nRF54H20 PDM DMIC only records noise.

[Anuj Pathak]

Hi, 

We are almost ready with our first board around nRF54H20, only one issue is remaining. We have prepared a sample, that records PDM audio as PCM wave, and stream it over UART, and a python script to assemble and save it as wav file, to play and test.

1. We tried on-board PDM (CLK->P1.1 and DATA=>P1.4), and we are only getting white noise.
2. Then we tried external DMIC , (CLK->P2.2 and DATA=>P2.5), and getting same white noise.
3. Then we added support for nRF5340DK and tested same external DMIC, and both samples and DMIC is working as expected. (This step verifies DMIC and Sample)


Following is the overlay we are using with our custom board.
- if we use cpuapp_dma_region as memory-regions, then sample fail at memory allocation
- if we use "PCLK32M_HFXO" just like nRF5340 we get failed to request clock error in driver

&pinctrl {

	/omit-if-no-ref/ pdm0_default: pdm0_default {
		group1 {
			psels = <NRF_PSEL(PDM_CLK, 2, 2)>,
				<NRF_PSEL(PDM_DIN, 2, 5)>;
		};
	};
};

dmic_dev: &pdm0 {
	status = "okay";
	pinctrl-0 = <&pdm0_default>;
	memory-regions = <&dma_fast_region>;
	pinctrl-names = "default";
	clock-source = "PCLK32M";
};

[Susheel Nuguru]

Hi Anuj, 

I think there are two different issues that you are seeing. 

nRF54H most likely does not expose the clock the same way nrF53 does.

I think some changes to your drm file is 

-	memory-regions = <&cpuapp_dma_region>;
-	clock-source = "PCLK32M_HFXO";
+	memory-regions = <&dma_fast_region>;
+	clock-source = "PCLK32M";

Not sure if this fixes the noise issue, but should move father in compilation atleast.

[Anuj Pathak]

I'm already using the suggested settings, please refer to the overlay attached in the post itself. 
And regarding noise issue, Just to be clear, I'm only getting noise, (not some audio with noise).

If you could point out any sample for nRF54H20 then that could be helpful

[Susheel Nuguru]

Anuj, I do not think we have any sample to demonstrate that on nRF54H. The Zephyr DMIC sample needs the porting efforts like the one you are doing now to make it work on nRF54H. 

[Abhay Joshi]

Hello Anuj,

Did you manage to resolve this issue? We are also facing the same problem, with only white noise recorded from the microphone while using the PDM peripheral with the above configuration.

Thanks,
Abhay

[Anuj Pathak]

Not yet, We are too, waiting for more feedback from Nordic.

[Anuj Pathak]

Susheel Nuguru 
we have got our latest revision board using nRF54H20, and the only thing pending is DMIC. Do we have any update on this?
we are planning to file an upstream PR for our board as soon as possible

[Susheel Nuguru]

Anuj,

I have not worked on DMIC before, but it does not look like the issue is with the nRF54H if you could make it work with nRF53.

When I look into nrf/tests/drivers/audio/pdm_instances/boards/nrf54h20dk_nrf54h20_cpuapp.overlay there is a comment saying that for best performance the PDB_CLK should be on the clock pin. I think if you use some other pin , then the clock is redirected to a non optimum performance. I am suspecting that using PDM_CLK on different pins might be coming with some timing jitter and hence causing only noise to appear.  

On your custom board, please try the same pins P1.2 for testing to see if that can help?

Another thing that I assume you have tested both non cacheable cpuapp_dma_region and cacheable dma_fast_region.

That said, we do not seem to be actively working to make the DMIC work internally on nRF54H apart from the test of dmic buffer dump tests,  Have you tried to run the test nrf/tests/drivers/audio/dmic_dump_buffer/src/main.c that seems to have nRF54H_DK boards as supported board. I think we need to spend time to port the DMIC sample to work on nRF54H which we have not done yet. Please talk to your Regional sales manager if you want this porting work of that sample on nRF54H to be prioritized.