Interrupts not waking FreeRTOS up in Tickless mode

[dfer]

Hi

I'm working with FreeRTOS with Tickless (RTC) and I was wondering what one should do in order to avoid the FreeRTOS Idle Task to be waken up every time an Interrupt Service Routine has completed the execution.

In Cortex-M4 the SLEEPONEXIT flag in SCR should help with this feature but I cannot let it work with Nordic. Any hints?

Thanks in Advance.

[Susheel Nuguru]

dfer said:

I forgot to mention that the tick interrupt will always reset the SLEEPONEXIT flag (a Task switch is Always necessary in tickless mode at this Point).

 This will be a good failsafe mechanism. I think it should work.

[dfer]

Hi Susheel do you have any idea why the SLEEPONEXIT functionality doesn't work?

[Susheel Nuguru]

I am not sure Davide, it should work, it is an ARM feature and does not seem to be optional.

[dfer]

Hi Susheel

after several attempts it seems that the SPEEPONEXIT functionality is somehow prevented by the softdevice.

Everything gets stuck after a time and I cannot understand why.

I would have another suggestion that would prevent the vPortSuppressTicksAndSleep to always be executed twice before managing to go to sleep:

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    /* Make sure the SysTick reload value does not overflow the counter. */
    if ( xExpectedIdleTime > portNRF_RTC_MAXTICKS - configEXPECTED_IDLE_TIME_BEFORE_SLEEP )
    {
        xExpectedIdleTime = portNRF_RTC_MAXTICKS - configEXPECTED_IDLE_TIME_BEFORE_SLEEP;
    }
    /* Block all the interrupts globally */
#ifdef SOFTDEVICE_PRESENT
    do{
        uint8_t dummy = 0;
        uint32_t err_code = sd_nvic_critical_region_enter(&dummy);
        APP_ERROR_CHECK(err_code);
    }while (0);
#else
    __disable_irq();
#endif

    __SEV(); __WFE();// reset the event flag, if an interrupt has occured and has triggered a task it will be cought in eTaskConfirmSleepModeStatus

    enterTime = nrf_rtc_counter_get(portNRF_RTC_REG);

    if ( eTaskConfirmSleepModeStatus() != eAbortSleep )
    {
        TickType_t xModifiableIdleTime;
        TickType_t wakeupTime = (enterTime + xExpectedIdleTime) & portNRF_RTC_MAXTICKS;

The __SEV(); __WFE(); sequence resets the Event flag. If it was set because an Interrupt has occured, and this Interrupt has triggered a FreeRTOS Task, the subsequent eTaskConfirmSleepModeStatus would detect this and Abort the Sleep sequence.

The Event flag is Always set because either a Task has been Yielded or an Interrupt has occured while the processor was not sleeping. The first time __WFE(); is executed will almost always go Forward without sleeping, causing another call to vPortSuppressTicksAndSleep form FreeRTOS.

What do you think about this? I've tested it quickly and it seems working.

[dfer]

Or even better here:

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    /* Make sure the SysTick reload value does not overflow the counter. */
    if ( xExpectedIdleTime > portNRF_RTC_MAXTICKS - configEXPECTED_IDLE_TIME_BEFORE_SLEEP )
    {
        xExpectedIdleTime = portNRF_RTC_MAXTICKS - configEXPECTED_IDLE_TIME_BEFORE_SLEEP;
    }

    __SEV(); __WFE();// reset the event flag, if an interrupt has occurred and has triggered a task it will be caught in eTaskConfirmSleepModeStatus

    /* Block all the interrupts globally */
#ifdef SOFTDEVICE_PRESENT
    do{
        uint8_t dummy = 0;
        uint32_t err_code = sd_nvic_critical_region_enter(&dummy);
        APP_ERROR_CHECK(err_code);
    }while (0);
#else
    __disable_irq();
#endif

    enterTime = nrf_rtc_counter_get(portNRF_RTC_REG);

    if ( eTaskConfirmSleepModeStatus() != eAbortSleep )
    {