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.
This commit is contained in:
Richard Barry 2017-03-28 03:13:48 +00:00
parent 7ee26c1b5e
commit 464c2660ad
16 changed files with 686 additions and 505 deletions

View file

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