Can one run out of PIO?

[tomcombriat]

I think this is a stupid question, but could not find the answer anywhere…

Several protocols can be emulated using PIOs state machines. For instance SoftwareSPI and I2S. I am not very experienced with PIOs so I am not sure I do understand completely how they work, but is it possible to create as many SoftwareSPI instances as one wants or is one going to run out of PIOs at some point? What for instance if these SPI ports are not used at the same time? As they freed to be used by another SoftwareSPI by calling end or endTransaction?

Sorry for the silly question…

[earlephilhower]

Yes, you can run out. You get 8 on the RP2040, 12 on the RP2350. The core uses 1 for a cycle counter if you run FreeRTOS, but OTW they're only allocated when your app uses one.

When you begin a PIO-SM-using device (SoftwareSPI, Tone, Servo, etc.) it'll allocate its needed SMs and you can't deallocate them while the library is running. For some when you end it may free the SM, but things like PIO instruction memory will still be allocated and not useful for other libraries. (endTransaction is not the same and doesn't affect PIO SM usage, just the protocol).

[tomcombriat]

Thanks for the reply! That's what I though but could not find the information clearly online. If I may bother for one more thing, this running out will only be seen at runtime right? (ie, compilation will succeed even if too many PIOs are allocated)

[earlephilhower]

Yes, that's correct.

[tomcombriat]

Thanks!