do_fourwireperipheral.py

import array
import digitalio
import board
import adafruit_pioasm
import rp2pio

program = adafruit_pioasm.Program(""".program clocked_input_chip_select

; Sample bits using an external clock, and push groups of bits into the RX FIFO.
; - IN pin 0 is the data pin
; - IN pin 1 is the dc pin
; - IN pin 2 is the clock pin
; - JMP pin is the chip select
; - Autopush is enabled, threshold 8
;
; This program waits for chip select to be asserted (low) before it begins
; clocking in data. Whilst chip select is low, data is clocked continuously. If
; chip select is deasserted part way through a data byte, the partial data is
; discarded. This makes use of the fact a mov to isr clears the input shift
; counter.

flush:
    mov isr, null         ; Clear ISR and input shift counter
    jmp check_chip_select ; Poll chip select again

.wrap_target
do_bit:
    wait 0 pin 2          ; Detect rising edge and sample input data
    wait 1 pin 2          ; (autopush takes care of moving each complete
    in pins, 2            ; data word to the FIFO)
check_chip_select:
    jmp pin, flush        ; Bail out if we see chip select high
.wrap
""", build_debuginfo=True)

print(program.assembled)
program.print_c_program('bob')

sm = rp2pio.StateMachine(
        program.assembled,
        first_in_pin=board.GP2,
        in_pin_count=3,
        pull_in_pin_up=0x7,
        jmp_pin=board.GP5,
        jmp_pin_pull=digitalio.Pull.UP,
        in_shift_right=False,
        auto_push=True,
        push_threshold=16,
        frequency=120_000_000,
        **program.pio_kwargs,
        )

lookup = [0] * 256
for i in range(256):
    bits = [(i >> j) & 1 for j in range(8)]
    k = (
            (bits[0] << 0) |
            (bits[1] << 2) |
            (bits[2] << 4) |
            (bits[3] << 6) |
            (bits[4] << 1) |
            (bits[5] << 3) |
            (bits[6] << 5) |
            (bits[7] << 7))
    lookup[k] = i
a = array.array('H', [0])
i = 0
while True:
    sm.readinto(a)
    i += 1
    v = a[0]
    command = not v & 2
    aa = (v & 0x55) | ((v >> 7) & 0xaa)
    vv = lookup[aa]
    if command:
        print(end=f"\nCMD {vv:02x}\n    ")
        i = 0
    else:
        i += 1
        print(f"{vv:02x}", end="\n" if i == 16 else " ")