Posted on April 13, 2018 at 08:55Nevermind, I will probably use SPI in slave mode, a Timer for generating clock and PDM filtering by software. One extra pin, but it should be doable.
Wasn't it the extra wasted pin you wanted to avoid at the first place?
Sure it's doable in any way, but why would you do it?
I wanted to know if MCU supports this or not. It seems like it, as examples don't use WS pin, but I'll have to try. I asked in case anybody did this before.
Yes, the MCU supports it. I did exactly this as an exercise during writing USB audio class stuff, as I used the 'F4 DISCO and needed some reasonable audio source. And it worked, if this is the assurance you wanted to hear.
... stock levels and price of STM32F4x3V...
I see.
STM32F407V which we use doesn't have it for some reason.
The 'F407 is a quite old model and DFSDM is a relatively new module in the STM32 offerings.
Nevertheless, the decimation/filtering is relatively computation-intensive. In that exercise I mentioned above, when using a decimation factor of 2x16 (i.e. 32 input bits to one 16-bit output word) and 4-stage filtering (resulting in not quite HiFi sound), at 48 samples per 1ms USB frame (i.e. 48ksps), a straightforward implementation ate up 0.353ms, i.e. one third of the total processor time, with the processor at full throttle i.e. 168MHz. Could bring it down to some 0.220ms with some algorithmic optimizations, but still not something I would like to have in a final application. YMMV.
JW
PS. Note, that the MP45DT02 are marked as NRND.
