nrf_drv_timer and sleep

[SentinelLighting]

The design I am working with has no RTC.  Is it possible to use nrf_drv_timer to "wake up" the CPU?  I understand I will not be able to use app_timer code, so I was trying to spin it with WFE/WFI and a timer_handler.  Here is a summary my first failed attempt:

main()

...
    // Initialize wake-up timer
    nrf_drv_timer_init(&TIMER, NULL, timer_handler);
    time_ticks = nrf_drv_timer_ms_to_ticks(&TIMER, time_ms);
    nrf_drv_timer_extended_compare(
         &TIMER, NRF_TIMER_CC_CHANNEL0, time_ticks, NRF_TIMER_SHORT_COMPARE0_CLEAR_MASK, true);
    nrf_drv_timer_enable(&TIMER);

...

while(TRUE){

    __SEV();
    __WFE();

   toggle_led()

}

Pretty new to Nordic, so any help would be appreciated!

[Ashish]

Hey,

nrf51 and nrf52 devices have inbuilt RTC(Real Time Counter). There is no need of an external RTC, so you should be able to use app_timer for waking up the CPU.

[SentinelLighting]

Ashish - the PCB has no 32768 RTC oscillator.  It only has the main crystal.  Are you saying I can remap the internal RTC to be run from the main oscillator?

[Ashish]

Hey,

To use  RTC(Real Time Counter), you only need to configure Low Frequency Clock Source.

If your board doesn't have an external Low Frequency Oscillator, you can use internal Low Frequency RC oscillator or synthesize the Low Frequency clock from the main oscillator.

Please take a look at the product specification of the specific device that you are using for more information.

All the documentation is available here

[SentinelLighting]

Thanks Ashish, between your help and doing a bunch more reading I realized I can can configure the RTC for using the RC option.  This is not optimal for using the BLE, but at this point the board is built without a XTAL!