boot.py

# boot.py — Initializes the USB CDC-ECM Ethernet device at boot time
# This runs BEFORE the USB subsystem starts, so the host sees the
# Ethernet adapter immediately on plug-in.

import usb.device
from ecm_interface import ECMInterface

# Create the ECM interface singleton — stored in the module so main.py
# can retrieve it via: from ecm_interface import _ecm_instance
ecm = ECMInterface()
ECMInterface._instance = ecm  # stash for main.py to find

# builtin_driver=True keeps the built-in CDC serial REPL available
# alongside our ECM Ethernet interface.
#
# Explicit device class/subclass/protocol (0xEF/0x02/0x01) tells the host
# this device uses Interface Association Descriptors (IAD), which ChromeOS
# requires for CDC-ECM Ethernet adapters.
usb.device.get().init(
    ecm,
    builtin_driver=True,
    device_class=0xEF,
    device_subclass=0x02,
    device_protocol=0x01,
    manufacturer_str="Raspberry Pi",
    product_str="Pico ECM Bridge",
)