How to configure the skip_gpio_cfg flag on my PDM microphone?

RE: How to configure the skip_gpio_cfg flag on my PDM microphone?

Sigurd Hellesvik — Wed, 06 Dec 2023 11:46:57 GMT

[quote user="clovett"]So this probably explains why P0.02 didn't work for me.[/quote]

I agree, it would seem like that is it.

There is also a less detailed drawing in silkscreen on the back of the DK showing how P0.02 is connected.

RE: How to configure the skip_gpio_cfg flag on my PDM microphone?

Chris Lovett — Tue, 05 Dec 2023 23:21:27 GMT

I did some further digging and found

CONFIG_NFCT_PINS_AS_GPIOS=y

which lead me to find that the nrf5340 DK has isolated P0.02 for NFC, and so I probably need to solder a jump pad to make it work as GPIO. I see the following info at infocenter.nordicsemi.com/.../hw_nfc_if.html

> Pins P0.02/NFC1 and P0.03/NFC2 are by default configured to use the NFC antenna. To use these pins as GPIO, R43 and R46 must be not connected (NC) and R42 and R45 must be shorted with an OR resistor.

So this probably explains why P0.02 didn't work for me.

RE: How to configure the skip_gpio_cfg flag on my PDM microphone?

Chris Lovett — Tue, 05 Dec 2023 17:59:10 GMT

Sounds like your answer is "there is no way". Thanks. It's not really an XY problem - I had a very specific question and you answered it. But since you are curious about the bigger picture, the reason I'm asking is that my pdm mic works on pins 25/26 but not on 02/05, (using the nrf5340 DK) so I was debugging into dmic_configure -> dmic_nrfx_pdm_configure -> nrfx_pdm_init -> pdm_configure which starts with:

if (!p_config->skip_gpio_cfg)

{

nrfy_gpio_pin_clear(p_config->clk_pin);

nrfy_gpio_cfg_output(p_config->clk_pin);

nrfy_gpio_cfg_input(p_config->din_pin, NRF_GPIO_PIN_NOPULL);

}

So that got me thinking, who is initializing the pins if this is not doing it? And perhaps if I initialize the pins 02 and 05 myself then it might start working? The easy way would be to enable this block of code somehow, hence my question. Interestingly, I also tried the hard way after I posted this question as follows:

nrfx_pdm_config_t* config = (nrfx_pdm_config_t*)dmic->config;

struct gpio_dt_spec pdm_clock;

pdm_clock.port = gpio_port_0;

pdm_clock.pin = config->clk_pin;

pdm_clock.dt_flags = GPIO_ACTIVE_LOW;

gpio_pin_configure_dt(&pdm_clock, GPIO_OUTPUT);

gpio_pin_set(pdm_clock.port, pdm_clock.pin, 0);

struct gpio_dt_spec pdm_data;

pdm_data.port = gpio_port_0;

pdm_data.pin = config->din_pin;

pdm_data.dt_flags = GPIO_ACTIVE_LOW;

gpio_pin_configure_dt(&pdm_data, GPIO_INPUT);

But that didn't work either, so I wonder if there's a hardware difference and PDM only works on certain gpio pins? Or my hard way code is wrong. I couldn't find anything about that in the PDM documentation on infocenter.nordicsemi.com/.../pdm.html

RE: How to configure the skip_gpio_cfg flag on my PDM microphone?

Sigurd Hellesvik — Tue, 05 Dec 2023 10:34:58 GMT

Hi,

From https://github.com/nrfconnect/sdk-zephyr/blob/2364b332d085341d78e9618125256ae3a5cc71b0/drivers/audio/dmic_nrfx_pdm.c#L568-L569, we can see that skip_gpio_cfg and skip_psel_cfg are hard-coded initialized to True.

My guess is that since Zephyr should have control over the different pin states, and therefore we do not want to allow PDM to control these from their drivers.

I realize that this may be an XY Problem: Why do you want to access nrfx_pdm_config_t directly?

Regards,
Sigurd Hellesvik