Improvements to the Cortex-M ports:

- Clear the SysTick current value register before starting the SysTick (only required if something uses SysTick before starting the scheduler).
- Ensure atomic operations are thread safe by executing clrex in the context switch.

FreeRTOS/Source/include/FreeRTOS.h

@@ -126,6 +126,10 @@ extern "C" {
 	#error Missing definition:  configMAX_PRIORITIES must be defined in FreeRTOSConfig.h.  See the Configuration section of the FreeRTOS API documentation for details.
 #endif
 
+#if configMAX_PRIORITIES < 1
+	#error configMAX_PRIORITIES must be defined to be greater than or equal to 1.
+#endif
+
 #ifndef configUSE_PREEMPTION
 	#error Missing definition:  configUSE_PREEMPTION must be defined in FreeRTOSConfig.h as either 1 or 0.  See the Configuration section of the FreeRTOS API documentation for details.
 #endif
@@ -142,10 +146,6 @@ extern "C" {
 	#error Missing definition:  configUSE_16_BIT_TICKS must be defined in FreeRTOSConfig.h as either 1 or 0.  See the Configuration section of the FreeRTOS API documentation for details.
 #endif
 
-#ifndef configMAX_PRIORITIES
-	#error configMAX_PRIORITIES must be defined to be greater than or equal to 1.
-#endif
-
 #ifndef configUSE_CO_ROUTINES
 	#define configUSE_CO_ROUTINES 0
 #endif

FreeRTOS/Source/portable/CCS/ARM_CM4F/port.c

@@ -563,6 +563,10 @@ void vPortSetupTimerInterrupt( void )
 	}
 	#endif /* configUSE_TICKLESS_IDLE */
 
+	/* Stop and clear the SysTick. */
+	portNVIC_SYSTICK_CTRL_REG = 0UL;
+	portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
+
 	/* Configure SysTick to interrupt at the requested rate. */
 	portNVIC_SYSTICK_LOAD_REG = ( configSYSTICK_CLOCK_HZ / configTICK_RATE_HZ ) - 1UL;
 	portNVIC_SYSTICK_CTRL_REG = ( portNVIC_SYSTICK_CLK_BIT | portNVIC_SYSTICK_INT_BIT | portNVIC_SYSTICK_ENABLE_BIT );

FreeRTOS/Source/portable/CCS/ARM_CM4F/portasm.asm

@@ -123,6 +123,9 @@ xPortPendSVHandler: .asmfunc
 	;/* Save the new top of stack into the first member of the TCB. */
 	str r0, [r2]
 
+	;/* Ensure thread safety of atomic operations. */
+	clrex
+
 	stmdb sp!, {r3}
 	ldr r0, ulMaxSyscallInterruptPriorityConst
 	ldr r1, [r0]

FreeRTOS/Source/portable/GCC/ARM_CM0/port.c

@@ -76,8 +76,9 @@
 #include "task.h"
 
 /* Constants required to manipulate the NVIC. */
-#define portNVIC_SYSTICK_CTRL		( ( volatile uint32_t *) 0xe000e010 )
-#define portNVIC_SYSTICK_LOAD		( ( volatile uint32_t *) 0xe000e014 )
+#define portNVIC_SYSTICK_CTRL			( ( volatile uint32_t * ) 0xe000e010 )
+#define portNVIC_SYSTICK_LOAD			( ( volatile uint32_t * ) 0xe000e014 )
+#define portNVIC_SYSTICK_CURRENT_VALUE	( ( volatile uint32_t * ) 0xe000e018 )
 #define portNVIC_INT_CTRL			( ( volatile uint32_t *) 0xe000ed04 )
 #define portNVIC_SYSPRI2			( ( volatile uint32_t *) 0xe000ed20 )
 #define portNVIC_SYSTICK_CLK		0x00000004
@@ -363,6 +364,10 @@ uint32_t ulPreviousMask;
  */
 void prvSetupTimerInterrupt( void )
 {
+	/* Stop and reset the SysTick. */
+	*(portNVIC_SYSTICK_CTRL) = 0UL;
+	*(portNVIC_SYSTICK_CURRENT_VALUE) = 0UL;
+
 	/* Configure SysTick to interrupt at the requested rate. */
 	*(portNVIC_SYSTICK_LOAD) = ( configCPU_CLOCK_HZ / configTICK_RATE_HZ ) - 1UL;
 	*(portNVIC_SYSTICK_CTRL) = portNVIC_SYSTICK_CLK | portNVIC_SYSTICK_INT | portNVIC_SYSTICK_ENABLE;

FreeRTOS/Source/portable/GCC/ARM_CM3/port.c

@@ -410,6 +410,7 @@ void xPortPendSVHandler( void )
 	"										\n"
 	"	stmdb r0!, {r4-r11}					\n" /* Save the remaining registers. */
 	"	str r0, [r2]						\n" /* Save the new top of stack into the first member of the TCB. */
+	"	clrex								\n" /* Ensure thread safety of atomic operations. */
 	"										\n"
 	"	stmdb sp!, {r3, r14}				\n"
 	"	mov r0, %0							\n"
@@ -622,6 +623,10 @@ __attribute__(( weak )) void vPortSetupTimerInterrupt( void )
 	}
 	#endif /* configUSE_TICKLESS_IDLE */
 
+	/* Stop and clear the SysTick. */
+	portNVIC_SYSTICK_CTRL_REG = 0UL;
+	portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
+
 	/* Configure SysTick to interrupt at the requested rate. */
 	portNVIC_SYSTICK_LOAD_REG = ( configSYSTICK_CLOCK_HZ / configTICK_RATE_HZ ) - 1UL;
 	portNVIC_SYSTICK_CTRL_REG = ( portNVIC_SYSTICK_CLK_BIT | portNVIC_SYSTICK_INT_BIT | portNVIC_SYSTICK_ENABLE_BIT );

FreeRTOS/Source/portable/GCC/ARM_CM3_MPU/port.c

@@ -89,6 +89,7 @@ task.h is included from an application file. */
 /* 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 ) )
+#define portNVIC_SYSTICK_CURRENT_VALUE_REG		( * ( ( volatile uint32_t * ) 0xe000e018 ) )
 #define portNVIC_SYSPRI2_REG					( *	( ( volatile uint32_t * ) 0xe000ed20 ) )
 #define portNVIC_SYSPRI1_REG					( * ( ( volatile uint32_t * ) 0xe000ed1c ) )
 #define portNVIC_SYS_CTRL_STATE_REG				( * ( ( volatile uint32_t * ) 0xe000ed24 ) )
@@ -449,6 +450,7 @@ void xPortPendSVHandler( void )
 		"	mrs r1, control						\n"
 		"	stmdb r0!, {r1, r4-r11}				\n" /* Save the remaining registers. */
 		"	str r0, [r2]						\n" /* Save the new top of stack into the first member of the TCB. */
+		"	clrex								\n" /* Ensure thread safety of atomic operations. */
 		"										\n"
 		"	stmdb sp!, {r3, r14}				\n"
 		"	mov r0, %0							\n"
@@ -500,6 +502,10 @@ uint32_t ulDummy;
  */
 static void prvSetupTimerInterrupt( void )
 {
+	/* Reset the SysTick timer. */
+	portNVIC_SYSTICK_CTRL_REG = 0UL;
+	portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
+
 	/* Configure SysTick to interrupt at the requested rate. */
 	portNVIC_SYSTICK_LOAD_REG = ( configCPU_CLOCK_HZ / configTICK_RATE_HZ ) - 1UL;
 	portNVIC_SYSTICK_CTRL_REG = portNVIC_SYSTICK_CLK | portNVIC_SYSTICK_INT | portNVIC_SYSTICK_ENABLE;

FreeRTOS/Source/portable/GCC/ARM_CM4F/port.c

@@ -449,8 +449,8 @@ void xPortPendSVHandler( void )
 	"	vstmdbeq r0!, {s16-s31}				\n"
 	"										\n"
 	"	stmdb r0!, {r4-r11, r14}			\n" /* Save the core registers. */
-	"										\n"
 	"	str r0, [r2]						\n" /* Save the new top of stack into the first member of the TCB. */
+	"	clrex								\n" /* Ensure thread safety of atomic operations. */
 	"										\n"
 	"	stmdb sp!, {r3}						\n"
 	"	mov r0, %0 							\n"
@@ -679,6 +679,10 @@ __attribute__(( weak )) void vPortSetupTimerInterrupt( void )
 	}
 	#endif /* configUSE_TICKLESS_IDLE */
 
+	/* Stop and clear the SysTick. */
+	portNVIC_SYSTICK_CTRL_REG = 0UL;
+	portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
+
 	/* Configure SysTick to interrupt at the requested rate. */
 	portNVIC_SYSTICK_LOAD_REG = ( configSYSTICK_CLOCK_HZ / configTICK_RATE_HZ ) - 1UL;
 	portNVIC_SYSTICK_CTRL_REG = ( portNVIC_SYSTICK_CLK_BIT | portNVIC_SYSTICK_INT_BIT | portNVIC_SYSTICK_ENABLE_BIT );

FreeRTOS/Source/portable/GCC/ARM_CM4_MPU/port.c

@@ -91,6 +91,7 @@ task.h is included from an application file. */
 /* 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 ) )
+#define portNVIC_SYSTICK_CURRENT_VALUE_REG		( * ( ( volatile uint32_t * ) 0xe000e018 ) )
 #define portNVIC_SYSPRI2_REG					( *	( ( volatile uint32_t * ) 0xe000ed20 ) )
 #define portNVIC_SYSPRI1_REG					( * ( ( volatile uint32_t * ) 0xe000ed1c ) )
 #define portNVIC_SYS_CTRL_STATE_REG				( * ( ( volatile uint32_t * ) 0xe000ed24 ) )
@@ -476,6 +477,7 @@ void xPortPendSVHandler( void )
 		"	mrs r1, control						\n"
 		"	stmdb r0!, {r1, r4-r11, r14}		\n" /* Save the remaining registers. */
 		"	str r0, [r2]						\n" /* Save the new top of stack into the first member of the TCB. */
+		"	clrex								\n" /* Ensure thread safety of atomic operations. */
 		"										\n"
 		"	stmdb sp!, {r3}						\n"
 		"	mov r0, %0							\n"
@@ -533,6 +535,10 @@ uint32_t ulDummy;
  */
 static void prvSetupTimerInterrupt( void )
 {
+	/* Clear the SysTick. */
+	portNVIC_SYSTICK_CTRL_REG = 0UL;
+	portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
+
 	/* Configure SysTick to interrupt at the requested rate. */
 	portNVIC_SYSTICK_LOAD_REG = ( configCPU_CLOCK_HZ / configTICK_RATE_HZ ) - 1UL;
 	portNVIC_SYSTICK_CTRL_REG = portNVIC_SYSTICK_CLK | portNVIC_SYSTICK_INT | portNVIC_SYSTICK_ENABLE;

FreeRTOS/Source/portable/GCC/ARM_CM7/r0p1/port.c

@@ -437,8 +437,8 @@ void xPortPendSVHandler( void )
 	"	vstmdbeq r0!, {s16-s31}				\n"
 	"										\n"
 	"	stmdb r0!, {r4-r11, r14}			\n" /* Save the core registers. */
-	"										\n"
 	"	str r0, [r2]						\n" /* Save the new top of stack into the first member of the TCB. */
+	"	clrex								\n" /* Ensure thread safety of atomic operations. */
 	"										\n"
 	"	stmdb sp!, {r3}						\n"
 	"	mov r0, %0 							\n"
@@ -669,6 +669,10 @@ __attribute__(( weak )) void vPortSetupTimerInterrupt( void )
 	}
 	#endif /* configUSE_TICKLESS_IDLE */
 
+	/* Stop and clear the SysTick. */
+	portNVIC_SYSTICK_CTRL_REG = 0UL;
+	portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
+
 	/* Configure SysTick to interrupt at the requested rate. */
 	portNVIC_SYSTICK_LOAD_REG = ( configSYSTICK_CLOCK_HZ / configTICK_RATE_HZ ) - 1UL;
 	portNVIC_SYSTICK_CTRL_REG = ( portNVIC_SYSTICK_CLK_BIT | portNVIC_SYSTICK_INT_BIT | portNVIC_SYSTICK_ENABLE_BIT );

FreeRTOS/Source/portable/IAR/ARM_CM0/port.c

@@ -79,8 +79,9 @@
 #include "task.h"
 
 /* Constants required to manipulate the NVIC. */
-#define portNVIC_SYSTICK_CTRL		( ( volatile uint32_t *) 0xe000e010 )
-#define portNVIC_SYSTICK_LOAD		( ( volatile uint32_t *) 0xe000e014 )
+#define portNVIC_SYSTICK_CTRL			( ( volatile uint32_t * ) 0xe000e010 )
+#define portNVIC_SYSTICK_LOAD			( ( volatile uint32_t * ) 0xe000e014 )
+#define portNVIC_SYSTICK_CURRENT_VALUE	( ( volatile uint32_t * ) 0xe000e018 )
 #define portNVIC_SYSPRI2			( ( volatile uint32_t *) 0xe000ed20 )
 #define portNVIC_SYSTICK_CLK		0x00000004
 #define portNVIC_SYSTICK_INT		0x00000002
@@ -247,6 +248,10 @@ uint32_t ulPreviousMask;
  */
 static void prvSetupTimerInterrupt( void )
 {
+	/* Stop and reset the SysTick. */
+	*(portNVIC_SYSTICK_CTRL) = 0UL;
+	*(portNVIC_SYSTICK_CURRENT_VALUE) = 0UL;
+
 	/* Configure SysTick to interrupt at the requested rate. */
 	*(portNVIC_SYSTICK_LOAD) = ( configCPU_CLOCK_HZ / configTICK_RATE_HZ ) - 1UL;
 	*(portNVIC_SYSTICK_CTRL) = portNVIC_SYSTICK_CLK | portNVIC_SYSTICK_INT | portNVIC_SYSTICK_ENABLE;

FreeRTOS/Source/portable/IAR/ARM_CM3/port.c

@@ -535,6 +535,10 @@ __weak void vPortSetupTimerInterrupt( void )
 	}
 	#endif /* configUSE_TICKLESS_IDLE */
 
+	/* Stop and clear the SysTick. */
+	portNVIC_SYSTICK_CTRL_REG = 0UL;
+	portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
+
 	/* Configure SysTick to interrupt at the requested rate. */
 	portNVIC_SYSTICK_LOAD_REG = ( configSYSTICK_CLOCK_HZ / configTICK_RATE_HZ ) - 1UL;
 	portNVIC_SYSTICK_CTRL_REG = ( portNVIC_SYSTICK_CLK_BIT | portNVIC_SYSTICK_INT_BIT | portNVIC_SYSTICK_ENABLE_BIT );

FreeRTOS/Source/portable/IAR/ARM_CM3/portasm.s

@@ -91,6 +91,7 @@ xPortPendSVHandler:
 
 	stmdb r0!, {r4-r11}				/* Save the remaining registers. */
 	str r0, [r2]					/* Save the new top of stack into the first member of the TCB. */
+	clrex							/* Ensure thread safety of atomic operations. */
 
 	stmdb sp!, {r3, r14}
 	mov r0, #configMAX_SYSCALL_INTERRUPT_PRIORITY

FreeRTOS/Source/portable/IAR/ARM_CM4F/port.c

@@ -576,6 +576,10 @@ __weak void vPortSetupTimerInterrupt( void )
 	}
 	#endif /* configUSE_TICKLESS_IDLE */
 
+	/* Stop and clear the SysTick. */
+	portNVIC_SYSTICK_CTRL_REG = 0UL;
+	portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
+
 	/* Configure SysTick to interrupt at the requested rate. */
 	portNVIC_SYSTICK_LOAD_REG = ( configSYSTICK_CLOCK_HZ / configTICK_RATE_HZ ) - 1UL;
 	portNVIC_SYSTICK_CTRL_REG = ( portNVIC_SYSTICK_CLK_BIT | portNVIC_SYSTICK_INT_BIT | portNVIC_SYSTICK_ENABLE_BIT );

FreeRTOS/Source/portable/IAR/ARM_CM4F/portasm.s

@@ -101,6 +101,9 @@ xPortPendSVHandler:
 	/* Save the new top of stack into the first member of the TCB. */
 	str r0, [r2]
 
+	/* Ensure thread safety of atomic operations. */
+	clrex
+
 	stmdb sp!, {r3}
 	mov r0, #configMAX_SYSCALL_INTERRUPT_PRIORITY
 	msr basepri, r0

FreeRTOS/Source/portable/IAR/ARM_CM7/r0p1/port.c

@@ -559,6 +559,10 @@ __weak void vPortSetupTimerInterrupt( void )
 	}
 	#endif /* configUSE_TICKLESS_IDLE */
 
+	/* Stop and clear the SysTick. */
+	portNVIC_SYSTICK_CTRL_REG = 0UL;
+	portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
+
 	/* Configure SysTick to interrupt at the requested rate. */
 	portNVIC_SYSTICK_LOAD_REG = ( configSYSTICK_CLOCK_HZ / configTICK_RATE_HZ ) - 1UL;
 	portNVIC_SYSTICK_CTRL_REG = ( portNVIC_SYSTICK_CLK_BIT | portNVIC_SYSTICK_INT_BIT | portNVIC_SYSTICK_ENABLE_BIT );

FreeRTOS/Source/portable/IAR/ARM_CM7/r0p1/portasm.s

@@ -101,6 +101,9 @@ xPortPendSVHandler:
 	/* Save the new top of stack into the first member of the TCB. */
 	str r0, [r2]
 
+	/* Ensure thread safety of atomic operations. */
+	clrex
+
 	stmdb sp!, {r3}
 	mov r0, #configMAX_SYSCALL_INTERRUPT_PRIORITY
 	cpsid i

FreeRTOS/Source/portable/MikroC/ARM_CM4F/port.c

@@ -457,7 +457,8 @@ void xPortPendSVHandler( void ) iv IVT_INT_PendSV ics ICS_OFF
 	stmdb r0!, (r4-r11, r14)		 /* Save the core registers. */
 
 	str r0, [r2]			 /* Save the new top of stack into the first member of the TCB. */
-/*_RB_?	mrs r0, psp why was this here? */
+
+	clrex					/* Ensure thread safety of atomic operations. */
 
 	stmdb sp!, (r3)
 	ldr r0, =_ucMaxSyscallInterruptPriority
@@ -680,6 +681,10 @@ void xPortSysTickHandler( void ) iv IVT_INT_SysTick ics ICS_AUTO
 			}
 			#endif /* configUSE_TICKLESS_IDLE */
 
+			/* Reset SysTick. */
+			portNVIC_SYSTICK_CTRL_REG = 0UL;
+			portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
+
 			/* Configure SysTick to interrupt at the requested rate. */
 			portNVIC_SYSTICK_LOAD_REG = ( configSYSTICK_CLOCK_HZ / configTICK_RATE_HZ ) - 1UL;
 			portNVIC_SYSTICK_CTRL_REG = ( portNVIC_SYSTICK_CLK_BIT | portNVIC_SYSTICK_INT_BIT | portNVIC_SYSTICK_ENABLE_BIT );

FreeRTOS/Source/portable/RVDS/ARM_CM0/port.c

@@ -76,8 +76,9 @@
 #include "task.h"
 
 /* Constants required to manipulate the NVIC. */
-#define portNVIC_SYSTICK_CTRL		( ( volatile uint32_t *) 0xe000e010 )
-#define portNVIC_SYSTICK_LOAD		( ( volatile uint32_t *) 0xe000e014 )
+#define portNVIC_SYSTICK_CTRL			( ( volatile uint32_t * ) 0xe000e010 )
+#define portNVIC_SYSTICK_LOAD			( ( volatile uint32_t * ) 0xe000e014 )
+#define portNVIC_SYSTICK_CURRENT_VALUE	( ( volatile uint32_t * ) 0xe000e018 )
 #define portNVIC_INT_CTRL			( ( volatile uint32_t *) 0xe000ed04 )
 #define portNVIC_SYSPRI2			( ( volatile uint32_t *) 0xe000ed20 )
 #define portNVIC_SYSTICK_CLK		0x00000004
@@ -341,6 +342,10 @@ uint32_t ulPreviousMask;
  */
 void prvSetupTimerInterrupt( void )
 {
+	/* Stop and reset the SysTick. */
+	*(portNVIC_SYSTICK_CTRL) = 0UL;
+	*(portNVIC_SYSTICK_CURRENT_VALUE) = 0UL;
+
 	/* Configure SysTick to interrupt at the requested rate. */
 	*(portNVIC_SYSTICK_LOAD) = ( configCPU_CLOCK_HZ / configTICK_RATE_HZ ) - 1UL;
 	*(portNVIC_SYSTICK_CTRL) = portNVIC_SYSTICK_CLK | portNVIC_SYSTICK_INT | portNVIC_SYSTICK_ENABLE;

FreeRTOS/Source/portable/RVDS/ARM_CM3/port.c

@@ -407,6 +407,7 @@ __asm void xPortPendSVHandler( void )
 
 	stmdb r0!, {r4-r11}			/* Save the remaining registers. */
 	str r0, [r2]				/* Save the new top of stack into the first member of the TCB. */
+	clrex						/* Ensure thread safety of atomic operations. */
 
 	stmdb sp!, {r3, r14}
 	mov r0, #configMAX_SYSCALL_INTERRUPT_PRIORITY
@@ -621,6 +622,10 @@ void xPortSysTickHandler( void )
 		}
 		#endif /* configUSE_TICKLESS_IDLE */
 
+		/* Stop and clear the SysTick. */
+		portNVIC_SYSTICK_CTRL_REG = 0UL;
+		portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
+
 		/* Configure SysTick to interrupt at the requested rate. */
 		portNVIC_SYSTICK_LOAD_REG = ( configSYSTICK_CLOCK_HZ / configTICK_RATE_HZ ) - 1UL;
 		portNVIC_SYSTICK_CTRL_REG = ( portNVIC_SYSTICK_CLK_BIT | portNVIC_SYSTICK_INT_BIT | portNVIC_SYSTICK_ENABLE_BIT );

FreeRTOS/Source/portable/RVDS/ARM_CM4F/port.c

@@ -479,6 +479,9 @@ __asm void xPortPendSVHandler( void )
 	/* Save the new top of stack into the first member of the TCB. */
 	str r0, [r2]
 
+	/* Ensure thread safety of atomic operations. */
+	clrex
+
 	stmdb sp!, {r3}
 	mov r0, #configMAX_SYSCALL_INTERRUPT_PRIORITY
 	msr basepri, r0
@@ -696,7 +699,7 @@ void xPortSysTickHandler( void )
  * Setup the SysTick timer to generate the tick interrupts at the required
  * frequency.
  */
-#if configOVERRIDE_DEFAULT_TICK_CONFIGURATION == 0
+#if( configOVERRIDE_DEFAULT_TICK_CONFIGURATION == 0 )
 
 	void vPortSetupTimerInterrupt( void )
 	{
@@ -709,6 +712,10 @@ void xPortSysTickHandler( void )
 		}
 		#endif /* configUSE_TICKLESS_IDLE */
 
+		/* Stop and clear the SysTick. */
+		portNVIC_SYSTICK_CTRL_REG = 0UL;
+		portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
+
 		/* Configure SysTick to interrupt at the requested rate. */
 		portNVIC_SYSTICK_LOAD_REG = ( configSYSTICK_CLOCK_HZ / configTICK_RATE_HZ ) - 1UL;
 		portNVIC_SYSTICK_CTRL_REG = ( portNVIC_SYSTICK_CLK_BIT | portNVIC_SYSTICK_INT_BIT | portNVIC_SYSTICK_ENABLE_BIT );

FreeRTOS/Source/portable/RVDS/ARM_CM4_MPU/port.c

@@ -91,6 +91,7 @@ task.h is included from an application file. */
 /* 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 ) )
+#define portNVIC_SYSTICK_CURRENT_VALUE_REG		( * ( ( volatile uint32_t * ) 0xe000e018 ) )
 #define portNVIC_SYSPRI2_REG					( *	( ( volatile uint32_t * ) 0xe000ed20 ) )
 #define portNVIC_SYSPRI1_REG					( * ( ( volatile uint32_t * ) 0xe000ed1c ) )
 #define portNVIC_SYS_CTRL_STATE_REG				( * ( ( volatile uint32_t * ) 0xe000ed24 ) )
@@ -491,6 +492,7 @@ __asm void xPortPendSVHandler( void )
 	mrs r1, control
 	stmdb r0!, {r1, r4-r11, r14}	/* Save the remaining registers. */
 	str r0, [r2]					/* Save the new top of stack into the first member of the TCB. */
+	clrex							/* Ensure thread safety of atomic operations. */
 
 	stmdb sp!, {r3}
 	mov r0, #configMAX_SYSCALL_INTERRUPT_PRIORITY
@@ -544,6 +546,10 @@ uint32_t ulDummy;
  */
 static void prvSetupTimerInterrupt( void )
 {
+	/* Reset the SysTick. */
+	portNVIC_SYSTICK_CTRL_REG = 0UL;
+	portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
+
 	/* Configure SysTick to interrupt at the requested rate. */
 	portNVIC_SYSTICK_LOAD_REG = ( configCPU_CLOCK_HZ / configTICK_RATE_HZ ) - 1UL;
 	portNVIC_SYSTICK_CTRL_REG = portNVIC_SYSTICK_CLK | portNVIC_SYSTICK_INT | portNVIC_SYSTICK_ENABLE;

FreeRTOS/Source/portable/RVDS/ARM_CM7/r0p1/port.c

@@ -463,6 +463,9 @@ __asm void xPortPendSVHandler( void )
 	/* Save the new top of stack into the first member of the TCB. */
 	str r0, [r2]
 
+	/* Ensure thread safety of atomic operations. */
+	clrex
+
 	stmdb sp!, {r3}
 	mov r0, #configMAX_SYSCALL_INTERRUPT_PRIORITY
 	cpsid i
@@ -695,6 +698,10 @@ void xPortSysTickHandler( void )
 		}
 		#endif /* configUSE_TICKLESS_IDLE */
 
+		/* Stop and clear the SysTick. */
+		portNVIC_SYSTICK_CTRL_REG = 0UL;
+		portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
+
 		/* Configure SysTick to interrupt at the requested rate. */
 		portNVIC_SYSTICK_LOAD_REG = ( configSYSTICK_CLOCK_HZ / configTICK_RATE_HZ ) - 1UL;
 		portNVIC_SYSTICK_CTRL_REG = ( portNVIC_SYSTICK_CLK_BIT | portNVIC_SYSTICK_INT_BIT | portNVIC_SYSTICK_ENABLE_BIT );

FreeRTOS/Source/tasks.c

@@ -1901,7 +1901,10 @@ BaseType_t xReturn;
 
 		/* If configGENERATE_RUN_TIME_STATS is defined then the following
 		macro must be defined to configure the timer/counter used to generate
-		the run time counter time base. */
+		the run time counter time base.   NOTE:  If configGENERATE_RUN_TIME_STATS
+		is set to 0 and the following line fails to build then ensure you do not
+		have portCONFIGURE_TIMER_FOR_RUN_TIME_STATS() defined in your
+		FreeRTOSConfig.h file. */
 		portCONFIGURE_TIMER_FOR_RUN_TIME_STATS();
 
 		/* Setting up the timer tick is hardware specific and thus in the