HOW TO ANALYSIS PDM DATA CONTINUOUSLY IN NRF52832

[nithin]

For my audio application, I need to convert pcm out from pdm module(nrf52832) to an audio format (mp3,wav) continuously. Is there any method or procedure for this??...or any sample example?? please help... Actually, MIC is outing pdm data, PDM_IRQHandler runs in code but i don't know whether data is correct or not...?? how can i process that data in buffers without storing data to internal flash.

void PDM_IRQHandler(void)
{
    if (nrf_pdm_event_check(NRF_PDM_EVENT_END))
    {
        nrf_pdm_event_clear(NRF_PDM_EVENT_END);      
        //Buffer is ready to process.
        if (nrf_pdm_buffer_get() == m_cb1.buffers[0])
        {
				//	printf("%d",*(m_cb1.buffers[1]));
			  //	printf("%d",*(m_cb1.buffers[1]));
           m_cb1.event_handler(m_cb1.buffers[1], m_cb1.buffer_length);
				//	drv_audio_pdm_event_handler(m_cb1.buffers[1], m_cb1.buffer_length);
        }
        else
        {
            m_cb1.event_handler(m_cb1.buffers[0], m_cb1.buffer_length);
        }
    }
    else if (nrf_pdm_event_check(NRF_PDM_EVENT_STARTED))
    {
        nrf_pdm_event_clear(NRF_PDM_EVENT_STARTED);
        m_cb1.status = NRF_PDM_STATE_RUNNING;
        
        //Swap buffer.
        if (nrf_pdm_buffer_get() == m_cb1.buffers[0])
        {
            nrf_pdm_buffer_set(m_cb1.buffers[1],m_cb1.buffer_length);
        }
        else
        {
            nrf_pdm_buffer_set(m_cb1.buffers[0],m_cb1.buffer_length);
        }
    }
    else if (nrf_pdm_event_check(NRF_PDM_EVENT_STOPPED))
    {
        nrf_pdm_event_clear(NRF_PDM_EVENT_STOPPED);
        nrf_pdm_disable();
        m_cb1.status = NRF_PDM_STATE_IDLE;
    }
}

[MartinBL]

Hi, I'm not sure if I understand your problem. You provide a buffer to the PDM module, and the PDM then gathers data in the background. When the buffer is full you process it. This is achieved with the EasyDMA feature and the data is always stored in RAM. Unfortunately there are no PDM examples, but here is the documentation of the PDM drivers.

[nithin]

hai Martin, thanks for your response. I have some doubts whether these buffers ( m_cb.buffers[1],m_cb.buffers[0]) holds actual pdm out i.e PCM ? and its buffer size(in RAM). How to convert this pcm data to wav or any other audio formate?. I want to analyze a particular range of sound from this mic (spk0838ht4h-b).

[MartinBL]

The output of the PDM module is raw PCM data which is stored in buffers in RAM. The buffers can be as long as you want (as long as they fit in RAM of course). Nordic doesn't provide any solution for converting PCM to audio files, so I suggest you look for that somewhere else. Converting PCM to WAV seems to be a matter of generating a proper file header and place it before your raw PCM data: Link.

[nithin]

OKay. How can I see that raw PCM data from RAM , could I use RTT or UART for that ?

[MartinBL]

Yes, RTT and UART should work.