uc2canopen — Python CANopen master for openUC2

Control UC2 microscope motors, lasers, LEDs, and galvos directly over CAN bus from Python — no ESP32 master required, no JSON-over-serial, just CANopen SDO/PDO.

Two transports are supported:

• MCP2515 SPI HAT (SocketCAN) — recommended on a Raspberry Pi. The HAT enumerates as a native can0 interface. This is the default.
• Waveshare USB-CAN-A — a USB dongle, handy on a laptop.

Same API shape as UC2-REST, different transport: CANopen instead of JSON-over-serial.

---

1. Raspberry Pi + MCP2515 HAT setup (one-time)

Skip this section if you use the Waveshare USB adapter — see Waveshare USB-CAN-A at the bottom.

The HAT is an MCP2515 CAN controller on SPI0 (CS = SPI0_CE0/GPIO8, INT = GPIO12) with an SN65HVD230 3.3 V transceiver and a 12 MHz crystal.

1a. Enable SPI and load the MCP2515 driver

Edit /boot/firmware/config.txt and add:

dtparam=spi=on
dtoverlay=mcp2515-can0,oscillator=12000000,interrupt=12,spimaxfrequency=10000000

• oscillator=12000000 must match the crystal on the board (12 MHz here). A wrong value = can0 comes up but never sees a frame.
• interrupt=12 is the INT line wiring (GPIO12). If SPI is flaky, drop spimaxfrequency to 2000000.

Reboot, then confirm the driver bound:

sudo reboot
# after it's back:
dmesg | grep -iE "mcp251|can0"
#   → mcp251x spi0.0 can0: MCP2515 successfully initialized.

1b. Bring the interface up @ 500 kbit/s

sudo ip link set can0 up type can bitrate 500000 restart-ms 100
ip -details link show can0          # state should be ERROR-ACTIVE

500 kbit/s is the UC2 firmware bitrate — it must match your nodes. restart-ms 100 auto-recovers from bus-off while debugging.

1c. Sanity-check the bus (optional but recommended)

sudo apt install -y can-utils
candump can0

You should see live traffic — CANopen heartbeats at 0x700 + node-ID (e.g. 0x70B = node 11) and motor TPDOs at 0x180 + node-ID. If frames scroll, the whole chain works. Send an NMT "start all":

cansend can0 000#0100

1d. Make can0 come up at boot (optional)

Create /etc/systemd/system/can0.service:

[Unit]
Description=Bring up can0 (MCP2515)
After=sys-subsystem-net-devices-can0.device
BindsTo=sys-subsystem-net-devices-can0.device

[Service]
Type=oneshot
RemainAfterExit=yes
ExecStart=/sbin/ip link set can0 up type can bitrate 500000 restart-ms 100
ExecStop=/sbin/ip link set can0 down

[Install]
WantedBy=multi-user.target

sudo systemctl enable --now can0.service

---

2. Install the Python package

# with uv (recommended)
uv pip install -e .

# or with pip
pip install -e .

python-can's SocketCAN backend is built in on Linux — nothing extra to install for the HAT. (pyserial is pulled in too, only needed for the Waveshare adapter.)

---

3. Run the demo

With can0 up (step 1b), from the repo root:

python src/motor_demo.py --motor-node 11

This scans for nodes, jogs motor node 11 back and forth, blinks the laser/LED board, and prints node status. Useful flags: --skip-laser --skip-led, --steps, --speed, --channel can1.

---

4. Python API

from uc2canopen import UC2Client, NODE

# Defaults to SocketCAN can0 (the MCP2515 HAT) — bring it up first with
#   sudo ip link set can0 up type can bitrate 500000
uc2 = UC2Client()
# Other channel:        UC2Client(channel="can1")
# Waveshare USB adapter: UC2Client(port="/dev/ttyUSB0")

# Move motor X axis 1000 steps
uc2.motor.move(axis=0, position=1000, speed=20000, node_id=NODE.MOT_X)
uc2.motor.wait_for_idle(axis=0, node_id=NODE.MOT_X)
print(f"Motor at {uc2.motor.get_position(axis=0, node_id=NODE.MOT_X)} steps")

uc2.laser.set_value(channel=0, pwm=512, node_id=NODE.LASER_0)   # laser 50%
uc2.led.fill(r=255, g=0, b=0, node_id=NODE.LED_0)               # LEDs red
print(f"Uptime: {uc2.state.get_uptime(NODE.MOT_X)}s")

uc2.close()

5. CLI

The uc2can command also defaults to SocketCAN can0:

uc2can scan                          # find nodes on the bus
uc2can move --node 11 --pos 1000 --speed 20000 --wait
uc2can laser --node 20 --ch 0 --pwm 512
uc2can led --node 20 --r 255 --g 0 --b_val 0
uc2can status --node 11
uc2can sniff                         # dump raw CAN frames
uc2can reboot --node 11

# pick a transport/channel (global flags, before the subcommand):
uc2can --channel can1 scan
uc2can --interface waveshare --port /dev/ttyUSB0 scan

---

Node-ID assignments

Role	Node-ID	Python constant
Master (this script)	1	NODE.MASTER
Motor X	11	NODE.MOT_X
Motor Y	12	NODE.MOT_Y
Motor Z	13	NODE.MOT_Z
Motor A	14	NODE.MOT_A
LED / combined illum. board	20	NODE.LED (alias: LED_0, LASER_0)
Laser (separate board)	21	NODE.LASER (alias: LASER_1)
Joystick	22	NODE.JOYSTICK
Galvo	30	NODE.GALVO
Galvo 2	31	NODE.GALVO_2
Encoder	40	NODE.ENCODER
PID	50	NODE.PID

Architecture

Your Python script
    │
    ▼
UC2Client
├── motor  → Motor()    SDO writes to 0x2000-0x200B
├── laser  → Laser()    SDO writes to 0x2100
├── led    → Led()      SDO writes to 0x2200
├── state  → State()    SDO reads from 0x2500+
│
├── SdoClient           raw SDO upload/download over python-can
├── TpdoListener        background thread for motor state (TPDO1)
│
└── python-can BusABC   ── SocketCAN can0 (MCP2515 HAT)   ← default
                        └─ WaveshareBus (USB-CAN-A serial)
        │
        ▼ CAN bus @ 500 kbit/s
        │
    ┌───┴───┬───────┬────────┐
    │       │       │        │
  Slave   Slave   Slave    Slave
  node11  node12  node13   node20
  (mot X) (mot Y) (mot Z)  (illum)

The whole SDO/PDO stack is transport-agnostic (it talks to a python-can BusABC), so the only difference between transports is which bus object UC2Client builds.

OD index reference

All indices are in uc2canopen.od.OD and match the firmware's UC2_OD_Indices.h (generated from uc2_canopen_registry.yaml).

Troubleshooting

Symptom	Most likely cause
No can0; dmesg empty/error	SPI not enabled, wrong interrupt=, or SPI wiring
can0 up but candump empty	Wrong oscillator= (crystal), bitrate ≠ 500 k, or missing 120 Ω termination
RuntimeError: No Waveshare ... adapter found	You asked for the Waveshare transport (--port/interface="waveshare") but none is attached; for the HAT just use the default
Failed to open CAN bus on the HAT	can0 isn't up — run sudo ip link set can0 up type can bitrate 500000 restart-ms 100
Error frames / bus-off	Bitrate mismatch, CANH↔CANL swapped, or no common GND

Waveshare USB-CAN-A (alternative)

No driver setup needed — plug it in and select it explicitly:

python src/motor_demo.py --interface waveshare --port /dev/ttyUSB0 --motor-node 11
uc2can --interface waveshare scan          # auto-detects the port

uc2 = UC2Client(port="/dev/ttyUSB0")       # a port implies the Waveshare transport

Requirements

• Python ≥ 3.10
• python-can ≥ 4.0 (SocketCAN backend built in on Linux)
• pyserial (only for the Waveshare adapter)
• Hardware: an MCP2515 SPI HAT or a Waveshare USB-CAN-A adapter, plus UC2 slave(s) on the bus

License

MIT — same as the UC2-ESP32 firmware.