A circuitpython program providing passthrough from the USB to a UART
I wrote this while debugging a esp32-c3 running the espressif AT command set, which outputs over the UART. This allows you to connect a circuitpython board (e.g. Adafruit Feather M4 Express in my case) to the UART tx/rx of the device and type at it with the USB connection on computer.
This also translates \r characters on USB input into \r\n sequences
since the espressif AT command set (and probably others) expect \r\n
to terminate commands, but the "screen" terminal program on MacOS only
outputs \r by default. Rather than try and figure out how to fix screen
it's easier to just do it here. It's disabled with a boolean flag below.
The neopixel is used for status:
- white: no USB connected
- blue: USB connected, idle
- green: reading bytes from USB
- red: reading bytes from UART
Your circuitpython board needs these libraries in /lib
adafruit_bus_device
adafruit_pixelbuf.mpy
neopixel.mpy
Note that for this to work you MUST have this in boot.py on circuitpython, to enable the usb_cdc connection:
import usb_cdc
usb_cdc.enable(console=True, data=True)
Note that if you change boot.py you must reset the board with the reset button or power cycle to take effect.
This will make a second USB device different from the circuitpython REPL
console. ie - console is /dev/ttyACM0 and the passthrough port is /dev/ttyACM1
(on Linux, names will be different on different systems). You want to connect
your terminal program to the passthrough port, e.g:
screen /dev/ttyACM1
on MacOS.
Steven Cogswell November 2022 https://github.com/scogswell
References:
https://learn.adafruit.com/adafruit-feather-m4-express-atsamd51/circuitpython-uart-serial https://docs.circuitpython.org/en/latest/shared-bindings/usb_cdc/index.html https://docs.espressif.com/projects/esp-at/en/latest/esp32c3/AT_Command_Set/Basic_AT_Commands.html