NRF52840 when using Timer and BLE services I found a problem

[zk12312]

when using the TIMER,  I set the TIMER's time_ticks=53328 which means that every 3.33ms, the TIMER will call its callback function and start ADC sample. However,  when I use BLE services and TIMER at the same time, I found that ADC cannot be triggered every 3.33ms precisely and the error is about 1%. The crystal oscillator I use is 32MHZ and I thought the error should not be so big. So whether the BLE services will affect the accuracy of  TIMER when using them at the same time?

[Henry_Chou]

May you show your create timer ,start timer ,stop timer & timer callback handler procedure?

Have you ever trigger timer with repeat mode?

[zk12312]

void saadc_sampling_event_init(void)
{
	  ret_code_t err_code;
	 // uint32_t time_ticks=53028;	
    uint32_t time_ticks=53672;//3.33ms tick=53328 TIME3=16MHZ,1ms tick=16000	
	
    err_code = nrf_drv_ppi_init();
    APP_ERROR_CHECK(err_code);
	  	
    nrf_drv_timer_config_t timer_cfg = NRF_DRV_TIMER_DEFAULT_CONFIG;
	  
    err_code = nrfx_timer_init(&TIMER_ADC, &timer_cfg, timer_adc_event_handler);
    APP_ERROR_CHECK(err_code);
   
    nrf_drv_timer_extended_compare(&TIMER_ADC, NRF_TIMER_CC_CHANNEL3, time_ticks, NRF_TIMER_SHORT_COMPARE3_CLEAR_MASK, true);
	   uint32_t timer_compare_event_addr = nrf_drv_timer_compare_event_address_get(&TIMER_ADC,
                                                                                NRF_TIMER_CC_CHANNEL3);
	
    uint32_t saadc_sample_task_addr   = nrf_drv_saadc_sample_task_get();
    err_code = nrf_drv_ppi_channel_alloc(&m_ppi_channel);
    APP_ERROR_CHECK(err_code);
	
	  err_code = nrf_drv_ppi_channel_assign(m_ppi_channel,
                                          timer_compare_event_addr,
                                          saadc_sample_task_addr);
																					
		APP_ERROR_CHECK(err_code);	 																		
}

this is my code about Timer and ppi init

[Kenneth]

I would double check that you don't by accident stop/start the timer here somewhere in your code, for instance for test you can comment out all places where stop/start are done today.

Kenneth

[zk12312]

I comment out the places that I start the timer by accident, but the timer still varies occasionally.

and I found that when I didn't start the ble and use the timer only, the timer wouldn't vary. However, when I start the ble and then open the timer, it will wary occasionally. So I thought that whether the ble will affect the timer?

[Kenneth]

The BLE can affect the timing, but not by 10ms, the difference is more like ~100us.

The code you refer to disable and enable the timer, you are not starting or stopping the timer somewhere also?

[zk12312]

Yes I didn't start or stop the timer anywhere else, and i build a project use timer and saadc only without ble, the problem was gone so I wonder how often the ble will affect the timer. every period when timer started or just affect it ocassionally. 

[zk12312]

and then I create a timer in the SDK's example ble_template with the same period. when the ble connected,  the timer will control the LED toggle in 300HZ. I also found that the period of timer is not accurate and still has error occasionally, So that's why I doubt the BLE will affect the timer