Document that piomatter requires entire /dev/pio0 peripheral

[omnislash772]

Tried using this with the Adafruit_Blinka_Raspberry_Pi5_Neopixel library and it seems I cannot instance both a Hub75 panel and a Neopixel strip at the same time. Only separately.

This can be tested by running the play_gif.py example code and then attempting to run any of the examples in the Neopixel examples (I am using pin D18 for this as it is free)

The result is that whichever example is run first will run but the second example will silently fail.

[jepler]

Yes, that is expected. This program requires all the resources of the PIO peripheral in order to operate.

Specifically, the GPIO pins used by the matrix are not required to be "in order", but can have gaps. Because of the way the PIO peripheral operates, this could only be accomplished in a specific way which would interfere with any other state machine operating in the same PIO peripheral. And, only one PIO peripheral is provided for use by Linux programs.

This could be better documented.