RE: NRF52840 SAADC Calibration

haakonsh — Fri, 05 Oct 2018 07:35:23 GMT

No, not yet.

RE: NRF52840 SAADC Calibration

Mary — Tue, 02 Oct 2018 15:07:43 GMT

I tried that, but it made no difference. The data was still shifted after calibration.

Were you able to reproduce the problem?

RE: NRF52840 SAADC Calibration

haakonsh — Thu, 27 Sep 2018 12:12:40 GMT

I think I found your problem, you need to wait for the EVENTS_CALIBRATEDONE because nrfx_saadc_calibrate_offset is non-blocking.

You need to add:

while(nrf_drv_saadc_calibrate_offset() != NRF_SUCCESS); //Trigger calibration task

while(!nrf_saadc_event_check(NRF_SAADC_EVENT_CALIBRATEDONE ))
{
    nrf_pwr_mgmt_run();
}

RE: NRF52840 SAADC Calibration

Mary — Thu, 20 Sep 2018 14:05:05 GMT

Below are the methods that I modified or added to the example.

saadc_callback() (modified) plus additional auto variable, m_saadc_cal_prepare, and some definitions

#define NUM_ADC_CHANNELS    4

typedef enum {
    CAL_PREPARE = 0,
    CAL_START
} CAL_ACTION_TYPE; 


static bool                    m_saadc_cal_prepare = false; 

void saadc_callback(nrf_drv_saadc_evt_t const * p_event)
{
    nrf_saadc_value_t *p_samples;

    ret_code_t err_code;

    if (p_event->type == NRF_DRV_SAADC_EVT_DONE)                                                        //Capture offset calibration complete event
    {
			
        LEDS_INVERT(BSP_LED_2_MASK);                                                                    //Toggle LED3 to indicate SAADC buffer full		

        //if((m_adc_evt_counter % SAADC_CALIBRATION_INTERVAL) == 0)                                  //Evaluate if offset calibration should be performed. Configure the SAADC_CALIBRATION_INTERVAL constant to change the calibration frequency
        if (m_saadc_cal_prepare)
        {
            nrf_drv_saadc_abort();                                                                      // Abort all ongoing conversions. Calibration cannot be run if SAADC is busy
            m_saadc_calibrate = true;                                                                   // Set flag to trigger calibration in main context when SAADC is stopped
        }
        

#ifdef UART_PRINTING_ENABLED
        NRF_LOG_INFO("ADC event number: %d \r\n",(int)m_adc_evt_counter);                                //Print the event number on UART

        for (int i = 0; i < p_event->data.done.size; i++)
        {
            NRF_LOG_INFO("%d\r\n", p_event->data.done.p_buffer[i]);                                     //Print the SAADC result on UART
            
        }
#endif //UART_PRINTING_ENABLED   

        if(m_saadc_calibrate == false)
        {
            err_code = nrf_drv_saadc_buffer_convert(p_event->data.done.p_buffer, SAADC_SAMPLES_IN_BUFFER * NUM_ADC_CHANNELS);             //Set buffer so the SAADC can write to it again. 
            APP_ERROR_CHECK(err_code);
        }
        
        m_adc_evt_counter++;

    }
    else if (p_event->type == NRF_DRV_SAADC_EVT_CALIBRATEDONE)
    {
        LEDS_INVERT(BSP_LED_2_MASK);                                                                    //Toggle LED3 to indicate SAADC calibration complete

        err_code = nrf_drv_saadc_buffer_convert(m_buffer_pool[0], SAADC_SAMPLES_IN_BUFFER * NUM_ADC_CHANNELS);             //Set buffer so the SAADC can write to it again. 
        APP_ERROR_CHECK(err_code);
        err_code = nrf_drv_saadc_buffer_convert(m_buffer_pool[1], SAADC_SAMPLES_IN_BUFFER * NUM_ADC_CHANNELS);             //Need to setup both buffers, as they were both removed with the call to nrf_drv_saadc_abort before calibration.
        APP_ERROR_CHECK(err_code);
        
#ifdef UART_PRINTING_ENABLED
        NRF_LOG_INFO("SAADC calibration complete ! \r\n");                                              //Print on UART
#endif //UART_PRINTING_ENABLED	
        
        m_adc_evt_counter = 0;

    }

}

Additional methods

bool adc_is_cal_prepared()
{
    return m_saadc_calibrate;
}

void adc_calibrate(int action)
{
    switch(action)
    {
        case CAL_PREPARE:
            m_saadc_cal_prepare = true;                             // Stop conversions when this one is done
            break;

        case CAL_START:
            NRF_LOG_INFO("SAADC calibration starting...  \r\n");    //Print on UART
            while(nrf_drv_saadc_calibrate_offset() != NRF_SUCCESS); //Trigger calibration task
            m_saadc_calibrate = false;
            m_saadc_cal_prepare = false;
            break;
    }
}

Buttons and main loop:

/***************************************************************************************************
 * @section Buttons
 **************************************************************************************************/

static void bsp_event_handler(bsp_event_t event)
{

    switch (event)
    {
        case BSP_EVENT_KEY_0:
        {
            adc_calibrate(CAL_PREPARE);
            break;
        }


        default:
            break;
    }
}



/***************************************************************************************************
 * @section Main
 **************************************************************************************************/

int main(int argc, char *argv[])
{

    LEDS_CONFIGURE(LEDS_MASK);                       //Configure all leds
    LEDS_OFF(LEDS_MASK);                             //Turn off all leds
	
    NRF_POWER->DCDCEN = 1;                           //Enabling the DCDC converter for lower current consumption
	
#ifdef UART_PRINTING_ENABLED
    uint32_t err_code = NRF_LOG_INIT(NULL);
    APP_ERROR_CHECK(err_code);                       //Configure Logging. LOGGING is used to show the SAADC sampled result. Default is UART, but RTT can be configured in sdk_config.h
    NRF_LOG_INFO("\n\rSAADC Low Power Example.\r\n");	
#endif //UART_PRINTING_ENABLED	
	

    lfclk_config();                                  //Configure low frequency 32kHz clock
    rtc_config();                                    //Configure RTC. The RTC will generate periodic interrupts. Requires 32kHz clock to operate.

    saadc_init();                                    //Initialize and start SAADC
 
    while(1)
    {
        // Calilbrate if ready
        if (adc_is_cal_prepared())
        {
            adc_calibrate(CAL_START);
        }

        nrf_pwr_mgmt_run();
#ifdef UART_PRINTING_ENABLED
        NRF_LOG_FLUSH();
#endif //UART_PRINTING_ENABLED

    
    }


}

This should be enough for you to repeat it.

Mary

RE: NRF52840 SAADC Calibration

haakonsh — Thu, 20 Sep 2018 12:55:10 GMT

Do you mind sharing the code relevant to the calibration?