PDM code implementation and testing

[sara]

static void bsp_event_handler(bsp_event_t event)
{
    ret_code_t err_code;

    switch (event)
    {
        case BSP_EVENT_SLEEP:
            sleep_mode_enter();
            break; // BSP_EVENT_SLEEP

        case BSP_EVENT_DISCONNECT:
            err_code = sd_ble_gap_disconnect(m_conn_handle,
                                             BLE_HCI_REMOTE_USER_TERMINATED_CONNECTION);
            if (err_code != NRF_ERROR_INVALID_STATE)
            {
                APP_ERROR_CHECK(err_code);
            }
            break; // BSP_EVENT_DISCONNECT

        case BSP_EVENT_WHITELIST_OFF:
            if (m_conn_handle == BLE_CONN_HANDLE_INVALID)
            {
                err_code = ble_advertising_restart_without_whitelist(&m_advertising);
                if (err_code != NRF_ERROR_INVALID_STATE)
                {
                    APP_ERROR_CHECK(err_code);
                }
            }
            break; // BSP_EVENT_KEY_0
          case BSP_EVENT_KEY_1:
            NRF_LOG_INFO("\n Press Button key 1\n");
            NRF_LOG_INFO("\n Erase the flash content !!\n");
//            err_code = pcm_pstorage_eraseall();
//            APP_ERROR_CHECK(err_code);
            break;

         case BSP_EVENT_KEY_2:
            NRF_LOG_INFO("\n Start:PDM --> PCM\n");
            err_code =  nrf_drv_pdm_start(); 
            APP_ERROR_CHECK(err_code);
            break;

         case BSP_EVENT_KEY_3:
            NRF_LOG_INFO("\n Stop:PDM --> PCM\n");
            // stop audio sample
            nrf_drv_pdm_stop();
            break;

        default:
            break;
    }
}









static void drv_audio_pdm_event_handler(uint32_t *p_buffer, uint16_t length)
{
	m_buffer_handler((int16_t *)p_buffer, length);
        int i;
//        for(i=0;i<= length;i++)
//        {
//          NRF_LOG_INFO("%s ",&p_buffer[i]);
//        }
//        NRF_LOG_INFO("\n ");
          NRF_LOG_INFO("pdm event handler \n");

}


uint32_t drv_audio_init(drv_audio_buffer_handler_t buffer_handler)
{
//    nrf_drv_pdm_config_t pdm_cfg = NRF_DRV_PDM_DEFAULT_CONFIG(CONFIG_IO_PDM_CLK,
//                                                              CONFIG_IO_PDM_DATA,
//                                                              m_pdm_buff[0],
//                                                              m_pdm_buff[1],
//                                                              CONFIG_PDM_BUFFER_SIZE_SAMPLES);
    nrf_drv_pdm_config_t pdm_cfg = NRF_DRV_PDM_DEFAULT_CONFIG(CONFIG_IO_PDM_CLK,CONFIG_IO_PDM_DATA);
    
    if (buffer_handler == NULL)
    {
        return NRF_ERROR_INVALID_PARAM;
    }
    
    m_buffer_handler    = buffer_handler;
    pdm_cfg.gain_l      = CONFIG_PDM_GAIN;
    pdm_cfg.gain_r      = CONFIG_PDM_GAIN;
    

    return nrf_drv_pdm_init(&pdm_cfg, drv_audio_pdm_event_handler);
}










int main(void)
{
    bool erase_bonds;

    // Initialize.
    log_init();
    timers_init();
    buttons_leds_init(&erase_bonds);
    power_management_init();
    ble_stack_init();
    gap_params_init();
    gatt_init();
    advertising_init();
    services_init();
    conn_params_init();
    peer_manager_init();

    // Start execution.
    NRF_LOG_INFO("Template example started.");
    application_timers_start();

//    advertising_start(erase_bonds);
    uint32_t err_code;
    err_code = drv_audio_init(drv_audio_pdm_event_handler);
    APP_ERROR_CHECK(err_code);
    
    // Enter main loop.
    for (;;)
    {
        idle_state_handle();
    }
}

I have to connect a MIC  working on PDM to nrf52 DK Board.For that, I have written the above code.  But when I am testing I am not able to get the clock pulses at the defined pin. Also do not know at which Freq it is working?

And when I read the pdm documentation it says I need to change the PSEL.CLK register value? Then how should I do it and with what value? same for PSEL.DIN register. I am confused a lot. Please suggest me the solution to all my doubts.I have checked the clk pin on Oscilloscope, the clock is not being generated.In order to generate clk at pin number 22 of nrf52 DK board should I define pin clk  as #define CONFIG_IO_PDM_CLK 0x22 or 0x16 (hex value of 22 )instead o rtf 0x22?

[haakonsh]

The PDM driver will call nrf_pdm_psel_connect who'll set the PSEL.CLK and PSEL.DIN. I suggest you read the implementation of nrfx_pdm_init and see how the driver and HAL configures the PDM registers. This will give you valuable insight into how our drivers and HALs work in relation to the peripherals HW documentation.

"should I define pin clk  as #define CONFIG_IO_PDM_CLK 0x22 or 0x16 (hex value of 22 )instead o rtf 0x22?"
pin numbers are decimal, so either 22 or 0x16. 

[sara]

Ok. But even though I am doing #define PDM_CONFIG_CLOCK_FREQ 134217728 which is 1MHz, Iam not getting the clock signal at pin 22. For this what should I do?

[haakonsh]

You need to call nrfx_pdm_start after nrfx_pdm_init i guess.

I suggest you debug the PDM peripheral as a stand-alone project. Remove all code that is not essential to the PDM.
Then I suggest you set a breakpoint after the init function and compare the TWIS registers values with what you expect them to be from the HW description in the datasheet.

[sara]

ok. will do that.

[sara]

TWIS registers means the registers shown on the debug window?

[haakonsh]

Not the CPU registers, but the TWIS registers.

What IDE are you using?

[sara]

I am using Segger Embedded Studio