# SocketCAN

SocketCAN lets a Linux PC, Jetson, or Raspberry Pi control CAN devices directly. After the board is connected through USB, Linux exposes the four CAN channels as `can0`, `can1`, `can2`, and `can3`. You can use `can-utils`, `python-can`, CANgaroo, or other SocketCAN software.

Use firmware V4.6 or later. SocketCAN only accesses CAN devices. For RS485, see [RS485 Raw Passthrough](rs485_passthrough).

## Connect and Identify the Board

1. Connect the board to the Linux host through USB.
2. Connect the motor to a CAN interface and supply motor power through the XT60 input.
3. Install CAN tools and load the driver:

```bash
sudo apt update
sudo apt install can-utils
sudo modprobe gs_usb
```

List CAN interfaces:

```bash
ip link show type can
```

A complete board normally exposes four `canX` interfaces. Linux numbering depends on USB enumeration and may not follow the board silkscreen. Confirm the physical mapping before controlling a motor.

## Configure a CAN Interface

Configure `can0` for 1 Mbps:

```bash
sudo ip link set can0 down
sudo ip link set can0 type can bitrate 1000000
sudo ip link set can0 up
```

The bitrate must match the motor. This setting only applies to the current Linux interface and must be repeated after a power cycle, USB reconnect, or host restart.

Show the current state and bitrate:

```bash
ip -details link show can0
```

Configure all four interfaces for 1 Mbps:

```bash
for iface in can0 can1 can2 can3; do
  sudo ip link set "$iface" down
  sudo ip link set "$iface" type can bitrate 1000000
  sudo ip link set "$iface" up
done
```

## Send and Receive CAN Frames

Monitor `can0` in one terminal:

```bash
candump can0
```

Send a standard frame from another terminal:

```bash
cansend can0 123#11223344
```

Send an extended frame:

```bash
cansend can0 0000FD01#0102030405060708
```

`cansend` normally prints nothing on success. A reply depends on the device protocol, ID, and state; not every test frame produces a response.

View traffic and error counters:

```bash
ip -s -details link show can0
```

## CyberGear Example

Download the [CyberGear SocketCAN example](https://gitcode.com/sanpo/robot/blob/main/products/spine/v4/f407/examples/socketcan/cybergear/socketcan_cybergear_demo_v6.py), then control motor ID 1 on `can0`:

```bash
sudo python3 socketcan_cybergear_demo_v6.py \
  --setup-links \
  --motor-map "can0:1"
```

For multiple interfaces and motors:

```text
--motor-map "can0:1,2,3;can1:4,5,6"
```

For example, `can0:1,2,3` means that `can0` is connected to motor IDs 1, 2, and 3. Update the interface names and motor IDs to match the actual wiring. `--setup-links` enables the listed interfaces at the default 1 Mbps bitrate.

## Troubleshooting

| Symptom | Action |
| --- | --- |
| No `canX` interface | Confirm firmware V4.6 or later, run `sudo modprobe gs_usb`, and reconnect USB |
| `RTNETLINK answers: Device or resource busy` | Run `sudo ip link set can0 down` before changing the bitrate |
| `Network is down` | Run `sudo ip link set can0 up` |
| Frames transmit but the motor does not reply | Check the `canX` mapping, motor ID, bitrate, wiring, termination, and motor power |
| `No buffer space available` or rising error counters | Check wiring, bitrate, and termination; after fixing the bus, set the interface down and up again |