In radio_signal_callback, after switching app_timer, it cannot generate app_timer interrupt

[Palmer Huang]

Hello,

I encountered a problem. When I turn off app_timer during timeslot interruption, it cannot generate app_timer interrupt
code show as below:

static nrf_radio_signal_callback_return_param_t *timeslot_cb(uint8_t signal)
{
    static nrf_radio_signal_callback_return_param_t ret = {
        .params.request.p_next = NULL,
        .callback_action       = NRF_RADIO_SIGNAL_CALLBACK_ACTION_NONE,
    };
    
    if(signal == NRF_RADIO_CALLBACK_SIGNAL_TYPE_RADIO){
        if (NRF_RADIO->EVENTS_DISABLED == 1) {
            NRF_RADIO->EVENTS_DISABLED = 0;
            NRF_LOG_DEBUG("radio disable evt");
            APP_ERROR_CHECK(app_timer_start(m_rx_timer, APP_TIMER_TICKS(SLEEP_INTERVAL), NULL));
            APP_ERROR_CHECK(app_timer_stop(m_rx_timer));
            APP_ERROR_CHECK(app_timer_start(m_rx_timer, APP_TIMER_TICKS(SLEEP_INTERVAL), NULL));
            NRF_LOG_INFO("timer active : %d", m_rx_timer->active);
        }
    }

I am using app_timer2 :

ret_code_t app_timer_start(app_timer_t * p_timer, uint32_t timeout_ticks, void * p_context)
{
    ASSERT(p_timer);
    app_timer_t * p_t = (app_timer_t *) p_timer;

    if (p_t->active)
    {
        return NRF_SUCCESS;
    }

    p_t->p_context = p_context;
    p_t->end_val = get_now() + timeout_ticks;

    if (p_t->repeat_period)
    {
        p_t->repeat_period = timeout_ticks;
    }

    return timer_req_schedule(TIMER_REQ_START, p_t);
}

Regards, 

Gray.

[Hung Bui]

Hi Gray, 

Please be aware that the app_timer uses a buffer to queue/schedule the tasks. And it only execute tasks when there is an RTC interrupt. The interrupt can be either normal RTC interrupt, or it can be triggered by calling drv_rtc_irq_trigger() inside timer_req_schedule(). In your case if you are in the radio callback, it's most likely you are on the highest priority meaning the RTC_IRG can't be executed until the function is finished. 

So it's normal that when you start the app timer inside the radio signal call back the active timer remains at 0. 

But it should be executed after the radio callback is finished. Please check to see if the rtc_irq() is called after that or not. 

[Palmer Huang]

Yes,rtc_irq() is called after  the radio callback.

I get it, thank you.

[Hung Bui]

Please note that regardless how many call to app_timer_start() or app_timer_stop() inside timeslot_cb() there will be only one RTC interrupt triggered after the timeslot_cb() finished. The reason is that the app_timer_start, app_timer_stop() triggers the interrupt, but the interrupt will be preempted by the high interrupt context of the radio interrupt handler . And then only one RTC_IRQ interrupt is triggered after that. 

I would suggest to think of using the RTC directly, or put the app_timer_stop, app_timer_start into a app scheduler so that it will be executed in main() context. 

[Palmer Huang]

I understand, thanks for your suggestion.