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?

[sara]

the return value is zero

[sara]

Hello Haakonsh, Please suggest me what next should I do to make my pdm driver work. As still I am not able to get the clock on CRO, which means pdm is not configured properly (I guess).

[haakonsh]

Are you sure you're measuring for the clock signal on p0.29 of the PCA10040 DK?

Are you able to toggle the pin state of p0.29 with a call to nrf_gpio_cfg_output and nrf_gpio_pin_toggle?

[sara]

yes, I am sure I am measuring on the pin p0.29. And its toggling. I have attached the screenshot for it.

And one more thing what is the use of CONFIG_IO_PDM_MIC_PWR_CTRL pin ?

[sara]

1) And what does this mean given in the datasheet of nrf52832 " 43.1 Master clock generator
The FREQ field in the master clock's PDMCLKCTRL register allows adjusting the PDM clock's frequency.
The master clock generator does not add any jitter to the HFCLK source chosen. It is recommended (but not
mandatory) to use the Xtal as HFCLK source " Do I need to set HFCLK ? and if yes then how?

2) And do I need to init any other interface ? I2C ?or any peripherals?

3) After pdm_init is called will I get the clock pulse?(If yes, then I am not getting clock pulse even after nrf_drv_pdm_init() )

[haakonsh]

1.  See sd_clock_hfclk_request. 
   
   
2. No you do not need to init another peripheral.
   
   
3. You need to call nrfx_pdm_start after nrfx_pdm_init i guess.

[sara]

1. Ok n if no softdevice is enabled then sd_clock_hflck_request should not be enabled for PDM init . Am I ryt?

[haakonsh]

Call nrfx_clock_init, then nrfx_clock_hfclk_start, then wait for the EVENTS_HFCLKSTARTED event:
while(!NRF_CLOCK->EVENTS_HFCLKSTARTED)();

[sara]

Hello Haakonsh, I got the pdm clock but now how should I print the PDM data on terminal using easyDMA?

[haakonsh]

Once a set of samples are taken they have already been transferred to RAM via EasyDMA. If you want to send this over UART to a terminal you need to start a UARTE transfer where the TX buffer pointer points to the PDM buffer. 

See UARTE driver API docs:

nrfx_uarte uarte0 = NRFX_UARTE_INSTANCE(0);

void uarte_handler(nrfx_uarte_evt_type_t evt)
{
    //Handle uarte events if needed
}

void uarte_init(void)
{
    nrfx_err_t err_code = NRFX_SUCCESS;
    nrfx_uarte_config_t uarte_cfg = NRFX_UARTE_DEFAULT_CONFIG; //Set config in sd_config.h
    
    err_code = nrfx_uarte_init(&uarte0, &uarte_cfg, uarte_handler);
    APP_ERROR_CHECK(err_code);
}

// In PDM handler, call: nrfx_uarte_tx(&uarte0, &YourPDMbuffer, LenghtOfPDMbuffer)