CircuitPython

Belay also supports CircuitPython. Unlike MicroPython, CircuitPython automatically mounts the device's filesystem as a USB drive. This is usually convenient, but it makes the filesystem read-only to the python interpreter. To get around this, we need to manually add the following lines to boot.py on-device.

import storage

storage.remount("/")

Afterwards, reset the device and it's prepared for Belay.

Reverting

To revert this configuration, there are multiple options:

  1. Edit boot.py using Thonny, then reboot. Thonny (like Belay), operates via the REPL, so it has write-access since it's operating through circuitpython.

  2. Through circuitpython's REPL via an interactive shell, such as rshell or python -m serial.tools.miniterm:

import os

os.remove("boot.py")

  1. Using Belay in an interactive python prompt on host:

from belay import Device

device = Device("/dev/ttyUSB0")  # replace with appropriate port
device("os.remove('boot.py')")
# Then reboot.

Physical Configuration

Storage mounting can be configured based on a physical pin state. Adding the following contents to /boot.py will configure the system to:

  • Be in "normal" circuitpython mode if pin 14 is floating/high (due to configured pullup) on boot.

  • Be in Belay-compatible mode if pin 14 is connected to ground on boot. This could be done, for example, by a push-button or a toggle switch.

import board
import storage
from digitalio import DigitalInOut, Pull

op_mode = DigitalInOut(board.GP14)  # Choose whichever pin you would like
op_mode.switch_to_input(Pull.UP)

if not op_mode.value:
    # Mount system in host-readonly, circuitpython-writeable mode (Belay compatible).
    storage.remount("/")