how to wake up from IDLE mode using ppi?

[Haruki Kawakami]

Hi

I want to know how to use ppi to wake up CPU from IDLE mode.

I've tried to use timer timeout event for triggering Port Event and wake up CPU, but can't assign NRF_GPIOTE->EVENTS_PORT to ppi channel. nrf_drv_ppi_channel_assign returns NRF_ERROR_INVALID_STATE.

ret_code_t err_code = nrf_drv_timer_init(&timer1, NULL, timer_event_handler);
APP_ERROR_CHECK(err_code);
nrf_drv_timer_extended_compare(&timer1, NRF_TIMER_CC_CHANNEL0, 0xFFFFUL, NRF_TIMER_SHORT_COMPARE0_CLEAR_MASK, false);

nrf_drv_gpiote_init();

err_code = nrf_drv_ppi_init();
APP_ERROR_CHECK(err_code);

// Configure 1st available PPI channel to stop TIMER0 counter on TIMER1 COMPARE[0] match, which is every even number of seconds.
err_code = nrf_drv_ppi_channel_alloc(&ppi_channel1);
APP_ERROR_CHECK(err_code);
err_code = nrf_drv_ppi_channel_assign(ppi_channel1,
                                      nrf_drv_timer_event_address_get(&timer1, NRF_TIMER_EVENT_COMPARE0),
                                      NRF_GPIOTE->EVENTS_PORT);
APP_ERROR_CHECK(err_code);

NRF_POWER->TASKS_CONSTLAT = 1;
nrf_drv_timer_enable(&timer1);
while (true)
{
   __WFI();

    if(LED_IS_ON(BSP_LED_0_MASK)){
        LEDS_OFF(BSP_LED_0_MASK);
    } else {
        LEDS_ON(BSP_LED_0_MASK);
    }
    NRF_GPIOTE->EVENTS_PORT = 0;
}

I don't want to configure any pin for GPIOTE, just want to use register.

Thanks!

[Einar Thorsrud]

PPI is used to connect peripherals, for example TIMER0 and TIMER1 in your case. If you want to wake the CPU on a compare event (for example on TIMER1 which you use to stop TIMER0) you should enable the compare interrupt. Using the timer driver you can do this with nrf_drv_timer_compare_int_enable().

[Haruki Kawakami]

do the compare event wake the CPU?

[Einar Thorsrud]

Yes, if you enable the interrupt for the relevant compare event in the INTENSET register (directly, or by using nrf_drv_timer_compare_int_enable() as you already use the timer driver).

[Haruki Kawakami]

I made it to wake CPU using nrf_drv_timer_compare_int_enable(), but I can't make CPU sleep again.

It seems that compare event is always true once happened. then I've used nrf_timer_event_clear to make compare event false, but cannot resolve this problem.

how can i make CPU sleep again?

 while (true)
{
    __WFI();
    printf("Current count\n\r");
    nrf_timer_event_clear(timer1.p_reg, nrf_timer_compare_event_get(NRF_TIMER_CC_CHANNEL0));
}

[Einar Thorsrud]

When you use the driver you should not have to clear the interrupt explicitly (as you do with nrf_timer_event_clear(), as it is done by the driver. You can see this in nrf_drv_timer.c, where the irq_handler() calls nrf_timer_event_clear() just before it calls the event handler you registered with the call to nrf_drv_timer_init().

I don't understand why your CPU does not go back to sleep, though. Can you double-check?