gamepad_pmod_circuitpython_pio

boot.py

import usb_hid
from joystick_xl.hid import create_joystick

# enable default CircuitPython USB HID devices as well as JoystickXL
usb_hid.enable(
  (
    usb_hid.Device.KEYBOARD,
    usb_hid.Device.MOUSE,
    usb_hid.Device.CONSUMER_CONTROL,
    create_joystick(axes=2, buttons=8, hats=1),
  )
)

code.py

"""
Tiny Tapeout Gamepad Pmod Driver for CircuitPython

https://github.com/psychogenic/gamepad-pmod

DATA   -> GP19  (gamepad_data)   –- sampled by PIO
CLOCK  -> GP18  (gamepad_clk)    –- edge-detect inside PIO
LATCH  -> GP17  (gamepad_latch)  –- read in plain Python

Protocol:
* While LATCH is low the pad shifts out 24 bits, MSB first, one bit
  per rising edge of CLOCK.
* When LATCH goes low→high the frame is considered complete and the
  current 24-bit word is printed.
"""

import array
import board
import rp2pio
import adafruit_pioasm
from joystick_xl.joystick import Joystick

# Pin mapping
LATCH_GPIO = 17
CLOCK_GPIO = 18
DATA_GPIO = 19
LATCH_PIN = board.GP17

# Gamepad buttons
GAMEPAD_BUTTONS = ['L', 'R', 'X', 'A', 'Right', 'Left', 'Down', 'Up', 'Start', 'Select', 'Y', 'B']
GP_L = 1 << 0
GP_R = 1 << 1
GP_X = 1 << 2
GP_A = 1 << 3
GP_RIGHT = 1 << 4
GP_LEFT = 1 << 5
GP_DOWN = 1 << 6
GP_UP = 1 << 7
GP_START = 1 << 8
GP_SELECT = 1 << 9
GP_Y = 1 << 10
GP_B = 1 << 11

# PIO program
PIO_SRC = f"""
.program gamepad_sniff
frame_wait:
    wait 0 gpio {LATCH_GPIO}

    set   x, 23                ; need 24 clock cycles
    mov   isr, null            ; clear previous data

bitloop:                       ; ---- shift 24 bits while latch is LOW ----
    wait 1 gpio {CLOCK_GPIO}   ; clk ↑
    mov   osr, pins
    out   null, 2              ; Discard clock / latch values
    in    osr, 1               ; sample DATA
    wait 0 gpio {CLOCK_GPIO}   ; clk ↓
    jmp  x-- bitloop           ; repeat 24×

    ; ---------- wait for latch HIGH (end-of-frame) ------------------
    wait 1 gpio {LATCH_GPIO}

    push                       ; send 24-bit word to FIFO
    jmp   frame_wait           ; capture next frame
"""
assembled = adafruit_pioasm.assemble(PIO_SRC)

# ---------------- State machine ---------------------------------------------
sm = rp2pio.StateMachine(
    assembled,
    frequency=2_000_000,        # state-machine clock – plenty for ~1 MHz CLK
    first_in_pin=LATCH_PIN,     # DATA is the one pin read by `IN PINS,1`
    in_pin_count=3,
    in_shift_right=False,       # shift MSB-first
)

def decode_message(value: int):
    result = []
    for i, btn in enumerate(GAMEPAD_BUTTONS):
        if value & (1 << i):
            result.append(btn)
    return result

def map_hat_directions(value: int):
    if value & GP_UP:
        if value & GP_LEFT:
            return 7
        if value & GP_RIGHT:
            return 1
        return 0
    if value & GP_DOWN:
        if value & GP_LEFT:
            return 5
        if value & GP_RIGHT:
            return 3
        return 4
    if value & GP_RIGHT:
        return 2
    if value & GP_LEFT:
        return 6
    return 8

buf = array.array('I', [0])
js = Joystick()
print("Ready – waiting for frames …")
while True:
    sm.readinto(buf)
    value = buf[0]
    js.update_button((0, value & GP_START))
    js.update_button((1, value & GP_SELECT))
    js.update_hat((0, map_hat_directions(value)))
    print(f"{value:024b}   0x{value:06X}   {decode_message(value)}")