STM32H7 DFSDM – Best way to read two microphones with one filter?

[MannyMarc35]

Hi everyone,

I'm working on an audio acquisition project using the STM32H743ZIT6 microcontroller. The goal is to build a microphone array with 8 digital MEMS microphones (MP34DT05-A), connected via DFSDM and streamed over USB to a PC using the USB Audio Class (UAC). At the moment, I'm starting small and testing with one or two microphones.

So far, I have successfully configured one DFSDM filter and one channel using regular conversion with DMA, and I'm receiving valid audio data.

Now I would like to add a second microphone, which is connected to a second DFSDM channel (with opposite clock edge). Both channels should ideally be handled by the same DFSDM filter.

I'm currently wondering:

• What is the best approach to sample two channels using a single DFSDM filter?

• Is it necessary or recommended to use injected conversion for the second channel in this case?

• How would I properly configure DMA and interrupts if both regular and injected conversions are used?

• Are there any known working examples for this kind of setup?

Any tips, experiences, or suggestions would be greatly appreciated!

Thanks in advance

[gmpetro]

Thanks for pointing out the topic with the Sync trigger and the right order to start.

However in my project on a STM32L4Q5, which is configured exactly as yours concerning the filters and channels, filter 1 always outputs rubbish data, i.e. unstable data, that doesn't depend on the audio content from the microphones. Even if I map the same input channel to both filters, filter 1 outputs that rubbish. Also if I start both filters with a software trigger, the same behavior is there.

EDIT: The problem moves with the sampling edge of the mic. Falling edge sampled mics create an offset of about 0xFE3080, rising edge sampled mics don't show it. I checked the PDM signals with a scope. The timing couldn't be more perfect for both edges, so it must be something inside the chip.

Thanks & kind regards,

Gerhard