the installation of the FreeRTOS interrupt handlers. */
+#define portSCB_VTOR_REG                      ( *( ( portISR_t ** ) 0xE000ED08 ) )
+#define portVECTOR_INDEX_SVC                  ( 11 )
+#define portVECTOR_INDEX_PENDSV               ( 14 )
+
 /* Constants required to check the validity of an interrupt priority. */
 #define portFIRST_USER_INTERRUPT_NUMBER       ( 16 )
 #define portNVIC_IP_REGISTERS_OFFSET_16       ( 0xE000E3F0 )
@@ -302,6 +311,40 @@ BaseType_t xPortStartScheduler( void )
     configASSERT( portCPUID != portCORTEX_M7_r0p1_ID );
     configASSERT( portCPUID != portCORTEX_M7_r0p0_ID );
 
+    /* An application can install FreeRTOS interrupt handlers in one of the
+     * folllowing ways:
+     * 1. Direct Routing - Install the functions vPortSVCHandler and
+     *    xPortPendSVHandler for SVCall and PendSV interrupts respectively.
+     * 2. Indirect Routing - Install separate handlers for SVCall and PendSV
+     *    interrupts and route program control from those handlers to
+     *    vPortSVCHandler and xPortPendSVHandler functions.
+     *
+     * Applications that use Indirect Routing must set
+     * configCHECK_HANDLER_INSTALLATION to 0 in their FreeRTOSConfig.h. Direct
+     * routing, which is validated here when configCHECK_HANDLER_INSTALLATION
+     * is 1, should be preferred when possible. */
+    #if ( configCHECK_HANDLER_INSTALLATION == 1 )
+    {
+        const portISR_t * const pxVectorTable = portSCB_VTOR_REG;
+
+        /* Validate that the application has correctly installed the FreeRTOS
+         * handlers for SVCall and PendSV interrupts. We do not check the
+         * installation of the SysTick handler because the application may
+         * choose to drive the RTOS tick using a timer other than the SysTick
+         * timer by overriding the weak function vPortSetupTimerInterrupt().
+         *
+         * Assertion failures here indicate incorrect installation of the
+         * FreeRTOS handlers. For help installing the FreeRTOS handlers, see
+         * https://www.FreeRTOS.org/FAQHelp.html.
+         *
+         * Systems with a configurable address for the interrupt vector table
+         * can also encounter assertion failures or even system faults here if
+         * VTOR is not set correctly to point to the application's vector table. */
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_SVC ] == vPortSVCHandler );
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_PENDSV ] == xPortPendSVHandler );
+    }
+    #endif /* configCHECK_HANDLER_INSTALLATION */
+
     #if ( configASSERT_DEFINED == 1 )
     {
         volatile uint8_t ucOriginalPriority;
@@ -386,9 +429,11 @@ BaseType_t xPortStartScheduler( void )
     }
     #endif /* configASSERT_DEFINED */
 
-    /* Make PendSV and SysTick the lowest priority interrupts. */
+    /* Make PendSV and SysTick the lowest priority interrupts, and make SVCall
+     * the highest priority. */
     portNVIC_SHPR3_REG |= portNVIC_PENDSV_PRI;
     portNVIC_SHPR3_REG |= portNVIC_SYSTICK_PRI;
+    portNVIC_SHPR2_REG = 0;
 
     /* Start the timer that generates the tick ISR.  Interrupts are disabled
      * here already. */

portable/GCC/ARM_CM4_MPU/port.c

@@ -62,6 +62,9 @@
     #define configALLOW_UNPRIVILEGED_CRITICAL_SECTIONS    1
 #endif
 
+/* Prototype of all Interrupt Service Routines (ISRs). */
+typedef void ( * portISR_t )( void );
+
 /* Constants required to access and manipulate the NVIC. */
 #define portNVIC_SYSTICK_CTRL_REG                 ( *( ( volatile uint32_t * ) 0xe000e010 ) )
 #define portNVIC_SYSTICK_LOAD_REG                 ( *( ( volatile uint32_t * ) 0xe000e014 ) )
@@ -97,7 +100,6 @@
 #define portMIN_INTERRUPT_PRIORITY                ( 255UL )
 #define portNVIC_PENDSV_PRI                       ( ( ( uint32_t ) portMIN_INTERRUPT_PRIORITY ) << 16UL )
 #define portNVIC_SYSTICK_PRI                      ( ( ( uint32_t ) portMIN_INTERRUPT_PRIORITY ) << 24UL )
-#define portNVIC_SVC_PRI                          ( ( ( uint32_t ) configMAX_SYSCALL_INTERRUPT_PRIORITY - 1UL ) << 24UL )
 
 /* Constants required to manipulate the VFP. */
 #define portFPCCR                                 ( ( volatile uint32_t * ) 0xe000ef34UL ) /* Floating point context control register. */
@@ -109,6 +111,11 @@
 #define portINITIAL_CONTROL_IF_UNPRIVILEGED       ( 0x03 )
 #define portINITIAL_CONTROL_IF_PRIVILEGED         ( 0x02 )
 
+/* Constants used to check the installation of the FreeRTOS interrupt handlers. */
+#define portSCB_VTOR_REG                          ( *( ( portISR_t ** ) 0xE000ED08 ) )
+#define portVECTOR_INDEX_SVC                      ( 11 )
+#define portVECTOR_INDEX_PENDSV                   ( 14 )
+
 /* Constants required to check the validity of an interrupt priority. */
 #define portFIRST_USER_INTERRUPT_NUMBER           ( 16 )
 #define portNVIC_IP_REGISTERS_OFFSET_16           ( 0xE000E3F0 )
@@ -448,7 +455,6 @@ void vSVCHandler_C( uint32_t * pulParam ) /* PRIVILEGED_FUNCTION */
     switch( ucSVCNumber )
     {
         case portSVC_START_SCHEDULER:
-            portNVIC_SHPR2_REG |= portNVIC_SVC_PRI;
             prvRestoreContextOfFirstTask();
             break;
 
@@ -823,6 +829,40 @@ BaseType_t xPortStartScheduler( void )
         configASSERT( portCPUID != portCORTEX_M7_r0p0_ID );
     #endif
 
+    /* An application can install FreeRTOS interrupt handlers in one of the
+     * folllowing ways:
+     * 1. Direct Routing - Install the functions vPortSVCHandler and
+     *    xPortPendSVHandler for SVCall and PendSV interrupts respectively.
+     * 2. Indirect Routing - Install separate handlers for SVCall and PendSV
+     *    interrupts and route program control from those handlers to
+     *    vPortSVCHandler and xPortPendSVHandler functions.
+     *
+     * Applications that use Indirect Routing must set
+     * configCHECK_HANDLER_INSTALLATION to 0 in their FreeRTOSConfig.h. Direct
+     * routing, which is validated here when configCHECK_HANDLER_INSTALLATION
+     * is 1, should be preferred when possible. */
+    #if ( configCHECK_HANDLER_INSTALLATION == 1 )
+    {
+        const portISR_t * const pxVectorTable = portSCB_VTOR_REG;
+
+        /* Validate that the application has correctly installed the FreeRTOS
+         * handlers for SVCall and PendSV interrupts. We do not check the
+         * installation of the SysTick handler because the application may
+         * choose to drive the RTOS tick using a timer other than the SysTick
+         * timer by overriding the weak function vPortSetupTimerInterrupt().
+         *
+         * Assertion failures here indicate incorrect installation of the
+         * FreeRTOS handlers. For help installing the FreeRTOS handlers, see
+         * https://www.FreeRTOS.org/FAQHelp.html.
+         *
+         * Systems with a configurable address for the interrupt vector table
+         * can also encounter assertion failures or even system faults here if
+         * VTOR is not set correctly to point to the application's vector table. */
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_SVC ] == vPortSVCHandler );
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_PENDSV ] == xPortPendSVHandler );
+    }
+    #endif /* configCHECK_HANDLER_INSTALLATION */
+
     #if ( configASSERT_DEFINED == 1 )
     {
         volatile uint8_t ucOriginalPriority;
@@ -907,11 +947,11 @@ BaseType_t xPortStartScheduler( void )
     }
     #endif /* configASSERT_DEFINED */
 
-    /* Make PendSV and SysTick the same priority as the kernel, and the SVC
+    /* Make PendSV and SysTick the lowest priority interrupts, and make SVCall
-     * handler higher priority so it can be used to exit a critical section (where
+     * the highest priority. */
-     * lower priorities are masked). */
     portNVIC_SHPR3_REG |= portNVIC_PENDSV_PRI;
     portNVIC_SHPR3_REG |= portNVIC_SYSTICK_PRI;
+    portNVIC_SHPR2_REG = 0;
 
     /* Configure the regions in the MPU that are common to all tasks. */
     prvSetupMPU();

portable/GCC/ARM_CM55/non_secure/port.c

@@ -80,6 +80,12 @@
 #endif
 /*-----------------------------------------------------------*/
 
+/**
+ * @brief Prototype of all Interrupt Service Routines (ISRs).
+ */
+typedef void ( * portISR_t )( void );
+/*-----------------------------------------------------------*/
+
 /**
  * @brief Constants required to manipulate the NVIC.
  */
@@ -101,10 +107,18 @@
 /**
  * @brief Constants required to manipulate the SCB.
  */
-#define portSCB_SYS_HANDLER_CTRL_STATE_REG    ( *( volatile uint32_t * ) 0xe000ed24 )
+#define portSCB_VTOR_REG                      ( *( ( portISR_t ** ) 0xe000ed08 ) )
+#define portSCB_SYS_HANDLER_CTRL_STATE_REG    ( *( ( volatile uint32_t * ) 0xe000ed24 ) )
 #define portSCB_MEM_FAULT_ENABLE_BIT          ( 1UL << 16UL )
 /*-----------------------------------------------------------*/
 
+/**
+ * @brief Constants used to check the installation of the FreeRTOS interrupt handlers.
+ */
+#define portVECTOR_INDEX_SVC       ( 11 )
+#define portVECTOR_INDEX_PENDSV    ( 14 )
+/*-----------------------------------------------------------*/
+
 /**
  * @brief Constants required to check the validity of an interrupt priority.
  */
@@ -1598,22 +1612,52 @@ void vPortSVCHandler_C( uint32_t * pulCallerStackAddress ) /* PRIVILEGED_FUNCTIO
 
 BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
 {
+    /* An application can install FreeRTOS interrupt handlers in one of the
+     * folllowing ways:
+     * 1. Direct Routing - Install the functions SVC_Handler and PendSV_Handler
+     *    for SVCall and PendSV interrupts respectively.
+     * 2. Indirect Routing - Install separate handlers for SVCall and PendSV
+     *    interrupts and route program control from those handlers to
+     *    SVC_Handler and PendSV_Handler functions.
+     *
+     * Applications that use Indirect Routing must set
+     * configCHECK_HANDLER_INSTALLATION to 0 in their FreeRTOSConfig.h. Direct
+     * routing, which is validated here when configCHECK_HANDLER_INSTALLATION
+     * is 1, should be preferred when possible. */
+    #if ( configCHECK_HANDLER_INSTALLATION == 1 )
+    {
+        const portISR_t * const pxVectorTable = portSCB_VTOR_REG;
+
+        /* Validate that the application has correctly installed the FreeRTOS
+         * handlers for SVCall and PendSV interrupts. We do not check the
+         * installation of the SysTick handler because the application may
+         * choose to drive the RTOS tick using a timer other than the SysTick
+         * timer by overriding the weak function vPortSetupTimerInterrupt().
+         *
+         * Assertion failures here indicate incorrect installation of the
+         * FreeRTOS handlers. For help installing the FreeRTOS handlers, see
+         * https://www.FreeRTOS.org/FAQHelp.html.
+         *
+         * Systems with a configurable address for the interrupt vector table
+         * can also encounter assertion failures or even system faults here if
+         * VTOR is not set correctly to point to the application's vector table. */
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_SVC ] == SVC_Handler );
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_PENDSV ] == PendSV_Handler );
+    }
+    #endif /* configCHECK_HANDLER_INSTALLATION */
+
     #if ( ( configASSERT_DEFINED == 1 ) && ( portHAS_ARMV8M_MAIN_EXTENSION == 1 ) )
     {
-        volatile uint32_t ulOriginalPriority;
         volatile uint32_t ulImplementedPrioBits = 0;
         volatile uint8_t ucMaxPriorityValue;
 
         /* Determine the maximum priority from which ISR safe FreeRTOS API
-         * functions can be called.  ISR safe functions are those that end in
+         * functions can be called. ISR safe functions are those that end in
-         * "FromISR".  FreeRTOS maintains separate thread and ISR API functions to
+         * "FromISR". FreeRTOS maintains separate thread and ISR API functions to
          * ensure interrupt entry is as fast and simple as possible.
          *
-         * Save the interrupt priority value that is about to be clobbered. */
+         * First, determine the number of priority bits available. Write to all
-        ulOriginalPriority = portNVIC_SHPR2_REG;
+         * possible bits in the priority setting for SVCall. */
-
-        /* Determine the number of priority bits available.  First write to all
-         * possible bits. */
         portNVIC_SHPR2_REG = 0xFF000000;
 
         /* Read the value back to see how many bits stuck. */
@@ -1636,7 +1680,6 @@ BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
 
         /* Calculate the maximum acceptable priority group value for the number
          * of bits read back. */
-
         while( ( ucMaxPriorityValue & portTOP_BIT_OF_BYTE ) == portTOP_BIT_OF_BYTE )
         {
             ulImplementedPrioBits++;
@@ -1674,16 +1717,14 @@ BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
          * register. */
         ulMaxPRIGROUPValue <<= portPRIGROUP_SHIFT;
         ulMaxPRIGROUPValue &= portPRIORITY_GROUP_MASK;
-
-        /* Restore the clobbered interrupt priority register to its original
-         * value. */
-        portNVIC_SHPR2_REG = ulOriginalPriority;
     }
     #endif /* #if ( ( configASSERT_DEFINED == 1 ) && ( portHAS_ARMV8M_MAIN_EXTENSION == 1 ) ) */
 
-    /* Make PendSV, CallSV and SysTick the same priority as the kernel. */
+    /* Make PendSV and SysTick the lowest priority interrupts, and make SVCall
+     * the highest priority. */
     portNVIC_SHPR3_REG |= portNVIC_PENDSV_PRI;
     portNVIC_SHPR3_REG |= portNVIC_SYSTICK_PRI;
+    portNVIC_SHPR2_REG = 0;
 
     #if ( configENABLE_MPU == 1 )
     {

portable/GCC/ARM_CM55_NTZ/non_secure/port.c

@@ -80,6 +80,12 @@
 #endif
 /*-----------------------------------------------------------*/
 
+/**
+ * @brief Prototype of all Interrupt Service Routines (ISRs).
+ */
+typedef void ( * portISR_t )( void );
+/*-----------------------------------------------------------*/
+
 /**
  * @brief Constants required to manipulate the NVIC.
  */
@@ -101,10 +107,18 @@
 /**
  * @brief Constants required to manipulate the SCB.
  */
-#define portSCB_SYS_HANDLER_CTRL_STATE_REG    ( *( volatile uint32_t * ) 0xe000ed24 )
+#define portSCB_VTOR_REG                      ( *( ( portISR_t ** ) 0xe000ed08 ) )
+#define portSCB_SYS_HANDLER_CTRL_STATE_REG    ( *( ( volatile uint32_t * ) 0xe000ed24 ) )
 #define portSCB_MEM_FAULT_ENABLE_BIT          ( 1UL << 16UL )
 /*-----------------------------------------------------------*/
 
+/**
+ * @brief Constants used to check the installation of the FreeRTOS interrupt handlers.
+ */
+#define portVECTOR_INDEX_SVC       ( 11 )
+#define portVECTOR_INDEX_PENDSV    ( 14 )
+/*-----------------------------------------------------------*/
+
 /**
  * @brief Constants required to check the validity of an interrupt priority.
  */
@@ -1598,22 +1612,52 @@ void vPortSVCHandler_C( uint32_t * pulCallerStackAddress ) /* PRIVILEGED_FUNCTIO
 
 BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
 {
+    /* An application can install FreeRTOS interrupt handlers in one of the
+     * folllowing ways:
+     * 1. Direct Routing - Install the functions SVC_Handler and PendSV_Handler
+     *    for SVCall and PendSV interrupts respectively.
+     * 2. Indirect Routing - Install separate handlers for SVCall and PendSV
+     *    interrupts and route program control from those handlers to
+     *    SVC_Handler and PendSV_Handler functions.
+     *
+     * Applications that use Indirect Routing must set
+     * configCHECK_HANDLER_INSTALLATION to 0 in their FreeRTOSConfig.h. Direct
+     * routing, which is validated here when configCHECK_HANDLER_INSTALLATION
+     * is 1, should be preferred when possible. */
+    #if ( configCHECK_HANDLER_INSTALLATION == 1 )
+    {
+        const portISR_t * const pxVectorTable = portSCB_VTOR_REG;
+
+        /* Validate that the application has correctly installed the FreeRTOS
+         * handlers for SVCall and PendSV interrupts. We do not check the
+         * installation of the SysTick handler because the application may
+         * choose to drive the RTOS tick using a timer other than the SysTick
+         * timer by overriding the weak function vPortSetupTimerInterrupt().
+         *
+         * Assertion failures here indicate incorrect installation of the
+         * FreeRTOS handlers. For help installing the FreeRTOS handlers, see
+         * https://www.FreeRTOS.org/FAQHelp.html.
+         *
+         * Systems with a configurable address for the interrupt vector table
+         * can also encounter assertion failures or even system faults here if
+         * VTOR is not set correctly to point to the application's vector table. */
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_SVC ] == SVC_Handler );
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_PENDSV ] == PendSV_Handler );
+    }
+    #endif /* configCHECK_HANDLER_INSTALLATION */
+
     #if ( ( configASSERT_DEFINED == 1 ) && ( portHAS_ARMV8M_MAIN_EXTENSION == 1 ) )
     {
-        volatile uint32_t ulOriginalPriority;
         volatile uint32_t ulImplementedPrioBits = 0;
         volatile uint8_t ucMaxPriorityValue;
 
         /* Determine the maximum priority from which ISR safe FreeRTOS API
-         * functions can be called.  ISR safe functions are those that end in
+         * functions can be called. ISR safe functions are those that end in
-         * "FromISR".  FreeRTOS maintains separate thread and ISR API functions to
+         * "FromISR". FreeRTOS maintains separate thread and ISR API functions to
          * ensure interrupt entry is as fast and simple as possible.
          *
-         * Save the interrupt priority value that is about to be clobbered. */
+         * First, determine the number of priority bits available. Write to all
-        ulOriginalPriority = portNVIC_SHPR2_REG;
+         * possible bits in the priority setting for SVCall. */
-
-        /* Determine the number of priority bits available.  First write to all
-         * possible bits. */
         portNVIC_SHPR2_REG = 0xFF000000;
 
         /* Read the value back to see how many bits stuck. */
@@ -1636,7 +1680,6 @@ BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
 
         /* Calculate the maximum acceptable priority group value for the number
          * of bits read back. */
-
         while( ( ucMaxPriorityValue & portTOP_BIT_OF_BYTE ) == portTOP_BIT_OF_BYTE )
         {
             ulImplementedPrioBits++;
@@ -1674,16 +1717,14 @@ BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
          * register. */
         ulMaxPRIGROUPValue <<= portPRIGROUP_SHIFT;
         ulMaxPRIGROUPValue &= portPRIORITY_GROUP_MASK;
-
-        /* Restore the clobbered interrupt priority register to its original
-         * value. */
-        portNVIC_SHPR2_REG = ulOriginalPriority;
     }
     #endif /* #if ( ( configASSERT_DEFINED == 1 ) && ( portHAS_ARMV8M_MAIN_EXTENSION == 1 ) ) */
 
-    /* Make PendSV, CallSV and SysTick the same priority as the kernel. */
+    /* Make PendSV and SysTick the lowest priority interrupts, and make SVCall
+     * the highest priority. */
     portNVIC_SHPR3_REG |= portNVIC_PENDSV_PRI;
     portNVIC_SHPR3_REG |= portNVIC_SYSTICK_PRI;
+    portNVIC_SHPR2_REG = 0;
 
     #if ( configENABLE_MPU == 1 )
     {

portable/GCC/ARM_CM7/r0p1/port.c

@@ -38,10 +38,14 @@
     #error This port can only be used when the project options are configured to enable hardware floating point support.
 #endif
 
+/* Prototype of all Interrupt Service Routines (ISRs). */
+typedef void ( * portISR_t )( void );
+
 /* Constants required to manipulate the core.  Registers first... */
 #define portNVIC_SYSTICK_CTRL_REG             ( *( ( volatile uint32_t * ) 0xe000e010 ) )
 #define portNVIC_SYSTICK_LOAD_REG             ( *( ( volatile uint32_t * ) 0xe000e014 ) )
 #define portNVIC_SYSTICK_CURRENT_VALUE_REG    ( *( ( volatile uint32_t * ) 0xe000e018 ) )
+#define portNVIC_SHPR2_REG                    ( *( ( volatile uint32_t * ) 0xe000ed1c ) )
 #define portNVIC_SHPR3_REG                    ( *( ( volatile uint32_t * ) 0xe000ed20 ) )
 /* ...then bits in the registers. */
 #define portNVIC_SYSTICK_CLK_BIT              ( 1UL << 2UL )
@@ -56,6 +60,11 @@
 #define portNVIC_PENDSV_PRI                   ( ( ( uint32_t ) portMIN_INTERRUPT_PRIORITY ) << 16UL )
 #define portNVIC_SYSTICK_PRI                  ( ( ( uint32_t ) portMIN_INTERRUPT_PRIORITY ) << 24UL )
 
+/* Constants used to check the installation of the FreeRTOS interrupt handlers. */
+#define portSCB_VTOR_REG                      ( *( ( portISR_t ** ) 0xE000ED08 ) )
+#define portVECTOR_INDEX_SVC                  ( 11 )
+#define portVECTOR_INDEX_PENDSV               ( 14 )
+
 /* Constants required to check the validity of an interrupt priority. */
 #define portFIRST_USER_INTERRUPT_NUMBER       ( 16 )
 #define portNVIC_IP_REGISTERS_OFFSET_16       ( 0xE000E3F0 )
@@ -290,6 +299,40 @@ static void prvPortStartFirstTask( void )
  */
 BaseType_t xPortStartScheduler( void )
 {
+    /* An application can install FreeRTOS interrupt handlers in one of the
+     * folllowing ways:
+     * 1. Direct Routing - Install the functions vPortSVCHandler and
+     *    xPortPendSVHandler for SVCall and PendSV interrupts respectively.
+     * 2. Indirect Routing - Install separate handlers for SVCall and PendSV
+     *    interrupts and route program control from those handlers to
+     *    vPortSVCHandler and xPortPendSVHandler functions.
+     *
+     * Applications that use Indirect Routing must set
+     * configCHECK_HANDLER_INSTALLATION to 0 in their FreeRTOSConfig.h. Direct
+     * routing, which is validated here when configCHECK_HANDLER_INSTALLATION
+     * is 1, should be preferred when possible. */
+    #if ( configCHECK_HANDLER_INSTALLATION == 1 )
+    {
+        const portISR_t * const pxVectorTable = portSCB_VTOR_REG;
+
+        /* Validate that the application has correctly installed the FreeRTOS
+         * handlers for SVCall and PendSV interrupts. We do not check the
+         * installation of the SysTick handler because the application may
+         * choose to drive the RTOS tick using a timer other than the SysTick
+         * timer by overriding the weak function vPortSetupTimerInterrupt().
+         *
+         * Assertion failures here indicate incorrect installation of the
+         * FreeRTOS handlers. For help installing the FreeRTOS handlers, see
+         * https://www.FreeRTOS.org/FAQHelp.html.
+         *
+         * Systems with a configurable address for the interrupt vector table
+         * can also encounter assertion failures or even system faults here if
+         * VTOR is not set correctly to point to the application's vector table. */
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_SVC ] == vPortSVCHandler );
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_PENDSV ] == xPortPendSVHandler );
+    }
+    #endif /* configCHECK_HANDLER_INSTALLATION */
+
     #if ( configASSERT_DEFINED == 1 )
     {
         volatile uint8_t ucOriginalPriority;
@@ -374,9 +417,11 @@ BaseType_t xPortStartScheduler( void )
     }
     #endif /* configASSERT_DEFINED */
 
-    /* Make PendSV and SysTick the lowest priority interrupts. */
+    /* Make PendSV and SysTick the lowest priority interrupts, and make SVCall
+     * the highest priority. */
     portNVIC_SHPR3_REG |= portNVIC_PENDSV_PRI;
     portNVIC_SHPR3_REG |= portNVIC_SYSTICK_PRI;
+    portNVIC_SHPR2_REG = 0;
 
     /* Start the timer that generates the tick ISR.  Interrupts are disabled
      * here already. */

portable/GCC/ARM_CM85/non_secure/port.c

@@ -80,6 +80,12 @@
 #endif
 /*-----------------------------------------------------------*/
 
+/**
+ * @brief Prototype of all Interrupt Service Routines (ISRs).
+ */
+typedef void ( * portISR_t )( void );
+/*-----------------------------------------------------------*/
+
 /**
  * @brief Constants required to manipulate the NVIC.
  */
@@ -101,10 +107,18 @@
 /**
  * @brief Constants required to manipulate the SCB.
  */
-#define portSCB_SYS_HANDLER_CTRL_STATE_REG    ( *( volatile uint32_t * ) 0xe000ed24 )
+#define portSCB_VTOR_REG                      ( *( ( portISR_t ** ) 0xe000ed08 ) )
+#define portSCB_SYS_HANDLER_CTRL_STATE_REG    ( *( ( volatile uint32_t * ) 0xe000ed24 ) )
 #define portSCB_MEM_FAULT_ENABLE_BIT          ( 1UL << 16UL )
 /*-----------------------------------------------------------*/
 
+/**
+ * @brief Constants used to check the installation of the FreeRTOS interrupt handlers.
+ */
+#define portVECTOR_INDEX_SVC       ( 11 )
+#define portVECTOR_INDEX_PENDSV    ( 14 )
+/*-----------------------------------------------------------*/
+
 /**
  * @brief Constants required to check the validity of an interrupt priority.
  */
@@ -1598,22 +1612,52 @@ void vPortSVCHandler_C( uint32_t * pulCallerStackAddress ) /* PRIVILEGED_FUNCTIO
 
 BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
 {
+    /* An application can install FreeRTOS interrupt handlers in one of the
+     * folllowing ways:
+     * 1. Direct Routing - Install the functions SVC_Handler and PendSV_Handler
+     *    for SVCall and PendSV interrupts respectively.
+     * 2. Indirect Routing - Install separate handlers for SVCall and PendSV
+     *    interrupts and route program control from those handlers to
+     *    SVC_Handler and PendSV_Handler functions.
+     *
+     * Applications that use Indirect Routing must set
+     * configCHECK_HANDLER_INSTALLATION to 0 in their FreeRTOSConfig.h. Direct
+     * routing, which is validated here when configCHECK_HANDLER_INSTALLATION
+     * is 1, should be preferred when possible. */
+    #if ( configCHECK_HANDLER_INSTALLATION == 1 )
+    {
+        const portISR_t * const pxVectorTable = portSCB_VTOR_REG;
+
+        /* Validate that the application has correctly installed the FreeRTOS
+         * handlers for SVCall and PendSV interrupts. We do not check the
+         * installation of the SysTick handler because the application may
+         * choose to drive the RTOS tick using a timer other than the SysTick
+         * timer by overriding the weak function vPortSetupTimerInterrupt().
+         *
+         * Assertion failures here indicate incorrect installation of the
+         * FreeRTOS handlers. For help installing the FreeRTOS handlers, see
+         * https://www.FreeRTOS.org/FAQHelp.html.
+         *
+         * Systems with a configurable address for the interrupt vector table
+         * can also encounter assertion failures or even system faults here if
+         * VTOR is not set correctly to point to the application's vector table. */
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_SVC ] == SVC_Handler );
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_PENDSV ] == PendSV_Handler );
+    }
+    #endif /* configCHECK_HANDLER_INSTALLATION */
+
     #if ( ( configASSERT_DEFINED == 1 ) && ( portHAS_ARMV8M_MAIN_EXTENSION == 1 ) )
     {
-        volatile uint32_t ulOriginalPriority;
         volatile uint32_t ulImplementedPrioBits = 0;
         volatile uint8_t ucMaxPriorityValue;
 
         /* Determine the maximum priority from which ISR safe FreeRTOS API
-         * functions can be called.  ISR safe functions are those that end in
+         * functions can be called. ISR safe functions are those that end in
-         * "FromISR".  FreeRTOS maintains separate thread and ISR API functions to
+         * "FromISR". FreeRTOS maintains separate thread and ISR API functions to
          * ensure interrupt entry is as fast and simple as possible.
          *
-         * Save the interrupt priority value that is about to be clobbered. */
+         * First, determine the number of priority bits available. Write to all
-        ulOriginalPriority = portNVIC_SHPR2_REG;
+         * possible bits in the priority setting for SVCall. */
-
-        /* Determine the number of priority bits available.  First write to all
-         * possible bits. */
         portNVIC_SHPR2_REG = 0xFF000000;
 
         /* Read the value back to see how many bits stuck. */
@@ -1636,7 +1680,6 @@ BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
 
         /* Calculate the maximum acceptable priority group value for the number
          * of bits read back. */
-
         while( ( ucMaxPriorityValue & portTOP_BIT_OF_BYTE ) == portTOP_BIT_OF_BYTE )
         {
             ulImplementedPrioBits++;
@@ -1674,16 +1717,14 @@ BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
          * register. */
         ulMaxPRIGROUPValue <<= portPRIGROUP_SHIFT;
         ulMaxPRIGROUPValue &= portPRIORITY_GROUP_MASK;
-
-        /* Restore the clobbered interrupt priority register to its original
-         * value. */
-        portNVIC_SHPR2_REG = ulOriginalPriority;
     }
     #endif /* #if ( ( configASSERT_DEFINED == 1 ) && ( portHAS_ARMV8M_MAIN_EXTENSION == 1 ) ) */
 
-    /* Make PendSV, CallSV and SysTick the same priority as the kernel. */
+    /* Make PendSV and SysTick the lowest priority interrupts, and make SVCall
+     * the highest priority. */
     portNVIC_SHPR3_REG |= portNVIC_PENDSV_PRI;
     portNVIC_SHPR3_REG |= portNVIC_SYSTICK_PRI;
+    portNVIC_SHPR2_REG = 0;
 
     #if ( configENABLE_MPU == 1 )
     {

portable/GCC/ARM_CM85_NTZ/non_secure/port.c

@@ -80,6 +80,12 @@
 #endif
 /*-----------------------------------------------------------*/
 
+/**
+ * @brief Prototype of all Interrupt Service Routines (ISRs).
+ */
+typedef void ( * portISR_t )( void );
+/*-----------------------------------------------------------*/
+
 /**
  * @brief Constants required to manipulate the NVIC.
  */
@@ -101,10 +107,18 @@
 /**
  * @brief Constants required to manipulate the SCB.
  */
-#define portSCB_SYS_HANDLER_CTRL_STATE_REG    ( *( volatile uint32_t * ) 0xe000ed24 )
+#define portSCB_VTOR_REG                      ( *( ( portISR_t ** ) 0xe000ed08 ) )
+#define portSCB_SYS_HANDLER_CTRL_STATE_REG    ( *( ( volatile uint32_t * ) 0xe000ed24 ) )
 #define portSCB_MEM_FAULT_ENABLE_BIT          ( 1UL << 16UL )
 /*-----------------------------------------------------------*/
 
+/**
+ * @brief Constants used to check the installation of the FreeRTOS interrupt handlers.
+ */
+#define portVECTOR_INDEX_SVC       ( 11 )
+#define portVECTOR_INDEX_PENDSV    ( 14 )
+/*-----------------------------------------------------------*/
+
 /**
  * @brief Constants required to check the validity of an interrupt priority.
  */
@@ -1598,22 +1612,52 @@ void vPortSVCHandler_C( uint32_t * pulCallerStackAddress ) /* PRIVILEGED_FUNCTIO
 
 BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
 {
+    /* An application can install FreeRTOS interrupt handlers in one of the
+     * folllowing ways:
+     * 1. Direct Routing - Install the functions SVC_Handler and PendSV_Handler
+     *    for SVCall and PendSV interrupts respectively.
+     * 2. Indirect Routing - Install separate handlers for SVCall and PendSV
+     *    interrupts and route program control from those handlers to
+     *    SVC_Handler and PendSV_Handler functions.
+     *
+     * Applications that use Indirect Routing must set
+     * configCHECK_HANDLER_INSTALLATION to 0 in their FreeRTOSConfig.h. Direct
+     * routing, which is validated here when configCHECK_HANDLER_INSTALLATION
+     * is 1, should be preferred when possible. */
+    #if ( configCHECK_HANDLER_INSTALLATION == 1 )
+    {
+        const portISR_t * const pxVectorTable = portSCB_VTOR_REG;
+
+        /* Validate that the application has correctly installed the FreeRTOS
+         * handlers for SVCall and PendSV interrupts. We do not check the
+         * installation of the SysTick handler because the application may
+         * choose to drive the RTOS tick using a timer other than the SysTick
+         * timer by overriding the weak function vPortSetupTimerInterrupt().
+         *
+         * Assertion failures here indicate incorrect installation of the
+         * FreeRTOS handlers. For help installing the FreeRTOS handlers, see
+         * https://www.FreeRTOS.org/FAQHelp.html.
+         *
+         * Systems with a configurable address for the interrupt vector table
+         * can also encounter assertion failures or even system faults here if
+         * VTOR is not set correctly to point to the application's vector table. */
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_SVC ] == SVC_Handler );
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_PENDSV ] == PendSV_Handler );
+    }
+    #endif /* configCHECK_HANDLER_INSTALLATION */
+
     #if ( ( configASSERT_DEFINED == 1 ) && ( portHAS_ARMV8M_MAIN_EXTENSION == 1 ) )
     {
-        volatile uint32_t ulOriginalPriority;
         volatile uint32_t ulImplementedPrioBits = 0;
         volatile uint8_t ucMaxPriorityValue;
 
         /* Determine the maximum priority from which ISR safe FreeRTOS API
-         * functions can be called.  ISR safe functions are those that end in
+         * functions can be called. ISR safe functions are those that end in
-         * "FromISR".  FreeRTOS maintains separate thread and ISR API functions to
+         * "FromISR". FreeRTOS maintains separate thread and ISR API functions to
          * ensure interrupt entry is as fast and simple as possible.
          *
-         * Save the interrupt priority value that is about to be clobbered. */
+         * First, determine the number of priority bits available. Write to all
-        ulOriginalPriority = portNVIC_SHPR2_REG;
+         * possible bits in the priority setting for SVCall. */
-
-        /* Determine the number of priority bits available.  First write to all
-         * possible bits. */
         portNVIC_SHPR2_REG = 0xFF000000;
 
         /* Read the value back to see how many bits stuck. */
@@ -1636,7 +1680,6 @@ BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
 
         /* Calculate the maximum acceptable priority group value for the number
          * of bits read back. */
-
         while( ( ucMaxPriorityValue & portTOP_BIT_OF_BYTE ) == portTOP_BIT_OF_BYTE )
         {
             ulImplementedPrioBits++;
@@ -1674,16 +1717,14 @@ BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
          * register. */
         ulMaxPRIGROUPValue <<= portPRIGROUP_SHIFT;
         ulMaxPRIGROUPValue &= portPRIORITY_GROUP_MASK;
-
-        /* Restore the clobbered interrupt priority register to its original
-         * value. */
-        portNVIC_SHPR2_REG = ulOriginalPriority;
     }
     #endif /* #if ( ( configASSERT_DEFINED == 1 ) && ( portHAS_ARMV8M_MAIN_EXTENSION == 1 ) ) */
 
-    /* Make PendSV, CallSV and SysTick the same priority as the kernel. */
+    /* Make PendSV and SysTick the lowest priority interrupts, and make SVCall
+     * the highest priority. */
     portNVIC_SHPR3_REG |= portNVIC_PENDSV_PRI;
     portNVIC_SHPR3_REG |= portNVIC_SYSTICK_PRI;
+    portNVIC_SHPR2_REG = 0;
 
     #if ( configENABLE_MPU == 1 )
     {

portable/IAR/ARM_CM0/port.c

@@ -37,6 +37,9 @@
 #include "FreeRTOS.h"
 #include "task.h"
 
+/* Prototype of all Interrupt Service Routines (ISRs). */
+typedef void ( * portISR_t )( void );
+
 /* Constants required to manipulate the NVIC. */
 #define portNVIC_SYSTICK_CTRL_REG             ( *( ( volatile uint32_t * ) 0xe000e010 ) )
 #define portNVIC_SYSTICK_LOAD_REG             ( *( ( volatile uint32_t * ) 0xe000e014 ) )
@@ -53,6 +56,10 @@
 #define portNVIC_PENDSV_PRI                   ( portMIN_INTERRUPT_PRIORITY << 16UL )
 #define portNVIC_SYSTICK_PRI                  ( portMIN_INTERRUPT_PRIORITY << 24UL )
 
+/* Constants used to check the installation of the FreeRTOS interrupt handlers. */
+#define portSCB_VTOR_REG                      ( *( ( portISR_t ** ) 0xe000ed08 ) )
+#define portVECTOR_INDEX_PENDSV               ( 14 )
+
 /* Constants required to set up the initial stack. */
 #define portINITIAL_XPSR                      ( 0x01000000 )
 
@@ -121,6 +128,10 @@ extern void vPortStartFirstTask( void );
  */
 static void prvTaskExitError( void );
 
+/*
+ * FreeRTOS handlers implemented in assembly.
+ */
+extern void xPortPendSVHandler( void );
 /*-----------------------------------------------------------*/
 
 /*
@@ -168,6 +179,41 @@ static void prvTaskExitError( void )
  */
 BaseType_t xPortStartScheduler( void )
 {
+    /* An application can install FreeRTOS interrupt handlers in one of the
+     * folllowing ways:
+     * 1. Direct Routing - Install the function xPortPendSVHandler for PendSV
+     *    interrupt.
+     * 2. Indirect Routing - Install separate handler for PendSV interrupt and
+     *    route program control from that handler to xPortPendSVHandler function.
+     *
+     * Applications that use Indirect Routing must set
+     * configCHECK_HANDLER_INSTALLATION to 0 in their FreeRTOSConfig.h. Direct
+     * routing, which is validated here when configCHECK_HANDLER_INSTALLATION
+     * is 1, should be preferred when possible. */
+    #if ( configCHECK_HANDLER_INSTALLATION == 1 )
+    {
+        /* Point pxVectorTable to the interrupt vector table. Systems without
+         * a VTOR register provide the value zero in the VTOR register and
+         * the vector table itself is located at the address 0x00000000. */
+        const portISR_t * const pxVectorTable = portSCB_VTOR_REG;
+
+        /* Validate that the application has correctly installed the FreeRTOS
+         * handler for PendSV interrupt. We do not check the installation of the
+         * SysTick handler because the application may choose to drive the RTOS
+         * tick using a timer other than the SysTick timer by overriding the
+         * weak function vPortSetupTimerInterrupt().
+         *
+         * Assertion failures here indicate incorrect installation of the
+         * FreeRTOS handler. For help installing the FreeRTOS handler, see
+         * https://www.FreeRTOS.org/FAQHelp.html.
+         *
+         * Systems with a configurable address for the interrupt vector table
+         * can also encounter assertion failures or even system faults here if
+         * VTOR is not set correctly to point to the application's vector table. */
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_PENDSV ] == xPortPendSVHandler );
+    }
+    #endif /* configCHECK_HANDLER_INSTALLATION */
+
     /* Make PendSV and SysTick the lowest priority interrupts. */
     portNVIC_SHPR3_REG |= portNVIC_PENDSV_PRI;
     portNVIC_SHPR3_REG |= portNVIC_SYSTICK_PRI;

portable/IAR/ARM_CM0/portasm.s

@@ -91,15 +91,15 @@ xPortPendSVHandler:
 
 vPortSVCHandler;
     /* This function is no longer used, but retained for backward
-    compatibility. */
+     * compatibility. */
     bx lr
 
 /*-----------------------------------------------------------*/
 
 vPortStartFirstTask
-    /* The MSP stack is not reset as, unlike on M3/4 parts, there is no vector
+    /* Don't reset the MSP stack as is done on CM3/4 devices. The vector table
-    table offset register that can be used to locate the initial stack value.
+     * in some CM0 devices cannot be modified and thus may not hold the
-    Not all M0 parts have the application vector table at address 0. */
+     * application's initial MSP value. */
 
     ldr r3, =pxCurrentTCB   /* Obtain location of pxCurrentTCB. */
     ldr r1, [r3]

portable/IAR/ARM_CM23/non_secure/port.c

@@ -80,6 +80,12 @@
 #endif
 /*-----------------------------------------------------------*/
 
+/**
+ * @brief Prototype of all Interrupt Service Routines (ISRs).
+ */
+typedef void ( * portISR_t )( void );
+/*-----------------------------------------------------------*/
+
 /**
  * @brief Constants required to manipulate the NVIC.
  */
@@ -101,10 +107,18 @@
 /**
  * @brief Constants required to manipulate the SCB.
  */
-#define portSCB_SYS_HANDLER_CTRL_STATE_REG    ( *( volatile uint32_t * ) 0xe000ed24 )
+#define portSCB_VTOR_REG                      ( *( ( portISR_t ** ) 0xe000ed08 ) )
+#define portSCB_SYS_HANDLER_CTRL_STATE_REG    ( *( ( volatile uint32_t * ) 0xe000ed24 ) )
 #define portSCB_MEM_FAULT_ENABLE_BIT          ( 1UL << 16UL )
 /*-----------------------------------------------------------*/
 
+/**
+ * @brief Constants used to check the installation of the FreeRTOS interrupt handlers.
+ */
+#define portVECTOR_INDEX_SVC       ( 11 )
+#define portVECTOR_INDEX_PENDSV    ( 14 )
+/*-----------------------------------------------------------*/
+
 /**
  * @brief Constants required to check the validity of an interrupt priority.
  */
@@ -1598,22 +1612,52 @@ void vPortSVCHandler_C( uint32_t * pulCallerStackAddress ) /* PRIVILEGED_FUNCTIO
 
 BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
 {
+    /* An application can install FreeRTOS interrupt handlers in one of the
+     * folllowing ways:
+     * 1. Direct Routing - Install the functions SVC_Handler and PendSV_Handler
+     *    for SVCall and PendSV interrupts respectively.
+     * 2. Indirect Routing - Install separate handlers for SVCall and PendSV
+     *    interrupts and route program control from those handlers to
+     *    SVC_Handler and PendSV_Handler functions.
+     *
+     * Applications that use Indirect Routing must set
+     * configCHECK_HANDLER_INSTALLATION to 0 in their FreeRTOSConfig.h. Direct
+     * routing, which is validated here when configCHECK_HANDLER_INSTALLATION
+     * is 1, should be preferred when possible. */
+    #if ( configCHECK_HANDLER_INSTALLATION == 1 )
+    {
+        const portISR_t * const pxVectorTable = portSCB_VTOR_REG;
+
+        /* Validate that the application has correctly installed the FreeRTOS
+         * handlers for SVCall and PendSV interrupts. We do not check the
+         * installation of the SysTick handler because the application may
+         * choose to drive the RTOS tick using a timer other than the SysTick
+         * timer by overriding the weak function vPortSetupTimerInterrupt().
+         *
+         * Assertion failures here indicate incorrect installation of the
+         * FreeRTOS handlers. For help installing the FreeRTOS handlers, see
+         * https://www.FreeRTOS.org/FAQHelp.html.
+         *
+         * Systems with a configurable address for the interrupt vector table
+         * can also encounter assertion failures or even system faults here if
+         * VTOR is not set correctly to point to the application's vector table. */
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_SVC ] == SVC_Handler );
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_PENDSV ] == PendSV_Handler );
+    }
+    #endif /* configCHECK_HANDLER_INSTALLATION */
+
     #if ( ( configASSERT_DEFINED == 1 ) && ( portHAS_ARMV8M_MAIN_EXTENSION == 1 ) )
     {
-        volatile uint32_t ulOriginalPriority;
         volatile uint32_t ulImplementedPrioBits = 0;
         volatile uint8_t ucMaxPriorityValue;
 
         /* Determine the maximum priority from which ISR safe FreeRTOS API
-         * functions can be called.  ISR safe functions are those that end in
+         * functions can be called. ISR safe functions are those that end in
-         * "FromISR".  FreeRTOS maintains separate thread and ISR API functions to
+         * "FromISR". FreeRTOS maintains separate thread and ISR API functions to
          * ensure interrupt entry is as fast and simple as possible.
          *
-         * Save the interrupt priority value that is about to be clobbered. */
+         * First, determine the number of priority bits available. Write to all
-        ulOriginalPriority = portNVIC_SHPR2_REG;
+         * possible bits in the priority setting for SVCall. */
-
-        /* Determine the number of priority bits available.  First write to all
-         * possible bits. */
         portNVIC_SHPR2_REG = 0xFF000000;
 
         /* Read the value back to see how many bits stuck. */
@@ -1636,7 +1680,6 @@ BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
 
         /* Calculate the maximum acceptable priority group value for the number
          * of bits read back. */
-
         while( ( ucMaxPriorityValue & portTOP_BIT_OF_BYTE ) == portTOP_BIT_OF_BYTE )
         {
             ulImplementedPrioBits++;
@@ -1674,16 +1717,14 @@ BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
          * register. */
         ulMaxPRIGROUPValue <<= portPRIGROUP_SHIFT;
         ulMaxPRIGROUPValue &= portPRIORITY_GROUP_MASK;
-
-        /* Restore the clobbered interrupt priority register to its original
-         * value. */
-        portNVIC_SHPR2_REG = ulOriginalPriority;
     }
     #endif /* #if ( ( configASSERT_DEFINED == 1 ) && ( portHAS_ARMV8M_MAIN_EXTENSION == 1 ) ) */
 
-    /* Make PendSV, CallSV and SysTick the same priority as the kernel. */
+    /* Make PendSV and SysTick the lowest priority interrupts, and make SVCall
+     * the highest priority. */
     portNVIC_SHPR3_REG |= portNVIC_PENDSV_PRI;
     portNVIC_SHPR3_REG |= portNVIC_SYSTICK_PRI;
+    portNVIC_SHPR2_REG = 0;
 
     #if ( configENABLE_MPU == 1 )
     {

portable/IAR/ARM_CM23_NTZ/non_secure/port.c

@@ -80,6 +80,12 @@
 #endif
 /*-----------------------------------------------------------*/
 
+/**
+ * @brief Prototype of all Interrupt Service Routines (ISRs).
+ */
+typedef void ( * portISR_t )( void );
+/*-----------------------------------------------------------*/
+
 /**
  * @brief Constants required to manipulate the NVIC.
  */
@@ -101,10 +107,18 @@
 /**
  * @brief Constants required to manipulate the SCB.
  */
-#define portSCB_SYS_HANDLER_CTRL_STATE_REG    ( *( volatile uint32_t * ) 0xe000ed24 )
+#define portSCB_VTOR_REG                      ( *( ( portISR_t ** ) 0xe000ed08 ) )
+#define portSCB_SYS_HANDLER_CTRL_STATE_REG    ( *( ( volatile uint32_t * ) 0xe000ed24 ) )
 #define portSCB_MEM_FAULT_ENABLE_BIT          ( 1UL << 16UL )
 /*-----------------------------------------------------------*/
 
+/**
+ * @brief Constants used to check the installation of the FreeRTOS interrupt handlers.
+ */
+#define portVECTOR_INDEX_SVC       ( 11 )
+#define portVECTOR_INDEX_PENDSV    ( 14 )
+/*-----------------------------------------------------------*/
+
 /**
  * @brief Constants required to check the validity of an interrupt priority.
  */
@@ -1598,22 +1612,52 @@ void vPortSVCHandler_C( uint32_t * pulCallerStackAddress ) /* PRIVILEGED_FUNCTIO
 
 BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
 {
+    /* An application can install FreeRTOS interrupt handlers in one of the
+     * folllowing ways:
+     * 1. Direct Routing - Install the functions SVC_Handler and PendSV_Handler
+     *    for SVCall and PendSV interrupts respectively.
+     * 2. Indirect Routing - Install separate handlers for SVCall and PendSV
+     *    interrupts and route program control from those handlers to
+     *    SVC_Handler and PendSV_Handler functions.
+     *
+     * Applications that use Indirect Routing must set
+     * configCHECK_HANDLER_INSTALLATION to 0 in their FreeRTOSConfig.h. Direct
+     * routing, which is validated here when configCHECK_HANDLER_INSTALLATION
+     * is 1, should be preferred when possible. */
+    #if ( configCHECK_HANDLER_INSTALLATION == 1 )
+    {
+        const portISR_t * const pxVectorTable = portSCB_VTOR_REG;
+
+        /* Validate that the application has correctly installed the FreeRTOS
+         * handlers for SVCall and PendSV interrupts. We do not check the
+         * installation of the SysTick handler because the application may
+         * choose to drive the RTOS tick using a timer other than the SysTick
+         * timer by overriding the weak function vPortSetupTimerInterrupt().
+         *
+         * Assertion failures here indicate incorrect installation of the
+         * FreeRTOS handlers. For help installing the FreeRTOS handlers, see
+         * https://www.FreeRTOS.org/FAQHelp.html.
+         *
+         * Systems with a configurable address for the interrupt vector table
+         * can also encounter assertion failures or even system faults here if
+         * VTOR is not set correctly to point to the application's vector table. */
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_SVC ] == SVC_Handler );
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_PENDSV ] == PendSV_Handler );
+    }
+    #endif /* configCHECK_HANDLER_INSTALLATION */
+
     #if ( ( configASSERT_DEFINED == 1 ) && ( portHAS_ARMV8M_MAIN_EXTENSION == 1 ) )
     {
-        volatile uint32_t ulOriginalPriority;
         volatile uint32_t ulImplementedPrioBits = 0;
         volatile uint8_t ucMaxPriorityValue;
 
         /* Determine the maximum priority from which ISR safe FreeRTOS API
-         * functions can be called.  ISR safe functions are those that end in
+         * functions can be called. ISR safe functions are those that end in
-         * "FromISR".  FreeRTOS maintains separate thread and ISR API functions to
+         * "FromISR". FreeRTOS maintains separate thread and ISR API functions to
          * ensure interrupt entry is as fast and simple as possible.
          *
-         * Save the interrupt priority value that is about to be clobbered. */
+         * First, determine the number of priority bits available. Write to all
-        ulOriginalPriority = portNVIC_SHPR2_REG;
+         * possible bits in the priority setting for SVCall. */
-
-        /* Determine the number of priority bits available.  First write to all
-         * possible bits. */
         portNVIC_SHPR2_REG = 0xFF000000;
 
         /* Read the value back to see how many bits stuck. */
@@ -1636,7 +1680,6 @@ BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
 
         /* Calculate the maximum acceptable priority group value for the number
          * of bits read back. */
-
         while( ( ucMaxPriorityValue & portTOP_BIT_OF_BYTE ) == portTOP_BIT_OF_BYTE )
         {
             ulImplementedPrioBits++;
@@ -1674,16 +1717,14 @@ BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
          * register. */
         ulMaxPRIGROUPValue <<= portPRIGROUP_SHIFT;
         ulMaxPRIGROUPValue &= portPRIORITY_GROUP_MASK;
-
-        /* Restore the clobbered interrupt priority register to its original
-         * value. */
-        portNVIC_SHPR2_REG = ulOriginalPriority;
     }
     #endif /* #if ( ( configASSERT_DEFINED == 1 ) && ( portHAS_ARMV8M_MAIN_EXTENSION == 1 ) ) */
 
-    /* Make PendSV, CallSV and SysTick the same priority as the kernel. */
+    /* Make PendSV and SysTick the lowest priority interrupts, and make SVCall
+     * the highest priority. */
     portNVIC_SHPR3_REG |= portNVIC_PENDSV_PRI;
     portNVIC_SHPR3_REG |= portNVIC_SYSTICK_PRI;
+    portNVIC_SHPR2_REG = 0;
 
     #if ( configENABLE_MPU == 1 )
     {

portable/IAR/ARM_CM3/port.c

@@ -41,10 +41,14 @@
     #error configMAX_SYSCALL_INTERRUPT_PRIORITY must not be set to 0.  See http: /*www.FreeRTOS.org/RTOS-Cortex-M3-M4.html */
 #endif
 
+/* Prototype of all Interrupt Service Routines (ISRs). */
+typedef void ( * portISR_t )( void );
+
 /* Constants required to manipulate the core.  Registers first... */
 #define portNVIC_SYSTICK_CTRL_REG             ( *( ( volatile uint32_t * ) 0xe000e010 ) )
 #define portNVIC_SYSTICK_LOAD_REG             ( *( ( volatile uint32_t * ) 0xe000e014 ) )
 #define portNVIC_SYSTICK_CURRENT_VALUE_REG    ( *( ( volatile uint32_t * ) 0xe000e018 ) )
+#define portNVIC_SHPR2_REG                    ( *( ( volatile uint32_t * ) 0xe000ed1c ) )
 #define portNVIC_SHPR3_REG                    ( *( ( volatile uint32_t * ) 0xe000ed20 ) )
 /* ...then bits in the registers. */
 #define portNVIC_SYSTICK_CLK_BIT              ( 1UL << 2UL )
@@ -59,6 +63,11 @@
 #define portNVIC_PENDSV_PRI                   ( ( ( uint32_t ) portMIN_INTERRUPT_PRIORITY ) << 16UL )
 #define portNVIC_SYSTICK_PRI                  ( ( ( uint32_t ) portMIN_INTERRUPT_PRIORITY ) << 24UL )
 
+/* Constants used to check the installation of the FreeRTOS interrupt handlers. */
+#define portSCB_VTOR_REG                      ( *( ( portISR_t ** ) 0xE000ED08 ) )
+#define portVECTOR_INDEX_SVC                  ( 11 )
+#define portVECTOR_INDEX_PENDSV               ( 14 )
+
 /* Constants required to check the validity of an interrupt priority. */
 #define portFIRST_USER_INTERRUPT_NUMBER       ( 16 )
 #define portNVIC_IP_REGISTERS_OFFSET_16       ( 0xE000E3F0 )
@@ -121,6 +130,11 @@ extern void vPortStartFirstTask( void );
  */
 static void prvTaskExitError( void );
 
+/*
+ * FreeRTOS handlers implemented in assembly.
+ */
+extern void vPortSVCHandler( void );
+extern void xPortPendSVHandler( void );
 /*-----------------------------------------------------------*/
 
 /* Each task maintains its own interrupt status in the critical nesting
@@ -208,6 +222,40 @@ static void prvTaskExitError( void )
  */
 BaseType_t xPortStartScheduler( void )
 {
+    /* An application can install FreeRTOS interrupt handlers in one of the
+     * folllowing ways:
+     * 1. Direct Routing - Install the functions vPortSVCHandler and
+     *    xPortPendSVHandler for SVCall and PendSV interrupts respectively.
+     * 2. Indirect Routing - Install separate handlers for SVCall and PendSV
+     *    interrupts and route program control from those handlers to
+     *    vPortSVCHandler and xPortPendSVHandler functions.
+     *
+     * Applications that use Indirect Routing must set
+     * configCHECK_HANDLER_INSTALLATION to 0 in their FreeRTOSConfig.h. Direct
+     * routing, which is validated here when configCHECK_HANDLER_INSTALLATION
+     * is 1, should be preferred when possible. */
+    #if ( configCHECK_HANDLER_INSTALLATION == 1 )
+    {
+        const portISR_t * const pxVectorTable = portSCB_VTOR_REG;
+
+        /* Validate that the application has correctly installed the FreeRTOS
+         * handlers for SVCall and PendSV interrupts. We do not check the
+         * installation of the SysTick handler because the application may
+         * choose to drive the RTOS tick using a timer other than the SysTick
+         * timer by overriding the weak function vPortSetupTimerInterrupt().
+         *
+         * Assertion failures here indicate incorrect installation of the
+         * FreeRTOS handlers. For help installing the FreeRTOS handlers, see
+         * https://www.FreeRTOS.org/FAQHelp.html.
+         *
+         * Systems with a configurable address for the interrupt vector table
+         * can also encounter assertion failures or even system faults here if
+         * VTOR is not set correctly to point to the application's vector table. */
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_SVC ] == vPortSVCHandler );
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_PENDSV ] == xPortPendSVHandler );
+    }
+    #endif /* configCHECK_HANDLER_INSTALLATION */
+
     #if ( configASSERT_DEFINED == 1 )
     {
         volatile uint8_t ucOriginalPriority;
@@ -292,9 +340,11 @@ BaseType_t xPortStartScheduler( void )
     }
     #endif /* configASSERT_DEFINED */
 
-    /* Make PendSV and SysTick the lowest priority interrupts. */
+    /* Make PendSV and SysTick the lowest priority interrupts, and make SVCall
+     * the highest priority. */
     portNVIC_SHPR3_REG |= portNVIC_PENDSV_PRI;
     portNVIC_SHPR3_REG |= portNVIC_SYSTICK_PRI;
+    portNVIC_SHPR2_REG = 0;
 
     /* Start the timer that generates the tick ISR.  Interrupts are disabled
      * here already. */

portable/IAR/ARM_CM33/non_secure/port.c

@@ -80,6 +80,12 @@
 #endif
 /*-----------------------------------------------------------*/
 
+/**
+ * @brief Prototype of all Interrupt Service Routines (ISRs).
+ */
+typedef void ( * portISR_t )( void );
+/*-----------------------------------------------------------*/
+
 /**
  * @brief Constants required to manipulate the NVIC.
  */
@@ -101,10 +107,18 @@
 /**
  * @brief Constants required to manipulate the SCB.
  */
-#define portSCB_SYS_HANDLER_CTRL_STATE_REG    ( *( volatile uint32_t * ) 0xe000ed24 )
+#define portSCB_VTOR_REG                      ( *( ( portISR_t ** ) 0xe000ed08 ) )
+#define portSCB_SYS_HANDLER_CTRL_STATE_REG    ( *( ( volatile uint32_t * ) 0xe000ed24 ) )
 #define portSCB_MEM_FAULT_ENABLE_BIT          ( 1UL << 16UL )
 /*-----------------------------------------------------------*/
 
+/**
+ * @brief Constants used to check the installation of the FreeRTOS interrupt handlers.
+ */
+#define portVECTOR_INDEX_SVC       ( 11 )
+#define portVECTOR_INDEX_PENDSV    ( 14 )
+/*-----------------------------------------------------------*/
+
 /**
  * @brief Constants required to check the validity of an interrupt priority.
  */
@@ -1598,22 +1612,52 @@ void vPortSVCHandler_C( uint32_t * pulCallerStackAddress ) /* PRIVILEGED_FUNCTIO
 
 BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
 {
+    /* An application can install FreeRTOS interrupt handlers in one of the
+     * folllowing ways:
+     * 1. Direct Routing - Install the functions SVC_Handler and PendSV_Handler
+     *    for SVCall and PendSV interrupts respectively.
+     * 2. Indirect Routing - Install separate handlers for SVCall and PendSV
+     *    interrupts and route program control from those handlers to
+     *    SVC_Handler and PendSV_Handler functions.
+     *
+     * Applications that use Indirect Routing must set
+     * configCHECK_HANDLER_INSTALLATION to 0 in their FreeRTOSConfig.h. Direct
+     * routing, which is validated here when configCHECK_HANDLER_INSTALLATION
+     * is 1, should be preferred when possible. */
+    #if ( configCHECK_HANDLER_INSTALLATION == 1 )
+    {
+        const portISR_t * const pxVectorTable = portSCB_VTOR_REG;
+
+        /* Validate that the application has correctly installed the FreeRTOS
+         * handlers for SVCall and PendSV interrupts. We do not check the
+         * installation of the SysTick handler because the application may
+         * choose to drive the RTOS tick using a timer other than the SysTick
+         * timer by overriding the weak function vPortSetupTimerInterrupt().
+         *
+         * Assertion failures here indicate incorrect installation of the
+         * FreeRTOS handlers. For help installing the FreeRTOS handlers, see
+         * https://www.FreeRTOS.org/FAQHelp.html.
+         *
+         * Systems with a configurable address for the interrupt vector table
+         * can also encounter assertion failures or even system faults here if
+         * VTOR is not set correctly to point to the application's vector table. */
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_SVC ] == SVC_Handler );
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_PENDSV ] == PendSV_Handler );
+    }
+    #endif /* configCHECK_HANDLER_INSTALLATION */
+
     #if ( ( configASSERT_DEFINED == 1 ) && ( portHAS_ARMV8M_MAIN_EXTENSION == 1 ) )
     {
-        volatile uint32_t ulOriginalPriority;
         volatile uint32_t ulImplementedPrioBits = 0;
         volatile uint8_t ucMaxPriorityValue;
 
         /* Determine the maximum priority from which ISR safe FreeRTOS API
-         * functions can be called.  ISR safe functions are those that end in
+         * functions can be called. ISR safe functions are those that end in
-         * "FromISR".  FreeRTOS maintains separate thread and ISR API functions to
+         * "FromISR". FreeRTOS maintains separate thread and ISR API functions to
          * ensure interrupt entry is as fast and simple as possible.
          *
-         * Save the interrupt priority value that is about to be clobbered. */
+         * First, determine the number of priority bits available. Write to all
-        ulOriginalPriority = portNVIC_SHPR2_REG;
+         * possible bits in the priority setting for SVCall. */
-
-        /* Determine the number of priority bits available.  First write to all
-         * possible bits. */
         portNVIC_SHPR2_REG = 0xFF000000;
 
         /* Read the value back to see how many bits stuck. */
@@ -1636,7 +1680,6 @@ BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
 
         /* Calculate the maximum acceptable priority group value for the number
          * of bits read back. */
-
         while( ( ucMaxPriorityValue & portTOP_BIT_OF_BYTE ) == portTOP_BIT_OF_BYTE )
         {
             ulImplementedPrioBits++;
@@ -1674,16 +1717,14 @@ BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
          * register. */
         ulMaxPRIGROUPValue <<= portPRIGROUP_SHIFT;
         ulMaxPRIGROUPValue &= portPRIORITY_GROUP_MASK;
-
-        /* Restore the clobbered interrupt priority register to its original
-         * value. */
-        portNVIC_SHPR2_REG = ulOriginalPriority;
     }
     #endif /* #if ( ( configASSERT_DEFINED == 1 ) && ( portHAS_ARMV8M_MAIN_EXTENSION == 1 ) ) */
 
-    /* Make PendSV, CallSV and SysTick the same priority as the kernel. */
+    /* Make PendSV and SysTick the lowest priority interrupts, and make SVCall
+     * the highest priority. */
     portNVIC_SHPR3_REG |= portNVIC_PENDSV_PRI;
     portNVIC_SHPR3_REG |= portNVIC_SYSTICK_PRI;
+    portNVIC_SHPR2_REG = 0;
 
     #if ( configENABLE_MPU == 1 )
     {

portable/IAR/ARM_CM33_NTZ/non_secure/port.c

@@ -80,6 +80,12 @@
 #endif
 /*-----------------------------------------------------------*/
 
+/**
+ * @brief Prototype of all Interrupt Service Routines (ISRs).
+ */
+typedef void ( * portISR_t )( void );
+/*-----------------------------------------------------------*/
+
 /**
  * @brief Constants required to manipulate the NVIC.
  */
@@ -101,10 +107,18 @@
 /**
  * @brief Constants required to manipulate the SCB.
  */
-#define portSCB_SYS_HANDLER_CTRL_STATE_REG    ( *( volatile uint32_t * ) 0xe000ed24 )
+#define portSCB_VTOR_REG                      ( *( ( portISR_t ** ) 0xe000ed08 ) )
+#define portSCB_SYS_HANDLER_CTRL_STATE_REG    ( *( ( volatile uint32_t * ) 0xe000ed24 ) )
 #define portSCB_MEM_FAULT_ENABLE_BIT          ( 1UL << 16UL )
 /*-----------------------------------------------------------*/
 
+/**
+ * @brief Constants used to check the installation of the FreeRTOS interrupt handlers.
+ */
+#define portVECTOR_INDEX_SVC       ( 11 )
+#define portVECTOR_INDEX_PENDSV    ( 14 )
+/*-----------------------------------------------------------*/
+
 /**
  * @brief Constants required to check the validity of an interrupt priority.
  */
@@ -1598,22 +1612,52 @@ void vPortSVCHandler_C( uint32_t * pulCallerStackAddress ) /* PRIVILEGED_FUNCTIO
 
 BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
 {
+    /* An application can install FreeRTOS interrupt handlers in one of the
+     * folllowing ways:
+     * 1. Direct Routing - Install the functions SVC_Handler and PendSV_Handler
+     *    for SVCall and PendSV interrupts respectively.
+     * 2. Indirect Routing - Install separate handlers for SVCall and PendSV
+     *    interrupts and route program control from those handlers to
+     *    SVC_Handler and PendSV_Handler functions.
+     *
+     * Applications that use Indirect Routing must set
+     * configCHECK_HANDLER_INSTALLATION to 0 in their FreeRTOSConfig.h. Direct
+     * routing, which is validated here when configCHECK_HANDLER_INSTALLATION
+     * is 1, should be preferred when possible. */
+    #if ( configCHECK_HANDLER_INSTALLATION == 1 )
+    {
+        const portISR_t * const pxVectorTable = portSCB_VTOR_REG;
+
+        /* Validate that the application has correctly installed the FreeRTOS
+         * handlers for SVCall and PendSV interrupts. We do not check the
+         * installation of the SysTick handler because the application may
+         * choose to drive the RTOS tick using a timer other than the SysTick
+         * timer by overriding the weak function vPortSetupTimerInterrupt().
+         *
+         * Assertion failures here indicate incorrect installation of the
+         * FreeRTOS handlers. For help installing the FreeRTOS handlers, see
+         * https://www.FreeRTOS.org/FAQHelp.html.
+         *
+         * Systems with a configurable address for the interrupt vector table
+         * can also encounter assertion failures or even system faults here if
+         * VTOR is not set correctly to point to the application's vector table. */
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_SVC ] == SVC_Handler );
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_PENDSV ] == PendSV_Handler );
+    }
+    #endif /* configCHECK_HANDLER_INSTALLATION */
+
     #if ( ( configASSERT_DEFINED == 1 ) && ( portHAS_ARMV8M_MAIN_EXTENSION == 1 ) )
     {
-        volatile uint32_t ulOriginalPriority;
         volatile uint32_t ulImplementedPrioBits = 0;
         volatile uint8_t ucMaxPriorityValue;
 
         /* Determine the maximum priority from which ISR safe FreeRTOS API
-         * functions can be called.  ISR safe functions are those that end in
+         * functions can be called. ISR safe functions are those that end in
-         * "FromISR".  FreeRTOS maintains separate thread and ISR API functions to
+         * "FromISR". FreeRTOS maintains separate thread and ISR API functions to
          * ensure interrupt entry is as fast and simple as possible.
          *
-         * Save the interrupt priority value that is about to be clobbered. */
+         * First, determine the number of priority bits available. Write to all
-        ulOriginalPriority = portNVIC_SHPR2_REG;
+         * possible bits in the priority setting for SVCall. */
-
-        /* Determine the number of priority bits available.  First write to all
-         * possible bits. */
         portNVIC_SHPR2_REG = 0xFF000000;
 
         /* Read the value back to see how many bits stuck. */
@@ -1636,7 +1680,6 @@ BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
 
         /* Calculate the maximum acceptable priority group value for the number
          * of bits read back. */
-
         while( ( ucMaxPriorityValue & portTOP_BIT_OF_BYTE ) == portTOP_BIT_OF_BYTE )
         {
             ulImplementedPrioBits++;
@@ -1674,16 +1717,14 @@ BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
          * register. */
         ulMaxPRIGROUPValue <<= portPRIGROUP_SHIFT;
         ulMaxPRIGROUPValue &= portPRIORITY_GROUP_MASK;
-
-        /* Restore the clobbered interrupt priority register to its original
-         * value. */
-        portNVIC_SHPR2_REG = ulOriginalPriority;
     }
     #endif /* #if ( ( configASSERT_DEFINED == 1 ) && ( portHAS_ARMV8M_MAIN_EXTENSION == 1 ) ) */
 
-    /* Make PendSV, CallSV and SysTick the same priority as the kernel. */
+    /* Make PendSV and SysTick the lowest priority interrupts, and make SVCall
+     * the highest priority. */
     portNVIC_SHPR3_REG |= portNVIC_PENDSV_PRI;
     portNVIC_SHPR3_REG |= portNVIC_SYSTICK_PRI;
+    portNVIC_SHPR2_REG = 0;
 
     #if ( configENABLE_MPU == 1 )
     {

portable/IAR/ARM_CM35P/non_secure/port.c

@@ -80,6 +80,12 @@
 #endif
 /*-----------------------------------------------------------*/
 
+/**
+ * @brief Prototype of all Interrupt Service Routines (ISRs).
+ */
+typedef void ( * portISR_t )( void );
+/*-----------------------------------------------------------*/
+
 /**
  * @brief Constants required to manipulate the NVIC.
  */
@@ -101,10 +107,18 @@
 /**
  * @brief Constants required to manipulate the SCB.
  */
-#define portSCB_SYS_HANDLER_CTRL_STATE_REG    ( *( volatile uint32_t * ) 0xe000ed24 )
+#define portSCB_VTOR_REG                      ( *( ( portISR_t ** ) 0xe000ed08 ) )
+#define portSCB_SYS_HANDLER_CTRL_STATE_REG    ( *( ( volatile uint32_t * ) 0xe000ed24 ) )
 #define portSCB_MEM_FAULT_ENABLE_BIT          ( 1UL << 16UL )
 /*-----------------------------------------------------------*/
 
+/**
+ * @brief Constants used to check the installation of the FreeRTOS interrupt handlers.
+ */
+#define portVECTOR_INDEX_SVC       ( 11 )
+#define portVECTOR_INDEX_PENDSV    ( 14 )
+/*-----------------------------------------------------------*/
+
 /**
  * @brief Constants required to check the validity of an interrupt priority.
  */
@@ -1598,22 +1612,52 @@ void vPortSVCHandler_C( uint32_t * pulCallerStackAddress ) /* PRIVILEGED_FUNCTIO
 
 BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
 {
+    /* An application can install FreeRTOS interrupt handlers in one of the
+     * folllowing ways:
+     * 1. Direct Routing - Install the functions SVC_Handler and PendSV_Handler
+     *    for SVCall and PendSV interrupts respectively.
+     * 2. Indirect Routing - Install separate handlers for SVCall and PendSV
+     *    interrupts and route program control from those handlers to
+     *    SVC_Handler and PendSV_Handler functions.
+     *
+     * Applications that use Indirect Routing must set
+     * configCHECK_HANDLER_INSTALLATION to 0 in their FreeRTOSConfig.h. Direct
+     * routing, which is validated here when configCHECK_HANDLER_INSTALLATION
+     * is 1, should be preferred when possible. */
+    #if ( configCHECK_HANDLER_INSTALLATION == 1 )
+    {
+        const portISR_t * const pxVectorTable = portSCB_VTOR_REG;
+
+        /* Validate that the application has correctly installed the FreeRTOS
+         * handlers for SVCall and PendSV interrupts. We do not check the
+         * installation of the SysTick handler because the application may
+         * choose to drive the RTOS tick using a timer other than the SysTick
+         * timer by overriding the weak function vPortSetupTimerInterrupt().
+         *
+         * Assertion failures here indicate incorrect installation of the
+         * FreeRTOS handlers. For help installing the FreeRTOS handlers, see
+         * https://www.FreeRTOS.org/FAQHelp.html.
+         *
+         * Systems with a configurable address for the interrupt vector table
+         * can also encounter assertion failures or even system faults here if
+         * VTOR is not set correctly to point to the application's vector table. */
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_SVC ] == SVC_Handler );
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_PENDSV ] == PendSV_Handler );
+    }
+    #endif /* configCHECK_HANDLER_INSTALLATION */
+
     #if ( ( configASSERT_DEFINED == 1 ) && ( portHAS_ARMV8M_MAIN_EXTENSION == 1 ) )
     {
-        volatile uint32_t ulOriginalPriority;
         volatile uint32_t ulImplementedPrioBits = 0;
         volatile uint8_t ucMaxPriorityValue;
 
         /* Determine the maximum priority from which ISR safe FreeRTOS API
-         * functions can be called.  ISR safe functions are those that end in
+         * functions can be called. ISR safe functions are those that end in
-         * "FromISR".  FreeRTOS maintains separate thread and ISR API functions to
+         * "FromISR". FreeRTOS maintains separate thread and ISR API functions to
          * ensure interrupt entry is as fast and simple as possible.
          *
-         * Save the interrupt priority value that is about to be clobbered. */
+         * First, determine the number of priority bits available. Write to all
-        ulOriginalPriority = portNVIC_SHPR2_REG;
+         * possible bits in the priority setting for SVCall. */
-
-        /* Determine the number of priority bits available.  First write to all
-         * possible bits. */
         portNVIC_SHPR2_REG = 0xFF000000;
 
         /* Read the value back to see how many bits stuck. */
@@ -1636,7 +1680,6 @@ BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
 
         /* Calculate the maximum acceptable priority group value for the number
          * of bits read back. */
-
         while( ( ucMaxPriorityValue & portTOP_BIT_OF_BYTE ) == portTOP_BIT_OF_BYTE )
         {
             ulImplementedPrioBits++;
@@ -1674,16 +1717,14 @@ BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
          * register. */
         ulMaxPRIGROUPValue <<= portPRIGROUP_SHIFT;
         ulMaxPRIGROUPValue &= portPRIORITY_GROUP_MASK;
-
-        /* Restore the clobbered interrupt priority register to its original
-         * value. */
-        portNVIC_SHPR2_REG = ulOriginalPriority;
     }
     #endif /* #if ( ( configASSERT_DEFINED == 1 ) && ( portHAS_ARMV8M_MAIN_EXTENSION == 1 ) ) */
 
-    /* Make PendSV, CallSV and SysTick the same priority as the kernel. */
+    /* Make PendSV and SysTick the lowest priority interrupts, and make SVCall
+     * the highest priority. */
     portNVIC_SHPR3_REG |= portNVIC_PENDSV_PRI;
     portNVIC_SHPR3_REG |= portNVIC_SYSTICK_PRI;
+    portNVIC_SHPR2_REG = 0;
 
     #if ( configENABLE_MPU == 1 )
     {

portable/IAR/ARM_CM35P_NTZ/non_secure/port.c

@@ -80,6 +80,12 @@
 #endif
 /*-----------------------------------------------------------*/
 
+/**
+ * @brief Prototype of all Interrupt Service Routines (ISRs).
+ */
+typedef void ( * portISR_t )( void );
+/*-----------------------------------------------------------*/
+
 /**
  * @brief Constants required to manipulate the NVIC.
  */
@@ -101,10 +107,18 @@
 /**
  * @brief Constants required to manipulate the SCB.
  */
-#define portSCB_SYS_HANDLER_CTRL_STATE_REG    ( *( volatile uint32_t * ) 0xe000ed24 )
+#define portSCB_VTOR_REG                      ( *( ( portISR_t ** ) 0xe000ed08 ) )
+#define portSCB_SYS_HANDLER_CTRL_STATE_REG    ( *( ( volatile uint32_t * ) 0xe000ed24 ) )
 #define portSCB_MEM_FAULT_ENABLE_BIT          ( 1UL << 16UL )
 /*-----------------------------------------------------------*/
 
+/**
+ * @brief Constants used to check the installation of the FreeRTOS interrupt handlers.
+ */
+#define portVECTOR_INDEX_SVC       ( 11 )
+#define portVECTOR_INDEX_PENDSV    ( 14 )
+/*-----------------------------------------------------------*/
+
 /**
  * @brief Constants required to check the validity of an interrupt priority.
  */
@@ -1598,22 +1612,52 @@ void vPortSVCHandler_C( uint32_t * pulCallerStackAddress ) /* PRIVILEGED_FUNCTIO
 
 BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
 {
+    /* An application can install FreeRTOS interrupt handlers in one of the
+     * folllowing ways:
+     * 1. Direct Routing - Install the functions SVC_Handler and PendSV_Handler
+     *    for SVCall and PendSV interrupts respectively.
+     * 2. Indirect Routing - Install separate handlers for SVCall and PendSV
+     *    interrupts and route program control from those handlers to
+     *    SVC_Handler and PendSV_Handler functions.
+     *
+     * Applications that use Indirect Routing must set
+     * configCHECK_HANDLER_INSTALLATION to 0 in their FreeRTOSConfig.h. Direct
+     * routing, which is validated here when configCHECK_HANDLER_INSTALLATION
+     * is 1, should be preferred when possible. */
+    #if ( configCHECK_HANDLER_INSTALLATION == 1 )
+    {
+        const portISR_t * const pxVectorTable = portSCB_VTOR_REG;
+
+        /* Validate that the application has correctly installed the FreeRTOS
+         * handlers for SVCall and PendSV interrupts. We do not check the
+         * installation of the SysTick handler because the application may
+         * choose to drive the RTOS tick using a timer other than the SysTick
+         * timer by overriding the weak function vPortSetupTimerInterrupt().
+         *
+         * Assertion failures here indicate incorrect installation of the
+         * FreeRTOS handlers. For help installing the FreeRTOS handlers, see
+         * https://www.FreeRTOS.org/FAQHelp.html.
+         *
+         * Systems with a configurable address for the interrupt vector table
+         * can also encounter assertion failures or even system faults here if
+         * VTOR is not set correctly to point to the application's vector table. */
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_SVC ] == SVC_Handler );
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_PENDSV ] == PendSV_Handler );
+    }
+    #endif /* configCHECK_HANDLER_INSTALLATION */
+
     #if ( ( configASSERT_DEFINED == 1 ) && ( portHAS_ARMV8M_MAIN_EXTENSION == 1 ) )
     {
-        volatile uint32_t ulOriginalPriority;
         volatile uint32_t ulImplementedPrioBits = 0;
         volatile uint8_t ucMaxPriorityValue;
 
         /* Determine the maximum priority from which ISR safe FreeRTOS API
-         * functions can be called.  ISR safe functions are those that end in
+         * functions can be called. ISR safe functions are those that end in
-         * "FromISR".  FreeRTOS maintains separate thread and ISR API functions to
+         * "FromISR". FreeRTOS maintains separate thread and ISR API functions to
          * ensure interrupt entry is as fast and simple as possible.
          *
-         * Save the interrupt priority value that is about to be clobbered. */
+         * First, determine the number of priority bits available. Write to all
-        ulOriginalPriority = portNVIC_SHPR2_REG;
+         * possible bits in the priority setting for SVCall. */
-
-        /* Determine the number of priority bits available.  First write to all
-         * possible bits. */
         portNVIC_SHPR2_REG = 0xFF000000;
 
         /* Read the value back to see how many bits stuck. */
@@ -1636,7 +1680,6 @@ BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
 
         /* Calculate the maximum acceptable priority group value for the number
          * of bits read back. */
-
         while( ( ucMaxPriorityValue & portTOP_BIT_OF_BYTE ) == portTOP_BIT_OF_BYTE )
         {
             ulImplementedPrioBits++;
@@ -1674,16 +1717,14 @@ BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
          * register. */
         ulMaxPRIGROUPValue <<= portPRIGROUP_SHIFT;
         ulMaxPRIGROUPValue &= portPRIORITY_GROUP_MASK;
-
-        /* Restore the clobbered interrupt priority register to its original
-         * value. */
-        portNVIC_SHPR2_REG = ulOriginalPriority;
     }
     #endif /* #if ( ( configASSERT_DEFINED == 1 ) && ( portHAS_ARMV8M_MAIN_EXTENSION == 1 ) ) */
 
-    /* Make PendSV, CallSV and SysTick the same priority as the kernel. */
+    /* Make PendSV and SysTick the lowest priority interrupts, and make SVCall
+     * the highest priority. */
     portNVIC_SHPR3_REG |= portNVIC_PENDSV_PRI;
     portNVIC_SHPR3_REG |= portNVIC_SYSTICK_PRI;
+    portNVIC_SHPR2_REG = 0;
 
     #if ( configENABLE_MPU == 1 )
     {

portable/IAR/ARM_CM4F/port.c

@@ -45,10 +45,14 @@
     #error configMAX_SYSCALL_INTERRUPT_PRIORITY must not be set to 0.  See http: /*www.FreeRTOS.org/RTOS-Cortex-M3-M4.html */
 #endif
 
+/* Prototype of all Interrupt Service Routines (ISRs). */
+typedef void ( * portISR_t )( void );
+
 /* Constants required to manipulate the core.  Registers first... */
 #define portNVIC_SYSTICK_CTRL_REG             ( *( ( volatile uint32_t * ) 0xe000e010 ) )
 #define portNVIC_SYSTICK_LOAD_REG             ( *( ( volatile uint32_t * ) 0xe000e014 ) )
 #define portNVIC_SYSTICK_CURRENT_VALUE_REG    ( *( ( volatile uint32_t * ) 0xe000e018 ) )
+#define portNVIC_SHPR2_REG                    ( *( ( volatile uint32_t * ) 0xe000ed1c ) )
 #define portNVIC_SHPR3_REG                    ( *( ( volatile uint32_t * ) 0xe000ed20 ) )
 /* ...then bits in the registers. */
 #define portNVIC_SYSTICK_CLK_BIT              ( 1UL << 2UL )
@@ -69,6 +73,11 @@
 #define portNVIC_PENDSV_PRI                   ( ( ( uint32_t ) portMIN_INTERRUPT_PRIORITY ) << 16UL )
 #define portNVIC_SYSTICK_PRI                  ( ( ( uint32_t ) portMIN_INTERRUPT_PRIORITY ) << 24UL )
 
+/* Constants used to check the installation of the FreeRTOS interrupt handlers. */
+#define portSCB_VTOR_REG                      ( *( ( portISR_t ** ) 0xE000ED08 ) )
+#define portVECTOR_INDEX_SVC                  ( 11 )
+#define portVECTOR_INDEX_PENDSV               ( 14 )
+
 /* Constants required to check the validity of an interrupt priority. */
 #define portFIRST_USER_INTERRUPT_NUMBER       ( 16 )
 #define portNVIC_IP_REGISTERS_OFFSET_16       ( 0xE000E3F0 )
@@ -141,6 +150,11 @@ extern void vPortEnableVFP( void );
  */
 static void prvTaskExitError( void );
 
+/*
+ * FreeRTOS handlers implemented in assembly.
+ */
+extern void vPortSVCHandler( void );
+extern void xPortPendSVHandler( void );
 /*-----------------------------------------------------------*/
 
 /* Each task maintains its own interrupt status in the critical nesting
@@ -246,6 +260,40 @@ BaseType_t xPortStartScheduler( void )
     configASSERT( portCPUID != portCORTEX_M7_r0p1_ID );
     configASSERT( portCPUID != portCORTEX_M7_r0p0_ID );
 
+    /* An application can install FreeRTOS interrupt handlers in one of the
+     * folllowing ways:
+     * 1. Direct Routing - Install the functions vPortSVCHandler and
+     *    xPortPendSVHandler for SVCall and PendSV interrupts respectively.
+     * 2. Indirect Routing - Install separate handlers for SVCall and PendSV
+     *    interrupts and route program control from those handlers to
+     *    vPortSVCHandler and xPortPendSVHandler functions.
+     *
+     * Applications that use Indirect Routing must set
+     * configCHECK_HANDLER_INSTALLATION to 0 in their FreeRTOSConfig.h. Direct
+     * routing, which is validated here when configCHECK_HANDLER_INSTALLATION
+     * is 1, should be preferred when possible. */
+    #if ( configCHECK_HANDLER_INSTALLATION == 1 )
+    {
+        const portISR_t * const pxVectorTable = portSCB_VTOR_REG;
+
+        /* Validate that the application has correctly installed the FreeRTOS
+         * handlers for SVCall and PendSV interrupts. We do not check the
+         * installation of the SysTick handler because the application may
+         * choose to drive the RTOS tick using a timer other than the SysTick
+         * timer by overriding the weak function vPortSetupTimerInterrupt().
+         *
+         * Assertion failures here indicate incorrect installation of the
+         * FreeRTOS handlers. For help installing the FreeRTOS handlers, see
+         * https://www.FreeRTOS.org/FAQHelp.html.
+         *
+         * Systems with a configurable address for the interrupt vector table
+         * can also encounter assertion failures or even system faults here if
+         * VTOR is not set correctly to point to the application's vector table. */
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_SVC ] == vPortSVCHandler );
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_PENDSV ] == xPortPendSVHandler );
+    }
+    #endif /* configCHECK_HANDLER_INSTALLATION */
+
     #if ( configASSERT_DEFINED == 1 )
     {
         volatile uint8_t ucOriginalPriority;
@@ -330,9 +378,11 @@ BaseType_t xPortStartScheduler( void )
     }
     #endif /* configASSERT_DEFINED */
 
-    /* Make PendSV and SysTick the lowest priority interrupts. */
+    /* Make PendSV and SysTick the lowest priority interrupts, and make SVCall
+     * the highest priority. */
     portNVIC_SHPR3_REG |= portNVIC_PENDSV_PRI;
     portNVIC_SHPR3_REG |= portNVIC_SYSTICK_PRI;
+    portNVIC_SHPR2_REG = 0;
 
     /* Start the timer that generates the tick ISR.  Interrupts are disabled
      * here already. */

portable/IAR/ARM_CM4F_MPU/port.c

@@ -69,6 +69,9 @@
     #define configALLOW_UNPRIVILEGED_CRITICAL_SECTIONS    1
 #endif
 
+/* Prototype of all Interrupt Service Routines (ISRs). */
+typedef void ( * portISR_t )( void );
+
 /* Constants required to manipulate the core.  Registers first... */
 #define portNVIC_SYSTICK_CTRL_REG                 ( *( ( volatile uint32_t * ) 0xe000e010 ) )
 #define portNVIC_SYSTICK_LOAD_REG                 ( *( ( volatile uint32_t * ) 0xe000e014 ) )
@@ -108,7 +111,11 @@
 #define portMIN_INTERRUPT_PRIORITY                ( 255UL )
 #define portNVIC_PENDSV_PRI                       ( ( ( uint32_t ) portMIN_INTERRUPT_PRIORITY ) << 16UL )
 #define portNVIC_SYSTICK_PRI                      ( ( ( uint32_t ) portMIN_INTERRUPT_PRIORITY ) << 24UL )
-#define portNVIC_SVC_PRI                          ( ( ( uint32_t ) configMAX_SYSCALL_INTERRUPT_PRIORITY - 1UL ) << 24UL )
+
+/* Constants used to check the installation of the FreeRTOS interrupt handlers. */
+#define portSCB_VTOR_REG                          ( *( ( portISR_t ** ) 0xE000ED08 ) )
+#define portVECTOR_INDEX_SVC                      ( 11 )
+#define portVECTOR_INDEX_PENDSV                   ( 14 )
 
 /* Constants required to check the validity of an interrupt priority. */
 #define portFIRST_USER_INTERRUPT_NUMBER           ( 16 )
@@ -282,6 +289,11 @@ BaseType_t xPortIsTaskPrivileged( void ) PRIVILEGED_FUNCTION;
  */
 void vPortSwitchToUserMode( void );
 
+/*
+ * FreeRTOS handlers implemented in assembly.
+ */
+extern void vPortSVCHandler( void ) PRIVILEGED_FUNCTION;
+extern void xPortPendSVHandler( void ) PRIVILEGED_FUNCTION;
 /*-----------------------------------------------------------*/
 
 /* Each task maintains its own interrupt status in the critical nesting
@@ -384,7 +396,6 @@ void vPortSVCHandler_C( uint32_t * pulParam ) /* PRIVILEGED_FUNCTION */
     switch( ucSVCNumber )
     {
         case portSVC_START_SCHEDULER:
-            portNVIC_SHPR2_REG |= portNVIC_SVC_PRI;
             vPortRestoreContextOfFirstTask();
             break;
 
@@ -713,6 +724,40 @@ BaseType_t xPortStartScheduler( void )
         configASSERT( portCPUID != portCORTEX_M7_r0p0_ID );
     #endif
 
+    /* An application can install FreeRTOS interrupt handlers in one of the
+     * folllowing ways:
+     * 1. Direct Routing - Install the functions vPortSVCHandler and
+     *    xPortPendSVHandler for SVCall and PendSV interrupts respectively.
+     * 2. Indirect Routing - Install separate handlers for SVCall and PendSV
+     *    interrupts and route program control from those handlers to
+     *    vPortSVCHandler and xPortPendSVHandler functions.
+     *
+     * Applications that use Indirect Routing must set
+     * configCHECK_HANDLER_INSTALLATION to 0 in their FreeRTOSConfig.h. Direct
+     * routing, which is validated here when configCHECK_HANDLER_INSTALLATION
+     * is 1, should be preferred when possible. */
+    #if ( configCHECK_HANDLER_INSTALLATION == 1 )
+    {
+        const portISR_t * const pxVectorTable = portSCB_VTOR_REG;
+
+        /* Validate that the application has correctly installed the FreeRTOS
+         * handlers for SVCall and PendSV interrupts. We do not check the
+         * installation of the SysTick handler because the application may
+         * choose to drive the RTOS tick using a timer other than the SysTick
+         * timer by overriding the weak function vPortSetupTimerInterrupt().
+         *
+         * Assertion failures here indicate incorrect installation of the
+         * FreeRTOS handlers. For help installing the FreeRTOS handlers, see
+         * https://www.FreeRTOS.org/FAQHelp.html.
+         *
+         * Systems with a configurable address for the interrupt vector table
+         * can also encounter assertion failures or even system faults here if
+         * VTOR is not set correctly to point to the application's vector table. */
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_SVC ] == vPortSVCHandler );
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_PENDSV ] == xPortPendSVHandler );
+    }
+    #endif /* configCHECK_HANDLER_INSTALLATION */
+
     #if ( configASSERT_DEFINED == 1 )
     {
         volatile uint8_t ucOriginalPriority;
@@ -797,9 +842,11 @@ BaseType_t xPortStartScheduler( void )
     }
     #endif /* configASSERT_DEFINED */
 
-    /* Make PendSV and SysTick the lowest priority interrupts. */
+    /* Make PendSV and SysTick the lowest priority interrupts, and make SVCall
+     * the highest priority. */
     portNVIC_SHPR3_REG |= portNVIC_PENDSV_PRI;
     portNVIC_SHPR3_REG |= portNVIC_SYSTICK_PRI;
+    portNVIC_SHPR2_REG = 0;
 
     /* Configure the regions in the MPU that are common to all tasks. */
     prvSetupMPU();

portable/IAR/ARM_CM55/non_secure/port.c

@@ -80,6 +80,12 @@
 #endif
 /*-----------------------------------------------------------*/
 
+/**
+ * @brief Prototype of all Interrupt Service Routines (ISRs).
+ */
+typedef void ( * portISR_t )( void );
+/*-----------------------------------------------------------*/
+
 /**
  * @brief Constants required to manipulate the NVIC.
  */
@@ -101,10 +107,18 @@
 /**
  * @brief Constants required to manipulate the SCB.
  */
-#define portSCB_SYS_HANDLER_CTRL_STATE_REG    ( *( volatile uint32_t * ) 0xe000ed24 )
+#define portSCB_VTOR_REG                      ( *( ( portISR_t ** ) 0xe000ed08 ) )
+#define portSCB_SYS_HANDLER_CTRL_STATE_REG    ( *( ( volatile uint32_t * ) 0xe000ed24 ) )
 #define portSCB_MEM_FAULT_ENABLE_BIT          ( 1UL << 16UL )
 /*-----------------------------------------------------------*/
 
+/**
+ * @brief Constants used to check the installation of the FreeRTOS interrupt handlers.
+ */
+#define portVECTOR_INDEX_SVC       ( 11 )
+#define portVECTOR_INDEX_PENDSV    ( 14 )
+/*-----------------------------------------------------------*/
+
 /**
  * @brief Constants required to check the validity of an interrupt priority.
  */
@@ -1598,22 +1612,52 @@ void vPortSVCHandler_C( uint32_t * pulCallerStackAddress ) /* PRIVILEGED_FUNCTIO
 
 BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
 {
+    /* An application can install FreeRTOS interrupt handlers in one of the
+     * folllowing ways:
+     * 1. Direct Routing - Install the functions SVC_Handler and PendSV_Handler
+     *    for SVCall and PendSV interrupts respectively.
+     * 2. Indirect Routing - Install separate handlers for SVCall and PendSV
+     *    interrupts and route program control from those handlers to
+     *    SVC_Handler and PendSV_Handler functions.
+     *
+     * Applications that use Indirect Routing must set
+     * configCHECK_HANDLER_INSTALLATION to 0 in their FreeRTOSConfig.h. Direct
+     * routing, which is validated here when configCHECK_HANDLER_INSTALLATION
+     * is 1, should be preferred when possible. */
+    #if ( configCHECK_HANDLER_INSTALLATION == 1 )
+    {
+        const portISR_t * const pxVectorTable = portSCB_VTOR_REG;
+
+        /* Validate that the application has correctly installed the FreeRTOS
+         * handlers for SVCall and PendSV interrupts. We do not check the
+         * installation of the SysTick handler because the application may
+         * choose to drive the RTOS tick using a timer other than the SysTick
+         * timer by overriding the weak function vPortSetupTimerInterrupt().
+         *
+         * Assertion failures here indicate incorrect installation of the
+         * FreeRTOS handlers. For help installing the FreeRTOS handlers, see
+         * https://www.FreeRTOS.org/FAQHelp.html.
+         *
+         * Systems with a configurable address for the interrupt vector table
+         * can also encounter assertion failures or even system faults here if
+         * VTOR is not set correctly to point to the application's vector table. */
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_SVC ] == SVC_Handler );
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_PENDSV ] == PendSV_Handler );
+    }
+    #endif /* configCHECK_HANDLER_INSTALLATION */
+
     #if ( ( configASSERT_DEFINED == 1 ) && ( portHAS_ARMV8M_MAIN_EXTENSION == 1 ) )
     {
-        volatile uint32_t ulOriginalPriority;
         volatile uint32_t ulImplementedPrioBits = 0;
         volatile uint8_t ucMaxPriorityValue;
 
         /* Determine the maximum priority from which ISR safe FreeRTOS API
-         * functions can be called.  ISR safe functions are those that end in
+         * functions can be called. ISR safe functions are those that end in
-         * "FromISR".  FreeRTOS maintains separate thread and ISR API functions to
+         * "FromISR". FreeRTOS maintains separate thread and ISR API functions to
          * ensure interrupt entry is as fast and simple as possible.
          *
-         * Save the interrupt priority value that is about to be clobbered. */
+         * First, determine the number of priority bits available. Write to all
-        ulOriginalPriority = portNVIC_SHPR2_REG;
+         * possible bits in the priority setting for SVCall. */
-
-        /* Determine the number of priority bits available.  First write to all
-         * possible bits. */
         portNVIC_SHPR2_REG = 0xFF000000;
 
         /* Read the value back to see how many bits stuck. */
@@ -1636,7 +1680,6 @@ BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
 
         /* Calculate the maximum acceptable priority group value for the number
          * of bits read back. */
-
         while( ( ucMaxPriorityValue & portTOP_BIT_OF_BYTE ) == portTOP_BIT_OF_BYTE )
         {
             ulImplementedPrioBits++;
@@ -1674,16 +1717,14 @@ BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
          * register. */
         ulMaxPRIGROUPValue <<= portPRIGROUP_SHIFT;
         ulMaxPRIGROUPValue &= portPRIORITY_GROUP_MASK;
-
-        /* Restore the clobbered interrupt priority register to its original
-         * value. */
-        portNVIC_SHPR2_REG = ulOriginalPriority;
     }
     #endif /* #if ( ( configASSERT_DEFINED == 1 ) && ( portHAS_ARMV8M_MAIN_EXTENSION == 1 ) ) */
 
-    /* Make PendSV, CallSV and SysTick the same priority as the kernel. */
+    /* Make PendSV and SysTick the lowest priority interrupts, and make SVCall
+     * the highest priority. */
     portNVIC_SHPR3_REG |= portNVIC_PENDSV_PRI;
     portNVIC_SHPR3_REG |= portNVIC_SYSTICK_PRI;
+    portNVIC_SHPR2_REG = 0;
 
     #if ( configENABLE_MPU == 1 )
     {

portable/IAR/ARM_CM55_NTZ/non_secure/port.c

@@ -80,6 +80,12 @@
 #endif
 /*-----------------------------------------------------------*/
 
+/**
+ * @brief Prototype of all Interrupt Service Routines (ISRs).
+ */
+typedef void ( * portISR_t )( void );
+/*-----------------------------------------------------------*/
+
 /**
  * @brief Constants required to manipulate the NVIC.
  */
@@ -101,10 +107,18 @@
 /**
  * @brief Constants required to manipulate the SCB.
  */
-#define portSCB_SYS_HANDLER_CTRL_STATE_REG    ( *( volatile uint32_t * ) 0xe000ed24 )
+#define portSCB_VTOR_REG                      ( *( ( portISR_t ** ) 0xe000ed08 ) )
+#define portSCB_SYS_HANDLER_CTRL_STATE_REG    ( *( ( volatile uint32_t * ) 0xe000ed24 ) )
 #define portSCB_MEM_FAULT_ENABLE_BIT          ( 1UL << 16UL )
 /*-----------------------------------------------------------*/
 
+/**
+ * @brief Constants used to check the installation of the FreeRTOS interrupt handlers.
+ */
+#define portVECTOR_INDEX_SVC       ( 11 )
+#define portVECTOR_INDEX_PENDSV    ( 14 )
+/*-----------------------------------------------------------*/
+
 /**
  * @brief Constants required to check the validity of an interrupt priority.
  */
@@ -1598,22 +1612,52 @@ void vPortSVCHandler_C( uint32_t * pulCallerStackAddress ) /* PRIVILEGED_FUNCTIO
 
 BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
 {
+    /* An application can install FreeRTOS interrupt handlers in one of the
+     * folllowing ways:
+     * 1. Direct Routing - Install the functions SVC_Handler and PendSV_Handler
+     *    for SVCall and PendSV interrupts respectively.
+     * 2. Indirect Routing - Install separate handlers for SVCall and PendSV
+     *    interrupts and route program control from those handlers to
+     *    SVC_Handler and PendSV_Handler functions.
+     *
+     * Applications that use Indirect Routing must set
+     * configCHECK_HANDLER_INSTALLATION to 0 in their FreeRTOSConfig.h. Direct
+     * routing, which is validated here when configCHECK_HANDLER_INSTALLATION
+     * is 1, should be preferred when possible. */
+    #if ( configCHECK_HANDLER_INSTALLATION == 1 )
+    {
+        const portISR_t * const pxVectorTable = portSCB_VTOR_REG;
+
+        /* Validate that the application has correctly installed the FreeRTOS
+         * handlers for SVCall and PendSV interrupts. We do not check the
+         * installation of the SysTick handler because the application may
+         * choose to drive the RTOS tick using a timer other than the SysTick
+         * timer by overriding the weak function vPortSetupTimerInterrupt().
+         *
+         * Assertion failures here indicate incorrect installation of the
+         * FreeRTOS handlers. For help installing the FreeRTOS handlers, see
+         * https://www.FreeRTOS.org/FAQHelp.html.
+         *
+         * Systems with a configurable address for the interrupt vector table
+         * can also encounter assertion failures or even system faults here if
+         * VTOR is not set correctly to point to the application's vector table. */
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_SVC ] == SVC_Handler );
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_PENDSV ] == PendSV_Handler );
+    }
+    #endif /* configCHECK_HANDLER_INSTALLATION */
+
     #if ( ( configASSERT_DEFINED == 1 ) && ( portHAS_ARMV8M_MAIN_EXTENSION == 1 ) )
     {
-        volatile uint32_t ulOriginalPriority;
         volatile uint32_t ulImplementedPrioBits = 0;
         volatile uint8_t ucMaxPriorityValue;
 
         /* Determine the maximum priority from which ISR safe FreeRTOS API
-         * functions can be called.  ISR safe functions are those that end in
+         * functions can be called. ISR safe functions are those that end in
-         * "FromISR".  FreeRTOS maintains separate thread and ISR API functions to
+         * "FromISR". FreeRTOS maintains separate thread and ISR API functions to
          * ensure interrupt entry is as fast and simple as possible.
          *
-         * Save the interrupt priority value that is about to be clobbered. */
+         * First, determine the number of priority bits available. Write to all
-        ulOriginalPriority = portNVIC_SHPR2_REG;
+         * possible bits in the priority setting for SVCall. */
-
-        /* Determine the number of priority bits available.  First write to all
-         * possible bits. */
         portNVIC_SHPR2_REG = 0xFF000000;
 
         /* Read the value back to see how many bits stuck. */
@@ -1636,7 +1680,6 @@ BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
 
         /* Calculate the maximum acceptable priority group value for the number
          * of bits read back. */
-
         while( ( ucMaxPriorityValue & portTOP_BIT_OF_BYTE ) == portTOP_BIT_OF_BYTE )
         {
             ulImplementedPrioBits++;
@@ -1674,16 +1717,14 @@ BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
          * register. */
         ulMaxPRIGROUPValue <<= portPRIGROUP_SHIFT;
         ulMaxPRIGROUPValue &= portPRIORITY_GROUP_MASK;
-
-        /* Restore the clobbered interrupt priority register to its original
-         * value. */
-        portNVIC_SHPR2_REG = ulOriginalPriority;
     }
     #endif /* #if ( ( configASSERT_DEFINED == 1 ) && ( portHAS_ARMV8M_MAIN_EXTENSION == 1 ) ) */
 
-    /* Make PendSV, CallSV and SysTick the same priority as the kernel. */
+    /* Make PendSV and SysTick the lowest priority interrupts, and make SVCall
+     * the highest priority. */
     portNVIC_SHPR3_REG |= portNVIC_PENDSV_PRI;
     portNVIC_SHPR3_REG |= portNVIC_SYSTICK_PRI;
+    portNVIC_SHPR2_REG = 0;
 
     #if ( configENABLE_MPU == 1 )
     {

portable/IAR/ARM_CM7/r0p1/port.c

@@ -45,10 +45,14 @@
     #error configMAX_SYSCALL_INTERRUPT_PRIORITY must not be set to 0.  See http: /*www.FreeRTOS.org/RTOS-Cortex-M3-M4.html */
 #endif
 
+/* Prototype of all Interrupt Service Routines (ISRs). */
+typedef void ( * portISR_t )( void );
+
 /* Constants required to manipulate the core.  Registers first... */
 #define portNVIC_SYSTICK_CTRL_REG             ( *( ( volatile uint32_t * ) 0xe000e010 ) )
 #define portNVIC_SYSTICK_LOAD_REG             ( *( ( volatile uint32_t * ) 0xe000e014 ) )
 #define portNVIC_SYSTICK_CURRENT_VALUE_REG    ( *( ( volatile uint32_t * ) 0xe000e018 ) )
+#define portNVIC_SHPR2_REG                    ( *( ( volatile uint32_t * ) 0xe000ed1c ) )
 #define portNVIC_SHPR3_REG                    ( *( ( volatile uint32_t * ) 0xe000ed20 ) )
 /* ...then bits in the registers. */
 #define portNVIC_SYSTICK_CLK_BIT              ( 1UL << 2UL )
@@ -63,6 +67,11 @@
 #define portNVIC_PENDSV_PRI                   ( ( ( uint32_t ) portMIN_INTERRUPT_PRIORITY ) << 16UL )
 #define portNVIC_SYSTICK_PRI                  ( ( ( uint32_t ) portMIN_INTERRUPT_PRIORITY ) << 24UL )
 
+/* Constants used to check the installation of the FreeRTOS interrupt handlers. */
+#define portSCB_VTOR_REG                      ( *( ( portISR_t ** ) 0xE000ED08 ) )
+#define portVECTOR_INDEX_SVC                  ( 11 )
+#define portVECTOR_INDEX_PENDSV               ( 14 )
+
 /* Constants required to check the validity of an interrupt priority. */
 #define portFIRST_USER_INTERRUPT_NUMBER       ( 16 )
 #define portNVIC_IP_REGISTERS_OFFSET_16       ( 0xE000E3F0 )
@@ -135,6 +144,11 @@ extern void vPortEnableVFP( void );
  */
 static void prvTaskExitError( void );
 
+/*
+ * FreeRTOS handlers implemented in assembly.
+ */
+extern void vPortSVCHandler( void );
+extern void xPortPendSVHandler( void );
 /*-----------------------------------------------------------*/
 
 /* Each task maintains its own interrupt status in the critical nesting
@@ -234,6 +248,40 @@ static void prvTaskExitError( void )
  */
 BaseType_t xPortStartScheduler( void )
 {
+    /* An application can install FreeRTOS interrupt handlers in one of the
+     * folllowing ways:
+     * 1. Direct Routing - Install the functions vPortSVCHandler and
+     *    xPortPendSVHandler for SVCall and PendSV interrupts respectively.
+     * 2. Indirect Routing - Install separate handlers for SVCall and PendSV
+     *    interrupts and route program control from those handlers to
+     *    vPortSVCHandler and xPortPendSVHandler functions.
+     *
+     * Applications that use Indirect Routing must set
+     * configCHECK_HANDLER_INSTALLATION to 0 in their FreeRTOSConfig.h. Direct
+     * routing, which is validated here when configCHECK_HANDLER_INSTALLATION
+     * is 1, should be preferred when possible. */
+    #if ( configCHECK_HANDLER_INSTALLATION == 1 )
+    {
+        const portISR_t * const pxVectorTable = portSCB_VTOR_REG;
+
+        /* Validate that the application has correctly installed the FreeRTOS
+         * handlers for SVCall and PendSV interrupts. We do not check the
+         * installation of the SysTick handler because the application may
+         * choose to drive the RTOS tick using a timer other than the SysTick
+         * timer by overriding the weak function vPortSetupTimerInterrupt().
+         *
+         * Assertion failures here indicate incorrect installation of the
+         * FreeRTOS handlers. For help installing the FreeRTOS handlers, see
+         * https://www.FreeRTOS.org/FAQHelp.html.
+         *
+         * Systems with a configurable address for the interrupt vector table
+         * can also encounter assertion failures or even system faults here if
+         * VTOR is not set correctly to point to the application's vector table. */
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_SVC ] == vPortSVCHandler );
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_PENDSV ] == xPortPendSVHandler );
+    }
+    #endif /* configCHECK_HANDLER_INSTALLATION */
+
     #if ( configASSERT_DEFINED == 1 )
     {
         volatile uint8_t ucOriginalPriority;
@@ -318,9 +366,11 @@ BaseType_t xPortStartScheduler( void )
     }
     #endif /* configASSERT_DEFINED */
 
-    /* Make PendSV and SysTick the lowest priority interrupts. */
+    /* Make PendSV and SysTick the lowest priority interrupts, and make SVCall
+     * the highest priority. */
     portNVIC_SHPR3_REG |= portNVIC_PENDSV_PRI;
     portNVIC_SHPR3_REG |= portNVIC_SYSTICK_PRI;
+    portNVIC_SHPR2_REG = 0;
 
     /* Start the timer that generates the tick ISR.  Interrupts are disabled
      * here already. */

portable/IAR/ARM_CM85/non_secure/port.c

@@ -80,6 +80,12 @@
 #endif
 /*-----------------------------------------------------------*/
 
+/**
+ * @brief Prototype of all Interrupt Service Routines (ISRs).
+ */
+typedef void ( * portISR_t )( void );
+/*-----------------------------------------------------------*/
+
 /**
  * @brief Constants required to manipulate the NVIC.
  */
@@ -101,10 +107,18 @@
 /**
  * @brief Constants required to manipulate the SCB.
  */
-#define portSCB_SYS_HANDLER_CTRL_STATE_REG    ( *( volatile uint32_t * ) 0xe000ed24 )
+#define portSCB_VTOR_REG                      ( *( ( portISR_t ** ) 0xe000ed08 ) )
+#define portSCB_SYS_HANDLER_CTRL_STATE_REG    ( *( ( volatile uint32_t * ) 0xe000ed24 ) )
 #define portSCB_MEM_FAULT_ENABLE_BIT          ( 1UL << 16UL )
 /*-----------------------------------------------------------*/
 
+/**
+ * @brief Constants used to check the installation of the FreeRTOS interrupt handlers.
+ */
+#define portVECTOR_INDEX_SVC       ( 11 )
+#define portVECTOR_INDEX_PENDSV    ( 14 )
+/*-----------------------------------------------------------*/
+
 /**
  * @brief Constants required to check the validity of an interrupt priority.
  */
@@ -1598,22 +1612,52 @@ void vPortSVCHandler_C( uint32_t * pulCallerStackAddress ) /* PRIVILEGED_FUNCTIO
 
 BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
 {
+    /* An application can install FreeRTOS interrupt handlers in one of the
+     * folllowing ways:
+     * 1. Direct Routing - Install the functions SVC_Handler and PendSV_Handler
+     *    for SVCall and PendSV interrupts respectively.
+     * 2. Indirect Routing - Install separate handlers for SVCall and PendSV
+     *    interrupts and route program control from those handlers to
+     *    SVC_Handler and PendSV_Handler functions.
+     *
+     * Applications that use Indirect Routing must set
+     * configCHECK_HANDLER_INSTALLATION to 0 in their FreeRTOSConfig.h. Direct
+     * routing, which is validated here when configCHECK_HANDLER_INSTALLATION
+     * is 1, should be preferred when possible. */
+    #if ( configCHECK_HANDLER_INSTALLATION == 1 )
+    {
+        const portISR_t * const pxVectorTable = portSCB_VTOR_REG;
+
+        /* Validate that the application has correctly installed the FreeRTOS
+         * handlers for SVCall and PendSV interrupts. We do not check the
+         * installation of the SysTick handler because the application may
+         * choose to drive the RTOS tick using a timer other than the SysTick
+         * timer by overriding the weak function vPortSetupTimerInterrupt().
+         *
+         * Assertion failures here indicate incorrect installation of the
+         * FreeRTOS handlers. For help installing the FreeRTOS handlers, see
+         * https://www.FreeRTOS.org/FAQHelp.html.
+         *
+         * Systems with a configurable address for the interrupt vector table
+         * can also encounter assertion failures or even system faults here if
+         * VTOR is not set correctly to point to the application's vector table. */
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_SVC ] == SVC_Handler );
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_PENDSV ] == PendSV_Handler );
+    }
+    #endif /* configCHECK_HANDLER_INSTALLATION */
+
     #if ( ( configASSERT_DEFINED == 1 ) && ( portHAS_ARMV8M_MAIN_EXTENSION == 1 ) )
     {
-        volatile uint32_t ulOriginalPriority;
         volatile uint32_t ulImplementedPrioBits = 0;
         volatile uint8_t ucMaxPriorityValue;
 
         /* Determine the maximum priority from which ISR safe FreeRTOS API
-         * functions can be called.  ISR safe functions are those that end in
+         * functions can be called. ISR safe functions are those that end in
-         * "FromISR".  FreeRTOS maintains separate thread and ISR API functions to
+         * "FromISR". FreeRTOS maintains separate thread and ISR API functions to
          * ensure interrupt entry is as fast and simple as possible.
          *
-         * Save the interrupt priority value that is about to be clobbered. */
+         * First, determine the number of priority bits available. Write to all
-        ulOriginalPriority = portNVIC_SHPR2_REG;
+         * possible bits in the priority setting for SVCall. */
-
-        /* Determine the number of priority bits available.  First write to all
-         * possible bits. */
         portNVIC_SHPR2_REG = 0xFF000000;
 
         /* Read the value back to see how many bits stuck. */
@@ -1636,7 +1680,6 @@ BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
 
         /* Calculate the maximum acceptable priority group value for the number
          * of bits read back. */
-
         while( ( ucMaxPriorityValue & portTOP_BIT_OF_BYTE ) == portTOP_BIT_OF_BYTE )
         {
             ulImplementedPrioBits++;
@@ -1674,16 +1717,14 @@ BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
          * register. */
         ulMaxPRIGROUPValue <<= portPRIGROUP_SHIFT;
         ulMaxPRIGROUPValue &= portPRIORITY_GROUP_MASK;
-
-        /* Restore the clobbered interrupt priority register to its original
-         * value. */
-        portNVIC_SHPR2_REG = ulOriginalPriority;
     }
     #endif /* #if ( ( configASSERT_DEFINED == 1 ) && ( portHAS_ARMV8M_MAIN_EXTENSION == 1 ) ) */
 
-    /* Make PendSV, CallSV and SysTick the same priority as the kernel. */
+    /* Make PendSV and SysTick the lowest priority interrupts, and make SVCall
+     * the highest priority. */
     portNVIC_SHPR3_REG |= portNVIC_PENDSV_PRI;
     portNVIC_SHPR3_REG |= portNVIC_SYSTICK_PRI;
+    portNVIC_SHPR2_REG = 0;
 
     #if ( configENABLE_MPU == 1 )
     {

portable/IAR/ARM_CM85_NTZ/non_secure/port.c

@@ -80,6 +80,12 @@
 #endif
 /*-----------------------------------------------------------*/
 
+/**
+ * @brief Prototype of all Interrupt Service Routines (ISRs).
+ */
+typedef void ( * portISR_t )( void );
+/*-----------------------------------------------------------*/
+
 /**
  * @brief Constants required to manipulate the NVIC.
  */
@@ -101,10 +107,18 @@
 /**
  * @brief Constants required to manipulate the SCB.
  */
-#define portSCB_SYS_HANDLER_CTRL_STATE_REG    ( *( volatile uint32_t * ) 0xe000ed24 )
+#define portSCB_VTOR_REG                      ( *( ( portISR_t ** ) 0xe000ed08 ) )
+#define portSCB_SYS_HANDLER_CTRL_STATE_REG    ( *( ( volatile uint32_t * ) 0xe000ed24 ) )
 #define portSCB_MEM_FAULT_ENABLE_BIT          ( 1UL << 16UL )
 /*-----------------------------------------------------------*/
 
+/**
+ * @brief Constants used to check the installation of the FreeRTOS interrupt handlers.
+ */
+#define portVECTOR_INDEX_SVC       ( 11 )
+#define portVECTOR_INDEX_PENDSV    ( 14 )
+/*-----------------------------------------------------------*/
+
 /**
  * @brief Constants required to check the validity of an interrupt priority.
  */
@@ -1598,22 +1612,52 @@ void vPortSVCHandler_C( uint32_t * pulCallerStackAddress ) /* PRIVILEGED_FUNCTIO
 
 BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
 {
+    /* An application can install FreeRTOS interrupt handlers in one of the
+     * folllowing ways:
+     * 1. Direct Routing - Install the functions SVC_Handler and PendSV_Handler
+     *    for SVCall and PendSV interrupts respectively.
+     * 2. Indirect Routing - Install separate handlers for SVCall and PendSV
+     *    interrupts and route program control from those handlers to
+     *    SVC_Handler and PendSV_Handler functions.
+     *
+     * Applications that use Indirect Routing must set
+     * configCHECK_HANDLER_INSTALLATION to 0 in their FreeRTOSConfig.h. Direct
+     * routing, which is validated here when configCHECK_HANDLER_INSTALLATION
+     * is 1, should be preferred when possible. */
+    #if ( configCHECK_HANDLER_INSTALLATION == 1 )
+    {
+        const portISR_t * const pxVectorTable = portSCB_VTOR_REG;
+
+        /* Validate that the application has correctly installed the FreeRTOS
+         * handlers for SVCall and PendSV interrupts. We do not check the
+         * installation of the SysTick handler because the application may
+         * choose to drive the RTOS tick using a timer other than the SysTick
+         * timer by overriding the weak function vPortSetupTimerInterrupt().
+         *
+         * Assertion failures here indicate incorrect installation of the
+         * FreeRTOS handlers. For help installing the FreeRTOS handlers, see
+         * https://www.FreeRTOS.org/FAQHelp.html.
+         *
+         * Systems with a configurable address for the interrupt vector table
+         * can also encounter assertion failures or even system faults here if
+         * VTOR is not set correctly to point to the application's vector table. */
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_SVC ] == SVC_Handler );
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_PENDSV ] == PendSV_Handler );
+    }
+    #endif /* configCHECK_HANDLER_INSTALLATION */
+
     #if ( ( configASSERT_DEFINED == 1 ) && ( portHAS_ARMV8M_MAIN_EXTENSION == 1 ) )
     {
-        volatile uint32_t ulOriginalPriority;
         volatile uint32_t ulImplementedPrioBits = 0;
         volatile uint8_t ucMaxPriorityValue;
 
         /* Determine the maximum priority from which ISR safe FreeRTOS API
-         * functions can be called.  ISR safe functions are those that end in
+         * functions can be called. ISR safe functions are those that end in
-         * "FromISR".  FreeRTOS maintains separate thread and ISR API functions to
+         * "FromISR". FreeRTOS maintains separate thread and ISR API functions to
          * ensure interrupt entry is as fast and simple as possible.
          *
-         * Save the interrupt priority value that is about to be clobbered. */
+         * First, determine the number of priority bits available. Write to all
-        ulOriginalPriority = portNVIC_SHPR2_REG;
+         * possible bits in the priority setting for SVCall. */
-
-        /* Determine the number of priority bits available.  First write to all
-         * possible bits. */
         portNVIC_SHPR2_REG = 0xFF000000;
 
         /* Read the value back to see how many bits stuck. */
@@ -1636,7 +1680,6 @@ BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
 
         /* Calculate the maximum acceptable priority group value for the number
          * of bits read back. */
-
         while( ( ucMaxPriorityValue & portTOP_BIT_OF_BYTE ) == portTOP_BIT_OF_BYTE )
         {
             ulImplementedPrioBits++;
@@ -1674,16 +1717,14 @@ BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
          * register. */
         ulMaxPRIGROUPValue <<= portPRIGROUP_SHIFT;
         ulMaxPRIGROUPValue &= portPRIORITY_GROUP_MASK;
-
-        /* Restore the clobbered interrupt priority register to its original
-         * value. */
-        portNVIC_SHPR2_REG = ulOriginalPriority;
     }
     #endif /* #if ( ( configASSERT_DEFINED == 1 ) && ( portHAS_ARMV8M_MAIN_EXTENSION == 1 ) ) */
 
-    /* Make PendSV, CallSV and SysTick the same priority as the kernel. */
+    /* Make PendSV and SysTick the lowest priority interrupts, and make SVCall
+     * the highest priority. */
     portNVIC_SHPR3_REG |= portNVIC_PENDSV_PRI;
     portNVIC_SHPR3_REG |= portNVIC_SYSTICK_PRI;
+    portNVIC_SHPR2_REG = 0;
 
     #if ( configENABLE_MPU == 1 )
     {

portable/RVDS/ARM_CM4_MPU/port.c

@@ -51,6 +51,9 @@
     #define configALLOW_UNPRIVILEGED_CRITICAL_SECTIONS    1
 #endif
 
+/* Prototype of all Interrupt Service Routines (ISRs). */
+typedef void ( * portISR_t )( void );
+
 /* Constants required to access and manipulate the NVIC. */
 #define portNVIC_SYSTICK_CTRL_REG                 ( *( ( volatile uint32_t * ) 0xe000e010 ) )
 #define portNVIC_SYSTICK_LOAD_REG                 ( *( ( volatile uint32_t * ) 0xe000e014 ) )
@@ -87,7 +90,6 @@
 #define portMIN_INTERRUPT_PRIORITY                ( 255UL )
 #define portNVIC_PENDSV_PRI                       ( ( ( uint32_t ) portMIN_INTERRUPT_PRIORITY ) << 16UL )
 #define portNVIC_SYSTICK_PRI                      ( ( ( uint32_t ) portMIN_INTERRUPT_PRIORITY ) << 24UL )
-#define portNVIC_SVC_PRI                          ( ( ( uint32_t ) configMAX_SYSCALL_INTERRUPT_PRIORITY - 1UL ) << 24UL )
 
 /* Constants required to manipulate the VFP. */
 #define portFPCCR                                 ( ( volatile uint32_t * ) 0xe000ef34UL ) /* Floating point context control register. */
@@ -99,6 +101,11 @@
 #define portINITIAL_CONTROL_IF_UNPRIVILEGED       ( 0x03 )
 #define portINITIAL_CONTROL_IF_PRIVILEGED         ( 0x02 )
 
+/* Constants used to check the installation of the FreeRTOS interrupt handlers. */
+#define portSCB_VTOR_REG                          ( *( ( portISR_t ** ) 0xE000ED08 ) )
+#define portVECTOR_INDEX_SVC                      ( 11 )
+#define portVECTOR_INDEX_PENDSV                   ( 14 )
+
 /* Constants required to check the validity of an interrupt priority. */
 #define portFIRST_USER_INTERRUPT_NUMBER           ( 16 )
 #define portNVIC_IP_REGISTERS_OFFSET_16           ( 0xE000E3F0 )
@@ -386,7 +393,6 @@ void vSVCHandler_C( uint32_t * pulParam )
     switch( ucSVCNumber )
     {
         case portSVC_START_SCHEDULER:
-            portNVIC_SHPR2_REG |= portNVIC_SVC_PRI;
             prvRestoreContextOfFirstTask();
             break;
 
@@ -822,6 +828,40 @@ BaseType_t xPortStartScheduler( void )
         configASSERT( portCPUID != portCORTEX_M7_r0p0_ID );
     #endif
 
+    /* An application can install FreeRTOS interrupt handlers in one of the
+     * folllowing ways:
+     * 1. Direct Routing - Install the functions vPortSVCHandler and
+     *    xPortPendSVHandler for SVCall and PendSV interrupts respectively.
+     * 2. Indirect Routing - Install separate handlers for SVCall and PendSV
+     *    interrupts and route program control from those handlers to
+     *    vPortSVCHandler and xPortPendSVHandler functions.
+     *
+     * Applications that use Indirect Routing must set
+     * configCHECK_HANDLER_INSTALLATION to 0 in their FreeRTOSConfig.h. Direct
+     * routing, which is validated here when configCHECK_HANDLER_INSTALLATION
+     * is 1, should be preferred when possible. */
+    #if ( configCHECK_HANDLER_INSTALLATION == 1 )
+    {
+        const portISR_t * const pxVectorTable = portSCB_VTOR_REG;
+
+        /* Validate that the application has correctly installed the FreeRTOS
+         * handlers for SVCall and PendSV interrupts. We do not check the
+         * installation of the SysTick handler because the application may
+         * choose to drive the RTOS tick using a timer other than the SysTick
+         * timer by overriding the weak function vPortSetupTimerInterrupt().
+         *
+         * Assertion failures here indicate incorrect installation of the
+         * FreeRTOS handlers. For help installing the FreeRTOS handlers, see
+         * https://www.FreeRTOS.org/FAQHelp.html.
+         *
+         * Systems with a configurable address for the interrupt vector table
+         * can also encounter assertion failures or even system faults here if
+         * VTOR is not set correctly to point to the application's vector table. */
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_SVC ] == vPortSVCHandler );
+        configASSERT( pxVectorTable[ portVECTOR_INDEX_PENDSV ] == xPortPendSVHandler );
+    }
+    #endif /* configCHECK_HANDLER_INSTALLATION */
+
     #if ( configASSERT_DEFINED == 1 )
     {
         volatile uint8_t ucOriginalPriority;
@@ -907,10 +947,11 @@ BaseType_t xPortStartScheduler( void )
     #endif /* configASSERT_DEFINED */
 
     /* Make PendSV and SysTick the same priority as the kernel, and the SVC
-     * handler higher priority so it can be used to exit a critical section (where
+     * handler highest priority so it can be used to exit a critical section
-     * lower priorities are masked). */
+     * (where lower priorities are masked). */
     portNVIC_SHPR3_REG |= portNVIC_PENDSV_PRI;
     portNVIC_SHPR3_REG |= portNVIC_SYSTICK_PRI;
+    portNVIC_SHPR2_REG = 0;
 
     /* Configure the regions in the MPU that are common to all tasks. */
     prvSetupMPU();
@@ -1196,6 +1237,7 @@ __asm void vPortEnableVFP( void )
     orr r1, r1, #( 0xf << 20 ) /* Enable CP10 and CP11 coprocessors, then save back. */
     str r1, [ r0 ]
     bx r14
+    nop
 /* *INDENT-ON* */
 }
 /*-----------------------------------------------------------*/