f842a40df4
The PIO state machines on the RP2040 have 4 word deep TX and RX FIFOs. If you only need one direction, you can "merge" them into either a single 8 word deep TX or RX FIFO. We simply add constants to the PIO object, and set the appropriate bits in `shiftctrl`. Resolves #6854. Signed-off-by: Tim Radvan <tim@tjvr.org>