PDM example on Stereo mode

[Leo2019]

I have two mic , how can I get data from Left and Right mic? Is there any example code to help me?

My code like this : ( I think the data from pdm_data_handler is like 0xFFFFxxxx or 0x0000xxxx, when I removed a mic from my PCBA)

void user_pdm_init(void)
{
uint32_t err_code = NRF_SUCCESS;
nrfx_pdm_config_t config = NRFX_PDM_DEFAULT_CONFIG(PDM_CLK,PDM_DIN);
err_code = nrfx_pdm_init(&config, pdm_data_handler);
APP_ERROR_CHECK(err_code);

nrf_gpio_cfg_output(PDM_LEFT_PIN);
nrf_gpio_cfg_output(PDM_RIGHT_PIN);

nrf_gpio_pin_set(PDM_RIGHT_PIN);
nrf_gpio_pin_clear(PDM_LEFT_PIN);
}

#define PDM_BUFF_LEN 320 //1000
#define PDM_CLCA_LEN 10

static uint32_t pdm_buffer_rx[2][PDM_BUFF_LEN];

static void pdm_data_handler(nrfx_pdm_evt_t const * p_evt)
{

ASSERT(p_evt);
if (p_evt->error == NRFX_PDM_ERROR_OVERFLOW )
{
return;
}
if(p_evt->buffer_released != 0)
{
pdm_block_to_fill = pdm_buffer_rx[get_finished_buffer()];
}
if(p_evt->buffer_requested)
{
/*curr_buff_index = get_finished_buffer();
uint32_t* buff = pdm_buffer_rx[curr_buff_index];
uint8_t i = 0;
for(i=0; i < 4;i++)
{
uint32_t h = ((buff[i]) >> 16) & (uint32_t)0xffff;
uint32_t l = ((buff[i]) ) & (uint32_t)0xffff;

//pdm_LOG("buff = %x, pdm_buffer_rx =%x,%x h =%x,l = %x\r\n",buff[i],(pdm_buffer_rx[curr_buff_index][i]),pdm_buffer_rx[curr_buff_index][i+1],h,l);
}
*/
nrfx_pdm_buffer_set((int16_t *)pdm_buffer_rx[1 - curr_buff_index],PDM_BUFF_LEN);
}
}

[Kenneth]

I believe the Smart Remote 3 DK add-on can do this:
https://infocenter.nordicsemi.com/topic/ug_sr3_nrf52/UG/sr3_nrf52/hw_descr_add_on/digital_mic.html 

Firmware can be download from:
https://www.nordicsemi.com/Software-and-Tools/Reference-Designs/nRFready-Smart-Remote-3-for-nRF52-Series/Download#infotabs 

[Leo2019]

Hi, Kenneth,

Soryy ,I guess I had not make you understand what I mean.

Our device is nrf52832 and work on SDK 15.0.0;

There are two digital mic on it,and I want to get the sample data from each . The document https://infocenter.nordicsemi.com/index.jsp?topic=%2Fug_sr3_nrf52%2FUG%2Fsr3_nrf52%2Fhw_descr_add_on%2Fdigital_mic.html  tell me to get sample data from EasyDMA buffer, but I got  uint32_t sample data like this :

pdm_buffer_rx =0xFF7FFF70
pdm_buffer_rx =0xFF88FF85
pdm_buffer_rx =0xFF6EFF7F

I think these data are wrong, because I only make sound to the left mic .  I think the data from pdm_data_handler is like 0xFFFFxxxx or 0x0000xxxx, the  bit 32-bit16 wont change,when the Right Mic working on quiet environment.

So ,my question is , how to sure right and left mic works well ,and how to get sample data from each other ?

 ..

the  finished_buffer = m_cb.active_buffer;

..

static void pdm_data_handler(nrfx_pdm_evt_t const * p_evt)
{

...

if(p_evt->buffer_released != 0)
{
pdm_block_to_fill = pdm_buffer_rx[get_finished_buffer()];
}
if(p_evt->buffer_requested)
{
curr_buff_index = get_finished_buffer();
uint32_t* buff = pdm_buffer_rx[curr_buff_index];
uint8_t i = 0;
for(i=0; i < 4;i++)
{
pdm_LOG("pdm_buffer_rx =%x\r\n"(pdm_buffer_rx[curr_buff_index][i]));
}

nrfx_pdm_buffer_set((int16_t *)pdm_buffer_rx[1 - curr_buff_index],PDM_BUFF_LEN);
}
}

[Leo2019]

Document this : infocenter.nordicsemi.com/.../pdm.html

[Kenneth]

Have you tried using external pull-down in this case? I assume the pin is floating in this case, so any data may occur.

Best regards,
Kenneth

[Leo2019]

I using external pull-down now,and removed the code of gpio set. but read the sample is same as before.the issue is still on.

[Kenneth]

Unfortunately I have not had time to try this myself, though I could find this example maybe it can be used as comparison:
https://devzone.nordicsemi.com/nordic/b/blog/posts/pdm-example-on-the-nrf52832

Best regards,
Kenneth