summaryrefslogtreecommitdiffstats
path: root/Documentation/networking/can.txt
diff options
context:
space:
mode:
Diffstat (limited to 'Documentation/networking/can.txt')
-rw-r--r--Documentation/networking/can.txt836
1 files changed, 0 insertions, 836 deletions
diff --git a/Documentation/networking/can.txt b/Documentation/networking/can.txt
deleted file mode 100644
index ac29539..0000000
--- a/Documentation/networking/can.txt
+++ /dev/null
@@ -1,836 +0,0 @@
-============================================================================
-
-can.txt
-
-Readme file for the Controller Area Network Protocol Family (aka Socket CAN)
-
-This file contains
-
- 1 Overview / What is Socket CAN
-
- 2 Motivation / Why using the socket API
-
- 3 Socket CAN concept
- 3.1 receive lists
- 3.2 local loopback of sent frames
- 3.3 network security issues (capabilities)
- 3.4 network problem notifications
-
- 4 How to use Socket CAN
- 4.1 RAW protocol sockets with can_filters (SOCK_RAW)
- 4.1.1 RAW socket option CAN_RAW_FILTER
- 4.1.2 RAW socket option CAN_RAW_ERR_FILTER
- 4.1.3 RAW socket option CAN_RAW_LOOPBACK
- 4.1.4 RAW socket option CAN_RAW_RECV_OWN_MSGS
- 4.1.5 RAW socket returned message flags
- 4.2 Broadcast Manager protocol sockets (SOCK_DGRAM)
- 4.3 connected transport protocols (SOCK_SEQPACKET)
- 4.4 unconnected transport protocols (SOCK_DGRAM)
-
- 5 Socket CAN core module
- 5.1 can.ko module params
- 5.2 procfs content
- 5.3 writing own CAN protocol modules
-
- 6 CAN network drivers
- 6.1 general settings
- 6.2 local loopback of sent frames
- 6.3 CAN controller hardware filters
- 6.4 The virtual CAN driver (vcan)
- 6.5 The CAN network device driver interface
- 6.5.1 Netlink interface to set/get devices properties
- 6.5.2 Setting the CAN bit-timing
- 6.5.3 Starting and stopping the CAN network device
- 6.6 supported CAN hardware
-
- 7 Socket CAN resources
-
- 8 Credits
-
-============================================================================
-
-1. Overview / What is Socket CAN
---------------------------------
-
-The socketcan package is an implementation of CAN protocols
-(Controller Area Network) for Linux. CAN is a networking technology
-which has widespread use in automation, embedded devices, and
-automotive fields. While there have been other CAN implementations
-for Linux based on character devices, Socket CAN uses the Berkeley
-socket API, the Linux network stack and implements the CAN device
-drivers as network interfaces. The CAN socket API has been designed
-as similar as possible to the TCP/IP protocols to allow programmers,
-familiar with network programming, to easily learn how to use CAN
-sockets.
-
-2. Motivation / Why using the socket API
-----------------------------------------
-
-There have been CAN implementations for Linux before Socket CAN so the
-question arises, why we have started another project. Most existing
-implementations come as a device driver for some CAN hardware, they
-are based on character devices and provide comparatively little
-functionality. Usually, there is only a hardware-specific device
-driver which provides a character device interface to send and
-receive raw CAN frames, directly to/from the controller hardware.
-Queueing of frames and higher-level transport protocols like ISO-TP
-have to be implemented in user space applications. Also, most
-character-device implementations support only one single process to
-open the device at a time, similar to a serial interface. Exchanging
-the CAN controller requires employment of another device driver and
-often the need for adaption of large parts of the application to the
-new driver's API.
-
-Socket CAN was designed to overcome all of these limitations. A new
-protocol family has been implemented which provides a socket interface
-to user space applications and which builds upon the Linux network
-layer, so to use all of the provided queueing functionality. A device
-driver for CAN controller hardware registers itself with the Linux
-network layer as a network device, so that CAN frames from the
-controller can be passed up to the network layer and on to the CAN
-protocol family module and also vice-versa. Also, the protocol family
-module provides an API for transport protocol modules to register, so
-that any number of transport protocols can be loaded or unloaded
-dynamically. In fact, the can core module alone does not provide any
-protocol and cannot be used without loading at least one additional
-protocol module. Multiple sockets can be opened at the same time,
-on different or the same protocol module and they can listen/send
-frames on different or the same CAN IDs. Several sockets listening on
-the same interface for frames with the same CAN ID are all passed the
-same received matching CAN frames. An application wishing to
-communicate using a specific transport protocol, e.g. ISO-TP, just
-selects that protocol when opening the socket, and then can read and
-write application data byte streams, without having to deal with
-CAN-IDs, frames, etc.
-
-Similar functionality visible from user-space could be provided by a
-character device, too, but this would lead to a technically inelegant
-solution for a couple of reasons:
-
-* Intricate usage. Instead of passing a protocol argument to
- socket(2) and using bind(2) to select a CAN interface and CAN ID, an
- application would have to do all these operations using ioctl(2)s.
-
-* Code duplication. A character device cannot make use of the Linux
- network queueing code, so all that code would have to be duplicated
- for CAN networking.
-
-* Abstraction. In most existing character-device implementations, the
- hardware-specific device driver for a CAN controller directly
- provides the character device for the application to work with.
- This is at least very unusual in Unix systems for both, char and
- block devices. For example you don't have a character device for a
- certain UART of a serial interface, a certain sound chip in your
- computer, a SCSI or IDE controller providing access to your hard
- disk or tape streamer device. Instead, you have abstraction layers
- which provide a unified character or block device interface to the
- application on the one hand, and a interface for hardware-specific
- device drivers on the other hand. These abstractions are provided
- by subsystems like the tty layer, the audio subsystem or the SCSI
- and IDE subsystems for the devices mentioned above.
-
- The easiest way to implement a CAN device driver is as a character
- device without such a (complete) abstraction layer, as is done by most
- existing drivers. The right way, however, would be to add such a
- layer with all the functionality like registering for certain CAN
- IDs, supporting several open file descriptors and (de)multiplexing
- CAN frames between them, (sophisticated) queueing of CAN frames, and
- providing an API for device drivers to register with. However, then
- it would be no more difficult, or may be even easier, to use the
- networking framework provided by the Linux kernel, and this is what
- Socket CAN does.
-
- The use of the networking framework of the Linux kernel is just the
- natural and most appropriate way to implement CAN for Linux.
-
-3. Socket CAN concept
----------------------
-
- As described in chapter 2 it is the main goal of Socket CAN to
- provide a socket interface to user space applications which builds
- upon the Linux network layer. In contrast to the commonly known
- TCP/IP and ethernet networking, the CAN bus is a broadcast-only(!)
- medium that has no MAC-layer addressing like ethernet. The CAN-identifier
- (can_id) is used for arbitration on the CAN-bus. Therefore the CAN-IDs
- have to be chosen uniquely on the bus. When designing a CAN-ECU
- network the CAN-IDs are mapped to be sent by a specific ECU.
- For this reason a CAN-ID can be treated best as a kind of source address.
-
- 3.1 receive lists
-
- The network transparent access of multiple applications leads to the
- problem that different applications may be interested in the same
- CAN-IDs from the same CAN network interface. The Socket CAN core
- module - which implements the protocol family CAN - provides several
- high efficient receive lists for this reason. If e.g. a user space
- application opens a CAN RAW socket, the raw protocol module itself
- requests the (range of) CAN-IDs from the Socket CAN core that are
- requested by the user. The subscription and unsubscription of
- CAN-IDs can be done for specific CAN interfaces or for all(!) known
- CAN interfaces with the can_rx_(un)register() functions provided to
- CAN protocol modules by the SocketCAN core (see chapter 5).
- To optimize the CPU usage at runtime the receive lists are split up
- into several specific lists per device that match the requested
- filter complexity for a given use-case.
-
- 3.2 local loopback of sent frames
-
- As known from other networking concepts the data exchanging
- applications may run on the same or different nodes without any
- change (except for the according addressing information):
-
- ___ ___ ___ _______ ___
- | _ | | _ | | _ | | _ _ | | _ |
- ||A|| ||B|| ||C|| ||A| |B|| ||C||
- |___| |___| |___| |_______| |___|
- | | | | |
- -----------------(1)- CAN bus -(2)---------------
-
- To ensure that application A receives the same information in the
- example (2) as it would receive in example (1) there is need for
- some kind of local loopback of the sent CAN frames on the appropriate
- node.
-
- The Linux network devices (by default) just can handle the
- transmission and reception of media dependent frames. Due to the
- arbitration on the CAN bus the transmission of a low prio CAN-ID
- may be delayed by the reception of a high prio CAN frame. To
- reflect the correct* traffic on the node the loopback of the sent
- data has to be performed right after a successful transmission. If
- the CAN network interface is not capable of performing the loopback for
- some reason the SocketCAN core can do this task as a fallback solution.
- See chapter 6.2 for details (recommended).
-
- The loopback functionality is enabled by default to reflect standard
- networking behaviour for CAN applications. Due to some requests from
- the RT-SocketCAN group the loopback optionally may be disabled for each
- separate socket. See sockopts from the CAN RAW sockets in chapter 4.1.
-
- * = you really like to have this when you're running analyser tools
- like 'candump' or 'cansniffer' on the (same) node.
-
- 3.3 network security issues (capabilities)
-
- The Controller Area Network is a local field bus transmitting only
- broadcast messages without any routing and security concepts.
- In the majority of cases the user application has to deal with
- raw CAN frames. Therefore it might be reasonable NOT to restrict
- the CAN access only to the user root, as known from other networks.
- Since the currently implemented CAN_RAW and CAN_BCM sockets can only
- send and receive frames to/from CAN interfaces it does not affect
- security of others networks to allow all users to access the CAN.
- To enable non-root users to access CAN_RAW and CAN_BCM protocol
- sockets the Kconfig options CAN_RAW_USER and/or CAN_BCM_USER may be
- selected at kernel compile time.
-
- 3.4 network problem notifications
-
- The use of the CAN bus may lead to several problems on the physical
- and media access control layer. Detecting and logging of these lower
- layer problems is a vital requirement for CAN users to identify
- hardware issues on the physical transceiver layer as well as
- arbitration problems and error frames caused by the different
- ECUs. The occurrence of detected errors are important for diagnosis
- and have to be logged together with the exact timestamp. For this
- reason the CAN interface driver can generate so called Error Frames
- that can optionally be passed to the user application in the same
- way as other CAN frames. Whenever an error on the physical layer
- or the MAC layer is detected (e.g. by the CAN controller) the driver
- creates an appropriate error frame. Error frames can be requested by
- the user application using the common CAN filter mechanisms. Inside
- this filter definition the (interested) type of errors may be
- selected. The reception of error frames is disabled by default.
- The format of the CAN error frame is briefly described in the Linux
- header file "include/linux/can/error.h".
-
-4. How to use Socket CAN
-------------------------
-
- Like TCP/IP, you first need to open a socket for communicating over a
- CAN network. Since Socket CAN implements a new protocol family, you
- need to pass PF_CAN as the first argument to the socket(2) system
- call. Currently, there are two CAN protocols to choose from, the raw
- socket protocol and the broadcast manager (BCM). So to open a socket,
- you would write
-
- s = socket(PF_CAN, SOCK_RAW, CAN_RAW);
-
- and
-
- s = socket(PF_CAN, SOCK_DGRAM, CAN_BCM);
-
- respectively. After the successful creation of the socket, you would
- normally use the bind(2) system call to bind the socket to a CAN
- interface (which is different from TCP/IP due to different addressing
- - see chapter 3). After binding (CAN_RAW) or connecting (CAN_BCM)
- the socket, you can read(2) and write(2) from/to the socket or use
- send(2), sendto(2), sendmsg(2) and the recv* counterpart operations
- on the socket as usual. There are also CAN specific socket options
- described below.
-
- The basic CAN frame structure and the sockaddr structure are defined
- in include/linux/can.h:
-
- struct can_frame {
- canid_t can_id; /* 32 bit CAN_ID + EFF/RTR/ERR flags */
- __u8 can_dlc; /* data length code: 0 .. 8 */
- __u8 data[8] __attribute__((aligned(8)));
- };
-
- The alignment of the (linear) payload data[] to a 64bit boundary
- allows the user to define own structs and unions to easily access the
- CAN payload. There is no given byteorder on the CAN bus by
- default. A read(2) system call on a CAN_RAW socket transfers a
- struct can_frame to the user space.
-
- The sockaddr_can structure has an interface index like the
- PF_PACKET socket, that also binds to a specific interface:
-
- struct sockaddr_can {
- sa_family_t can_family;
- int can_ifindex;
- union {
- /* transport protocol class address info (e.g. ISOTP) */
- struct { canid_t rx_id, tx_id; } tp;
-
- /* reserved for future CAN protocols address information */
- } can_addr;
- };
-
- To determine the interface index an appropriate ioctl() has to
- be used (example for CAN_RAW sockets without error checking):
-
- int s;
- struct sockaddr_can addr;
- struct ifreq ifr;
-
- s = socket(PF_CAN, SOCK_RAW, CAN_RAW);
-
- strcpy(ifr.ifr_name, "can0" );
- ioctl(s, SIOCGIFINDEX, &ifr);
-
- addr.can_family = AF_CAN;
- addr.can_ifindex = ifr.ifr_ifindex;
-
- bind(s, (struct sockaddr *)&addr, sizeof(addr));
-
- (..)
-
- To bind a socket to all(!) CAN interfaces the interface index must
- be 0 (zero). In this case the socket receives CAN frames from every
- enabled CAN interface. To determine the originating CAN interface
- the system call recvfrom(2) may be used instead of read(2). To send
- on a socket that is bound to 'any' interface sendto(2) is needed to
- specify the outgoing interface.
-
- Reading CAN frames from a bound CAN_RAW socket (see above) consists
- of reading a struct can_frame:
-
- struct can_frame frame;
-
- nbytes = read(s, &frame, sizeof(struct can_frame));
-
- if (nbytes < 0) {
- perror("can raw socket read");
- return 1;
- }
-
- /* paranoid check ... */
- if (nbytes < sizeof(struct can_frame)) {
- fprintf(stderr, "read: incomplete CAN frame\n");
- return 1;
- }
-
- /* do something with the received CAN frame */
-
- Writing CAN frames can be done similarly, with the write(2) system call:
-
- nbytes = write(s, &frame, sizeof(struct can_frame));
-
- When the CAN interface is bound to 'any' existing CAN interface
- (addr.can_ifindex = 0) it is recommended to use recvfrom(2) if the
- information about the originating CAN interface is needed:
-
- struct sockaddr_can addr;
- struct ifreq ifr;
- socklen_t len = sizeof(addr);
- struct can_frame frame;
-
- nbytes = recvfrom(s, &frame, sizeof(struct can_frame),
- 0, (struct sockaddr*)&addr, &len);
-
- /* get interface name of the received CAN frame */
- ifr.ifr_ifindex = addr.can_ifindex;
- ioctl(s, SIOCGIFNAME, &ifr);
- printf("Received a CAN frame from interface %s", ifr.ifr_name);
-
- To write CAN frames on sockets bound to 'any' CAN interface the
- outgoing interface has to be defined certainly.
-
- strcpy(ifr.ifr_name, "can0");
- ioctl(s, SIOCGIFINDEX, &ifr);
- addr.can_ifindex = ifr.ifr_ifindex;
- addr.can_family = AF_CAN;
-
- nbytes = sendto(s, &frame, sizeof(struct can_frame),
- 0, (struct sockaddr*)&addr, sizeof(addr));
-
- 4.1 RAW protocol sockets with can_filters (SOCK_RAW)
-
- Using CAN_RAW sockets is extensively comparable to the commonly
- known access to CAN character devices. To meet the new possibilities
- provided by the multi user SocketCAN approach, some reasonable
- defaults are set at RAW socket binding time:
-
- - The filters are set to exactly one filter receiving everything
- - The socket only receives valid data frames (=> no error frames)
- - The loopback of sent CAN frames is enabled (see chapter 3.2)
- - The socket does not receive its own sent frames (in loopback mode)
-
- These default settings may be changed before or after binding the socket.
- To use the referenced definitions of the socket options for CAN_RAW
- sockets, include <linux/can/raw.h>.
-
- 4.1.1 RAW socket option CAN_RAW_FILTER
-
- The reception of CAN frames using CAN_RAW sockets can be controlled
- by defining 0 .. n filters with the CAN_RAW_FILTER socket option.
-
- The CAN filter structure is defined in include/linux/can.h:
-
- struct can_filter {
- 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 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 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)
- 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 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 = sizeof(struct can_frame);
-
- The struct can_frame is the payload of each socket buffer 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 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 frame (see also
- chapter 3.4).
-
- 6.6 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)