I2S "PDM" mode? (Help with debugging wanted)

[Lana-chan]

I don't know a lot about I2S but it seems like the M5 Cardputer (ESP32-S3) uses a SPM1423 MEMS microphone. I'm trying to use it to record from in MicroPython, but it seems to want only a WS pin (43) and a SD pin (46), there's no SCK pin indicated. The cardputer also has an I2S output (NS4168) which shares the WS pin and has a SCK pin at 41. I tried using an I2S recording example using 41 as SCK pin (since MicroPython doesn't allow you to leave it blank) and the microphone's WS and SD pins, but it generated a completely empty output. Does anyone know how I can record using this hardware setup?

I'm running on:
MicroPython v1.23.0-preview.248.g77f08b72c on 2024-03-19; Generic ESP32S3 module with ESP32S3

EDIT: So I see that PDM is not currently supported in MicroPython as of 2022... is there any hope for support for it in 2024, at least for ESP32 which has it built-in?

[Lana-chan]

well i decided to try and implement it myself: https://github.com/Lana-chan/micropython/tree/feature-pdm-rx

currently, i can compile the firmware and run a test. initializing I2S in PDM_RX mode seem to work, however when using readinto, it raises an odd OSError: [Errno 1] EPERM. all other I2S modes are unaffected by my changes. no matter how i try to follow ESP-IDF docs on debugging, i simply cannot get any means of debugging to work. if anyone could look over my changes or help me debug them, that would be greatly appreciated.

[Lana-chan]

i found that the issue was that extmod/machine_i2s needs I2S to be in RX mode to be able to be read from. since PDM_RX is a new mode, it needed some modifications.

i've opened a PR here: #14176