# SocketCAN (Linux)

SocketCAN lets a Linux PC, Jetson, or Raspberry Pi control CAN and CAN FD devices directly. After the board is connected through USB, Linux exposes the four CAN/CAN FD channels as four `canX` network interfaces. You can use `can-utils`, `python-can`, or other SocketCAN software.

SocketCAN does not use SANPO `ST`, `ET`, `SF`, or `EF` headers. RS485 is not accessed through SocketCAN.

## Connect and Identify the Board

1. Connect the board to the Linux host through USB.
2. Connect and power the motor on a board CAN interface.
3. Install 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 assigns numbers by enumeration order, so `can0` to `can3` do not identify physical board connectors by themselves.

For first use, connect one motor and send a query on each interface to identify the mapping. You can also inspect the USB path:

```bash
readlink -f /sys/class/net/can0/device
udevadm info -q property -p "$(readlink -f /sys/class/net/can0/device)"
```

For long-term use, create `udev` rules based on the USB physical port or device serial number to assign stable interface names.

## Classic CAN

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
```

Monitor the bus:

```bash
candump can0
```

Send a standard frame:

```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 motor protocol, ID, and current state.

## CAN FD

Configure `can0` for 1 Mbps arbitration, 5 Mbps data, and CAN FD:

```bash
sudo ip link set can0 down
sudo ip link set can0 type can bitrate 1000000 dbitrate 5000000 fd on
sudo ip link set can0 up
```

Send a CAN FD standard frame with BRS:

```bash
cansend can0 123##11122334455667788
```

Send a CAN FD extended frame with BRS:

```bash
cansend can0 0000FD01##11122334455667788
```

After `##`, the first hexadecimal digit contains CAN FD flags. `1` enables BRS; the remaining digits are data.

## Check Interface State

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

With CAN FD enabled, the output should show `fd on`, `bitrate`, and `dbitrate`. If error counters continue increasing, stop transmission and check bitrate, termination, wiring, and device power.

SocketCAN settings are not saved to the board. Reapply `ip link` settings after a power cycle, USB reconnect, or re-enumeration.

## CyberGear Example

Example: [SocketCAN CyberGear](https://gitcode.com/sanpo/robot/blob/unified-main/products/spine/v6/demo/socketcan/socketcan_cybergear_demo_v6.py)

Control motor ID 1 on `can0`:

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

Multiple interfaces:

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

Update interface names and motor IDs to match the actual enumeration and wiring.

## Troubleshooting

| Symptom | Action |
| --- | --- |
| No `canX` interface | Confirm both MCU devices have V6 firmware, run `sudo modprobe gs_usb`, and reconnect USB |
| `Network is down` | Run `sudo ip link set can0 up` for the selected interface |
| `Device or resource busy` | Set the interface down before configuring it again |
| `No buffer space available` | Check wiring, bitrate, and termination; after fixing the bus, set the interface down and up again |
| Frames transmit but the motor does not reply | Check `canX` mapping, motor ID, protocol, power, and bus settings |