imx8mmevk - 8mic-rpi-mx8: switch microphone geometry configuration

[Antares]

Hello,

I am using a imx8mmevk with the 8mic-rpi-mx8. I built an image using Yocto (Zeus - 5.4.70) and flashed the imx8mmevk. I had to set "fdt_file" env in bootloader to "imx8mm-evk-8mic-revE.dtb" to be able to record data.

The microphone is now recognized by pulseaudio as "micfil" (alsa_input.platform-sound-micfil.stereo-fallback) - s16le - 2ch - 48000Hz.

From the quick start guide, the default configuration should be a 8 channels microphone. Do you have any idea why I get only 2 channels with pulseaudio ?

Secondly, I need to switch the geometry of the microphone to its 6 channels configuration. How could I do that ?

Best regards,

Loic

[igorpadykov]

Hi Loic

one can try to change PDM configuration using Table 86. PDM Microphone controls,

sect.7.5 Audio Mixer (AUDMIX)   i.MX Linux Reference Manual​

https://source.codeaurora.org/external/imx/imx-test/tree/test/mxc_amix_test?h=lf-5.10.52_2.1.0

Best regards
igor

[Antares]

Hi Igor,

Thanks for the clue. I read this part of documentation and I can indeed change some PDM configuration.

But, I don't see anyway to update the mic array geometry in table 86. I can play with some parameters but it does not explain how to turn off some microphones.

Moreover, it says : "The captured audio format is 8-channels 32-bit wide linear
PCM audio data @ 48kHz". But pulseaudio, which get data from alsa, does not list any source supporting 8 channels capture. The micfil interface appears as above in pulse:

"alsa_input.platform-sound-micfil.stereo-fallback module-alsa-card.c s16le 2ch 44100Hz"

Best regards,

Loic