I2S stacking?

[thestumbler]

I'm currently running two PCM1802 I2S audio ADC chips per board, but I'd like to test the limit. How many chips can I run on a single RP2350B. Given the one way nature of the link between the PCM1802 and the MCU, can I just parallel the existing ones into appropriate spare pins on the MCU? Basically run each ADC into 2 or 3 or 4 inputs, without having to spin a new PCB with multiple PCM1802 chains.

[earlephilhower]

No, you can't just fan out the LRCLK/SCK pins. The PIOs need to generate their clocking, and multiple PIO SMs aren't all going to start at the exact same time and phase. You could maybe roll your own PIO and C code to do this, but it's not doable with what's in the core.

Probably 4 or 8 are doable on the 2350. Just make a sketch with multiple I2S objects and .begin() on them one by one. Eventually you'll fail (run out of PIO SMs or out of DMA channels). No need to actually wire anything up, this would all be on-chip resource limited and safe to test on a plain Pico2 board.

[thestumbler]

Thanks for that. I had been primarily worried about my processing time. Not doing anything extremely intensive, but currently the processing for each pair of audio channels takes about 1.25 ms each, done every 10 ms. Just based on that, 8 pairs would almost completely consume the MCU core, requiring any other tasks run on the second core. Now I'm aware the other chip constraints as you mentioned, but getting 8 pairs running on a single chip doesn't seem entirely out of the question.