Documentation/networking/can_ucan_protocol.rst - linux - Git at Google

 =================
 The UCAN Protocol
 =================

 UCAN is the protocol used by the microcontroller-based USB-CAN
 adapter that is integrated on System-on-Modules from Theobroma Systems
 and that is also available as a standalone USB stick.

 The UCAN protocol has been designed to be hardware-independent.
 It is modeled closely after how Linux represents CAN devices
 internally. All multi-byte integers are encoded as Little Endian.

 All structures mentioned in this document are defined in
 ``drivers/net/can/usb/ucan.c``.

 USB Endpoints
 =============

 UCAN devices use three USB endpoints:

 CONTROL endpoint
   The driver sends device management commands on this endpoint

 IN endpoint
   The device sends CAN data frames and CAN error frames

 OUT endpoint
   The driver sends CAN data frames on the out endpoint


 CONTROL Messages
 ================

 UCAN devices are configured using vendor requests on the control pipe.

 To support multiple CAN interfaces in a single USB device all
 configuration commands target the corresponding interface in the USB
 descriptor.

 The driver uses ``ucan_ctrl_command_in/out`` and
 ``ucan_device_request_in`` to deliver commands to the device.

 Setup Packet
 ------------

 =================  =====================================================
 ``bmRequestType``  Direction | Vendor | (Interface or Device)
 ``bRequest``       Command Number
 ``wValue``         Subcommand Number (16 Bit) or 0 if not used
 ``wIndex``         USB Interface Index (0 for device commands)
 ``wLength``        * Host to Device - Number of bytes to transmit
                    * Device to Host - Maximum Number of bytes to
                      receive. If the device send less. Commom ZLP
                      semantics are used.
 =================  =====================================================

 Error Handling
 --------------

 The device indicates failed control commands by stalling the
 pipe.

 Device Commands
 ---------------

 UCAN_DEVICE_GET_FW_STRING
 ~~~~~~~~~~~~~~~~~~~~~~~~~

 *Dev2Host; optional*

 Request the device firmware string.


 Interface Commands
 ------------------

 UCAN_COMMAND_START
 ~~~~~~~~~~~~~~~~~~

 *Host2Dev; mandatory*

 Bring the CAN interface up.

 Payload Format
   ``ucan_ctl_payload_t.cmd_start``

 ====  ============================
 mode  or mask of ``UCAN_MODE_*``
 ====  ============================

 UCAN_COMMAND_STOP
 ~~~~~~~~~~~~~~~~~~

 *Host2Dev; mandatory*

 Stop the CAN interface

 Payload Format
   *empty*

 UCAN_COMMAND_RESET
 ~~~~~~~~~~~~~~~~~~

 *Host2Dev; mandatory*

 Reset the CAN controller (including error counters)

 Payload Format
   *empty*

 UCAN_COMMAND_GET
 ~~~~~~~~~~~~~~~~

 *Host2Dev; mandatory*

 Get Information from the Device

 Subcommands
 ^^^^^^^^^^^

 UCAN_COMMAND_GET_INFO
   Request the device information structure ``ucan_ctl_payload_t.device_info``.

   See the ``device_info`` field for details, and
   ``uapi/linux/can/netlink.h`` for an explanation of the
   ``can_bittiming fields``.

   Payload Format
     ``ucan_ctl_payload_t.device_info``

 UCAN_COMMAND_GET_PROTOCOL_VERSION

   Request the device protocol version
   ``ucan_ctl_payload_t.protocol_version``. The current protocol version is 3.

   Payload Format
     ``ucan_ctl_payload_t.protocol_version``

 .. note:: Devices that do not implement this command use the old
           protocol version 1

 UCAN_COMMAND_SET_BITTIMING
 ~~~~~~~~~~~~~~~~~~~~~~~~~~

 *Host2Dev; mandatory*

 Setup bittiming by sending the the structure
 ``ucan_ctl_payload_t.cmd_set_bittiming`` (see ``struct bittiming`` for
 details)

 Payload Format
   ``ucan_ctl_payload_t.cmd_set_bittiming``.

 UCAN_SLEEP/WAKE
 ~~~~~~~~~~~~~~~

 *Host2Dev; optional*

 Configure sleep and wake modes. Not yet supported by the driver.

 UCAN_FILTER
 ~~~~~~~~~~~

 *Host2Dev; optional*

 Setup hardware CAN filters. Not yet supported by the driver.

 Allowed interface commands
 --------------------------

 ==================  ===================  ==================
 Legal Device State  Command              New Device State
 ==================  ===================  ==================
 stopped             SET_BITTIMING        stopped
 stopped             START                started
 started             STOP or RESET        stopped
 stopped             STOP or RESET        stopped
 started             RESTART              started
 any                 GET                  *no change*
 ==================  ===================  ==================

 IN Message Format
 =================

 A data packet on the USB IN endpoint contains one or more
 ``ucan_message_in`` values. If multiple messages are batched in a USB
 data packet, the ``len`` field can be used to jump to the next
 ``ucan_message_in`` value (take care to sanity-check the ``len`` value
 against the actual data size).

 .. _can_ucan_in_message_len:

 ``len`` field
 -------------

 Each ``ucan_message_in`` must be aligned to a 4-byte boundary (relative
 to the start of the start of the data buffer). That means that there
 may be padding bytes between multiple ``ucan_message_in`` values:

 .. code::

     +----------------------------+ < 0
     |                            |
     |   struct ucan_message_in   |
     |                            |
     +----------------------------+ < len
               [padding]
     +----------------------------+ < round_up(len, 4)
     |                            |
     |   struct ucan_message_in   |
     |                            |
     +----------------------------+
                 [...]

 ``type`` field
 --------------

 The ``type`` field specifies the type of the message.

 UCAN_IN_RX
 ~~~~~~~~~~

 ``subtype``
   zero

 Data received from the CAN bus (ID + payload).

 UCAN_IN_TX_COMPLETE
 ~~~~~~~~~~~~~~~~~~~

 ``subtype``
   zero

 The CAN device has sent a message to the CAN bus. It answers with a
 list of of tuples <echo-ids, flags>.

 The echo-id identifies the frame from (echos the id from a previous
 UCAN_OUT_TX message). The flag indicates the result of the
 transmission. Whereas a set Bit 0 indicates success. All other bits
 are reserved and set to zero.

 Flow Control
 ------------

 When receiving CAN messages there is no flow control on the USB
 buffer. The driver has to handle inbound message quickly enough to
 avoid drops. I case the device buffer overflow the condition is
 reported by sending corresponding error frames (see
 :ref:`can_ucan_error_handling`)


 OUT Message Format
 ==================

 A data packet on the USB OUT endpoint contains one or more ``struct
 ucan_message_out`` values. If multiple messages are batched into one
 data packet, the device uses the ``len`` field to jump to the next
 ucan_message_out value. Each ucan_message_out must be aligned to 4
 bytes (relative to the start of the data buffer). The mechanism is
 same as described in :ref:`can_ucan_in_message_len`.

 .. code::

     +----------------------------+ < 0
     |                            |
     |   struct ucan_message_out  |
     |                            |
     +----------------------------+ < len
               [padding]
     +----------------------------+ < round_up(len, 4)
     |                            |
     |   struct ucan_message_out  |
     |                            |
     +----------------------------+
                 [...]

 ``type`` field
 --------------

 In protocol version 3 only ``UCAN_OUT_TX`` is defined, others are used
 only by legacy devices (protocol version 1).

 UCAN_OUT_TX
 ~~~~~~~~~~~
 ``subtype``
   echo id to be replied within a CAN_IN_TX_COMPLETE message

 Transmit a CAN frame. (parameters: ``id``, ``data``)

 Flow Control
 ------------

 When the device outbound buffers are full it starts sending *NAKs* on
 the *OUT* pipe until more buffers are available. The driver stops the
 queue when a certain threshold of out packets are incomplete.

 .. _can_ucan_error_handling:

 CAN Error Handling
 ==================

 If error reporting is turned on the device encodes errors into CAN
 error frames (see ``uapi/linux/can/error.h``) and sends it using the
 IN endpoint. The driver updates its error statistics and forwards
 it.

 Although UCAN devices can suppress error frames completely, in Linux
 the driver is always interested. Hence, the device is always started with
 the ``UCAN_MODE_BERR_REPORT`` set. Filtering those messages for the
 user space is done by the driver.

 Bus OFF
 -------

 - The device does not recover from bus of automatically.
 - Bus OFF is indicated by an error frame (see ``uapi/linux/can/error.h``)
 - Bus OFF recovery is started by ``UCAN_COMMAND_RESTART``
 - Once Bus OFF recover is completed the device sends an error frame
   indicating that it is on ERROR-ACTIVE state.
 - During Bus OFF no frames are sent by the device.
 - During Bus OFF transmission requests from the host are completed
   immediately with the success bit left unset.

 Example Conversation
 ====================

 #) Device is connected to USB
 #) Host sends command ``UCAN_COMMAND_RESET``, subcmd 0
 #) Host sends command ``UCAN_COMMAND_GET``, subcmd ``UCAN_COMMAND_GET_INFO``
 #) Device sends ``UCAN_IN_DEVICE_INFO``
 #) Host sends command ``UCAN_OUT_SET_BITTIMING``
 #) Host sends command ``UCAN_COMMAND_START``, subcmd 0, mode ``UCAN_MODE_BERR_REPORT``
	=================
	The UCAN Protocol
	=================

	UCAN is the protocol used by the microcontroller-based USB-CAN
	adapter that is integrated on System-on-Modules from Theobroma Systems
	and that is also available as a standalone USB stick.

	The UCAN protocol has been designed to be hardware-independent.
	It is modeled closely after how Linux represents CAN devices
	internally. All multi-byte integers are encoded as Little Endian.

	All structures mentioned in this document are defined in
	``drivers/net/can/usb/ucan.c``.

	USB Endpoints
	=============

	UCAN devices use three USB endpoints:

	CONTROL endpoint
	The driver sends device management commands on this endpoint

	IN endpoint
	The device sends CAN data frames and CAN error frames

	OUT endpoint
	The driver sends CAN data frames on the out endpoint


	CONTROL Messages
	================

	UCAN devices are configured using vendor requests on the control pipe.

	To support multiple CAN interfaces in a single USB device all
	configuration commands target the corresponding interface in the USB
	descriptor.

	The driver uses ``ucan_ctrl_command_in/out`` and
	``ucan_device_request_in`` to deliver commands to the device.

	Setup Packet
	------------

	================= =====================================================
	``bmRequestType`` Direction \| Vendor \| (Interface or Device)
	``bRequest`` Command Number
	``wValue`` Subcommand Number (16 Bit) or 0 if not used
	``wIndex`` USB Interface Index (0 for device commands)
	``wLength`` * Host to Device - Number of bytes to transmit
	* Device to Host - Maximum Number of bytes to
	receive. If the device send less. Commom ZLP
	semantics are used.
	================= =====================================================

	Error Handling
	--------------

	The device indicates failed control commands by stalling the
	pipe.

	Device Commands
	---------------

	UCAN_DEVICE_GET_FW_STRING
	~~~~~~~~~~~~~~~~~~~~~~~~~

	Dev2Host; optional

	Request the device firmware string.


	Interface Commands
	------------------

	UCAN_COMMAND_START
	~~~~~~~~~~~~~~~~~~

	Host2Dev; mandatory

	Bring the CAN interface up.

	Payload Format
	``ucan_ctl_payload_t.cmd_start``

	==== ============================
	mode or mask of ``UCAN_MODE_*``
	==== ============================

	UCAN_COMMAND_STOP
	~~~~~~~~~~~~~~~~~~

	Host2Dev; mandatory

	Stop the CAN interface

	Payload Format
	empty

	UCAN_COMMAND_RESET
	~~~~~~~~~~~~~~~~~~

	Host2Dev; mandatory

	Reset the CAN controller (including error counters)

	Payload Format
	empty

	UCAN_COMMAND_GET
	~~~~~~~~~~~~~~~~

	Host2Dev; mandatory

	Get Information from the Device

	Subcommands
	^^^^^^^^^^^

	UCAN_COMMAND_GET_INFO
	Request the device information structure ``ucan_ctl_payload_t.device_info``.

	See the ``device_info`` field for details, and
	``uapi/linux/can/netlink.h`` for an explanation of the
	``can_bittiming fields``.

	Payload Format
	``ucan_ctl_payload_t.device_info``

	UCAN_COMMAND_GET_PROTOCOL_VERSION

	Request the device protocol version
	``ucan_ctl_payload_t.protocol_version``. The current protocol version is 3.

	Payload Format
	``ucan_ctl_payload_t.protocol_version``

	.. note:: Devices that do not implement this command use the old
	protocol version 1

	UCAN_COMMAND_SET_BITTIMING
	~~~~~~~~~~~~~~~~~~~~~~~~~~

	Host2Dev; mandatory

	Setup bittiming by sending the the structure
	``ucan_ctl_payload_t.cmd_set_bittiming`` (see ``struct bittiming`` for
	details)

	Payload Format
	``ucan_ctl_payload_t.cmd_set_bittiming``.

	UCAN_SLEEP/WAKE
	~~~~~~~~~~~~~~~

	Host2Dev; optional

	Configure sleep and wake modes. Not yet supported by the driver.

	UCAN_FILTER
	~~~~~~~~~~~

	Host2Dev; optional

	Setup hardware CAN filters. Not yet supported by the driver.

	Allowed interface commands
	--------------------------

	================== =================== ==================
	Legal Device State Command New Device State
	================== =================== ==================
	stopped SET_BITTIMING stopped
	stopped START started
	started STOP or RESET stopped
	stopped STOP or RESET stopped
	started RESTART started
	any GET no change
	================== =================== ==================

	IN Message Format
	=================

	A data packet on the USB IN endpoint contains one or more
	``ucan_message_in`` values. If multiple messages are batched in a USB
	data packet, the ``len`` field can be used to jump to the next
	``ucan_message_in`` value (take care to sanity-check the ``len`` value
	against the actual data size).

	.. _can_ucan_in_message_len:

	``len`` field
	-------------

	Each ``ucan_message_in`` must be aligned to a 4-byte boundary (relative
	to the start of the start of the data buffer). That means that there
	may be padding bytes between multiple ``ucan_message_in`` values:

	.. code::

	+----------------------------+ < 0
	\| \|
	\| struct ucan_message_in \|
	\| \|
	+----------------------------+ < len
	[padding]
	+----------------------------+ < round_up(len, 4)
	\| \|
	\| struct ucan_message_in \|
	\| \|
	+----------------------------+
	[...]

	``type`` field
	--------------

	The ``type`` field specifies the type of the message.

	UCAN_IN_RX
	~~~~~~~~~~

	``subtype``
	zero

	Data received from the CAN bus (ID + payload).

	UCAN_IN_TX_COMPLETE
	~~~~~~~~~~~~~~~~~~~

	``subtype``
	zero

	The CAN device has sent a message to the CAN bus. It answers with a
	list of of tuples <echo-ids, flags>.

	The echo-id identifies the frame from (echos the id from a previous
	UCAN_OUT_TX message). The flag indicates the result of the
	transmission. Whereas a set Bit 0 indicates success. All other bits
	are reserved and set to zero.

	Flow Control
	------------

	When receiving CAN messages there is no flow control on the USB
	buffer. The driver has to handle inbound message quickly enough to
	avoid drops. I case the device buffer overflow the condition is
	reported by sending corresponding error frames (see
	:ref:`can_ucan_error_handling`)


	OUT Message Format
	==================

	A data packet on the USB OUT endpoint contains one or more ``struct
	ucan_message_out`` values. If multiple messages are batched into one
	data packet, the device uses the ``len`` field to jump to the next
	ucan_message_out value. Each ucan_message_out must be aligned to 4
	bytes (relative to the start of the data buffer). The mechanism is
	same as described in :ref:`can_ucan_in_message_len`.

	.. code::

	+----------------------------+ < 0
	\| \|
	\| struct ucan_message_out \|
	\| \|
	+----------------------------+ < len
	[padding]
	+----------------------------+ < round_up(len, 4)
	\| \|
	\| struct ucan_message_out \|
	\| \|
	+----------------------------+
	[...]

	``type`` field
	--------------

	In protocol version 3 only ``UCAN_OUT_TX`` is defined, others are used
	only by legacy devices (protocol version 1).

	UCAN_OUT_TX
	~~~~~~~~~~~
	``subtype``
	echo id to be replied within a CAN_IN_TX_COMPLETE message

	Transmit a CAN frame. (parameters: ``id``, ``data``)

	Flow Control
	------------

	When the device outbound buffers are full it starts sending NAKs on
	the OUT pipe until more buffers are available. The driver stops the
	queue when a certain threshold of out packets are incomplete.

	.. _can_ucan_error_handling:

	CAN Error Handling
	==================

	If error reporting is turned on the device encodes errors into CAN
	error frames (see ``uapi/linux/can/error.h``) and sends it using the
	IN endpoint. The driver updates its error statistics and forwards
	it.

	Although UCAN devices can suppress error frames completely, in Linux
	the driver is always interested. Hence, the device is always started with
	the ``UCAN_MODE_BERR_REPORT`` set. Filtering those messages for the
	user space is done by the driver.

	Bus OFF
	-------

	- The device does not recover from bus of automatically.
	- Bus OFF is indicated by an error frame (see ``uapi/linux/can/error.h``)
	- Bus OFF recovery is started by ``UCAN_COMMAND_RESTART``
	- Once Bus OFF recover is completed the device sends an error frame
	indicating that it is on ERROR-ACTIVE state.
	- During Bus OFF no frames are sent by the device.
	- During Bus OFF transmission requests from the host are completed
	immediately with the success bit left unset.

	Example Conversation
	====================

	#) Device is connected to USB
	#) Host sends command ``UCAN_COMMAND_RESET``, subcmd 0
	#) Host sends command ``UCAN_COMMAND_GET``, subcmd ``UCAN_COMMAND_GET_INFO``
	#) Device sends ``UCAN_IN_DEVICE_INFO``
	#) Host sends command ``UCAN_OUT_SET_BITTIMING``
	#) Host sends command ``UCAN_COMMAND_START``, subcmd 0, mode ``UCAN_MODE_BERR_REPORT``