1 ============================================================================
5 Readme file for the Controller Area Network Protocol Family (aka Socket CAN)
9 1 Overview / What is Socket CAN
11 2 Motivation / Why using the socket API
15 3.2 local loopback of sent frames
16 3.3 network security issues (capabilities)
17 3.4 network problem notifications
19 4 How to use Socket CAN
20 4.1 RAW protocol sockets with can_filters (SOCK_RAW)
21 4.1.1 RAW socket option CAN_RAW_FILTER
22 4.1.2 RAW socket option CAN_RAW_ERR_FILTER
23 4.1.3 RAW socket option CAN_RAW_LOOPBACK
24 4.1.4 RAW socket option CAN_RAW_RECV_OWN_MSGS
25 4.2 Broadcast Manager protocol sockets (SOCK_DGRAM)
26 4.3 connected transport protocols (SOCK_SEQPACKET)
27 4.4 unconnected transport protocols (SOCK_DGRAM)
30 5 Socket CAN core module
31 5.1 can.ko module params
33 5.3 writing own CAN protocol modules
37 6.2 local loopback of sent frames
38 6.3 CAN controller hardware filters
39 6.4 The virtual CAN driver (vcan)
40 6.5 The CAN network device driver interface
41 6.5.1 Netlink interface to set/get devices properties
42 6.5.2 Setting the CAN bit-timing
43 6.5.3 Starting and stopping the CAN network device
44 6.6 supported CAN hardware
46 7 Socket CAN resources
50 ============================================================================
52 1. Overview / What is Socket CAN
53 --------------------------------
55 The socketcan package is an implementation of CAN protocols
56 (Controller Area Network) for Linux. CAN is a networking technology
57 which has widespread use in automation, embedded devices, and
58 automotive fields. While there have been other CAN implementations
59 for Linux based on character devices, Socket CAN uses the Berkeley
60 socket API, the Linux network stack and implements the CAN device
61 drivers as network interfaces. The CAN socket API has been designed
62 as similar as possible to the TCP/IP protocols to allow programmers,
63 familiar with network programming, to easily learn how to use CAN
66 2. Motivation / Why using the socket API
67 ----------------------------------------
69 There have been CAN implementations for Linux before Socket CAN so the
70 question arises, why we have started another project. Most existing
71 implementations come as a device driver for some CAN hardware, they
72 are based on character devices and provide comparatively little
73 functionality. Usually, there is only a hardware-specific device
74 driver which provides a character device interface to send and
75 receive raw CAN frames, directly to/from the controller hardware.
76 Queueing of frames and higher-level transport protocols like ISO-TP
77 have to be implemented in user space applications. Also, most
78 character-device implementations support only one single process to
79 open the device at a time, similar to a serial interface. Exchanging
80 the CAN controller requires employment of another device driver and
81 often the need for adaption of large parts of the application to the
84 Socket CAN was designed to overcome all of these limitations. A new
85 protocol family has been implemented which provides a socket interface
86 to user space applications and which builds upon the Linux network
87 layer, so to use all of the provided queueing functionality. A device
88 driver for CAN controller hardware registers itself with the Linux
89 network layer as a network device, so that CAN frames from the
90 controller can be passed up to the network layer and on to the CAN
91 protocol family module and also vice-versa. Also, the protocol family
92 module provides an API for transport protocol modules to register, so
93 that any number of transport protocols can be loaded or unloaded
94 dynamically. In fact, the can core module alone does not provide any
95 protocol and cannot be used without loading at least one additional
96 protocol module. Multiple sockets can be opened at the same time,
97 on different or the same protocol module and they can listen/send
98 frames on different or the same CAN IDs. Several sockets listening on
99 the same interface for frames with the same CAN ID are all passed the
100 same received matching CAN frames. An application wishing to
101 communicate using a specific transport protocol, e.g. ISO-TP, just
102 selects that protocol when opening the socket, and then can read and
103 write application data byte streams, without having to deal with
104 CAN-IDs, frames, etc.
106 Similar functionality visible from user-space could be provided by a
107 character device, too, but this would lead to a technically inelegant
108 solution for a couple of reasons:
110 * Intricate usage. Instead of passing a protocol argument to
111 socket(2) and using bind(2) to select a CAN interface and CAN ID, an
112 application would have to do all these operations using ioctl(2)s.
114 * Code duplication. A character device cannot make use of the Linux
115 network queueing code, so all that code would have to be duplicated
118 * Abstraction. In most existing character-device implementations, the
119 hardware-specific device driver for a CAN controller directly
120 provides the character device for the application to work with.
121 This is at least very unusual in Unix systems for both, char and
122 block devices. For example you don't have a character device for a
123 certain UART of a serial interface, a certain sound chip in your
124 computer, a SCSI or IDE controller providing access to your hard
125 disk or tape streamer device. Instead, you have abstraction layers
126 which provide a unified character or block device interface to the
127 application on the one hand, and a interface for hardware-specific
128 device drivers on the other hand. These abstractions are provided
129 by subsystems like the tty layer, the audio subsystem or the SCSI
130 and IDE subsystems for the devices mentioned above.
132 The easiest way to implement a CAN device driver is as a character
133 device without such a (complete) abstraction layer, as is done by most
134 existing drivers. The right way, however, would be to add such a
135 layer with all the functionality like registering for certain CAN
136 IDs, supporting several open file descriptors and (de)multiplexing
137 CAN frames between them, (sophisticated) queueing of CAN frames, and
138 providing an API for device drivers to register with. However, then
139 it would be no more difficult, or may be even easier, to use the
140 networking framework provided by the Linux kernel, and this is what
143 The use of the networking framework of the Linux kernel is just the
144 natural and most appropriate way to implement CAN for Linux.
146 3. Socket CAN concept
147 ---------------------
149 As described in chapter 2 it is the main goal of Socket CAN to
150 provide a socket interface to user space applications which builds
151 upon the Linux network layer. In contrast to the commonly known
152 TCP/IP and ethernet networking, the CAN bus is a broadcast-only(!)
153 medium that has no MAC-layer addressing like ethernet. The CAN-identifier
154 (can_id) is used for arbitration on the CAN-bus. Therefore the CAN-IDs
155 have to be chosen uniquely on the bus. When designing a CAN-ECU
156 network the CAN-IDs are mapped to be sent by a specific ECU.
157 For this reason a CAN-ID can be treated best as a kind of source address.
161 The network transparent access of multiple applications leads to the
162 problem that different applications may be interested in the same
163 CAN-IDs from the same CAN network interface. The Socket CAN core
164 module - which implements the protocol family CAN - provides several
165 high efficient receive lists for this reason. If e.g. a user space
166 application opens a CAN RAW socket, the raw protocol module itself
167 requests the (range of) CAN-IDs from the Socket CAN core that are
168 requested by the user. The subscription and unsubscription of
169 CAN-IDs can be done for specific CAN interfaces or for all(!) known
170 CAN interfaces with the can_rx_(un)register() functions provided to
171 CAN protocol modules by the SocketCAN core (see chapter 5).
172 To optimize the CPU usage at runtime the receive lists are split up
173 into several specific lists per device that match the requested
174 filter complexity for a given use-case.
176 3.2 local loopback of sent frames
178 As known from other networking concepts the data exchanging
179 applications may run on the same or different nodes without any
180 change (except for the according addressing information):
182 ___ ___ ___ _______ ___
183 | _ | | _ | | _ | | _ _ | | _ |
184 ||A|| ||B|| ||C|| ||A| |B|| ||C||
185 |___| |___| |___| |_______| |___|
187 -----------------(1)- CAN bus -(2)---------------
189 To ensure that application A receives the same information in the
190 example (2) as it would receive in example (1) there is need for
191 some kind of local loopback of the sent CAN frames on the appropriate
194 The Linux network devices (by default) just can handle the
195 transmission and reception of media dependent frames. Due to the
196 arbitration on the CAN bus the transmission of a low prio CAN-ID
197 may be delayed by the reception of a high prio CAN frame. To
198 reflect the correct* traffic on the node the loopback of the sent
199 data has to be performed right after a successful transmission. If
200 the CAN network interface is not capable of performing the loopback for
201 some reason the SocketCAN core can do this task as a fallback solution.
202 See chapter 6.2 for details (recommended).
204 The loopback functionality is enabled by default to reflect standard
205 networking behaviour for CAN applications. Due to some requests from
206 the RT-SocketCAN group the loopback optionally may be disabled for each
207 separate socket. See sockopts from the CAN RAW sockets in chapter 4.1.
209 * = you really like to have this when you're running analyser tools
210 like 'candump' or 'cansniffer' on the (same) node.
212 3.3 network security issues (capabilities)
214 The Controller Area Network is a local field bus transmitting only
215 broadcast messages without any routing and security concepts.
216 In the majority of cases the user application has to deal with
217 raw CAN frames. Therefore it might be reasonable NOT to restrict
218 the CAN access only to the user root, as known from other networks.
219 Since the currently implemented CAN_RAW and CAN_BCM sockets can only
220 send and receive frames to/from CAN interfaces it does not affect
221 security of others networks to allow all users to access the CAN.
222 To enable non-root users to access CAN_RAW and CAN_BCM protocol
223 sockets the Kconfig options CAN_RAW_USER and/or CAN_BCM_USER may be
224 selected at kernel compile time.
226 3.4 network problem notifications
228 The use of the CAN bus may lead to several problems on the physical
229 and media access control layer. Detecting and logging of these lower
230 layer problems is a vital requirement for CAN users to identify
231 hardware issues on the physical transceiver layer as well as
232 arbitration problems and error frames caused by the different
233 ECUs. The occurrence of detected errors are important for diagnosis
234 and have to be logged together with the exact timestamp. For this
235 reason the CAN interface driver can generate so called Error Frames
236 that can optionally be passed to the user application in the same
237 way as other CAN frames. Whenever an error on the physical layer
238 or the MAC layer is detected (e.g. by the CAN controller) the driver
239 creates an appropriate error frame. Error frames can be requested by
240 the user application using the common CAN filter mechanisms. Inside
241 this filter definition the (interested) type of errors may be
242 selected. The reception of error frames is disabled by default.
243 The format of the CAN error frame is briefly decribed in the Linux
244 header file "include/linux/can/error.h".
246 4. How to use Socket CAN
247 ------------------------
249 Like TCP/IP, you first need to open a socket for communicating over a
250 CAN network. Since Socket CAN implements a new protocol family, you
251 need to pass PF_CAN as the first argument to the socket(2) system
252 call. Currently, there are two CAN protocols to choose from, the raw
253 socket protocol and the broadcast manager (BCM). So to open a socket,
256 s = socket(PF_CAN, SOCK_RAW, CAN_RAW);
260 s = socket(PF_CAN, SOCK_DGRAM, CAN_BCM);
262 respectively. After the successful creation of the socket, you would
263 normally use the bind(2) system call to bind the socket to a CAN
264 interface (which is different from TCP/IP due to different addressing
265 - see chapter 3). After binding (CAN_RAW) or connecting (CAN_BCM)
266 the socket, you can read(2) and write(2) from/to the socket or use
267 send(2), sendto(2), sendmsg(2) and the recv* counterpart operations
268 on the socket as usual. There are also CAN specific socket options
271 The basic CAN frame structure and the sockaddr structure are defined
272 in include/linux/can.h:
275 canid_t can_id; /* 32 bit CAN_ID + EFF/RTR/ERR flags */
276 __u8 can_dlc; /* data length code: 0 .. 8 */
277 __u8 data[8] __attribute__((aligned(8)));
280 The alignment of the (linear) payload data[] to a 64bit boundary
281 allows the user to define own structs and unions to easily access the
282 CAN payload. There is no given byteorder on the CAN bus by
283 default. A read(2) system call on a CAN_RAW socket transfers a
284 struct can_frame to the user space.
286 The sockaddr_can structure has an interface index like the
287 PF_PACKET socket, that also binds to a specific interface:
289 struct sockaddr_can {
290 sa_family_t can_family;
293 /* transport protocol class address info (e.g. ISOTP) */
294 struct { canid_t rx_id, tx_id; } tp;
296 /* reserved for future CAN protocols address information */
300 To determine the interface index an appropriate ioctl() has to
301 be used (example for CAN_RAW sockets without error checking):
304 struct sockaddr_can addr;
307 s = socket(PF_CAN, SOCK_RAW, CAN_RAW);
309 strcpy(ifr.ifr_name, "can0" );
310 ioctl(s, SIOCGIFINDEX, &ifr);
312 addr.can_family = AF_CAN;
313 addr.can_ifindex = ifr.ifr_ifindex;
315 bind(s, (struct sockaddr *)&addr, sizeof(addr));
319 To bind a socket to all(!) CAN interfaces the interface index must
320 be 0 (zero). In this case the socket receives CAN frames from every
321 enabled CAN interface. To determine the originating CAN interface
322 the system call recvfrom(2) may be used instead of read(2). To send
323 on a socket that is bound to 'any' interface sendto(2) is needed to
324 specify the outgoing interface.
326 Reading CAN frames from a bound CAN_RAW socket (see above) consists
327 of reading a struct can_frame:
329 struct can_frame frame;
331 nbytes = read(s, &frame, sizeof(struct can_frame));
334 perror("can raw socket read");
338 /* paranoid check ... */
339 if (nbytes < sizeof(struct can_frame)) {
340 fprintf(stderr, "read: incomplete CAN frame\n");
344 /* do something with the received CAN frame */
346 Writing CAN frames can be done similarly, with the write(2) system call:
348 nbytes = write(s, &frame, sizeof(struct can_frame));
350 When the CAN interface is bound to 'any' existing CAN interface
351 (addr.can_ifindex = 0) it is recommended to use recvfrom(2) if the
352 information about the originating CAN interface is needed:
354 struct sockaddr_can addr;
356 socklen_t len = sizeof(addr);
357 struct can_frame frame;
359 nbytes = recvfrom(s, &frame, sizeof(struct can_frame),
360 0, (struct sockaddr*)&addr, &len);
362 /* get interface name of the received CAN frame */
363 ifr.ifr_ifindex = addr.can_ifindex;
364 ioctl(s, SIOCGIFNAME, &ifr);
365 printf("Received a CAN frame from interface %s", ifr.ifr_name);
367 To write CAN frames on sockets bound to 'any' CAN interface the
368 outgoing interface has to be defined certainly.
370 strcpy(ifr.ifr_name, "can0");
371 ioctl(s, SIOCGIFINDEX, &ifr);
372 addr.can_ifindex = ifr.ifr_ifindex;
373 addr.can_family = AF_CAN;
375 nbytes = sendto(s, &frame, sizeof(struct can_frame),
376 0, (struct sockaddr*)&addr, sizeof(addr));
378 4.1 RAW protocol sockets with can_filters (SOCK_RAW)
380 Using CAN_RAW sockets is extensively comparable to the commonly
381 known access to CAN character devices. To meet the new possibilities
382 provided by the multi user SocketCAN approach, some reasonable
383 defaults are set at RAW socket binding time:
385 - The filters are set to exactly one filter receiving everything
386 - The socket only receives valid data frames (=> no error frames)
387 - The loopback of sent CAN frames is enabled (see chapter 3.2)
388 - The socket does not receive its own sent frames (in loopback mode)
390 These default settings may be changed before or after binding the socket.
391 To use the referenced definitions of the socket options for CAN_RAW
392 sockets, include <linux/can/raw.h>.
394 4.1.1 RAW socket option CAN_RAW_FILTER
396 The reception of CAN frames using CAN_RAW sockets can be controlled
397 by defining 0 .. n filters with the CAN_RAW_FILTER socket option.
399 The CAN filter structure is defined in include/linux/can.h:
406 A filter matches, when
408 <received_can_id> & mask == can_id & mask
410 which is analogous to known CAN controllers hardware filter semantics.
411 The filter can be inverted in this semantic, when the CAN_INV_FILTER
412 bit is set in can_id element of the can_filter structure. In
413 contrast to CAN controller hardware filters the user may set 0 .. n
414 receive filters for each open socket separately:
416 struct can_filter rfilter[2];
418 rfilter[0].can_id = 0x123;
419 rfilter[0].can_mask = CAN_SFF_MASK;
420 rfilter[1].can_id = 0x200;
421 rfilter[1].can_mask = 0x700;
423 setsockopt(s, SOL_CAN_RAW, CAN_RAW_FILTER, &rfilter, sizeof(rfilter));
425 To disable the reception of CAN frames on the selected CAN_RAW socket:
427 setsockopt(s, SOL_CAN_RAW, CAN_RAW_FILTER, NULL, 0);
429 To set the filters to zero filters is quite obsolete as not read
430 data causes the raw socket to discard the received CAN frames. But
431 having this 'send only' use-case we may remove the receive list in the
432 Kernel to save a little (really a very little!) CPU usage.
434 4.1.2 RAW socket option CAN_RAW_ERR_FILTER
436 As described in chapter 3.4 the CAN interface driver can generate so
437 called Error Frames that can optionally be passed to the user
438 application in the same way as other CAN frames. The possible
439 errors are divided into different error classes that may be filtered
440 using the appropriate error mask. To register for every possible
441 error condition CAN_ERR_MASK can be used as value for the error mask.
442 The values for the error mask are defined in linux/can/error.h .
444 can_err_mask_t err_mask = ( CAN_ERR_TX_TIMEOUT | CAN_ERR_BUSOFF );
446 setsockopt(s, SOL_CAN_RAW, CAN_RAW_ERR_FILTER,
447 &err_mask, sizeof(err_mask));
449 4.1.3 RAW socket option CAN_RAW_LOOPBACK
451 To meet multi user needs the local loopback is enabled by default
452 (see chapter 3.2 for details). But in some embedded use-cases
453 (e.g. when only one application uses the CAN bus) this loopback
454 functionality can be disabled (separately for each socket):
456 int loopback = 0; /* 0 = disabled, 1 = enabled (default) */
458 setsockopt(s, SOL_CAN_RAW, CAN_RAW_LOOPBACK, &loopback, sizeof(loopback));
460 4.1.4 RAW socket option CAN_RAW_RECV_OWN_MSGS
462 When the local loopback is enabled, all the sent CAN frames are
463 looped back to the open CAN sockets that registered for the CAN
464 frames' CAN-ID on this given interface to meet the multi user
465 needs. The reception of the CAN frames on the same socket that was
466 sending the CAN frame is assumed to be unwanted and therefore
467 disabled by default. This default behaviour may be changed on
470 int recv_own_msgs = 1; /* 0 = disabled (default), 1 = enabled */
472 setsockopt(s, SOL_CAN_RAW, CAN_RAW_RECV_OWN_MSGS,
473 &recv_own_msgs, sizeof(recv_own_msgs));
475 4.2 Broadcast Manager protocol sockets (SOCK_DGRAM)
476 4.3 connected transport protocols (SOCK_SEQPACKET)
477 4.4 unconnected transport protocols (SOCK_DGRAM)
481 For applications in the CAN environment it is often of interest an
482 accurate timestamp of the instant a message from CAN bus has been received.
483 Such a timestamp can be read with ioctl(2) after reading a message from
487 ioctl(s, SIOCGSTAMP, &tv);
489 The timestamp on Linux has a resolution of one microsecond and it is set
490 automatically at the reception of a CAN frame.
492 Alternatively the timestamp can be obtained as a control message (cmsg) using
493 the recvmsg() system call. After enabling the timestamps in the cmsg's by
495 const int timestamp = 1;
496 setsockopt(s, SOL_SOCKET, SO_TIMESTAMP, ×tamp, sizeof(timestamp));
498 the data structures filled by recvmsg() need to be parsed for
499 cmsg->cmsg_type == SO_TIMESTAMP to get the timestamp. See cmsg() manpage.
501 5. Socket CAN core module
502 -------------------------
504 The Socket CAN core module implements the protocol family
505 PF_CAN. CAN protocol modules are loaded by the core module at
506 runtime. The core module provides an interface for CAN protocol
507 modules to subscribe needed CAN IDs (see chapter 3.1).
509 5.1 can.ko module params
511 - stats_timer: To calculate the Socket CAN core statistics
512 (e.g. current/maximum frames per second) this 1 second timer is
513 invoked at can.ko module start time by default. This timer can be
514 disabled by using stattimer=0 on the module commandline.
516 - debug: (removed since SocketCAN SVN r546)
520 As described in chapter 3.1 the Socket CAN core uses several filter
521 lists to deliver received CAN frames to CAN protocol modules. These
522 receive lists, their filters and the count of filter matches can be
523 checked in the appropriate receive list. All entries contain the
524 device and a protocol module identifier:
526 foo@bar:~$ cat /proc/net/can/rcvlist_all
528 receive list 'rx_all':
532 device can_id can_mask function userdata matches ident
533 vcan0 000 00000000 f88e6370 f6c6f400 0 raw
536 In this example an application requests any CAN traffic from vcan0.
538 rcvlist_all - list for unfiltered entries (no filter operations)
539 rcvlist_eff - list for single extended frame (EFF) entries
540 rcvlist_err - list for error frames masks
541 rcvlist_fil - list for mask/value filters
542 rcvlist_inv - list for mask/value filters (inverse semantic)
543 rcvlist_sff - list for single standard frame (SFF) entries
545 Additional procfs files in /proc/net/can
547 stats - Socket CAN core statistics (rx/tx frames, match ratios, ...)
548 reset_stats - manual statistic reset
549 version - prints the Socket CAN core version and the ABI version
551 5.3 writing own CAN protocol modules
553 To implement a new protocol in the protocol family PF_CAN a new
554 protocol has to be defined in include/linux/can.h .
555 The prototypes and definitions to use the Socket CAN core can be
556 accessed by including include/linux/can/core.h .
557 In addition to functions that register the CAN protocol and the
558 CAN device notifier chain there are functions to subscribe CAN
559 frames received by CAN interfaces and to send CAN frames:
561 can_rx_register - subscribe CAN frames from a specific interface
562 can_rx_unregister - unsubscribe CAN frames from a specific interface
563 can_send - transmit a CAN frame (optional with local loopback)
565 For details see the kerneldoc documentation in net/can/af_can.c or
566 the source code of net/can/raw.c or net/can/bcm.c .
568 6. CAN network drivers
569 ----------------------
571 Writing a CAN network device driver is much easier than writing a
572 CAN character device driver. Similar to other known network device
573 drivers you mainly have to deal with:
575 - TX: Put the CAN frame from the socket buffer to the CAN controller.
576 - RX: Put the CAN frame from the CAN controller to the socket buffer.
578 See e.g. at Documentation/networking/netdevices.txt . The differences
579 for writing CAN network device driver are described below:
583 dev->type = ARPHRD_CAN; /* the netdevice hardware type */
584 dev->flags = IFF_NOARP; /* CAN has no arp */
586 dev->mtu = sizeof(struct can_frame);
588 The struct can_frame is the payload of each socket buffer in the
589 protocol family PF_CAN.
591 6.2 local loopback of sent frames
593 As described in chapter 3.2 the CAN network device driver should
594 support a local loopback functionality similar to the local echo
595 e.g. of tty devices. In this case the driver flag IFF_ECHO has to be
596 set to prevent the PF_CAN core from locally echoing sent frames
597 (aka loopback) as fallback solution:
599 dev->flags = (IFF_NOARP | IFF_ECHO);
601 6.3 CAN controller hardware filters
603 To reduce the interrupt load on deep embedded systems some CAN
604 controllers support the filtering of CAN IDs or ranges of CAN IDs.
605 These hardware filter capabilities vary from controller to
606 controller and have to be identified as not feasible in a multi-user
607 networking approach. The use of the very controller specific
608 hardware filters could make sense in a very dedicated use-case, as a
609 filter on driver level would affect all users in the multi-user
610 system. The high efficient filter sets inside the PF_CAN core allow
611 to set different multiple filters for each socket separately.
612 Therefore the use of hardware filters goes to the category 'handmade
613 tuning on deep embedded systems'. The author is running a MPC603e
614 @133MHz with four SJA1000 CAN controllers from 2002 under heavy bus
615 load without any problems ...
617 6.4 The virtual CAN driver (vcan)
619 Similar to the network loopback devices, vcan offers a virtual local
620 CAN interface. A full qualified address on CAN consists of
622 - a unique CAN Identifier (CAN ID)
623 - the CAN bus this CAN ID is transmitted on (e.g. can0)
625 so in common use cases more than one virtual CAN interface is needed.
627 The virtual CAN interfaces allow the transmission and reception of CAN
628 frames without real CAN controller hardware. Virtual CAN network
629 devices are usually named 'vcanX', like vcan0 vcan1 vcan2 ...
630 When compiled as a module the virtual CAN driver module is called vcan.ko
632 Since Linux Kernel version 2.6.24 the vcan driver supports the Kernel
633 netlink interface to create vcan network devices. The creation and
634 removal of vcan network devices can be managed with the ip(8) tool:
636 - Create a virtual CAN network interface:
637 $ ip link add type vcan
639 - Create a virtual CAN network interface with a specific name 'vcan42':
640 $ ip link add dev vcan42 type vcan
642 - Remove a (virtual CAN) network interface 'vcan42':
645 6.5 The CAN network device driver interface
647 The CAN network device driver interface provides a generic interface
648 to setup, configure and monitor CAN network devices. The user can then
649 configure the CAN device, like setting the bit-timing parameters, via
650 the netlink interface using the program "ip" from the "IPROUTE2"
651 utility suite. The following chapter describes briefly how to use it.
652 Furthermore, the interface uses a common data structure and exports a
653 set of common functions, which all real CAN network device drivers
654 should use. Please have a look to the SJA1000 or MSCAN driver to
655 understand how to use them. The name of the module is can-dev.ko.
657 6.5.1 Netlink interface to set/get devices properties
659 The CAN device must be configured via netlink interface. The supported
660 netlink message types are defined and briefly described in
661 "include/linux/can/netlink.h". CAN link support for the program "ip"
662 of the IPROUTE2 utility suite is avaiable and it can be used as shown
665 - Setting CAN device properties:
667 $ ip link set can0 type can help
668 Usage: ip link set DEVICE type can
669 [ bitrate BITRATE [ sample-point SAMPLE-POINT] ] |
670 [ tq TQ prop-seg PROP_SEG phase-seg1 PHASE-SEG1
671 phase-seg2 PHASE-SEG2 [ sjw SJW ] ]
673 [ loopback { on | off } ]
674 [ listen-only { on | off } ]
675 [ triple-sampling { on | off } ]
677 [ restart-ms TIME-MS ]
680 Where: BITRATE := { 1..1000000 }
681 SAMPLE-POINT := { 0.000..0.999 }
684 PHASE-SEG1 := { 1..8 }
685 PHASE-SEG2 := { 1..8 }
687 RESTART-MS := { 0 | NUMBER }
689 - Display CAN device details and statistics:
691 $ ip -details -statistics link show can0
692 2: can0: <NOARP,UP,LOWER_UP,ECHO> mtu 16 qdisc pfifo_fast state UP qlen 10
694 can <TRIPLE-SAMPLING> state ERROR-ACTIVE restart-ms 100
695 bitrate 125000 sample_point 0.875
696 tq 125 prop-seg 6 phase-seg1 7 phase-seg2 2 sjw 1
697 sja1000: tseg1 1..16 tseg2 1..8 sjw 1..4 brp 1..64 brp-inc 1
699 re-started bus-errors arbit-lost error-warn error-pass bus-off
701 RX: bytes packets errors dropped overrun mcast
702 140859 17608 17457 0 0 0
703 TX: bytes packets errors dropped carrier collsns
706 More info to the above output:
709 Shows the list of selected CAN controller modes: LOOPBACK,
710 LISTEN-ONLY, or TRIPLE-SAMPLING.
713 The current state of the CAN controller: "ERROR-ACTIVE",
714 "ERROR-WARNING", "ERROR-PASSIVE", "BUS-OFF" or "STOPPED"
717 Automatic restart delay time. If set to a non-zero value, a
718 restart of the CAN controller will be triggered automatically
719 in case of a bus-off condition after the specified delay time
720 in milliseconds. By default it's off.
722 "bitrate 125000 sample_point 0.875"
723 Shows the real bit-rate in bits/sec and the sample-point in the
724 range 0.000..0.999. If the calculation of bit-timing parameters
725 is enabled in the kernel (CONFIG_CAN_CALC_BITTIMING=y), the
726 bit-timing can be defined by setting the "bitrate" argument.
727 Optionally the "sample-point" can be specified. By default it's
728 0.000 assuming CIA-recommended sample-points.
730 "tq 125 prop-seg 6 phase-seg1 7 phase-seg2 2 sjw 1"
731 Shows the time quanta in ns, propagation segment, phase buffer
732 segment 1 and 2 and the synchronisation jump width in units of
733 tq. They allow to define the CAN bit-timing in a hardware
734 independent format as proposed by the Bosch CAN 2.0 spec (see
735 chapter 8 of http://www.semiconductors.bosch.de/pdf/can2spec.pdf).
737 "sja1000: tseg1 1..16 tseg2 1..8 sjw 1..4 brp 1..64 brp-inc 1
739 Shows the bit-timing constants of the CAN controller, here the
740 "sja1000". The minimum and maximum values of the time segment 1
741 and 2, the synchronisation jump width in units of tq, the
742 bitrate pre-scaler and the CAN system clock frequency in Hz.
743 These constants could be used for user-defined (non-standard)
744 bit-timing calculation algorithms in user-space.
746 "re-started bus-errors arbit-lost error-warn error-pass bus-off"
747 Shows the number of restarts, bus and arbitration lost errors,
748 and the state changes to the error-warning, error-passive and
749 bus-off state. RX overrun errors are listed in the "overrun"
750 field of the standard network statistics.
752 6.5.2 Setting the CAN bit-timing
754 The CAN bit-timing parameters can always be defined in a hardware
755 independent format as proposed in the Bosch CAN 2.0 specification
756 specifying the arguments "tq", "prop_seg", "phase_seg1", "phase_seg2"
759 $ ip link set canX type can tq 125 prop-seg 6 \
760 phase-seg1 7 phase-seg2 2 sjw 1
762 If the kernel option CONFIG_CAN_CALC_BITTIMING is enabled, CIA
763 recommended CAN bit-timing parameters will be calculated if the bit-
764 rate is specified with the argument "bitrate":
766 $ ip link set canX type can bitrate 125000
768 Note that this works fine for the most common CAN controllers with
769 standard bit-rates but may *fail* for exotic bit-rates or CAN system
770 clock frequencies. Disabling CONFIG_CAN_CALC_BITTIMING saves some
771 space and allows user-space tools to solely determine and set the
772 bit-timing parameters. The CAN controller specific bit-timing
773 constants can be used for that purpose. They are listed by the
776 $ ip -details link show can0
778 sja1000: clock 8000000 tseg1 1..16 tseg2 1..8 sjw 1..4 brp 1..64 brp-inc 1
780 6.5.3 Starting and stopping the CAN network device
782 A CAN network device is started or stopped as usual with the command
783 "ifconfig canX up/down" or "ip link set canX up/down". Be aware that
784 you *must* define proper bit-timing parameters for real CAN devices
785 before you can start it to avoid error-prone default settings:
787 $ ip link set canX up type can bitrate 125000
789 A device may enter the "bus-off" state if too much errors occurred on
790 the CAN bus. Then no more messages are received or sent. An automatic
791 bus-off recovery can be enabled by setting the "restart-ms" to a
792 non-zero value, e.g.:
794 $ ip link set canX type can restart-ms 100
796 Alternatively, the application may realize the "bus-off" condition
797 by monitoring CAN error frames and do a restart when appropriate with
800 $ ip link set canX type can restart
802 Note that a restart will also create a CAN error frame (see also
805 6.6 Supported CAN hardware
807 Please check the "Kconfig" file in "drivers/net/can" to get an actual
808 list of the support CAN hardware. On the Socket CAN project website
809 (see chapter 7) there might be further drivers available, also for
810 older kernel versions.
812 7. Socket CAN resources
813 -----------------------
815 You can find further resources for Socket CAN like user space tools,
816 support for old kernel versions, more drivers, mailing lists, etc.
817 at the BerliOS OSS project website for Socket CAN:
819 http://developer.berlios.de/projects/socketcan
821 If you have questions, bug fixes, etc., don't hesitate to post them to
822 the Socketcan-Users mailing list. But please search the archives first.
827 Oliver Hartkopp (PF_CAN core, filters, drivers, bcm, SJA1000 driver)
828 Urs Thuermann (PF_CAN core, kernel integration, socket interfaces, raw, vcan)
829 Jan Kizka (RT-SocketCAN core, Socket-API reconciliation)
830 Wolfgang Grandegger (RT-SocketCAN core & drivers, Raw Socket-API reviews,
831 CAN device driver interface, MSCAN driver)
832 Robert Schwebel (design reviews, PTXdist integration)
833 Marc Kleine-Budde (design reviews, Kernel 2.6 cleanups, drivers)
834 Benedikt Spranger (reviews)
835 Thomas Gleixner (LKML reviews, coding style, posting hints)
836 Andrey Volkov (kernel subtree structure, ioctls, MSCAN driver)
837 Matthias Brukner (first SJA1000 CAN netdevice implementation Q2/2003)
838 Klaus Hitschler (PEAK driver integration)
839 Uwe Koppe (CAN netdevices with PF_PACKET approach)
840 Michael Schulze (driver layer loopback requirement, RT CAN drivers review)
841 Pavel Pisa (Bit-timing calculation)
842 Sascha Hauer (SJA1000 platform driver)
843 Sebastian Haas (SJA1000 EMS PCI driver)
844 Markus Plessing (SJA1000 EMS PCI driver)
845 Per Dalen (SJA1000 Kvaser PCI driver)
846 Sam Ravnborg (reviews, coding style, kbuild help)