How to set nRF52840 into sleep mode and wake up on RTC

Development CPU
#1

Hello,

I’m working on nRF52840’s power management and I want to develop a sleep mode state that wakes the board up from RTC, for example, sleep for 10 seconds and wake up. I successfully managed to put it into a sleep mode using __WFE() “Wait for Event” function, however, the only way I can wake it up is from GPIO event, like pressing a button.

I guess the module has no RTC configuration, so I chose the Z-TIMER for seconds counter. How can I set into sleep mode and wake up on RTC using Z-TIMER?

I have tried calling ZTIMER and __SEV() after __WFE(), also writing direclty into memory, but with no success.

1 Like
#2

Hi and welcome!

IIRC the nRF52 does a lot of automatic power management in hardware. Is a ztimer_sleep(ZTIMER_MSEC, 10 * MS_PER_SEC) not sufficient for your use case?

#3

Thank you for answering!

Unfortunately the board is not saving any power when I set ztimer_sleep(ZTIMER_MSEC, 10 * MS_PER_SEC). On Idle mode it measures 4 mA consumption and on sleep mode it is about 1.5 mA, but it doesn’t change on ztimer call, only when __WFE() is called.

void timer(void)
{
    NRF_POWER->TASKS_LOWPWR = 1;
    #ifdef MODULE_ZTIMER_USEC
        ztimer_sleep(ZTIMER_MSEC, 10000);
    #endif

    __SEV(); 
}


void nrf52_sys_on(void) {
    /* Clear Event Register */
    __SEV();
    /* Wait for event */
    __WFE();
    /* Wait for event */
    __WFE();

}

void pm_set(unsigned mode)
{
    switch (mode) {
        case 0:
            //GPIO wake up source sleep
            nrf52_sys_on();
        break;
        case 1:
            //RTC wake up source sleep
            nrf52_sys_on();

            timer();
       

        break;
        default:
        //no sleep
        break;
    }
}