Documentation/networking/can_ucan_protocol.rst

5 UCAN is the protocol used by the microcontroller-based USB-CAN
6 adapter that is integrated on System-on-Modules from Theobroma Systems
7 and that is also available as a standalone USB stick.
9 The UCAN protocol has been designed to be hardware-independent.
11 internally. All multi-byte integers are encoded as Little Endian.
14 ``drivers/net/can/usb/ucan.c``.
16 USB Endpoints
19 UCAN devices use three USB endpoints:
36 To support multiple CAN interfaces in a single USB device all
37 configuration commands target the corresponding interface in the USB
44 ------------
50 ``wIndex``         USB Interface Index (0 for device commands)
51 ``wLength``        * Host to Device - Number of bytes to transmit
52                    * Device to Host - Maximum Number of bytes to
58 --------------
64 ---------------
75 ------------------
133   Request the device protocol version
134   ``ucan_ctl_payload_t.protocol_version``. The current protocol version is 3.
140           protocol version 1
169 --------------------------
185 A data packet on the USB IN endpoint contains one or more
186 ``ucan_message_in`` values. If multiple messages are batched in a USB
188 ``ucan_message_in`` value (take care to sanity-check the ``len`` value
194 -------------
196 Each ``ucan_message_in`` must be aligned to a 4-byte boundary (relative
202     +----------------------------+ < 0
206     +----------------------------+ < len
208     +----------------------------+ < round_up(len, 4)
212     +----------------------------+
216 --------------
235 list of tuples <echo-ids, flags>.
237 The echo-id identifies the frame from (echos the id from a previous
243 ------------
245 When receiving CAN messages there is no flow control on the USB
255 A data packet on the USB OUT endpoint contains one or more ``struct
264     +----------------------------+ < 0
268     +----------------------------+ < len
270     +----------------------------+ < round_up(len, 4)
274     +----------------------------+
278 --------------
280 In protocol version 3 only ``UCAN_OUT_TX`` is defined, others are used
281 only by legacy devices (protocol version 1).
291 ------------
313 -------
315 - The device does not recover from bus of automatically.
316 - Bus OFF is indicated by an error frame (see ``uapi/linux/can/error.h``)
317 - Bus OFF recovery is started by ``UCAN_COMMAND_RESTART``
318 - Once Bus OFF recover is completed the device sends an error frame
319   indicating that it is on ERROR-ACTIVE state.
320 - During Bus OFF no frames are sent by the device.
321 - During Bus OFF transmission requests from the host are completed
327 #) Device is connected to USB