How to do a low power sleep without interrupts?

RE: How to do a low power sleep without interrupts?

rgrr2 — Tue, 02 Apr 2019 14:31:17 GMT

Ok, I've found a way to implement a low power delay which seems to work always.

Beforehand the problem was, that depending on the state of the Cortex EV flag, the __WFE() did not return. Situation could be reproduced if there have been the NFC->GPIO configuration selected, which actually reprograms some values in UICR and then does a NVIC_SystemReset(). On this boot the loop hung.

My solution is to use the watchdog timer for the low power boot delay, i.e. if RESETREAS shows 0, the watchdog is initialized to "bark" after 1s. After init of this the program goes into an __WFE() loop and waits for the watchdog.

On the watchdog reboot, RESETREAS shows nonzero and the program continues.

Disadvantage is, that on application start, the DOG bit is always set in RESETREAS. But I can actually live with that ;-)

Hardy

PS: note, that this only works as low power delay on startup.

PPS: just for the record: my feeling says, that NVIC_SystemReset() does not do a complete reset.

RE: How to do a low power sleep without interrupts?

Sigurd — Wed, 08 Aug 2018 13:55:41 GMT

What is the value of SCB->SCR register and SCB->CCR register before you enter __WFE?

You could also try to use nrfjprog, and call nrfjprog --run, in case the CPU is somehow halted.

RE: How to do a low power sleep without interrupts?

rgrr2 — Mon, 06 Aug 2018 10:35:13 GMT

custom board, eclipse, Jlink Ultra+

RE: How to do a low power sleep without interrupts?

Sigurd — Mon, 06 Aug 2018 09:22:32 GMT

I'm not able to recreate this behavior.

Is this a custom board or the nRF52-DK?

What toolchain / IDE are you using ?

What kind of Jlink adapter is this?

RE: How to do a low power sleep without interrupts?

rgrr2 — Fri, 03 Aug 2018 09:20:14 GMT

Almost no changes to startup_nrf52.s...

Nevertheless I've found my culprit: it's the Jlink adapter! When I'm disconnecting it, device will start. When it's connected, __WFE() waits forever.

Whats wrong with that?

RE: How to do a low power sleep without interrupts?

Sigurd — Fri, 03 Aug 2018 08:22:33 GMT

This works fine here:

void Reset_Handler_Delay( void )
{
   NRF_POWER->TASKS_LOWPWR = 1;
   SCB->SCR |= SCB_SCR_SEVONPEND_Msk; 

    //
    // enable clock as Internal 32KHz oscillator
    //
    NRF_CLOCK->LFCLKSRC            = (CLOCK_LFCLKSRC_SRC_RC << CLOCK_LFCLKSRC_SRC_Pos);
    NRF_CLOCK->EVENTS_LFCLKSTARTED = 0;
    NRF_CLOCK->TASKS_LFCLKSTART    = 1;
    while (NRF_CLOCK->EVENTS_LFCLKSTARTED == 0) {
    }
    NRF_CLOCK->EVENTS_LFCLKSTARTED = 0;

    NRF_RTC1->TASKS_STOP  = 1;
    NRF_RTC1->TASKS_CLEAR = 1;
    NRF_RTC1->PRESCALER   = 0;
    NRF_RTC1->INTENCLR    = 0xffffffffUL;
    NRF_RTC1->EVTENCLR    = 0xffffffffUL;
    NRF_RTC1->INTENSET    = RTC_INTENSET_COMPARE3_Msk;         // TODO CC[0] and [1] are not working
    NRF_RTC1->EVTENSET    = RTC_EVTENSET_COMPARE3_Msk;
    NRF_RTC1->EVENTS_COMPARE[3] = 0;
    NRF_RTC1->CC[3] = NRF_RTC1->COUNTER + (1000 * 32768UL) / 1000UL;
    NRF_RTC1->TASKS_START = 1;
    __SEV();
    while ( !NRF_RTC1->EVENTS_COMPARE[3]) {
        __WFE();
    }

    NRF_RTC1->TASKS_STOP = 1;
    NRF_RTC1->TASKS_CLEAR = 1;
    NRF_RTC1->INTENCLR = 0xffffffffUL;
    NRF_RTC1->EVTENCLR = 0xffffffffUL;
    NRF_CLOCK->TASKS_LFCLKSTOP = 1;
    
    
    SCB->SCR &= ~(1UL << SCB_SCR_SEVONPEND_Pos);
    
    
}   // Reset_Handler_Delay

How does your Reset_Handler look like ?

What toolchain / IDE are you using ?

If you are using Keil, have you made any changes in arm_startup_nrf52.s ?

RE: How to do a low power sleep without interrupts?

rgrr2 — Fri, 03 Aug 2018 07:33:31 GMT

Hi Sigurd,

thanks for the suggestion. Unfortunately it does not help, the MCU still stucks...

Current code:

extern "C" void Reset_Handler_Delay( void )
{
    NRF_POWER->TASKS_LOWPWR = 1;

    //
    // enable clock as Internal 32KHz oscillator
    //
    NRF_CLOCK->LFCLKSRC            = (CLOCK_LFCLKSRC_SRC_RC << CLOCK_LFCLKSRC_SRC_Pos);
    NRF_CLOCK->EVENTS_LFCLKSTARTED = 0;
    NRF_CLOCK->TASKS_LFCLKSTART    = 1;
    while (NRF_CLOCK->EVENTS_LFCLKSTARTED == 0) {
    }
    NRF_CLOCK->EVENTS_LFCLKSTARTED = 0;

    //
    // Start HF oscillator -> current consumption increases
    //
    NRF_CLOCK->EVENTS_HFCLKSTARTED = 0;
    NRF_CLOCK->TASKS_HFCLKSTART    = 1;
    while (NRF_CLOCK->EVENTS_HFCLKSTARTED == 0) {
    }

    SCB->SCR |= SCB_SCR_SEVONPEND_Msk;

#if 0
    NRF_RTC1->TASKS_STOP  = 1;
    NRF_RTC1->TASKS_CLEAR = 1;
    NRF_RTC1->PRESCALER   = 0;
    NRF_RTC1->INTENCLR    = 0xffffffffUL;
    NRF_RTC1->EVTENCLR    = 0xffffffffUL;
    NRF_RTC1->INTENSET    = RTC_INTENSET_COMPARE3_Msk;         // TODO CC[0] and [1] are not working
    NRF_RTC1->EVTENSET    = RTC_EVTENSET_COMPARE3_Msk;
    NRF_RTC1->EVENTS_COMPARE[3] = 0;
    NRF_RTC1->CC[3] = NRF_RTC1->COUNTER + (1000 * 32768UL) / 1000UL;
    NRF_RTC1->TASKS_START = 1;
    while ( !NRF_RTC1->EVENTS_COMPARE[3]) {
        __WFE();
    }

    NRF_RTC1->TASKS_STOP = 1;
    NRF_RTC1->TASKS_CLEAR = 1;
    NRF_RTC1->INTENCLR = 0xffffffffUL;
    NRF_RTC1->EVTENCLR = 0xffffffffUL;
    NRF_CLOCK->TASKS_LFCLKSTOP = 1;
#endif

#if 1
    NRF_TIMER0->MODE = 0;
    NRF_TIMER0->BITMODE = 3;
    NRF_TIMER0->CC[0] = 1000;
    NRF_TIMER0->PRESCALER = 10;
    NRF_TIMER0->EVENTS_COMPARE[0] = 0;
    NRF_TIMER0->TASKS_START = 1;
    while ( !NRF_TIMER0->EVENTS_COMPARE[0]) {
        __WFE();
    }
#endif

    SCB->SCR &= ~(1UL << SCB_SCR_SEVONPEND_Pos);
}   // Reset_Handler_Delay

Neither loop (RTC/TIMER) terminates if __WFE() is contained. Both terminate if __WFE() is removed.

Any idea why? Is there anything more required to generate an SEV?

RE: How to do a low power sleep without interrupts?

Sigurd — Thu, 02 Aug 2018 15:11:05 GMT

Hi,

Try setting the SEVONPEND flag at the start of your Reset_Handler_Delay() function.

SCB->SCR |= SCB_SCR_SEVONPEND_Msk;

Clear the flag at the end of your Reset_Handler_Delay() function.

SCB->SCR &= ~(1UL << SCB_SCR_SEVONPEND_Pos);

Some more information about this can be found in this post.