SolarOS 4.17.7 manual · hardware

Classic CAN

The twai-can expansion driver exposes one ESP32 or ESP32-S3 classic CAN controller. Connect TX and RX to a compatible external CAN transceiver. The transceiver provides the CANH/CANL electrical interface; ESP32 pins do not connect directly to those bus wires. Use the same bitrate on all nodes and terminate the bus at its two ends.

expansion attach twai-can can0 tx=16 rx=17 bitrate=500 listen=0
can list
can status can0
can send can0 0x123 01020304
can recv can0 100
expansion detach can0

Choose available pins on your board. Bitrates are 25, 50, 100, 125, 250, 500, 800, or 1000 kbit/s. Default listen=1 receives without acknowledging or transmitting. Set listen=0 for normal bus participation. Optional select=<gpio-or-controller:line> controls a transceiver enable or signal multiplexer; active=0|1 selects its enabled level (default 1). Detaching releases selection and all resource claims.

In the io app, press n, select can, and set the controller name, TX/RX GPIOs, bitrate, and mode. An optional Select GPIO and Active level control a transceiver enable pin. CAN controllers appear in the Buses view, where runtime controllers have Autostart and Remove CAN bus actions. The CAN option is available when the twai-can driver is installed and supported by the board. Use expansion attach for selection through an external GPIO controller.

Frames carry up to eight data bytes. IDs default to standard 11-bit form; add ext for a 29-bit ID. Hex data contains two digits per byte, without spaces; - sends a zero-length frame. Add rtr for a remote request; its DLC is the length of the supplied hex argument, and its data bytes are ignored. The command reports when a frame is queued. Check controller status for transmission failures; queue admission is not a delivery acknowledgment. CAN FD and application protocols such as CANopen are not provided.

can recv waits up to 1000 ms, with zero as the default. The C service API also bounds send and receive waits to 1000 ms. Operations and detach are serialized. A receive timeout returns without producing a frame.

After bus-off, can recover can0 starts the controller's bus-free recovery. Poll can status can0 until its state becomes stopped, then run can start can0. Detach is refused while recovery is in progress.

Quick reference

can [list] lists the attached controller. can status <name> shows its state, queue depths, error counters, failed transmissions, and missed receives. can send <name> <id> <hex-or-> [ext] [rtr] queues a frame. can recv <name> [timeout-ms] reads one frame. can recover <name> begins bus-off recovery; can start <name> restarts a stopped controller.