Raspberry Pi Pico serial tap

README.md

RP2040 Serial Tap

I wanted a very basic serial tap, a device I can insert between two other devices that are communicating via UART serial, so that I can inspect the messages going over the wire in real time.

The following are two implementations of this basic tap using an RP2040-based board, like a Raspberry Pi Pico. It takes advantage of the fact that the RP2040 has two UARTs, in addition to the USB serial used for programming and the REPL. There is one implementation in CircuitPython and another in MicroPython.

tap_circuitpython.py

'''
A basic serial tap, where this device sits between two others
and transparently echoes serial comms. This is useful for
debugging and for "logic level" shifting between to devices
with serial interfaces running at different speeds.
'''
import board
import busio
import digitalio

DEFAULT_BPS = 115200

# Set up the default UARTs
u0 = busio.UART(board.GP0, board.GP1, baudrate=DEFAULT_BPS)
u1 = busio.UART(board.GP4, board.GP5, baudrate=DEFAULT_BPS)


def config(u0_baudrate=DEFAULT_BPS, u1_baudrate=DEFAULT_BPS):
    global u0
    global u1
    
    u0.reset_input_buffer()
    u1.reset_input_buffer()
    
    u0.deinit()
    u1.deinit()
    
    u0 = busio.UART(board.GP0, board.GP1, baudrate=u0_baudrate)
    u1 = busio.UART(board.GP4, board.GP5, baudrate=u1_baudrate)
    

def exchange_bytes():
    if u0.in_waiting:
        b0 = u0.read(1)
        u1.write(b0)
        print(f"u0 -> {b0} -> u1")
    if u1.in_waiting:
        b1 = u1.read(1)
        u0.write(b1)
        print(f"u0 <- {b1} <- u1")

tap_micropython.py

'''
A basic serial tap, where this device sits between two others
and transparently echoes serial comms. This is useful for
debugging and for "logic level" shifting between to devices
with serial interfaces running at different speeds.
'''
from machine import UART, Pin

# Set up the default UARTs
u0 = UART(0)
u1 = UART(1)

DEFAULT_BPS = 115200

def config(u0_bps=DEFAULT_BPS, u1_bps=DEFAULT_BPS):
    global u0
    global u1
    
    u0.deinit()
    u1.deinit()
    u0 = UART(0, baudrate=u0_bps)
    u1 = UART(1, baudrate=u1_bps)
    

def exchange_bytes():
    if u0.any():
        b0 = u0.read(1)
        u1.write(b0)
        print(f"u0 -> {b0} -> u1")
    if u1.any():
        b1 = u1.read(1)
        u0.write(b1)
        print(f"u0 <- {b1} <- u1")