mirror of
https://github.com/FreeRTOS/FreeRTOS-Kernel.git
synced 2025-08-20 01:58:32 -04:00
Updates to the Cortex-M tickless idle code to reduce clock slippage.
Updates to prevent the vTaskSwitchContext() function being removed from GCC builds when link time optimisation is used.
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16 changed files with 686 additions and 505 deletions
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@ -196,7 +196,7 @@ static void prvTaskExitError( void );
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/*
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* The number of SysTick increments that make up one tick period.
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*/
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#if configUSE_TICKLESS_IDLE == 1
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#if( configUSE_TICKLESS_IDLE == 1 )
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static uint32_t ulTimerCountsForOneTick = 0;
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#endif /* configUSE_TICKLESS_IDLE */
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@ -204,7 +204,7 @@ static void prvTaskExitError( void );
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* The maximum number of tick periods that can be suppressed is limited by the
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* 24 bit resolution of the SysTick timer.
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*/
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#if configUSE_TICKLESS_IDLE == 1
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#if( configUSE_TICKLESS_IDLE == 1 )
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static uint32_t xMaximumPossibleSuppressedTicks = 0;
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#endif /* configUSE_TICKLESS_IDLE */
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@ -212,7 +212,7 @@ static void prvTaskExitError( void );
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* Compensate for the CPU cycles that pass while the SysTick is stopped (low
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* power functionality only.
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*/
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#if configUSE_TICKLESS_IDLE == 1
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#if( configUSE_TICKLESS_IDLE == 1 )
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static uint32_t ulStoppedTimerCompensation = 0;
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#endif /* configUSE_TICKLESS_IDLE */
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@ -535,7 +535,7 @@ void xPortSysTickHandler( void ) iv IVT_INT_SysTick ics ICS_AUTO
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void vPortSuppressTicksAndSleep( TickType_t xExpectedIdleTime )
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{
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uint32_t ulReloadValue, ulCompleteTickPeriods, ulCompletedSysTickDecrements, ulSysTickCTRL;
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uint32_t ulReloadValue, ulCompleteTickPeriods, ulCompletedSysTickDecrements;
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TickType_t xModifiableIdleTime;
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/* Make sure the SysTick reload value does not overflow the counter. */
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@ -611,25 +611,41 @@ void xPortSysTickHandler( void ) iv IVT_INT_SysTick ics ICS_AUTO
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}
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configPOST_SLEEP_PROCESSING( xExpectedIdleTime );
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/* Stop SysTick. Again, the time the SysTick is stopped for is
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accounted for as best it can be, but using the tickless mode will
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inevitably result in some tiny drift of the time maintained by the
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kernel with respect to calendar time. */
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ulSysTickCTRL = portNVIC_SYSTICK_CTRL_REG;
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portNVIC_SYSTICK_CTRL_REG = ( ulSysTickCTRL & ~portNVIC_SYSTICK_ENABLE_BIT );
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/* Re-enable interrupts - see comments above the cpsid instruction()
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above. */
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/* Re-enable interrupts to allow the interrupt that brought the MCU
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out of sleep mode to execute immediately. see comments above
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__disable_interrupt() call above. */
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__asm { "cpsie i" };
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__asm { "wfi" };
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__asm { "isb" };
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__asm { "dsb" };
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__asm { "isb" };
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if( ( ulSysTickCTRL & portNVIC_SYSTICK_COUNT_FLAG_BIT ) != 0 )
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/* Disable interrupts again because the clock is about to be stopped
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and interrupts that execute while the clock is stopped will increase
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any slippage between the time maintained by the RTOS and calendar
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time. */
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__asm { "cpsid i" };
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__asm { "dsb" };
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__asm { "isb" };
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/* Disable the SysTick clock without reading the
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portNVIC_SYSTICK_CTRL_REG register to ensure the
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portNVIC_SYSTICK_COUNT_FLAG_BIT is not cleared if it is set. Again,
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the time the SysTick is stopped for is accounted for as best it can
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be, but using the tickless mode will inevitably result in some tiny
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drift of the time maintained by the kernel with respect to calendar
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time*/
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portNVIC_SYSTICK_CTRL_REG = ( portNVIC_SYSTICK_CLK_BIT | portNVIC_SYSTICK_INT_BIT );
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/* Determine if the SysTick clock has already counted to zero and
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been set back to the current reload value (the reload back being
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correct for the entire expected idle time) or if the SysTick is yet
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to count to zero (in which case an interrupt other than the SysTick
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must have brought the system out of sleep mode). */
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if( ( portNVIC_SYSTICK_CTRL_REG & portNVIC_SYSTICK_COUNT_FLAG_BIT ) != 0 )
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{
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uint32_t ulCalculatedLoadValue;
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/* The tick interrupt has already executed, and the SysTick
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count reloaded with ulReloadValue. Reset the
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/* The tick interrupt is already pending, and the SysTick count
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reloaded with ulReloadValue. Reset the
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portNVIC_SYSTICK_LOAD_REG with whatever remains of this tick
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period. */
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ulCalculatedLoadValue = ( ulTimerCountsForOneTick - 1UL ) - ( ulReloadValue - portNVIC_SYSTICK_CURRENT_VALUE_REG );
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@ -644,11 +660,9 @@ void xPortSysTickHandler( void ) iv IVT_INT_SysTick ics ICS_AUTO
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portNVIC_SYSTICK_LOAD_REG = ulCalculatedLoadValue;
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/* The tick interrupt handler will already have pended the tick
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processing in the kernel. As the pending tick will be
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processed as soon as this function exits, the tick value
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maintained by the tick is stepped forward by one less than the
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time spent waiting. */
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/* As the pending tick will be processed as soon as this
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function exits, the tick value maintained by the tick is stepped
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forward by one less than the time spent waiting. */
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ulCompleteTickPeriods = xExpectedIdleTime - 1UL;
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}
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else
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@ -665,22 +679,19 @@ void xPortSysTickHandler( void ) iv IVT_INT_SysTick ics ICS_AUTO
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/* The reload value is set to whatever fraction of a single tick
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period remains. */
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portNVIC_SYSTICK_LOAD_REG = ( ( ulCompleteTickPeriods + 1 ) * ulTimerCountsForOneTick ) - ulCompletedSysTickDecrements;
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portNVIC_SYSTICK_LOAD_REG = ( ( ulCompleteTickPeriods + 1UL ) * ulTimerCountsForOneTick ) - ulCompletedSysTickDecrements;
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}
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/* Restart SysTick so it runs from portNVIC_SYSTICK_LOAD_REG
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again, then set portNVIC_SYSTICK_LOAD_REG back to its standard
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value. The critical section is used to ensure the tick interrupt
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can only execute once in the case that the reload register is near
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zero. */
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value. */
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portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
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portENTER_CRITICAL();
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{
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portNVIC_SYSTICK_CTRL_REG |= portNVIC_SYSTICK_ENABLE_BIT;
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vTaskStepTick( ulCompleteTickPeriods );
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portNVIC_SYSTICK_LOAD_REG = ulTimerCountsForOneTick - 1UL;
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}
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portEXIT_CRITICAL();
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portNVIC_SYSTICK_CTRL_REG |= portNVIC_SYSTICK_ENABLE_BIT;
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vTaskStepTick( ulCompleteTickPeriods );
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portNVIC_SYSTICK_LOAD_REG = ulTimerCountsForOneTick - 1UL;
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/* Exit with interrpts enabled. */
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__asm { "cpsie i" };
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}
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}
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@ -696,7 +707,7 @@ void xPortSysTickHandler( void ) iv IVT_INT_SysTick ics ICS_AUTO
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void vPortSetupTimerInterrupt( void )
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{
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/* Calculate the constants required to configure the tick interrupt. */
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#if configUSE_TICKLESS_IDLE == 1
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#if( configUSE_TICKLESS_IDLE == 1 )
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{
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ulTimerCountsForOneTick = ( configSYSTICK_CLOCK_HZ / configTICK_RATE_HZ );
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xMaximumPossibleSuppressedTicks = portMAX_24_BIT_NUMBER / ulTimerCountsForOneTick;
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@ -812,7 +823,7 @@ BaseType_t xReturn;
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devices by calling NVIC_SetPriorityGrouping( 0 ); before starting the
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scheduler. Note however that some vendor specific peripheral libraries
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assume a non-zero priority group setting, in which cases using a value
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of zero will result in unpredicable behaviour. */
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of zero will result in unpredictable behaviour. */
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configASSERT( ( portAIRCR_REG & portPRIORITY_GROUP_MASK ) <= ulMaxPRIGROUPValue );
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}
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