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51b2f451b5
This patch adds documentation about the broadcast manager. It's based on Brian Thorne's initial patch http://marc.info/?l=linux-can&m=138119382015496&w=2 and Daniele Venzano's work http://brownhat.org/docs/socketcan.html . Signed-off-by: Brian Thorne <hardbyte@gmail.com> Cc: Daniele Venzano <linux@brownhat.org> Cc: Andre Naujoks <nautsch2@gmail.com> Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net> Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
1192 lines
51 KiB
Plaintext
1192 lines
51 KiB
Plaintext
============================================================================
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can.txt
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Readme file for the Controller Area Network Protocol Family (aka Socket CAN)
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This file contains
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1 Overview / What is Socket CAN
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2 Motivation / Why using the socket API
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3 Socket CAN concept
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3.1 receive lists
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3.2 local loopback of sent frames
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3.3 network security issues (capabilities)
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3.4 network problem notifications
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4 How to use Socket CAN
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4.1 RAW protocol sockets with can_filters (SOCK_RAW)
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4.1.1 RAW socket option CAN_RAW_FILTER
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4.1.2 RAW socket option CAN_RAW_ERR_FILTER
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4.1.3 RAW socket option CAN_RAW_LOOPBACK
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4.1.4 RAW socket option CAN_RAW_RECV_OWN_MSGS
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4.1.5 RAW socket option CAN_RAW_FD_FRAMES
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4.1.6 RAW socket returned message flags
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4.2 Broadcast Manager protocol sockets (SOCK_DGRAM)
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4.2.1 Broadcast Manager operations
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4.2.2 Broadcast Manager message flags
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4.2.3 Broadcast Manager transmission timers
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4.2.4 Broadcast Manager message sequence transmission
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4.2.5 Broadcast Manager receive filter timers
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4.2.6 Broadcast Manager multiplex message receive filter
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4.3 connected transport protocols (SOCK_SEQPACKET)
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4.4 unconnected transport protocols (SOCK_DGRAM)
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5 Socket CAN core module
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5.1 can.ko module params
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5.2 procfs content
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5.3 writing own CAN protocol modules
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6 CAN network drivers
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6.1 general settings
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6.2 local loopback of sent frames
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6.3 CAN controller hardware filters
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6.4 The virtual CAN driver (vcan)
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6.5 The CAN network device driver interface
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6.5.1 Netlink interface to set/get devices properties
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6.5.2 Setting the CAN bit-timing
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6.5.3 Starting and stopping the CAN network device
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6.6 CAN FD (flexible data rate) driver support
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6.7 supported CAN hardware
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7 Socket CAN resources
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8 Credits
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============================================================================
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1. Overview / What is Socket CAN
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--------------------------------
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The socketcan package is an implementation of CAN protocols
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(Controller Area Network) for Linux. CAN is a networking technology
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which has widespread use in automation, embedded devices, and
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automotive fields. While there have been other CAN implementations
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for Linux based on character devices, Socket CAN uses the Berkeley
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socket API, the Linux network stack and implements the CAN device
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drivers as network interfaces. The CAN socket API has been designed
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as similar as possible to the TCP/IP protocols to allow programmers,
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familiar with network programming, to easily learn how to use CAN
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sockets.
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2. Motivation / Why using the socket API
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----------------------------------------
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There have been CAN implementations for Linux before Socket CAN so the
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question arises, why we have started another project. Most existing
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implementations come as a device driver for some CAN hardware, they
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are based on character devices and provide comparatively little
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functionality. Usually, there is only a hardware-specific device
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driver which provides a character device interface to send and
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receive raw CAN frames, directly to/from the controller hardware.
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Queueing of frames and higher-level transport protocols like ISO-TP
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have to be implemented in user space applications. Also, most
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character-device implementations support only one single process to
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open the device at a time, similar to a serial interface. Exchanging
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the CAN controller requires employment of another device driver and
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often the need for adaption of large parts of the application to the
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new driver's API.
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Socket CAN was designed to overcome all of these limitations. A new
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protocol family has been implemented which provides a socket interface
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to user space applications and which builds upon the Linux network
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layer, so to use all of the provided queueing functionality. A device
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driver for CAN controller hardware registers itself with the Linux
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network layer as a network device, so that CAN frames from the
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controller can be passed up to the network layer and on to the CAN
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protocol family module and also vice-versa. Also, the protocol family
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module provides an API for transport protocol modules to register, so
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that any number of transport protocols can be loaded or unloaded
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dynamically. In fact, the can core module alone does not provide any
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protocol and cannot be used without loading at least one additional
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protocol module. Multiple sockets can be opened at the same time,
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on different or the same protocol module and they can listen/send
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frames on different or the same CAN IDs. Several sockets listening on
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the same interface for frames with the same CAN ID are all passed the
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same received matching CAN frames. An application wishing to
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communicate using a specific transport protocol, e.g. ISO-TP, just
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selects that protocol when opening the socket, and then can read and
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write application data byte streams, without having to deal with
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CAN-IDs, frames, etc.
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Similar functionality visible from user-space could be provided by a
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character device, too, but this would lead to a technically inelegant
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solution for a couple of reasons:
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* Intricate usage. Instead of passing a protocol argument to
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socket(2) and using bind(2) to select a CAN interface and CAN ID, an
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application would have to do all these operations using ioctl(2)s.
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* Code duplication. A character device cannot make use of the Linux
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network queueing code, so all that code would have to be duplicated
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for CAN networking.
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* Abstraction. In most existing character-device implementations, the
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hardware-specific device driver for a CAN controller directly
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provides the character device for the application to work with.
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This is at least very unusual in Unix systems for both, char and
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block devices. For example you don't have a character device for a
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certain UART of a serial interface, a certain sound chip in your
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computer, a SCSI or IDE controller providing access to your hard
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disk or tape streamer device. Instead, you have abstraction layers
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which provide a unified character or block device interface to the
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application on the one hand, and a interface for hardware-specific
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device drivers on the other hand. These abstractions are provided
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by subsystems like the tty layer, the audio subsystem or the SCSI
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and IDE subsystems for the devices mentioned above.
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The easiest way to implement a CAN device driver is as a character
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device without such a (complete) abstraction layer, as is done by most
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existing drivers. The right way, however, would be to add such a
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layer with all the functionality like registering for certain CAN
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IDs, supporting several open file descriptors and (de)multiplexing
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CAN frames between them, (sophisticated) queueing of CAN frames, and
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providing an API for device drivers to register with. However, then
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it would be no more difficult, or may be even easier, to use the
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networking framework provided by the Linux kernel, and this is what
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Socket CAN does.
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The use of the networking framework of the Linux kernel is just the
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natural and most appropriate way to implement CAN for Linux.
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3. Socket CAN concept
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---------------------
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As described in chapter 2 it is the main goal of Socket CAN to
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provide a socket interface to user space applications which builds
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upon the Linux network layer. In contrast to the commonly known
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TCP/IP and ethernet networking, the CAN bus is a broadcast-only(!)
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medium that has no MAC-layer addressing like ethernet. The CAN-identifier
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(can_id) is used for arbitration on the CAN-bus. Therefore the CAN-IDs
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have to be chosen uniquely on the bus. When designing a CAN-ECU
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network the CAN-IDs are mapped to be sent by a specific ECU.
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For this reason a CAN-ID can be treated best as a kind of source address.
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3.1 receive lists
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The network transparent access of multiple applications leads to the
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problem that different applications may be interested in the same
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CAN-IDs from the same CAN network interface. The Socket CAN core
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module - which implements the protocol family CAN - provides several
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high efficient receive lists for this reason. If e.g. a user space
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application opens a CAN RAW socket, the raw protocol module itself
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requests the (range of) CAN-IDs from the Socket CAN core that are
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requested by the user. The subscription and unsubscription of
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CAN-IDs can be done for specific CAN interfaces or for all(!) known
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CAN interfaces with the can_rx_(un)register() functions provided to
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CAN protocol modules by the SocketCAN core (see chapter 5).
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To optimize the CPU usage at runtime the receive lists are split up
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into several specific lists per device that match the requested
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filter complexity for a given use-case.
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3.2 local loopback of sent frames
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As known from other networking concepts the data exchanging
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applications may run on the same or different nodes without any
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change (except for the according addressing information):
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___ ___ ___ _______ ___
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| _ | | _ | | _ | | _ _ | | _ |
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||A|| ||B|| ||C|| ||A| |B|| ||C||
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|___| |___| |___| |_______| |___|
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| | | | |
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-----------------(1)- CAN bus -(2)---------------
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To ensure that application A receives the same information in the
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example (2) as it would receive in example (1) there is need for
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some kind of local loopback of the sent CAN frames on the appropriate
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node.
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The Linux network devices (by default) just can handle the
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transmission and reception of media dependent frames. Due to the
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arbitration on the CAN bus the transmission of a low prio CAN-ID
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may be delayed by the reception of a high prio CAN frame. To
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reflect the correct* traffic on the node the loopback of the sent
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data has to be performed right after a successful transmission. If
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the CAN network interface is not capable of performing the loopback for
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some reason the SocketCAN core can do this task as a fallback solution.
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See chapter 6.2 for details (recommended).
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The loopback functionality is enabled by default to reflect standard
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networking behaviour for CAN applications. Due to some requests from
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the RT-SocketCAN group the loopback optionally may be disabled for each
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separate socket. See sockopts from the CAN RAW sockets in chapter 4.1.
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* = you really like to have this when you're running analyser tools
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like 'candump' or 'cansniffer' on the (same) node.
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3.3 network security issues (capabilities)
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The Controller Area Network is a local field bus transmitting only
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broadcast messages without any routing and security concepts.
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In the majority of cases the user application has to deal with
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raw CAN frames. Therefore it might be reasonable NOT to restrict
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the CAN access only to the user root, as known from other networks.
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Since the currently implemented CAN_RAW and CAN_BCM sockets can only
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send and receive frames to/from CAN interfaces it does not affect
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security of others networks to allow all users to access the CAN.
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To enable non-root users to access CAN_RAW and CAN_BCM protocol
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sockets the Kconfig options CAN_RAW_USER and/or CAN_BCM_USER may be
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selected at kernel compile time.
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3.4 network problem notifications
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The use of the CAN bus may lead to several problems on the physical
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and media access control layer. Detecting and logging of these lower
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layer problems is a vital requirement for CAN users to identify
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hardware issues on the physical transceiver layer as well as
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arbitration problems and error frames caused by the different
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ECUs. The occurrence of detected errors are important for diagnosis
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and have to be logged together with the exact timestamp. For this
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reason the CAN interface driver can generate so called Error Message
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Frames that can optionally be passed to the user application in the
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same way as other CAN frames. Whenever an error on the physical layer
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or the MAC layer is detected (e.g. by the CAN controller) the driver
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creates an appropriate error message frame. Error messages frames can
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be requested by the user application using the common CAN filter
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mechanisms. Inside this filter definition the (interested) type of
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errors may be selected. The reception of error messages is disabled
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by default. The format of the CAN error message frame is briefly
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described in the Linux header file "include/linux/can/error.h".
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4. How to use Socket CAN
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------------------------
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Like TCP/IP, you first need to open a socket for communicating over a
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CAN network. Since Socket CAN implements a new protocol family, you
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need to pass PF_CAN as the first argument to the socket(2) system
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call. Currently, there are two CAN protocols to choose from, the raw
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socket protocol and the broadcast manager (BCM). So to open a socket,
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you would write
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s = socket(PF_CAN, SOCK_RAW, CAN_RAW);
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and
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s = socket(PF_CAN, SOCK_DGRAM, CAN_BCM);
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respectively. After the successful creation of the socket, you would
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normally use the bind(2) system call to bind the socket to a CAN
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interface (which is different from TCP/IP due to different addressing
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- see chapter 3). After binding (CAN_RAW) or connecting (CAN_BCM)
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the socket, you can read(2) and write(2) from/to the socket or use
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send(2), sendto(2), sendmsg(2) and the recv* counterpart operations
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on the socket as usual. There are also CAN specific socket options
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described below.
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The basic CAN frame structure and the sockaddr structure are defined
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in include/linux/can.h:
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struct can_frame {
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canid_t can_id; /* 32 bit CAN_ID + EFF/RTR/ERR flags */
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__u8 can_dlc; /* frame payload length in byte (0 .. 8) */
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__u8 data[8] __attribute__((aligned(8)));
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};
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The alignment of the (linear) payload data[] to a 64bit boundary
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allows the user to define own structs and unions to easily access the
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CAN payload. There is no given byteorder on the CAN bus by
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default. A read(2) system call on a CAN_RAW socket transfers a
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struct can_frame to the user space.
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The sockaddr_can structure has an interface index like the
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PF_PACKET socket, that also binds to a specific interface:
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struct sockaddr_can {
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sa_family_t can_family;
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int can_ifindex;
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union {
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/* transport protocol class address info (e.g. ISOTP) */
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struct { canid_t rx_id, tx_id; } tp;
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/* reserved for future CAN protocols address information */
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} can_addr;
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};
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To determine the interface index an appropriate ioctl() has to
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be used (example for CAN_RAW sockets without error checking):
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int s;
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struct sockaddr_can addr;
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struct ifreq ifr;
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s = socket(PF_CAN, SOCK_RAW, CAN_RAW);
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strcpy(ifr.ifr_name, "can0" );
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ioctl(s, SIOCGIFINDEX, &ifr);
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addr.can_family = AF_CAN;
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addr.can_ifindex = ifr.ifr_ifindex;
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bind(s, (struct sockaddr *)&addr, sizeof(addr));
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(..)
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To bind a socket to all(!) CAN interfaces the interface index must
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be 0 (zero). In this case the socket receives CAN frames from every
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enabled CAN interface. To determine the originating CAN interface
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the system call recvfrom(2) may be used instead of read(2). To send
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on a socket that is bound to 'any' interface sendto(2) is needed to
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specify the outgoing interface.
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Reading CAN frames from a bound CAN_RAW socket (see above) consists
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of reading a struct can_frame:
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struct can_frame frame;
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nbytes = read(s, &frame, sizeof(struct can_frame));
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if (nbytes < 0) {
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perror("can raw socket read");
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return 1;
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}
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/* paranoid check ... */
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if (nbytes < sizeof(struct can_frame)) {
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fprintf(stderr, "read: incomplete CAN frame\n");
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return 1;
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}
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/* do something with the received CAN frame */
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Writing CAN frames can be done similarly, with the write(2) system call:
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nbytes = write(s, &frame, sizeof(struct can_frame));
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When the CAN interface is bound to 'any' existing CAN interface
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(addr.can_ifindex = 0) it is recommended to use recvfrom(2) if the
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information about the originating CAN interface is needed:
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struct sockaddr_can addr;
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struct ifreq ifr;
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socklen_t len = sizeof(addr);
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struct can_frame frame;
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nbytes = recvfrom(s, &frame, sizeof(struct can_frame),
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0, (struct sockaddr*)&addr, &len);
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/* get interface name of the received CAN frame */
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ifr.ifr_ifindex = addr.can_ifindex;
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ioctl(s, SIOCGIFNAME, &ifr);
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printf("Received a CAN frame from interface %s", ifr.ifr_name);
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To write CAN frames on sockets bound to 'any' CAN interface the
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outgoing interface has to be defined certainly.
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strcpy(ifr.ifr_name, "can0");
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ioctl(s, SIOCGIFINDEX, &ifr);
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addr.can_ifindex = ifr.ifr_ifindex;
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addr.can_family = AF_CAN;
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nbytes = sendto(s, &frame, sizeof(struct can_frame),
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0, (struct sockaddr*)&addr, sizeof(addr));
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Remark about CAN FD (flexible data rate) support:
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Generally the handling of CAN FD is very similar to the formerly described
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examples. The new CAN FD capable CAN controllers support two different
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bitrates for the arbitration phase and the payload phase of the CAN FD frame
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and up to 64 bytes of payload. This extended payload length breaks all the
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kernel interfaces (ABI) which heavily rely on the CAN frame with fixed eight
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bytes of payload (struct can_frame) like the CAN_RAW socket. Therefore e.g.
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the CAN_RAW socket supports a new socket option CAN_RAW_FD_FRAMES that
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switches the socket into a mode that allows the handling of CAN FD frames
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and (legacy) CAN frames simultaneously (see section 4.1.5).
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The struct canfd_frame is defined in include/linux/can.h:
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struct canfd_frame {
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canid_t can_id; /* 32 bit CAN_ID + EFF/RTR/ERR flags */
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__u8 len; /* frame payload length in byte (0 .. 64) */
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__u8 flags; /* additional flags for CAN FD */
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__u8 __res0; /* reserved / padding */
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__u8 __res1; /* reserved / padding */
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__u8 data[64] __attribute__((aligned(8)));
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};
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The struct canfd_frame and the existing struct can_frame have the can_id,
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the payload length and the payload data at the same offset inside their
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structures. This allows to handle the different structures very similar.
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When the content of a struct can_frame is copied into a struct canfd_frame
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all structure elements can be used as-is - only the data[] becomes extended.
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When introducing the struct canfd_frame it turned out that the data length
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code (DLC) of the struct can_frame was used as a length information as the
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length and the DLC has a 1:1 mapping in the range of 0 .. 8. To preserve
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the easy handling of the length information the canfd_frame.len element
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contains a plain length value from 0 .. 64. So both canfd_frame.len and
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can_frame.can_dlc are equal and contain a length information and no DLC.
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For details about the distinction of CAN and CAN FD capable devices and
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the mapping to the bus-relevant data length code (DLC), see chapter 6.6.
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The length of the two CAN(FD) frame structures define the maximum transfer
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unit (MTU) of the CAN(FD) network interface and skbuff data length. Two
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definitions are specified for CAN specific MTUs in include/linux/can.h :
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#define CAN_MTU (sizeof(struct can_frame)) == 16 => 'legacy' CAN frame
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#define CANFD_MTU (sizeof(struct canfd_frame)) == 72 => CAN FD frame
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4.1 RAW protocol sockets with can_filters (SOCK_RAW)
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Using CAN_RAW sockets is extensively comparable to the commonly
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known access to CAN character devices. To meet the new possibilities
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provided by the multi user SocketCAN approach, some reasonable
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defaults are set at RAW socket binding time:
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- The filters are set to exactly one filter receiving everything
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- The socket only receives valid data frames (=> no error message frames)
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- The loopback of sent CAN frames is enabled (see chapter 3.2)
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- The socket does not receive its own sent frames (in loopback mode)
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These default settings may be changed before or after binding the socket.
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To use the referenced definitions of the socket options for CAN_RAW
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sockets, include <linux/can/raw.h>.
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4.1.1 RAW socket option CAN_RAW_FILTER
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The reception of CAN frames using CAN_RAW sockets can be controlled
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by defining 0 .. n filters with the CAN_RAW_FILTER socket option.
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The CAN filter structure is defined in include/linux/can.h:
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struct can_filter {
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canid_t can_id;
|
|
canid_t can_mask;
|
|
};
|
|
|
|
A filter matches, when
|
|
|
|
<received_can_id> & mask == can_id & mask
|
|
|
|
which is analogous to known CAN controllers hardware filter semantics.
|
|
The filter can be inverted in this semantic, when the CAN_INV_FILTER
|
|
bit is set in can_id element of the can_filter structure. In
|
|
contrast to CAN controller hardware filters the user may set 0 .. n
|
|
receive filters for each open socket separately:
|
|
|
|
struct can_filter rfilter[2];
|
|
|
|
rfilter[0].can_id = 0x123;
|
|
rfilter[0].can_mask = CAN_SFF_MASK;
|
|
rfilter[1].can_id = 0x200;
|
|
rfilter[1].can_mask = 0x700;
|
|
|
|
setsockopt(s, SOL_CAN_RAW, CAN_RAW_FILTER, &rfilter, sizeof(rfilter));
|
|
|
|
To disable the reception of CAN frames on the selected CAN_RAW socket:
|
|
|
|
setsockopt(s, SOL_CAN_RAW, CAN_RAW_FILTER, NULL, 0);
|
|
|
|
To set the filters to zero filters is quite obsolete as not read
|
|
data causes the raw socket to discard the received CAN frames. But
|
|
having this 'send only' use-case we may remove the receive list in the
|
|
Kernel to save a little (really a very little!) CPU usage.
|
|
|
|
4.1.2 RAW socket option CAN_RAW_ERR_FILTER
|
|
|
|
As described in chapter 3.4 the CAN interface driver can generate so
|
|
called Error Message Frames that can optionally be passed to the user
|
|
application in the same way as other CAN frames. The possible
|
|
errors are divided into different error classes that may be filtered
|
|
using the appropriate error mask. To register for every possible
|
|
error condition CAN_ERR_MASK can be used as value for the error mask.
|
|
The values for the error mask are defined in linux/can/error.h .
|
|
|
|
can_err_mask_t err_mask = ( CAN_ERR_TX_TIMEOUT | CAN_ERR_BUSOFF );
|
|
|
|
setsockopt(s, SOL_CAN_RAW, CAN_RAW_ERR_FILTER,
|
|
&err_mask, sizeof(err_mask));
|
|
|
|
4.1.3 RAW socket option CAN_RAW_LOOPBACK
|
|
|
|
To meet multi user needs the local loopback is enabled by default
|
|
(see chapter 3.2 for details). But in some embedded use-cases
|
|
(e.g. when only one application uses the CAN bus) this loopback
|
|
functionality can be disabled (separately for each socket):
|
|
|
|
int loopback = 0; /* 0 = disabled, 1 = enabled (default) */
|
|
|
|
setsockopt(s, SOL_CAN_RAW, CAN_RAW_LOOPBACK, &loopback, sizeof(loopback));
|
|
|
|
4.1.4 RAW socket option CAN_RAW_RECV_OWN_MSGS
|
|
|
|
When the local loopback is enabled, all the sent CAN frames are
|
|
looped back to the open CAN sockets that registered for the CAN
|
|
frames' CAN-ID on this given interface to meet the multi user
|
|
needs. The reception of the CAN frames on the same socket that was
|
|
sending the CAN frame is assumed to be unwanted and therefore
|
|
disabled by default. This default behaviour may be changed on
|
|
demand:
|
|
|
|
int recv_own_msgs = 1; /* 0 = disabled (default), 1 = enabled */
|
|
|
|
setsockopt(s, SOL_CAN_RAW, CAN_RAW_RECV_OWN_MSGS,
|
|
&recv_own_msgs, sizeof(recv_own_msgs));
|
|
|
|
4.1.5 RAW socket option CAN_RAW_FD_FRAMES
|
|
|
|
CAN FD support in CAN_RAW sockets can be enabled with a new socket option
|
|
CAN_RAW_FD_FRAMES which is off by default. When the new socket option is
|
|
not supported by the CAN_RAW socket (e.g. on older kernels), switching the
|
|
CAN_RAW_FD_FRAMES option returns the error -ENOPROTOOPT.
|
|
|
|
Once CAN_RAW_FD_FRAMES is enabled the application can send both CAN frames
|
|
and CAN FD frames. OTOH the application has to handle CAN and CAN FD frames
|
|
when reading from the socket.
|
|
|
|
CAN_RAW_FD_FRAMES enabled: CAN_MTU and CANFD_MTU are allowed
|
|
CAN_RAW_FD_FRAMES disabled: only CAN_MTU is allowed (default)
|
|
|
|
Example:
|
|
[ remember: CANFD_MTU == sizeof(struct canfd_frame) ]
|
|
|
|
struct canfd_frame cfd;
|
|
|
|
nbytes = read(s, &cfd, CANFD_MTU);
|
|
|
|
if (nbytes == CANFD_MTU) {
|
|
printf("got CAN FD frame with length %d\n", cfd.len);
|
|
/* cfd.flags contains valid data */
|
|
} else if (nbytes == CAN_MTU) {
|
|
printf("got legacy CAN frame with length %d\n", cfd.len);
|
|
/* cfd.flags is undefined */
|
|
} else {
|
|
fprintf(stderr, "read: invalid CAN(FD) frame\n");
|
|
return 1;
|
|
}
|
|
|
|
/* the content can be handled independently from the received MTU size */
|
|
|
|
printf("can_id: %X data length: %d data: ", cfd.can_id, cfd.len);
|
|
for (i = 0; i < cfd.len; i++)
|
|
printf("%02X ", cfd.data[i]);
|
|
|
|
When reading with size CANFD_MTU only returns CAN_MTU bytes that have
|
|
been received from the socket a legacy CAN frame has been read into the
|
|
provided CAN FD structure. Note that the canfd_frame.flags data field is
|
|
not specified in the struct can_frame and therefore it is only valid in
|
|
CANFD_MTU sized CAN FD frames.
|
|
|
|
As long as the payload length is <=8 the received CAN frames from CAN FD
|
|
capable CAN devices can be received and read by legacy sockets too. When
|
|
user-generated CAN FD frames have a payload length <=8 these can be send
|
|
by legacy CAN network interfaces too. Sending CAN FD frames with payload
|
|
length > 8 to a legacy CAN network interface returns an -EMSGSIZE error.
|
|
|
|
Implementation hint for new CAN applications:
|
|
|
|
To build a CAN FD aware application use struct canfd_frame as basic CAN
|
|
data structure for CAN_RAW based applications. When the application is
|
|
executed on an older Linux kernel and switching the CAN_RAW_FD_FRAMES
|
|
socket option returns an error: No problem. You'll get legacy CAN frames
|
|
or CAN FD frames and can process them the same way.
|
|
|
|
When sending to CAN devices make sure that the device is capable to handle
|
|
CAN FD frames by checking if the device maximum transfer unit is CANFD_MTU.
|
|
The CAN device MTU can be retrieved e.g. with a SIOCGIFMTU ioctl() syscall.
|
|
|
|
4.1.6 RAW socket returned message flags
|
|
|
|
When using recvmsg() call, the msg->msg_flags may contain following flags:
|
|
|
|
MSG_DONTROUTE: set when the received frame was created on the local host.
|
|
|
|
MSG_CONFIRM: set when the frame was sent via the socket it is received on.
|
|
This flag can be interpreted as a 'transmission confirmation' when the
|
|
CAN driver supports the echo of frames on driver level, see 3.2 and 6.2.
|
|
In order to receive such messages, CAN_RAW_RECV_OWN_MSGS must be set.
|
|
|
|
4.2 Broadcast Manager protocol sockets (SOCK_DGRAM)
|
|
|
|
The Broadcast Manager protocol provides a command based configuration
|
|
interface to filter and send (e.g. cyclic) CAN messages in kernel space.
|
|
|
|
Receive filters can be used to down sample frequent messages; detect events
|
|
such as message contents changes, packet length changes, and do time-out
|
|
monitoring of received messages.
|
|
|
|
Periodic transmission tasks of CAN frames or a sequence of CAN frames can be
|
|
created and modified at runtime; both the message content and the two
|
|
possible transmit intervals can be altered.
|
|
|
|
A BCM socket is not intended for sending individual CAN frames using the
|
|
struct can_frame as known from the CAN_RAW socket. Instead a special BCM
|
|
configuration message is defined. The basic BCM configuration message used
|
|
to communicate with the broadcast manager and the available operations are
|
|
defined in the linux/can/bcm.h include. The BCM message consists of a
|
|
message header with a command ('opcode') followed by zero or more CAN frames.
|
|
The broadcast manager sends responses to user space in the same form:
|
|
|
|
struct bcm_msg_head {
|
|
__u32 opcode; /* command */
|
|
__u32 flags; /* special flags */
|
|
__u32 count; /* run 'count' times with ival1 */
|
|
struct timeval ival1, ival2; /* count and subsequent interval */
|
|
canid_t can_id; /* unique can_id for task */
|
|
__u32 nframes; /* number of can_frames following */
|
|
struct can_frame frames[0];
|
|
};
|
|
|
|
The aligned payload 'frames' uses the same basic CAN frame structure defined
|
|
at the beginning of section 4 and in the include/linux/can.h include. All
|
|
messages to the broadcast manager from user space have this structure.
|
|
|
|
Note a CAN_BCM socket must be connected instead of bound after socket
|
|
creation (example without error checking):
|
|
|
|
int s;
|
|
struct sockaddr_can addr;
|
|
struct ifreq ifr;
|
|
|
|
s = socket(PF_CAN, SOCK_DGRAM, CAN_BCM);
|
|
|
|
strcpy(ifr.ifr_name, "can0");
|
|
ioctl(s, SIOCGIFINDEX, &ifr);
|
|
|
|
addr.can_family = AF_CAN;
|
|
addr.can_ifindex = ifr.ifr_ifindex;
|
|
|
|
connect(s, (struct sockaddr *)&addr, sizeof(addr))
|
|
|
|
(..)
|
|
|
|
The broadcast manager socket is able to handle any number of in flight
|
|
transmissions or receive filters concurrently. The different RX/TX jobs are
|
|
distinguished by the unique can_id in each BCM message. However additional
|
|
CAN_BCM sockets are recommended to communicate on multiple CAN interfaces.
|
|
When the broadcast manager socket is bound to 'any' CAN interface (=> the
|
|
interface index is set to zero) the configured receive filters apply to any
|
|
CAN interface unless the sendto() syscall is used to overrule the 'any' CAN
|
|
interface index. When using recvfrom() instead of read() to retrieve BCM
|
|
socket messages the originating CAN interface is provided in can_ifindex.
|
|
|
|
4.2.1 Broadcast Manager operations
|
|
|
|
The opcode defines the operation for the broadcast manager to carry out,
|
|
or details the broadcast managers response to several events, including
|
|
user requests.
|
|
|
|
Transmit Operations (user space to broadcast manager):
|
|
|
|
TX_SETUP: Create (cyclic) transmission task.
|
|
|
|
TX_DELETE: Remove (cyclic) transmission task, requires only can_id.
|
|
|
|
TX_READ: Read properties of (cyclic) transmission task for can_id.
|
|
|
|
TX_SEND: Send one CAN frame.
|
|
|
|
Transmit Responses (broadcast manager to user space):
|
|
|
|
TX_STATUS: Reply to TX_READ request (transmission task configuration).
|
|
|
|
TX_EXPIRED: Notification when counter finishes sending at initial interval
|
|
'ival1'. Requires the TX_COUNTEVT flag to be set at TX_SETUP.
|
|
|
|
Receive Operations (user space to broadcast manager):
|
|
|
|
RX_SETUP: Create RX content filter subscription.
|
|
|
|
RX_DELETE: Remove RX content filter subscription, requires only can_id.
|
|
|
|
RX_READ: Read properties of RX content filter subscription for can_id.
|
|
|
|
Receive Responses (broadcast manager to user space):
|
|
|
|
RX_STATUS: Reply to RX_READ request (filter task configuration).
|
|
|
|
RX_TIMEOUT: Cyclic message is detected to be absent (timer ival1 expired).
|
|
|
|
RX_CHANGED: BCM message with updated CAN frame (detected content change).
|
|
Sent on first message received or on receipt of revised CAN messages.
|
|
|
|
4.2.2 Broadcast Manager message flags
|
|
|
|
When sending a message to the broadcast manager the 'flags' element may
|
|
contain the following flag definitions which influence the behaviour:
|
|
|
|
SETTIMER: Set the values of ival1, ival2 and count
|
|
|
|
STARTTIMER: Start the timer with the actual values of ival1, ival2
|
|
and count. Starting the timer leads simultaneously to emit a CAN frame.
|
|
|
|
TX_COUNTEVT: Create the message TX_EXPIRED when count expires
|
|
|
|
TX_ANNOUNCE: A change of data by the process is emitted immediately.
|
|
|
|
TX_CP_CAN_ID: Copies the can_id from the message header to each
|
|
subsequent frame in frames. This is intended as usage simplification. For
|
|
TX tasks the unique can_id from the message header may differ from the
|
|
can_id(s) stored for transmission in the subsequent struct can_frame(s).
|
|
|
|
RX_FILTER_ID: Filter by can_id alone, no frames required (nframes=0).
|
|
|
|
RX_CHECK_DLC: A change of the DLC leads to an RX_CHANGED.
|
|
|
|
RX_NO_AUTOTIMER: Prevent automatically starting the timeout monitor.
|
|
|
|
RX_ANNOUNCE_RESUME: If passed at RX_SETUP and a receive timeout occured, a
|
|
RX_CHANGED message will be generated when the (cyclic) receive restarts.
|
|
|
|
TX_RESET_MULTI_IDX: Reset the index for the multiple frame transmission.
|
|
|
|
RX_RTR_FRAME: Send reply for RTR-request (placed in op->frames[0]).
|
|
|
|
4.2.3 Broadcast Manager transmission timers
|
|
|
|
Periodic transmission configurations may use up to two interval timers.
|
|
In this case the BCM sends a number of messages ('count') at an interval
|
|
'ival1', then continuing to send at another given interval 'ival2'. When
|
|
only one timer is needed 'count' is set to zero and only 'ival2' is used.
|
|
When SET_TIMER and START_TIMER flag were set the timers are activated.
|
|
The timer values can be altered at runtime when only SET_TIMER is set.
|
|
|
|
4.2.4 Broadcast Manager message sequence transmission
|
|
|
|
Up to 256 CAN frames can be transmitted in a sequence in the case of a cyclic
|
|
TX task configuration. The number of CAN frames is provided in the 'nframes'
|
|
element of the BCM message head. The defined number of CAN frames are added
|
|
as array to the TX_SETUP BCM configuration message.
|
|
|
|
/* create a struct to set up a sequence of four CAN frames */
|
|
struct {
|
|
struct bcm_msg_head msg_head;
|
|
struct can_frame frame[4];
|
|
} mytxmsg;
|
|
|
|
(..)
|
|
mytxmsg.nframes = 4;
|
|
(..)
|
|
|
|
write(s, &mytxmsg, sizeof(mytxmsg));
|
|
|
|
With every transmission the index in the array of CAN frames is increased
|
|
and set to zero at index overflow.
|
|
|
|
4.2.5 Broadcast Manager receive filter timers
|
|
|
|
The timer values ival1 or ival2 may be set to non-zero values at RX_SETUP.
|
|
When the SET_TIMER flag is set the timers are enabled:
|
|
|
|
ival1: Send RX_TIMEOUT when a received message is not received again within
|
|
the given time. When START_TIMER is set at RX_SETUP the timeout detection
|
|
is activated directly - even without a former CAN frame reception.
|
|
|
|
ival2: Throttle the received message rate down to the value of ival2. This
|
|
is useful to reduce messages for the application when the signal inside the
|
|
CAN frame is stateless as state changes within the ival2 periode may get
|
|
lost.
|
|
|
|
4.2.6 Broadcast Manager multiplex message receive filter
|
|
|
|
To filter for content changes in multiplex message sequences an array of more
|
|
than one CAN frames can be passed in a RX_SETUP configuration message. The
|
|
data bytes of the first CAN frame contain the mask of relevant bits that
|
|
have to match in the subsequent CAN frames with the received CAN frame.
|
|
If one of the subsequent CAN frames is matching the bits in that frame data
|
|
mark the relevant content to be compared with the previous received content.
|
|
Up to 257 CAN frames (multiplex filter bit mask CAN frame plus 256 CAN
|
|
filters) can be added as array to the TX_SETUP BCM configuration message.
|
|
|
|
/* usually used to clear CAN frame data[] - beware of endian problems! */
|
|
#define U64_DATA(p) (*(unsigned long long*)(p)->data)
|
|
|
|
struct {
|
|
struct bcm_msg_head msg_head;
|
|
struct can_frame frame[5];
|
|
} msg;
|
|
|
|
msg.msg_head.opcode = RX_SETUP;
|
|
msg.msg_head.can_id = 0x42;
|
|
msg.msg_head.flags = 0;
|
|
msg.msg_head.nframes = 5;
|
|
U64_DATA(&msg.frame[0]) = 0xFF00000000000000ULL; /* MUX mask */
|
|
U64_DATA(&msg.frame[1]) = 0x01000000000000FFULL; /* data mask (MUX 0x01) */
|
|
U64_DATA(&msg.frame[2]) = 0x0200FFFF000000FFULL; /* data mask (MUX 0x02) */
|
|
U64_DATA(&msg.frame[3]) = 0x330000FFFFFF0003ULL; /* data mask (MUX 0x33) */
|
|
U64_DATA(&msg.frame[4]) = 0x4F07FC0FF0000000ULL; /* data mask (MUX 0x4F) */
|
|
|
|
write(s, &msg, sizeof(msg));
|
|
|
|
4.3 connected transport protocols (SOCK_SEQPACKET)
|
|
4.4 unconnected transport protocols (SOCK_DGRAM)
|
|
|
|
|
|
5. Socket CAN core module
|
|
-------------------------
|
|
|
|
The Socket CAN core module implements the protocol family
|
|
PF_CAN. CAN protocol modules are loaded by the core module at
|
|
runtime. The core module provides an interface for CAN protocol
|
|
modules to subscribe needed CAN IDs (see chapter 3.1).
|
|
|
|
5.1 can.ko module params
|
|
|
|
- stats_timer: To calculate the Socket CAN core statistics
|
|
(e.g. current/maximum frames per second) this 1 second timer is
|
|
invoked at can.ko module start time by default. This timer can be
|
|
disabled by using stattimer=0 on the module commandline.
|
|
|
|
- debug: (removed since SocketCAN SVN r546)
|
|
|
|
5.2 procfs content
|
|
|
|
As described in chapter 3.1 the Socket CAN core uses several filter
|
|
lists to deliver received CAN frames to CAN protocol modules. These
|
|
receive lists, their filters and the count of filter matches can be
|
|
checked in the appropriate receive list. All entries contain the
|
|
device and a protocol module identifier:
|
|
|
|
foo@bar:~$ cat /proc/net/can/rcvlist_all
|
|
|
|
receive list 'rx_all':
|
|
(vcan3: no entry)
|
|
(vcan2: no entry)
|
|
(vcan1: no entry)
|
|
device can_id can_mask function userdata matches ident
|
|
vcan0 000 00000000 f88e6370 f6c6f400 0 raw
|
|
(any: no entry)
|
|
|
|
In this example an application requests any CAN traffic from vcan0.
|
|
|
|
rcvlist_all - list for unfiltered entries (no filter operations)
|
|
rcvlist_eff - list for single extended frame (EFF) entries
|
|
rcvlist_err - list for error message frames masks
|
|
rcvlist_fil - list for mask/value filters
|
|
rcvlist_inv - list for mask/value filters (inverse semantic)
|
|
rcvlist_sff - list for single standard frame (SFF) entries
|
|
|
|
Additional procfs files in /proc/net/can
|
|
|
|
stats - Socket CAN core statistics (rx/tx frames, match ratios, ...)
|
|
reset_stats - manual statistic reset
|
|
version - prints the Socket CAN core version and the ABI version
|
|
|
|
5.3 writing own CAN protocol modules
|
|
|
|
To implement a new protocol in the protocol family PF_CAN a new
|
|
protocol has to be defined in include/linux/can.h .
|
|
The prototypes and definitions to use the Socket CAN core can be
|
|
accessed by including include/linux/can/core.h .
|
|
In addition to functions that register the CAN protocol and the
|
|
CAN device notifier chain there are functions to subscribe CAN
|
|
frames received by CAN interfaces and to send CAN frames:
|
|
|
|
can_rx_register - subscribe CAN frames from a specific interface
|
|
can_rx_unregister - unsubscribe CAN frames from a specific interface
|
|
can_send - transmit a CAN frame (optional with local loopback)
|
|
|
|
For details see the kerneldoc documentation in net/can/af_can.c or
|
|
the source code of net/can/raw.c or net/can/bcm.c .
|
|
|
|
6. CAN network drivers
|
|
----------------------
|
|
|
|
Writing a CAN network device driver is much easier than writing a
|
|
CAN character device driver. Similar to other known network device
|
|
drivers you mainly have to deal with:
|
|
|
|
- TX: Put the CAN frame from the socket buffer to the CAN controller.
|
|
- RX: Put the CAN frame from the CAN controller to the socket buffer.
|
|
|
|
See e.g. at Documentation/networking/netdevices.txt . The differences
|
|
for writing CAN network device driver are described below:
|
|
|
|
6.1 general settings
|
|
|
|
dev->type = ARPHRD_CAN; /* the netdevice hardware type */
|
|
dev->flags = IFF_NOARP; /* CAN has no arp */
|
|
|
|
dev->mtu = CAN_MTU; /* sizeof(struct can_frame) -> legacy CAN interface */
|
|
|
|
or alternative, when the controller supports CAN with flexible data rate:
|
|
dev->mtu = CANFD_MTU; /* sizeof(struct canfd_frame) -> CAN FD interface */
|
|
|
|
The struct can_frame or struct canfd_frame is the payload of each socket
|
|
buffer (skbuff) in the protocol family PF_CAN.
|
|
|
|
6.2 local loopback of sent frames
|
|
|
|
As described in chapter 3.2 the CAN network device driver should
|
|
support a local loopback functionality similar to the local echo
|
|
e.g. of tty devices. In this case the driver flag IFF_ECHO has to be
|
|
set to prevent the PF_CAN core from locally echoing sent frames
|
|
(aka loopback) as fallback solution:
|
|
|
|
dev->flags = (IFF_NOARP | IFF_ECHO);
|
|
|
|
6.3 CAN controller hardware filters
|
|
|
|
To reduce the interrupt load on deep embedded systems some CAN
|
|
controllers support the filtering of CAN IDs or ranges of CAN IDs.
|
|
These hardware filter capabilities vary from controller to
|
|
controller and have to be identified as not feasible in a multi-user
|
|
networking approach. The use of the very controller specific
|
|
hardware filters could make sense in a very dedicated use-case, as a
|
|
filter on driver level would affect all users in the multi-user
|
|
system. The high efficient filter sets inside the PF_CAN core allow
|
|
to set different multiple filters for each socket separately.
|
|
Therefore the use of hardware filters goes to the category 'handmade
|
|
tuning on deep embedded systems'. The author is running a MPC603e
|
|
@133MHz with four SJA1000 CAN controllers from 2002 under heavy bus
|
|
load without any problems ...
|
|
|
|
6.4 The virtual CAN driver (vcan)
|
|
|
|
Similar to the network loopback devices, vcan offers a virtual local
|
|
CAN interface. A full qualified address on CAN consists of
|
|
|
|
- a unique CAN Identifier (CAN ID)
|
|
- the CAN bus this CAN ID is transmitted on (e.g. can0)
|
|
|
|
so in common use cases more than one virtual CAN interface is needed.
|
|
|
|
The virtual CAN interfaces allow the transmission and reception of CAN
|
|
frames without real CAN controller hardware. Virtual CAN network
|
|
devices are usually named 'vcanX', like vcan0 vcan1 vcan2 ...
|
|
When compiled as a module the virtual CAN driver module is called vcan.ko
|
|
|
|
Since Linux Kernel version 2.6.24 the vcan driver supports the Kernel
|
|
netlink interface to create vcan network devices. The creation and
|
|
removal of vcan network devices can be managed with the ip(8) tool:
|
|
|
|
- Create a virtual CAN network interface:
|
|
$ ip link add type vcan
|
|
|
|
- Create a virtual CAN network interface with a specific name 'vcan42':
|
|
$ ip link add dev vcan42 type vcan
|
|
|
|
- Remove a (virtual CAN) network interface 'vcan42':
|
|
$ ip link del vcan42
|
|
|
|
6.5 The CAN network device driver interface
|
|
|
|
The CAN network device driver interface provides a generic interface
|
|
to setup, configure and monitor CAN network devices. The user can then
|
|
configure the CAN device, like setting the bit-timing parameters, via
|
|
the netlink interface using the program "ip" from the "IPROUTE2"
|
|
utility suite. The following chapter describes briefly how to use it.
|
|
Furthermore, the interface uses a common data structure and exports a
|
|
set of common functions, which all real CAN network device drivers
|
|
should use. Please have a look to the SJA1000 or MSCAN driver to
|
|
understand how to use them. The name of the module is can-dev.ko.
|
|
|
|
6.5.1 Netlink interface to set/get devices properties
|
|
|
|
The CAN device must be configured via netlink interface. The supported
|
|
netlink message types are defined and briefly described in
|
|
"include/linux/can/netlink.h". CAN link support for the program "ip"
|
|
of the IPROUTE2 utility suite is available and it can be used as shown
|
|
below:
|
|
|
|
- Setting CAN device properties:
|
|
|
|
$ ip link set can0 type can help
|
|
Usage: ip link set DEVICE type can
|
|
[ bitrate BITRATE [ sample-point SAMPLE-POINT] ] |
|
|
[ tq TQ prop-seg PROP_SEG phase-seg1 PHASE-SEG1
|
|
phase-seg2 PHASE-SEG2 [ sjw SJW ] ]
|
|
|
|
[ loopback { on | off } ]
|
|
[ listen-only { on | off } ]
|
|
[ triple-sampling { on | off } ]
|
|
|
|
[ restart-ms TIME-MS ]
|
|
[ restart ]
|
|
|
|
Where: BITRATE := { 1..1000000 }
|
|
SAMPLE-POINT := { 0.000..0.999 }
|
|
TQ := { NUMBER }
|
|
PROP-SEG := { 1..8 }
|
|
PHASE-SEG1 := { 1..8 }
|
|
PHASE-SEG2 := { 1..8 }
|
|
SJW := { 1..4 }
|
|
RESTART-MS := { 0 | NUMBER }
|
|
|
|
- Display CAN device details and statistics:
|
|
|
|
$ ip -details -statistics link show can0
|
|
2: can0: <NOARP,UP,LOWER_UP,ECHO> mtu 16 qdisc pfifo_fast state UP qlen 10
|
|
link/can
|
|
can <TRIPLE-SAMPLING> state ERROR-ACTIVE restart-ms 100
|
|
bitrate 125000 sample_point 0.875
|
|
tq 125 prop-seg 6 phase-seg1 7 phase-seg2 2 sjw 1
|
|
sja1000: tseg1 1..16 tseg2 1..8 sjw 1..4 brp 1..64 brp-inc 1
|
|
clock 8000000
|
|
re-started bus-errors arbit-lost error-warn error-pass bus-off
|
|
41 17457 0 41 42 41
|
|
RX: bytes packets errors dropped overrun mcast
|
|
140859 17608 17457 0 0 0
|
|
TX: bytes packets errors dropped carrier collsns
|
|
861 112 0 41 0 0
|
|
|
|
More info to the above output:
|
|
|
|
"<TRIPLE-SAMPLING>"
|
|
Shows the list of selected CAN controller modes: LOOPBACK,
|
|
LISTEN-ONLY, or TRIPLE-SAMPLING.
|
|
|
|
"state ERROR-ACTIVE"
|
|
The current state of the CAN controller: "ERROR-ACTIVE",
|
|
"ERROR-WARNING", "ERROR-PASSIVE", "BUS-OFF" or "STOPPED"
|
|
|
|
"restart-ms 100"
|
|
Automatic restart delay time. If set to a non-zero value, a
|
|
restart of the CAN controller will be triggered automatically
|
|
in case of a bus-off condition after the specified delay time
|
|
in milliseconds. By default it's off.
|
|
|
|
"bitrate 125000 sample_point 0.875"
|
|
Shows the real bit-rate in bits/sec and the sample-point in the
|
|
range 0.000..0.999. If the calculation of bit-timing parameters
|
|
is enabled in the kernel (CONFIG_CAN_CALC_BITTIMING=y), the
|
|
bit-timing can be defined by setting the "bitrate" argument.
|
|
Optionally the "sample-point" can be specified. By default it's
|
|
0.000 assuming CIA-recommended sample-points.
|
|
|
|
"tq 125 prop-seg 6 phase-seg1 7 phase-seg2 2 sjw 1"
|
|
Shows the time quanta in ns, propagation segment, phase buffer
|
|
segment 1 and 2 and the synchronisation jump width in units of
|
|
tq. They allow to define the CAN bit-timing in a hardware
|
|
independent format as proposed by the Bosch CAN 2.0 spec (see
|
|
chapter 8 of http://www.semiconductors.bosch.de/pdf/can2spec.pdf).
|
|
|
|
"sja1000: tseg1 1..16 tseg2 1..8 sjw 1..4 brp 1..64 brp-inc 1
|
|
clock 8000000"
|
|
Shows the bit-timing constants of the CAN controller, here the
|
|
"sja1000". The minimum and maximum values of the time segment 1
|
|
and 2, the synchronisation jump width in units of tq, the
|
|
bitrate pre-scaler and the CAN system clock frequency in Hz.
|
|
These constants could be used for user-defined (non-standard)
|
|
bit-timing calculation algorithms in user-space.
|
|
|
|
"re-started bus-errors arbit-lost error-warn error-pass bus-off"
|
|
Shows the number of restarts, bus and arbitration lost errors,
|
|
and the state changes to the error-warning, error-passive and
|
|
bus-off state. RX overrun errors are listed in the "overrun"
|
|
field of the standard network statistics.
|
|
|
|
6.5.2 Setting the CAN bit-timing
|
|
|
|
The CAN bit-timing parameters can always be defined in a hardware
|
|
independent format as proposed in the Bosch CAN 2.0 specification
|
|
specifying the arguments "tq", "prop_seg", "phase_seg1", "phase_seg2"
|
|
and "sjw":
|
|
|
|
$ ip link set canX type can tq 125 prop-seg 6 \
|
|
phase-seg1 7 phase-seg2 2 sjw 1
|
|
|
|
If the kernel option CONFIG_CAN_CALC_BITTIMING is enabled, CIA
|
|
recommended CAN bit-timing parameters will be calculated if the bit-
|
|
rate is specified with the argument "bitrate":
|
|
|
|
$ ip link set canX type can bitrate 125000
|
|
|
|
Note that this works fine for the most common CAN controllers with
|
|
standard bit-rates but may *fail* for exotic bit-rates or CAN system
|
|
clock frequencies. Disabling CONFIG_CAN_CALC_BITTIMING saves some
|
|
space and allows user-space tools to solely determine and set the
|
|
bit-timing parameters. The CAN controller specific bit-timing
|
|
constants can be used for that purpose. They are listed by the
|
|
following command:
|
|
|
|
$ ip -details link show can0
|
|
...
|
|
sja1000: clock 8000000 tseg1 1..16 tseg2 1..8 sjw 1..4 brp 1..64 brp-inc 1
|
|
|
|
6.5.3 Starting and stopping the CAN network device
|
|
|
|
A CAN network device is started or stopped as usual with the command
|
|
"ifconfig canX up/down" or "ip link set canX up/down". Be aware that
|
|
you *must* define proper bit-timing parameters for real CAN devices
|
|
before you can start it to avoid error-prone default settings:
|
|
|
|
$ ip link set canX up type can bitrate 125000
|
|
|
|
A device may enter the "bus-off" state if too much errors occurred on
|
|
the CAN bus. Then no more messages are received or sent. An automatic
|
|
bus-off recovery can be enabled by setting the "restart-ms" to a
|
|
non-zero value, e.g.:
|
|
|
|
$ ip link set canX type can restart-ms 100
|
|
|
|
Alternatively, the application may realize the "bus-off" condition
|
|
by monitoring CAN error message frames and do a restart when
|
|
appropriate with the command:
|
|
|
|
$ ip link set canX type can restart
|
|
|
|
Note that a restart will also create a CAN error message frame (see
|
|
also chapter 3.4).
|
|
|
|
6.6 CAN FD (flexible data rate) driver support
|
|
|
|
CAN FD capable CAN controllers support two different bitrates for the
|
|
arbitration phase and the payload phase of the CAN FD frame. Therefore a
|
|
second bittiming has to be specified in order to enable the CAN FD bitrate.
|
|
|
|
Additionally CAN FD capable CAN controllers support up to 64 bytes of
|
|
payload. The representation of this length in can_frame.can_dlc and
|
|
canfd_frame.len for userspace applications and inside the Linux network
|
|
layer is a plain value from 0 .. 64 instead of the CAN 'data length code'.
|
|
The data length code was a 1:1 mapping to the payload length in the legacy
|
|
CAN frames anyway. The payload length to the bus-relevant DLC mapping is
|
|
only performed inside the CAN drivers, preferably with the helper
|
|
functions can_dlc2len() and can_len2dlc().
|
|
|
|
The CAN netdevice driver capabilities can be distinguished by the network
|
|
devices maximum transfer unit (MTU):
|
|
|
|
MTU = 16 (CAN_MTU) => sizeof(struct can_frame) => 'legacy' CAN device
|
|
MTU = 72 (CANFD_MTU) => sizeof(struct canfd_frame) => CAN FD capable device
|
|
|
|
The CAN device MTU can be retrieved e.g. with a SIOCGIFMTU ioctl() syscall.
|
|
N.B. CAN FD capable devices can also handle and send legacy CAN frames.
|
|
|
|
FIXME: Add details about the CAN FD controller configuration when available.
|
|
|
|
6.7 Supported CAN hardware
|
|
|
|
Please check the "Kconfig" file in "drivers/net/can" to get an actual
|
|
list of the support CAN hardware. On the Socket CAN project website
|
|
(see chapter 7) there might be further drivers available, also for
|
|
older kernel versions.
|
|
|
|
7. Socket CAN resources
|
|
-----------------------
|
|
|
|
You can find further resources for Socket CAN like user space tools,
|
|
support for old kernel versions, more drivers, mailing lists, etc.
|
|
at the BerliOS OSS project website for Socket CAN:
|
|
|
|
http://developer.berlios.de/projects/socketcan
|
|
|
|
If you have questions, bug fixes, etc., don't hesitate to post them to
|
|
the Socketcan-Users mailing list. But please search the archives first.
|
|
|
|
8. Credits
|
|
----------
|
|
|
|
Oliver Hartkopp (PF_CAN core, filters, drivers, bcm, SJA1000 driver)
|
|
Urs Thuermann (PF_CAN core, kernel integration, socket interfaces, raw, vcan)
|
|
Jan Kizka (RT-SocketCAN core, Socket-API reconciliation)
|
|
Wolfgang Grandegger (RT-SocketCAN core & drivers, Raw Socket-API reviews,
|
|
CAN device driver interface, MSCAN driver)
|
|
Robert Schwebel (design reviews, PTXdist integration)
|
|
Marc Kleine-Budde (design reviews, Kernel 2.6 cleanups, drivers)
|
|
Benedikt Spranger (reviews)
|
|
Thomas Gleixner (LKML reviews, coding style, posting hints)
|
|
Andrey Volkov (kernel subtree structure, ioctls, MSCAN driver)
|
|
Matthias Brukner (first SJA1000 CAN netdevice implementation Q2/2003)
|
|
Klaus Hitschler (PEAK driver integration)
|
|
Uwe Koppe (CAN netdevices with PF_PACKET approach)
|
|
Michael Schulze (driver layer loopback requirement, RT CAN drivers review)
|
|
Pavel Pisa (Bit-timing calculation)
|
|
Sascha Hauer (SJA1000 platform driver)
|
|
Sebastian Haas (SJA1000 EMS PCI driver)
|
|
Markus Plessing (SJA1000 EMS PCI driver)
|
|
Per Dalen (SJA1000 Kvaser PCI driver)
|
|
Sam Ravnborg (reviews, coding style, kbuild help)
|