Storing and accessing PDM data from microphone input

[RajB]

Hi

I'm new to programming and recently started working on nrf52832.

I'm working on a wearable device that monitors patient's vital. I'm using MP34DB02 digital microphone to record patient breathing to detect difficulty in breathing. I can't read input from the mic and creating and accessing pdm data stored in buffer. This is the code I have so far:

ret_code_t drv_audio_enable(void)
    {
        nrf_delay_ms(100);
        
        //Start audio capture
        return nrf_drv_pdm_start();
    }

ret_code_t drv_audio_disable(void)
    {
        ret_code_t status;

        //Stop audio capture
        status = nrf_drv_pdm_stop();
        if(status!= NRF_SUCCESS)
        {
          return status;
        }
        
        return NRF_SUCCESS;
    }


static void drv_audio_pdm_event_handler(nrf_drv_pdm_evt_t const * const p_evt)
{
    int16_t *p_buffer_released = p_evt->buffer_released;

    
    
    if(p_evt->buffer_requested)
    {
       int16_t *p_buffer;
       
       
       if(!p_buffer)
       {
          NRF_LOG_WARNING("%s(): WARNING: Cannot allocate audio buffer!", __func__);
          //We have to provide fresh buffer to keep PDM running.
          //Since pool is empty, our sole option is to reuse the released buffer.

          if(p_buffer_released)
          {
             p_buffer          = p_buffer_released;
             p_buffer_released = NULL;
             
          }
       }

       if(p_buffer)
       {
          NRF_LOG_DEBUG("Buffer Request: 0x%08X%s",
                         p_buffer,
                         (p_buffer == p_evt->buffer_released) ?"(reusing released buffer)":"");

          APP_ERROR_CHECK(nrf_drv_pdm_buffer_set(p_buffer, CONFIG_PDM_BUFFER_SIZE_SAMPLES));
       }

   }

   if(p_buffer_released)
   {
        NRF_LOG_DEBUG("Buffer Release: 0x%08X", p_buffer_released);

   }

}


ret_code_t drv_audio_init(void)
{
    nrf_drv_pdm_config_t pdm_cfg = NRF_DRV_PDM_DEFAULT_CONFIG(clk_audio,
                                                              dout);
                                                              
    ret_code_t err_code; // a variable to hold error code value
    pdm_cfg.gain_l      = CONFIG_PDM_GAIN;
    pdm_cfg.gain_r      = CONFIG_PDM_GAIN;
    pdm_cfg.edge = NRF_PDM_EDGE_LEFTFALLING;

    nrf_gpio_cfg_output(lrsel);
    nrf_gpio_pin_clear(lrsel);

    NRF_LOG_FLUSH(); // flushing is important, if you set the deffered to 1, if deffered is set to 0 then we don't need to flush the log buffer. 
    
    //Initialize PDM driver
    return nrf_drv_pdm_init(&pdm_cfg, drv_audio_pdm_event_handler);

}



int main(void)
{

// initialize the Logger so that we can print msgs on the logger
  APP_ERROR_CHECK(NRF_LOG_INIT(NULL)); 
  NRF_LOG_DEFAULT_BACKENDS_INIT();
  
  
  NRF_LOG_INFO("Application Started");
  
  
  NRF_LOG_FLUSH(); // flushing is necessary if deferred is set to 1(check this video tutorial to know it better)

  
  APP_ERROR_CHECK(drv_audio_init());
  drv_audio_enable();
  //nrf_delay_ms(100);
  drv_audio_disable();



}

What am I missing?

Regards

Raj

[dejans]

Hi Raj,

Which SDK do you use?

Is your application based on any sample application from SDK?

Do you use nRF52-DK or custom board with nRF52832?

Best regards,
Dejan

[RajB]

Hi Dejan

Thank you for the reply. I use SDK 17.0.0.

I'm trying to integrate mic into a health monitoring device I'm working on. The original code is based on the ble_app_uart_pca10040_s132 example. I'm trying to make the mic work separately first in a new project that's not based on any sample application before I try to integrate it into the original program.

I'm using a custom board with nrF52832. Hope this helps.

Regards

Raj

[dejans]

Hi Raj,

Have you seen this thread? It gives you some starting code for PDM on nRF52832.

Best regards,
Dejan

[RajB]

I checked out that thread and the code was a little outdated. I updated it a bit and having the same issues mentioned in the thread. Getting constant values. Tried playing with clock frequency and varying edge type but the values seem to be constant. Would you happen to know why?

Regards

Raj 

[dejans]

Hi Raj,

Do you get constant values after some number of samples as in the mentioned thread? Which values do you get? Do you get the same constant values each time you change parameters?

Best regards,
Dejan