SAADC Always busy, error 17. SDK15

[Sylvain]

Hello DevZone,

I know that the subject has already be treat but in the others posts people seems to say that the error comes from the double buffering.

But in my case, I have no double buffering active. And I try to use the following function :

err_code = nrfx_saadc_sample_convert(0, ADC_value);

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/** @file
 * @defgroup nrf_adc_example main.c
 * @{
 * @ingroup nrf_adc_example
 * @brief ADC Example Application main file.
 *
 * This file contains the source code for a sample application using ADC.
 *
 * @image html example_board_setup_a.jpg "Use board setup A for this example."
 */

#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <string.h>
#include "nrf.h"
#include "nrf_drv_saadc.h"
#include "nrf_drv_ppi.h"
#include "nrf_drv_timer.h"
#include "nrf_drv_twi.h"
#include "boards.h"
#include "app_error.h"
#include "nrf_delay.h"
#include "app_util_platform.h"
#include "nrf_pwr_mgmt.h"

#include "nrf_log.h"
#include "nrf_log_ctrl.h"
#include "nrf_log_default_backends.h"

#define SAMPLES_IN_BUFFER 1
volatile uint8_t state = 1;

static nrf_saadc_value_t     m_buffer_pool [SAMPLES_IN_BUFFER];//[2][SAMPLES_IN_BUFFER];

static uint32_t              m_adc_evt_counter;

static uint16_t ADC_value [1];


void saadc_callback(nrf_drv_saadc_evt_t const * p_event)
{
    if (p_event->type == NRF_DRV_SAADC_EVT_DONE)
    {
        ret_code_t err_code;

        err_code = nrf_drv_saadc_buffer_convert(p_event->data.done.p_buffer, SAMPLES_IN_BUFFER);
        APP_ERROR_CHECK(err_code);

        int i;
        NRF_LOG_INFO("ADC event number: %d", (int)m_adc_evt_counter);
        
        flag = 1;

        for (i = 0; i < SAMPLES_IN_BUFFER; i++)
        {
          ADC_value [0] = p_event->data.done.p_buffer[i];
          
          if (ADC_value [0] < 0)
          {
            ADC_value [0] = 0;
          }
          NRF_LOG_INFO("ADC value: %d", ADC_value[0]);
        }
        m_adc_evt_counter++;
    }
}

void saadc_init(void)
{
    ret_code_t err_code;
    nrf_drv_saadc_config_t saadc_config;

    nrf_saadc_channel_config_t channel_config =
      NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_SE(NRF_SAADC_INPUT_AIN5);
    
    channel_config.reference =  NRF_SAADC_REFERENCE_INTERNAL;
    channel_config.gain =       SAADC_CH_CONFIG_GAIN_Gain1_4;
    channel_config.acq_time =   SAADC_CH_CONFIG_TACQ_3us;

    saadc_config.resolution =   SAADC_RESOLUTION_VAL_14bit;
    saadc_config.oversample =   NRF_SAADC_OVERSAMPLE_64X;//NRF_SAADC_OVERSAMPLE_DISABLED;

    err_code = nrf_drv_saadc_init(&saadc_config, saadc_callback);
    APP_ERROR_CHECK(err_code);

    err_code = nrf_drv_saadc_channel_init(0, &channel_config);
    APP_ERROR_CHECK(err_code);

    err_code = nrf_drv_saadc_buffer_convert(m_buffer_pool[0], SAMPLES_IN_BUFFER);
    APP_ERROR_CHECK(err_code);
}


/**
 * @brief Function for main application entry.
 */
int main(void)
{
    uint32_t err_code = NRF_LOG_INIT(NULL);
    APP_ERROR_CHECK(err_code);

    NRF_LOG_DEFAULT_BACKENDS_INIT();

    ret_code_t ret_code = nrf_pwr_mgmt_init();
    APP_ERROR_CHECK(ret_code);

    saadc_init();

    NRF_LOG_INFO("SAADC HAL simple example started.");
    
    while (1)
    {
        err_code = nrfx_saadc_sample_convert(0, ADC_value);
        APP_ERROR_CHECK(err_code);

    }
}

/** @} */


Here's my code:
Anyone know, where does come from the error?

Thanks,
Sylvain.

[Sylvain]

Ok the problem comes from the initialisation.

This function block everything:

err_code = nrf_drv_saadc_buffer_convert(m_buffer_pool[0], SAMPLES_IN_BUFFER);
APP_ERROR_CHECK(err_code);

[Håkon Alseth]

Hi,

 

Does this mean you found the source of your issue?

If not, could you post the err_code you get from the function call?

 

Kind regards,

Håkon

[Sylvain]

Hello,

Yes since I don't use nrf_drv_saadc_buffer_convert . It works ...

I have an other problem. When I try to oversampling (8X) the following function return 8 times the same value and after that 8 times another value ... and always like that.

Is it Normal ? I was thinking that the function returns an average value ...

Sincerely,
Sylvain.

err_code = nrfx_saadc_sample_convert(0, ADC_value);
APP_ERROR_CHECK(err_code);

[Håkon Alseth]

Hi,

 

The SAADC peripheral provides one value, and handles the 8x oversampling internally, and should not provide you with 8 values.

It might be that you get the same value if you sample a steady DC signal.

 

Have you timed this function to see if there's any discrepancies wrt. sampling time?

 

Kind regards,

Håkon

[Sylvain]

Hello,

Definitely, when I use the polling function it returns x times the same value and after that x times an other value and so on.  (x=oversampling value)

My goals is to reduce the noise of a DC signal but the oversampling does not seems to work properly ...

Note : In my infinite loop, a delay of 500ms is implemented. So it isn't possible to have the same measured value depending of the oversampled value.

[Håkon Alseth]

Hi,

 

Sorry for not seeing this before in your code, but yes; this would be the expected behavior when checking the _END event, as it will fire for each ADC sample.

Could you try waiting for the _END event instead of the _DONE event in your saadc_callback()?

Kind regards,

Håkon

[Sylvain]

Hi Hakon,

I don't check the END event because there is no macro for this in the driver. I only found this macro : "NRF_DRV_SAADC_EVT_DONE". Since, I've enabled the interruption relative to the END events and disable the other and now It works. But it could be restrictif in some case.

Best regards,
Sylvain.