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

[zk12312]

I have not used this function, should I add it to the main? 

[zk12312]

it doesn't work

[Kenneth]

I am not sure what you mean by it doesn't work. Does the sd_clock_hfclk_request() return an error? Are you calling this function after softdevice is enabled or are you not using a softdevice?

[zk12312]

I mean that I put this function after the softdevice enabled but the problem about saadc sample time is still there. I test the period of the saadc sample and it should be 320ms, while when using the ble services it will jump to 330ms ocassionally.

[Henry_Chou]

Almost the ble case with softdevice. The examples are applied the RTC1 timer for timer handling ( Because SD occupied RTC0). I re-command that you may refer the time handling example.

app_timer2.c 

app_timer_init(()

app_timer_create()

app_timer_start()

app_timer_stop()

or the app_buton.c  button timer handling method that can fix your problems.

But I doubt that if the ADC sampling timer is more longer. Why the value accuracy is bad?

 

[zk12312]

I mean that the sample time I need is 320ms and it will be triggered by a hardware timer to ensure its accuracy. However, when I don't change its frequency, It sometimes goes to 330ms which may affect the number of packs I receiving from ble sent to my PC device and that is my problem.

[Kenneth]

This was quite a big delay (320ms->330ms), is it consistently +10ms (330ms) when it occurs or does it vary? Also, what is the next period (310ms or 320ms)?

Are you sure you are not START or STOP timer somewhere in your code?

Kenneth

[zk12312]

it varies and the next period will be 320ms, it just occasionally turns to 330ms. I stop or start the timer when ble disconnected or connected.

it's random and I found that when only enable the timer and saadc and don't use the ble the timer goes fine.

[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?