This can be used where the standard API calls for a list of pins, to check that they satisfy the requirements of the rp2pio state machine, e.g.,
```python
def __init__(self, pin_a, pin_b):
if not rp2pio.pins_are_sequential([pin_a, pin_b]):
raise ValueError("Pins must be sequential")
```
This adds I2SOut and PDMIn support via PIO.
StateMachines can now:
* read and read while writing
* transfer in 1, 2 or 4 byte increments
* init pins based on expected defaults automatically
* be stopped and restarted
* rxfifo can be cleared and rxstalls detected (good for tracking when
the reading code isn't keeping up)
Fixes#4162
@Jerryneedell noticed that this problem affected strips short enough
to not use the DMA peripheral, thanks for the hot tip!
Instead of checking for background tasks after every byte transfer,
try up to 32 transfers before attending to background tasks.
This fixes the problem I was seeing on my 5-pixel circuit.
Closes#4135.
The RP2040 is new microcontroller from Raspberry Pi that features
two Cortex M0s and eight PIO state machines that are good for
crunching lots of data. It has 264k RAM and a built in UF2
bootloader too.
Datasheet: https://pico.raspberrypi.org/files/rp2040_datasheet.pdf
