cob-cpcusb

CPC-USB/ARM7 adapter support for canopen-bench: a python-can backend plus the bench's adapter-card UI, in one package. It registers two entry points — a can.interface driver for any python-can user, and a canopen_bench.plugins adapter card for the bench specifically.

This is a separate distribution. It shares the canopen-bench repository but not its package: own pyproject.toml, own version, own tests, installed on its own. pip install canopen-bench does not bring it — install it only if you have this adapter. It is here as the worked reference for what a plugin package looks like.

Protocol

The adapter's USB protocol — identifiers, endpoints, transfer framing, message types, SJA1000 register semantics, bit timing and the required initialization order — is documented in PROTOCOL.md. That interface data was read off the mainline Linux driver drivers/net/can/usb/ems_usb.c (© 2004–2009 EMS Dr. Thomas Wuensche), which is its only public verified description. The implementation here is a pyusb/libusb userspace driver against that protocol; none of the kernel driver's own machinery (URB handling, sk_buff/netdev integration, the Linux CAN error-frame state machine, TX queue and echo handling) has a counterpart in it.

License

MIT, see LICENSE — same as the canopen-bench core.

This package was GPL-2.0-only until decode_bulk_packet was reimplemented against PROTOCOL.md; that one function had followed the kernel driver's control flow rather than just its protocol facts. The reasoning, and what remains in common, is written up in PROTOCOL.md.

Install

pip install cob-cpcusb
pip install -e ./plugins/cob-cpcusb     # or editable, from a clone's root

The driver needs only python-can and pyusb:

import can
bus = can.Bus(interface="cpcusb", bitrate=250_000)

The adapter card shows up in canopen-bench (1.x) once both are installed; pip does not bring the bench along.

pyusb needs libusb. On Windows it comes with the install (libusb-package), and the device must be bound to WinUSB once — a Zadig step (select the CPC-USB/ARM7 device, driver = WinUSB). On Linux and macOS it is the system's libusb-1.0 (apt install libusb-1.0-0, brew install libusb).

What's in here

• cob_cpcusb/bus.py — can.BusABC implementation, driven over native USB bulk transfers (no vendor DLL, no COM-port framing)
• cob_cpcusb/plugin.py — the bench-side adapter card (BenchPlugin.adapters() / adapter_backends())
• cob_cpcusb/protocol.py — CPC-USB wire protocol constants/framing

Both halves ship in one package deliberately: the adapter card is meaningless without the driver it points at, and vice versa.

Tests

pip install -e .[dev]
pytest tests/