pyusbxpress

Cross-platform Python client for Silicon Labs USBXpress devices (C8051F32x / C8051F34x / C8051F38x) — without the vendor driver.

Silicon Labs' USBXpress host driver (SiUSBXp.sys / SiUSBXp.dll) is Windows-only and version-fragile, and the wire protocol between the host driver and the device firmware library is not publicly documented. This project documents that protocol and provides a small Python client that talks to USBXpress devices directly over libusb/WinUSB, so the same code runs on Windows, Linux and macOS.

Disclaimer — this is an unofficial project based on interoperability research. It is not affiliated with or endorsed by Silicon Labs. It contains no Silicon Labs code or binaries; the protocol description was derived from black-box observation and analysis of the behaviour of the device firmware library. "USBXpress" and "Silicon Labs" are trademarks of Silicon Labs, used here only to describe compatibility.

Status

Alpha (v0.1.0). Verified on Windows 10/11 with a C8051F380 target (see docs/DEVICES.md); Linux/macOS are supported by design (libusb backend) and reports are welcome.

Install

pip install pyusbxpress

or from a checkout:

pip install -e .

The libusb backend needs a USB driver that lets user space claim the device:

Quick start

usbxpress list                       # list matching devices
usbxpress info                       # USB info + optional command exchange
usbxpress info --send "01"           # send one 64-byte packet, print the answer
usbxpress monitor                    # print every packet the device sends
usbxpress write --hex "01 55"        # send a single packet

As a library:

from usbxpress import UsbXpressDevice

with UsbXpressDevice() as dev:               # VID 10C4 / PID EA61 by default
    reply = dev.command(b"\x01")             # send one packet, wait for a
    print(reply.hex(" "))                    # packet that starts with 0x01

UsbXpressDevice is deliberately thin: one 64-byte packet per call, plus a command() helper that skips unsolicited packets (some firmwares emit periodic heartbeats). The meaning of the packets is up to your device firmware — see examples/ for a minimal ping and for a complete bootloader flashing example.

How it works (short version)

USBXpress is a vendor-specific USB device (interface class 0xFF) with two bulk endpoints (64-byte packets) and a small set of vendor control requests. The data path stays disabled until the host sends the DEVICE_OPEN control request — this handshake is the piece that the public documentation does not describe, and the reason "enumeration works but no data ever arrives" is a common complaint.

Full details, including the device-side event bits and the recommended host sequence, are in docs/PROTOCOL.md. The method used to derive the protocol is described in docs/INTERNALS.md.

Backends

--backend auto (the default) uses libusb when a WinUSB-bound device is present, and falls back to the SiLabs driver on Windows when it is not.

CLI reference

usbxpress [-h] [--version] {list,info,monitor,write} ...

common options:
  --vid HEX      vendor ID (default 10c4)
  --pid HEX      product ID (default ea61)
  --index N      device index when several are attached
  --serial S     select by serial string
  --backend      auto | libusb | siusbxp
  --dll PATH     SiUSBXp.dll location (siusbxp backend only)
  --timeout SEC  per-transfer timeout (default 1.0)

list      show matching devices and the backend that can see them
info      open the device, print USB info; --send HEX performs one exchange
monitor   print incoming packets with timestamps; --send HEX [--interval S] repeats a packet
write     send one packet: --hex "01 55" | --text "hello" | --file image.bin

Documentation

Examples

Tests

python -m unittest discover -s tests -v

The tests cover the protocol helpers and the packet/response logic with a fake backend; no hardware is required.

License

MIT — see LICENSE.