MCU wakeup from sleep by a timer

[enkavak]

Hello,

       I am using nRF52832 IC with softdevice and SDK v15.

       I wish to make the MCU in sleep mode and then a couple of milliseconds (let's say 250ms) wakes up the MCU. For this purpose, can I use the timer? Or do you have any idea ?

       

[haakonsh]

You'll want to use the RTC — Real-time counter. See the Real Time Counter Example and RTC API documentation. 

[enkavak]

Can I use it with the softdevice?

I have external xtal. Do I need to use "lfclk"?

In addition, does the resolution is second? I need resolution in milliseconds 

[haakonsh]

You can use RTC1-2. You can also use the Timer library (app_timer), see also Application Timer API docs. 

[enkavak]

will this awake the MCU from sleep mode?

I have external xtal. Do I need to use "lfclk"?

[haakonsh]

Any interrupt will wake the CPU. 

"I have external xtal. Do I need to use "lfclk"?"
- Well, yes for the RTC you ned a LF clock source. If you've got a 32kHz crystal you can use the LFXO as the source. . 

[enkavak]

When I do not use the below code into mine softdevice code, the code crashes at the line "ble_stack_init();" 

static void rtc_handler(nrf_drv_rtc_int_type_t int_type)
{
    if (int_type == NRF_DRV_RTC_INT_COMPARE0)
    {
        nrf_gpio_pin_toggle(COMPARE_EVENT_OUTPUT);
    }
    else if (int_type == NRF_DRV_RTC_INT_TICK)
    {
        nrf_gpio_pin_toggle(TICK_EVENT_OUTPUT);
    }
}

/** @brief Function configuring gpio for pin toggling.
 */
static void leds_config(void)
{
    bsp_board_init(BSP_INIT_LEDS);
}

/** @brief Function starting the internal LFCLK XTAL oscillator.
 */
static void lfclk_config(void)
{
    ret_code_t err_code = nrf_drv_clock_init();
    APP_ERROR_CHECK(err_code);

    nrf_drv_clock_lfclk_request(NULL);
}

/** @brief Function initialization and configuration of RTC driver instance.
 */
static void rtc_config(void)
{
    uint32_t err_code;

    //Initialize RTC instance
    nrf_drv_rtc_config_t config = NRF_DRV_RTC_DEFAULT_CONFIG;
    config.prescaler = 4095;
    err_code = nrf_drv_rtc_init(&rtc, &config, rtc_handler);
    APP_ERROR_CHECK(err_code);

    //Enable tick event & interrupt
    nrf_drv_rtc_tick_enable(&rtc,true);

    //Set compare channel to trigger interrupt after COMPARE_COUNTERTIME seconds
    err_code = nrf_drv_rtc_cc_set(&rtc,0,COMPARE_COUNTERTIME * 8,true);
    APP_ERROR_CHECK(err_code);

    //Power on RTC instance
    nrf_drv_rtc_enable(&rtc);
}