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 4.1.5 RAW socket returned message flags
26 4.2 Broadcast Manager protocol sockets (SOCK_DGRAM)
27 4.3 connected transport protocols (SOCK_SEQPACKET)
28 4.4 unconnected transport protocols (SOCK_DGRAM)
31 5 Socket CAN core module
32 5.1 can.ko module params
34 5.3 writing own CAN protocol modules
38 6.2 local loopback of sent frames
39 6.3 CAN controller hardware filters
40 6.4 The virtual CAN driver (vcan)
41 6.5 The CAN network device driver interface
42 6.5.1 Netlink interface to set/get devices properties
43 6.5.2 Setting the CAN bit-timing
44 6.5.3 Starting and stopping the CAN network device
45 6.6 supported CAN hardware
47 7 Socket CAN resources
51 ============================================================================
53 1. Overview / What is Socket CAN
54 --------------------------------
56 The socketcan package is an implementation of CAN protocols
57 (Controller Area Network) for Linux. CAN is a networking technology
58 which has widespread use in automation, embedded devices, and
59 automotive fields. While there have been other CAN implementations
60 for Linux based on character devices, Socket CAN uses the Berkeley
61 socket API, the Linux network stack and implements the CAN device
62 drivers as network interfaces. The CAN socket API has been designed
63 as similar as possible to the TCP/IP protocols to allow programmers,
64 familiar with network programming, to easily learn how to use CAN
67 2. Motivation / Why using the socket API
68 ----------------------------------------
70 There have been CAN implementations for Linux before Socket CAN so the
71 question arises, why we have started another project. Most existing
72 implementations come as a device driver for some CAN hardware, they
73 are based on character devices and provide comparatively little
74 functionality. Usually, there is only a hardware-specific device
75 driver which provides a character device interface to send and
76 receive raw CAN frames, directly to/from the controller hardware.
77 Queueing of frames and higher-level transport protocols like ISO-TP
78 have to be implemented in user space applications. Also, most
79 character-device implementations support only one single process to
80 open the device at a time, similar to a serial interface. Exchanging
81 the CAN controller requires employment of another device driver and
82 often the need for adaption of large parts of the application to the
85 Socket CAN was designed to overcome all of these limitations. A new
86 protocol family has been implemented which provides a socket interface
87 to user space applications and which builds upon the Linux network
88 layer, so to use all of the provided queueing functionality. A device
89 driver for CAN controller hardware registers itself with the Linux
90 network layer as a network device, so that CAN frames from the
91 controller can be passed up to the network layer and on to the CAN
92 protocol family module and also vice-versa. Also, the protocol family
93 module provides an API for transport protocol modules to register, so
94 that any number of transport protocols can be loaded or unloaded
95 dynamically. In fact, the can core module alone does not provide any
96 protocol and cannot be used without loading at least one additional
97 protocol module. Multiple sockets can be opened at the same time,
98 on different or the same protocol module and they can listen/send
99 frames on different or the same CAN IDs. Several sockets listening on
100 the same interface for frames with the same CAN ID are all passed the
101 same received matching CAN frames. An application wishing to
102 communicate using a specific transport protocol, e.g. ISO-TP, just
103 selects that protocol when opening the socket, and then can read and
104 write application data byte streams, without having to deal with
105 CAN-IDs, frames, etc.
107 Similar functionality visible from user-space could be provided by a
108 character device, too, but this would lead to a technically inelegant
109 solution for a couple of reasons:
111 * Intricate usage. Instead of passing a protocol argument to
112 socket(2) and using bind(2) to select a CAN interface and CAN ID, an
113 application would have to do all these operations using ioctl(2)s.
115 * Code duplication. A character device cannot make use of the Linux
116 network queueing code, so all that code would have to be duplicated
119 * Abstraction. In most existing character-device implementations, the
120 hardware-specific device driver for a CAN controller directly
121 provides the character device for the application to work with.
122 This is at least very unusual in Unix systems for both, char and
123 block devices. For example you don't have a character device for a
124 certain UART of a serial interface, a certain sound chip in your
125 computer, a SCSI or IDE controller providing access to your hard
126 disk or tape streamer device. Instead, you have abstraction layers
127 which provide a unified character or block device interface to the
128 application on the one hand, and a interface for hardware-specific
129 device drivers on the other hand. These abstractions are provided
130 by subsystems like the tty layer, the audio subsystem or the SCSI
131 and IDE subsystems for the devices mentioned above.
133 The easiest way to implement a CAN device driver is as a character
134 device without such a (complete) abstraction layer, as is done by most
135 existing drivers. The right way, however, would be to add such a
136 layer with all the functionality like registering for certain CAN
137 IDs, supporting several open file descriptors and (de)multiplexing
138 CAN frames between them, (sophisticated) queueing of CAN frames, and
139 providing an API for device drivers to register with. However, then
140 it would be no more difficult, or may be even easier, to use the
141 networking framework provided by the Linux kernel, and this is what
144 The use of the networking framework of the Linux kernel is just the
145 natural and most appropriate way to implement CAN for Linux.
147 3. Socket CAN concept
148 ---------------------
150 As described in chapter 2 it is the main goal of Socket CAN to
151 provide a socket interface to user space applications which builds
152 upon the Linux network layer. In contrast to the commonly known
153 TCP/IP and ethernet networking, the CAN bus is a broadcast-only(!)
154 medium that has no MAC-layer addressing like ethernet. The CAN-identifier
155 (can_id) is used for arbitration on the CAN-bus. Therefore the CAN-IDs
156 have to be chosen uniquely on the bus. When designing a CAN-ECU
157 network the CAN-IDs are mapped to be sent by a specific ECU.
158 For this reason a CAN-ID can be treated best as a kind of source address.
162 The network transparent access of multiple applications leads to the
163 problem that different applications may be interested in the same
164 CAN-IDs from the same CAN network interface. The Socket CAN core
165 module - which implements the protocol family CAN - provides several
166 high efficient receive lists for this reason. If e.g. a user space
167 application opens a CAN RAW socket, the raw protocol module itself
168 requests the (range of) CAN-IDs from the Socket CAN core that are
169 requested by the user. The subscription and unsubscription of
170 CAN-IDs can be done for specific CAN interfaces or for all(!) known
171 CAN interfaces with the can_rx_(un)register() functions provided to
172 CAN protocol modules by the SocketCAN core (see chapter 5).
173 To optimize the CPU usage at runtime the receive lists are split up
174 into several specific lists per device that match the requested
175 filter complexity for a given use-case.
177 3.2 local loopback of sent frames
179 As known from other networking concepts the data exchanging
180 applications may run on the same or different nodes without any
181 change (except for the according addressing information):
183 ___ ___ ___ _______ ___
184 | _ | | _ | | _ | | _ _ | | _ |
185 ||A|| ||B|| ||C|| ||A| |B|| ||C||
186 |___| |___| |___| |_______| |___|
188 -----------------(1)- CAN bus -(2)---------------
190 To ensure that application A receives the same information in the
191 example (2) as it would receive in example (1) there is need for
192 some kind of local loopback of the sent CAN frames on the appropriate
195 The Linux network devices (by default) just can handle the
196 transmission and reception of media dependent frames. Due to the
197 arbitration on the CAN bus the transmission of a low prio CAN-ID
198 may be delayed by the reception of a high prio CAN frame. To
199 reflect the correct* traffic on the node the loopback of the sent
200 data has to be performed right after a successful transmission. If
201 the CAN network interface is not capable of performing the loopback for
202 some reason the SocketCAN core can do this task as a fallback solution.
203 See chapter 6.2 for details (recommended).
205 The loopback functionality is enabled by default to reflect standard
206 networking behaviour for CAN applications. Due to some requests from
207 the RT-SocketCAN group the loopback optionally may be disabled for each
208 separate socket. See sockopts from the CAN RAW sockets in chapter 4.1.
210 * = you really like to have this when you're running analyser tools
211 like 'candump' or 'cansniffer' on the (same) node.
213 3.3 network security issues (capabilities)
215 The Controller Area Network is a local field bus transmitting only
216 broadcast messages without any routing and security concepts.
217 In the majority of cases the user application has to deal with
218 raw CAN frames. Therefore it might be reasonable NOT to restrict
219 the CAN access only to the user root, as known from other networks.
220 Since the currently implemented CAN_RAW and CAN_BCM sockets can only
221 send and receive frames to/from CAN interfaces it does not affect
222 security of others networks to allow all users to access the CAN.
223 To enable non-root users to access CAN_RAW and CAN_BCM protocol
224 sockets the Kconfig options CAN_RAW_USER and/or CAN_BCM_USER may be
225 selected at kernel compile time.
227 3.4 network problem notifications
229 The use of the CAN bus may lead to several problems on the physical
230 and media access control layer. Detecting and logging of these lower
231 layer problems is a vital requirement for CAN users to identify
232 hardware issues on the physical transceiver layer as well as
233 arbitration problems and error frames caused by the different
234 ECUs. The occurrence of detected errors are important for diagnosis
235 and have to be logged together with the exact timestamp. For this
236 reason the CAN interface driver can generate so called Error Frames
237 that can optionally be passed to the user application in the same
238 way as other CAN frames. Whenever an error on the physical layer
239 or the MAC layer is detected (e.g. by the CAN controller) the driver
240 creates an appropriate error frame. Error frames can be requested by
241 the user application using the common CAN filter mechanisms. Inside
242 this filter definition the (interested) type of errors may be
243 selected. The reception of error frames is disabled by default.
244 The format of the CAN error frame is briefly described in the Linux
245 header file "include/linux/can/error.h".
247 4. How to use Socket CAN
248 ------------------------
250 Like TCP/IP, you first need to open a socket for communicating over a
251 CAN network. Since Socket CAN implements a new protocol family, you
252 need to pass PF_CAN as the first argument to the socket(2) system
253 call. Currently, there are two CAN protocols to choose from, the raw
254 socket protocol and the broadcast manager (BCM). So to open a socket,
257 s = socket(PF_CAN, SOCK_RAW, CAN_RAW);
261 s = socket(PF_CAN, SOCK_DGRAM, CAN_BCM);
263 respectively. After the successful creation of the socket, you would
264 normally use the bind(2) system call to bind the socket to a CAN
265 interface (which is different from TCP/IP due to different addressing
266 - see chapter 3). After binding (CAN_RAW) or connecting (CAN_BCM)
267 the socket, you can read(2) and write(2) from/to the socket or use
268 send(2), sendto(2), sendmsg(2) and the recv* counterpart operations
269 on the socket as usual. There are also CAN specific socket options
272 The basic CAN frame structure and the sockaddr structure are defined
273 in include/linux/can.h:
276 canid_t can_id; /* 32 bit CAN_ID + EFF/RTR/ERR flags */
277 __u8 can_dlc; /* data length code: 0 .. 8 */
278 __u8 data[8] __attribute__((aligned(8)));
281 The alignment of the (linear) payload data[] to a 64bit boundary
282 allows the user to define own structs and unions to easily access the
283 CAN payload. There is no given byteorder on the CAN bus by
284 default. A read(2) system call on a CAN_RAW socket transfers a
285 struct can_frame to the user space.
287 The sockaddr_can structure has an interface index like the
288 PF_PACKET socket, that also binds to a specific interface:
290 struct sockaddr_can {
291 sa_family_t can_family;
294 /* transport protocol class address info (e.g. ISOTP) */
295 struct { canid_t rx_id, tx_id; } tp;
297 /* reserved for future CAN protocols address information */
301 To determine the interface index an appropriate ioctl() has to
302 be used (example for CAN_RAW sockets without error checking):
305 struct sockaddr_can addr;
308 s = socket(PF_CAN, SOCK_RAW, CAN_RAW);
310 strcpy(ifr.ifr_name, "can0" );
311 ioctl(s, SIOCGIFINDEX, &ifr);
313 addr.can_family = AF_CAN;
314 addr.can_ifindex = ifr.ifr_ifindex;
316 bind(s, (struct sockaddr *)&addr, sizeof(addr));
320 To bind a socket to all(!) CAN interfaces the interface index must
321 be 0 (zero). In this case the socket receives CAN frames from every
322 enabled CAN interface. To determine the originating CAN interface
323 the system call recvfrom(2) may be used instead of read(2). To send
324 on a socket that is bound to 'any' interface sendto(2) is needed to
325 specify the outgoing interface.
327 Reading CAN frames from a bound CAN_RAW socket (see above) consists
328 of reading a struct can_frame:
330 struct can_frame frame;
332 nbytes = read(s, &frame, sizeof(struct can_frame));
335 perror("can raw socket read");
339 /* paranoid check ... */
340 if (nbytes < sizeof(struct can_frame)) {
341 fprintf(stderr, "read: incomplete CAN frame\n");
345 /* do something with the received CAN frame */
347 Writing CAN frames can be done similarly, with the write(2) system call:
349 nbytes = write(s, &frame, sizeof(struct can_frame));
351 When the CAN interface is bound to 'any' existing CAN interface
352 (addr.can_ifindex = 0) it is recommended to use recvfrom(2) if the
353 information about the originating CAN interface is needed:
355 struct sockaddr_can addr;
357 socklen_t len = sizeof(addr);
358 struct can_frame frame;
360 nbytes = recvfrom(s, &frame, sizeof(struct can_frame),
361 0, (struct sockaddr*)&addr, &len);
363 /* get interface name of the received CAN frame */
364 ifr.ifr_ifindex = addr.can_ifindex;
365 ioctl(s, SIOCGIFNAME, &ifr);
366 printf("Received a CAN frame from interface %s", ifr.ifr_name);
368 To write CAN frames on sockets bound to 'any' CAN interface the
369 outgoing interface has to be defined certainly.
371 strcpy(ifr.ifr_name, "can0");
372 ioctl(s, SIOCGIFINDEX, &ifr);
373 addr.can_ifindex = ifr.ifr_ifindex;
374 addr.can_family = AF_CAN;
376 nbytes = sendto(s, &frame, sizeof(struct can_frame),
377 0, (struct sockaddr*)&addr, sizeof(addr));
379 4.1 RAW protocol sockets with can_filters (SOCK_RAW)
381 Using CAN_RAW sockets is extensively comparable to the commonly
382 known access to CAN character devices. To meet the new possibilities
383 provided by the multi user SocketCAN approach, some reasonable
384 defaults are set at RAW socket binding time:
386 - The filters are set to exactly one filter receiving everything
387 - The socket only receives valid data frames (=> no error frames)
388 - The loopback of sent CAN frames is enabled (see chapter 3.2)
389 - The socket does not receive its own sent frames (in loopback mode)
391 These default settings may be changed before or after binding the socket.
392 To use the referenced definitions of the socket options for CAN_RAW
393 sockets, include <linux/can/raw.h>.
395 4.1.1 RAW socket option CAN_RAW_FILTER
397 The reception of CAN frames using CAN_RAW sockets can be controlled
398 by defining 0 .. n filters with the CAN_RAW_FILTER socket option.
400 The CAN filter structure is defined in include/linux/can.h:
407 A filter matches, when
409 <received_can_id> & mask == can_id & mask
411 which is analogous to known CAN controllers hardware filter semantics.
412 The filter can be inverted in this semantic, when the CAN_INV_FILTER
413 bit is set in can_id element of the can_filter structure. In
414 contrast to CAN controller hardware filters the user may set 0 .. n
415 receive filters for each open socket separately:
417 struct can_filter rfilter[2];
419 rfilter[0].can_id = 0x123;
420 rfilter[0].can_mask = CAN_SFF_MASK;
421 rfilter[1].can_id = 0x200;
422 rfilter[1].can_mask = 0x700;
424 setsockopt(s, SOL_CAN_RAW, CAN_RAW_FILTER, &rfilter, sizeof(rfilter));
426 To disable the reception of CAN frames on the selected CAN_RAW socket:
428 setsockopt(s, SOL_CAN_RAW, CAN_RAW_FILTER, NULL, 0);
430 To set the filters to zero filters is quite obsolete as not read
431 data causes the raw socket to discard the received CAN frames. But
432 having this 'send only' use-case we may remove the receive list in the
433 Kernel to save a little (really a very little!) CPU usage.
435 4.1.2 RAW socket option CAN_RAW_ERR_FILTER
437 As described in chapter 3.4 the CAN interface driver can generate so
438 called Error Frames that can optionally be passed to the user
439 application in the same way as other CAN frames. The possible
440 errors are divided into different error classes that may be filtered
441 using the appropriate error mask. To register for every possible
442 error condition CAN_ERR_MASK can be used as value for the error mask.
443 The values for the error mask are defined in linux/can/error.h .
445 can_err_mask_t err_mask = ( CAN_ERR_TX_TIMEOUT | CAN_ERR_BUSOFF );
447 setsockopt(s, SOL_CAN_RAW, CAN_RAW_ERR_FILTER,
448 &err_mask, sizeof(err_mask));
450 4.1.3 RAW socket option CAN_RAW_LOOPBACK
452 To meet multi user needs the local loopback is enabled by default
453 (see chapter 3.2 for details). But in some embedded use-cases
454 (e.g. when only one application uses the CAN bus) this loopback
455 functionality can be disabled (separately for each socket):
457 int loopback = 0; /* 0 = disabled, 1 = enabled (default) */
459 setsockopt(s, SOL_CAN_RAW, CAN_RAW_LOOPBACK, &loopback, sizeof(loopback));
461 4.1.4 RAW socket option CAN_RAW_RECV_OWN_MSGS
463 When the local loopback is enabled, all the sent CAN frames are
464 looped back to the open CAN sockets that registered for the CAN
465 frames' CAN-ID on this given interface to meet the multi user
466 needs. The reception of the CAN frames on the same socket that was
467 sending the CAN frame is assumed to be unwanted and therefore
468 disabled by default. This default behaviour may be changed on
471 int recv_own_msgs = 1; /* 0 = disabled (default), 1 = enabled */
473 setsockopt(s, SOL_CAN_RAW, CAN_RAW_RECV_OWN_MSGS,
474 &recv_own_msgs, sizeof(recv_own_msgs));
476 4.1.5 RAW socket returned message flags
478 When using recvmsg() call, the msg->msg_flags may contain following flags:
480 MSG_DONTROUTE: set when the received frame was created on the local host.
482 MSG_CONFIRM: set when the frame was sent via the socket it is received on.
483 This flag can be interpreted as a 'transmission confirmation' when the
484 CAN driver supports the echo of frames on driver level, see 3.2 and 6.2.
485 In order to receive such messages, CAN_RAW_RECV_OWN_MSGS must be set.
487 4.2 Broadcast Manager protocol sockets (SOCK_DGRAM)
488 4.3 connected transport protocols (SOCK_SEQPACKET)
489 4.4 unconnected transport protocols (SOCK_DGRAM)
493 For applications in the CAN environment it is often of interest an
494 accurate timestamp of the instant a message from CAN bus has been received.
495 Such a timestamp can be read with ioctl(2) after reading a message from
499 ioctl(s, SIOCGSTAMP, &tv);
501 The timestamp on Linux has a resolution of one microsecond and it is set
502 automatically at the reception of a CAN frame.
504 Alternatively the timestamp can be obtained as a control message (cmsg) using
505 the recvmsg() system call. After enabling the timestamps in the cmsg's by
507 const int timestamp = 1;
508 setsockopt(s, SOL_SOCKET, SO_TIMESTAMP, ×tamp, sizeof(timestamp));
510 the data structures filled by recvmsg() need to be parsed for
511 cmsg->cmsg_type == SO_TIMESTAMP to get the timestamp. See cmsg() manpage.
513 5. Socket CAN core module
514 -------------------------
516 The Socket CAN core module implements the protocol family
517 PF_CAN. CAN protocol modules are loaded by the core module at
518 runtime. The core module provides an interface for CAN protocol
519 modules to subscribe needed CAN IDs (see chapter 3.1).
521 5.1 can.ko module params
523 - stats_timer: To calculate the Socket CAN core statistics
524 (e.g. current/maximum frames per second) this 1 second timer is
525 invoked at can.ko module start time by default. This timer can be
526 disabled by using stattimer=0 on the module commandline.
528 - debug: (removed since SocketCAN SVN r546)
532 As described in chapter 3.1 the Socket CAN core uses several filter
533 lists to deliver received CAN frames to CAN protocol modules. These
534 receive lists, their filters and the count of filter matches can be
535 checked in the appropriate receive list. All entries contain the
536 device and a protocol module identifier:
538 foo@bar:~$ cat /proc/net/can/rcvlist_all
540 receive list 'rx_all':
544 device can_id can_mask function userdata matches ident
545 vcan0 000 00000000 f88e6370 f6c6f400 0 raw
548 In this example an application requests any CAN traffic from vcan0.
550 rcvlist_all - list for unfiltered entries (no filter operations)
551 rcvlist_eff - list for single extended frame (EFF) entries
552 rcvlist_err - list for error frames masks
553 rcvlist_fil - list for mask/value filters
554 rcvlist_inv - list for mask/value filters (inverse semantic)
555 rcvlist_sff - list for single standard frame (SFF) entries
557 Additional procfs files in /proc/net/can
559 stats - Socket CAN core statistics (rx/tx frames, match ratios, ...)
560 reset_stats - manual statistic reset
561 version - prints the Socket CAN core version and the ABI version
563 5.3 writing own CAN protocol modules
565 To implement a new protocol in the protocol family PF_CAN a new
566 protocol has to be defined in include/linux/can.h .
567 The prototypes and definitions to use the Socket CAN core can be
568 accessed by including include/linux/can/core.h .
569 In addition to functions that register the CAN protocol and the
570 CAN device notifier chain there are functions to subscribe CAN
571 frames received by CAN interfaces and to send CAN frames:
573 can_rx_register - subscribe CAN frames from a specific interface
574 can_rx_unregister - unsubscribe CAN frames from a specific interface
575 can_send - transmit a CAN frame (optional with local loopback)
577 For details see the kerneldoc documentation in net/can/af_can.c or
578 the source code of net/can/raw.c or net/can/bcm.c .
580 6. CAN network drivers
581 ----------------------
583 Writing a CAN network device driver is much easier than writing a
584 CAN character device driver. Similar to other known network device
585 drivers you mainly have to deal with:
587 - TX: Put the CAN frame from the socket buffer to the CAN controller.
588 - RX: Put the CAN frame from the CAN controller to the socket buffer.
590 See e.g. at Documentation/networking/netdevices.txt . The differences
591 for writing CAN network device driver are described below:
595 dev->type = ARPHRD_CAN; /* the netdevice hardware type */
596 dev->flags = IFF_NOARP; /* CAN has no arp */
598 dev->mtu = sizeof(struct can_frame);
600 The struct can_frame is the payload of each socket buffer in the
601 protocol family PF_CAN.
603 6.2 local loopback of sent frames
605 As described in chapter 3.2 the CAN network device driver should
606 support a local loopback functionality similar to the local echo
607 e.g. of tty devices. In this case the driver flag IFF_ECHO has to be
608 set to prevent the PF_CAN core from locally echoing sent frames
609 (aka loopback) as fallback solution:
611 dev->flags = (IFF_NOARP | IFF_ECHO);
613 6.3 CAN controller hardware filters
615 To reduce the interrupt load on deep embedded systems some CAN
616 controllers support the filtering of CAN IDs or ranges of CAN IDs.
617 These hardware filter capabilities vary from controller to
618 controller and have to be identified as not feasible in a multi-user
619 networking approach. The use of the very controller specific
620 hardware filters could make sense in a very dedicated use-case, as a
621 filter on driver level would affect all users in the multi-user
622 system. The high efficient filter sets inside the PF_CAN core allow
623 to set different multiple filters for each socket separately.
624 Therefore the use of hardware filters goes to the category 'handmade
625 tuning on deep embedded systems'. The author is running a MPC603e
626 @133MHz with four SJA1000 CAN controllers from 2002 under heavy bus
627 load without any problems ...
629 6.4 The virtual CAN driver (vcan)
631 Similar to the network loopback devices, vcan offers a virtual local
632 CAN interface. A full qualified address on CAN consists of
634 - a unique CAN Identifier (CAN ID)
635 - the CAN bus this CAN ID is transmitted on (e.g. can0)
637 so in common use cases more than one virtual CAN interface is needed.
639 The virtual CAN interfaces allow the transmission and reception of CAN
640 frames without real CAN controller hardware. Virtual CAN network
641 devices are usually named 'vcanX', like vcan0 vcan1 vcan2 ...
642 When compiled as a module the virtual CAN driver module is called vcan.ko
644 Since Linux Kernel version 2.6.24 the vcan driver supports the Kernel
645 netlink interface to create vcan network devices. The creation and
646 removal of vcan network devices can be managed with the ip(8) tool:
648 - Create a virtual CAN network interface:
649 $ ip link add type vcan
651 - Create a virtual CAN network interface with a specific name 'vcan42':
652 $ ip link add dev vcan42 type vcan
654 - Remove a (virtual CAN) network interface 'vcan42':
657 6.5 The CAN network device driver interface
659 The CAN network device driver interface provides a generic interface
660 to setup, configure and monitor CAN network devices. The user can then
661 configure the CAN device, like setting the bit-timing parameters, via
662 the netlink interface using the program "ip" from the "IPROUTE2"
663 utility suite. The following chapter describes briefly how to use it.
664 Furthermore, the interface uses a common data structure and exports a
665 set of common functions, which all real CAN network device drivers
666 should use. Please have a look to the SJA1000 or MSCAN driver to
667 understand how to use them. The name of the module is can-dev.ko.
669 6.5.1 Netlink interface to set/get devices properties
671 The CAN device must be configured via netlink interface. The supported
672 netlink message types are defined and briefly described in
673 "include/linux/can/netlink.h". CAN link support for the program "ip"
674 of the IPROUTE2 utility suite is avaiable and it can be used as shown
677 - Setting CAN device properties:
679 $ ip link set can0 type can help
680 Usage: ip link set DEVICE type can
681 [ bitrate BITRATE [ sample-point SAMPLE-POINT] ] |
682 [ tq TQ prop-seg PROP_SEG phase-seg1 PHASE-SEG1
683 phase-seg2 PHASE-SEG2 [ sjw SJW ] ]
685 [ loopback { on | off } ]
686 [ listen-only { on | off } ]
687 [ triple-sampling { on | off } ]
689 [ restart-ms TIME-MS ]
692 Where: BITRATE := { 1..1000000 }
693 SAMPLE-POINT := { 0.000..0.999 }
696 PHASE-SEG1 := { 1..8 }
697 PHASE-SEG2 := { 1..8 }
699 RESTART-MS := { 0 | NUMBER }
701 - Display CAN device details and statistics:
703 $ ip -details -statistics link show can0
704 2: can0: <NOARP,UP,LOWER_UP,ECHO> mtu 16 qdisc pfifo_fast state UP qlen 10
706 can <TRIPLE-SAMPLING> state ERROR-ACTIVE restart-ms 100
707 bitrate 125000 sample_point 0.875
708 tq 125 prop-seg 6 phase-seg1 7 phase-seg2 2 sjw 1
709 sja1000: tseg1 1..16 tseg2 1..8 sjw 1..4 brp 1..64 brp-inc 1
711 re-started bus-errors arbit-lost error-warn error-pass bus-off
713 RX: bytes packets errors dropped overrun mcast
714 140859 17608 17457 0 0 0
715 TX: bytes packets errors dropped carrier collsns
718 More info to the above output:
721 Shows the list of selected CAN controller modes: LOOPBACK,
722 LISTEN-ONLY, or TRIPLE-SAMPLING.
725 The current state of the CAN controller: "ERROR-ACTIVE",
726 "ERROR-WARNING", "ERROR-PASSIVE", "BUS-OFF" or "STOPPED"
729 Automatic restart delay time. If set to a non-zero value, a
730 restart of the CAN controller will be triggered automatically
731 in case of a bus-off condition after the specified delay time
732 in milliseconds. By default it's off.
734 "bitrate 125000 sample_point 0.875"
735 Shows the real bit-rate in bits/sec and the sample-point in the
736 range 0.000..0.999. If the calculation of bit-timing parameters
737 is enabled in the kernel (CONFIG_CAN_CALC_BITTIMING=y), the
738 bit-timing can be defined by setting the "bitrate" argument.
739 Optionally the "sample-point" can be specified. By default it's
740 0.000 assuming CIA-recommended sample-points.
742 "tq 125 prop-seg 6 phase-seg1 7 phase-seg2 2 sjw 1"
743 Shows the time quanta in ns, propagation segment, phase buffer
744 segment 1 and 2 and the synchronisation jump width in units of
745 tq. They allow to define the CAN bit-timing in a hardware
746 independent format as proposed by the Bosch CAN 2.0 spec (see
747 chapter 8 of http://www.semiconductors.bosch.de/pdf/can2spec.pdf).
749 "sja1000: tseg1 1..16 tseg2 1..8 sjw 1..4 brp 1..64 brp-inc 1
751 Shows the bit-timing constants of the CAN controller, here the
752 "sja1000". The minimum and maximum values of the time segment 1
753 and 2, the synchronisation jump width in units of tq, the
754 bitrate pre-scaler and the CAN system clock frequency in Hz.
755 These constants could be used for user-defined (non-standard)
756 bit-timing calculation algorithms in user-space.
758 "re-started bus-errors arbit-lost error-warn error-pass bus-off"
759 Shows the number of restarts, bus and arbitration lost errors,
760 and the state changes to the error-warning, error-passive and
761 bus-off state. RX overrun errors are listed in the "overrun"
762 field of the standard network statistics.
764 6.5.2 Setting the CAN bit-timing
766 The CAN bit-timing parameters can always be defined in a hardware
767 independent format as proposed in the Bosch CAN 2.0 specification
768 specifying the arguments "tq", "prop_seg", "phase_seg1", "phase_seg2"
771 $ ip link set canX type can tq 125 prop-seg 6 \
772 phase-seg1 7 phase-seg2 2 sjw 1
774 If the kernel option CONFIG_CAN_CALC_BITTIMING is enabled, CIA
775 recommended CAN bit-timing parameters will be calculated if the bit-
776 rate is specified with the argument "bitrate":
778 $ ip link set canX type can bitrate 125000
780 Note that this works fine for the most common CAN controllers with
781 standard bit-rates but may *fail* for exotic bit-rates or CAN system
782 clock frequencies. Disabling CONFIG_CAN_CALC_BITTIMING saves some
783 space and allows user-space tools to solely determine and set the
784 bit-timing parameters. The CAN controller specific bit-timing
785 constants can be used for that purpose. They are listed by the
788 $ ip -details link show can0
790 sja1000: clock 8000000 tseg1 1..16 tseg2 1..8 sjw 1..4 brp 1..64 brp-inc 1
792 6.5.3 Starting and stopping the CAN network device
794 A CAN network device is started or stopped as usual with the command
795 "ifconfig canX up/down" or "ip link set canX up/down". Be aware that
796 you *must* define proper bit-timing parameters for real CAN devices
797 before you can start it to avoid error-prone default settings:
799 $ ip link set canX up type can bitrate 125000
801 A device may enter the "bus-off" state if too much errors occurred on
802 the CAN bus. Then no more messages are received or sent. An automatic
803 bus-off recovery can be enabled by setting the "restart-ms" to a
804 non-zero value, e.g.:
806 $ ip link set canX type can restart-ms 100
808 Alternatively, the application may realize the "bus-off" condition
809 by monitoring CAN error frames and do a restart when appropriate with
812 $ ip link set canX type can restart
814 Note that a restart will also create a CAN error frame (see also
817 6.6 Supported CAN hardware
819 Please check the "Kconfig" file in "drivers/net/can" to get an actual
820 list of the support CAN hardware. On the Socket CAN project website
821 (see chapter 7) there might be further drivers available, also for
822 older kernel versions.
824 7. Socket CAN resources
825 -----------------------
827 You can find further resources for Socket CAN like user space tools,
828 support for old kernel versions, more drivers, mailing lists, etc.
829 at the BerliOS OSS project website for Socket CAN:
831 http://developer.berlios.de/projects/socketcan
833 If you have questions, bug fixes, etc., don't hesitate to post them to
834 the Socketcan-Users mailing list. But please search the archives first.
839 Oliver Hartkopp (PF_CAN core, filters, drivers, bcm, SJA1000 driver)
840 Urs Thuermann (PF_CAN core, kernel integration, socket interfaces, raw, vcan)
841 Jan Kizka (RT-SocketCAN core, Socket-API reconciliation)
842 Wolfgang Grandegger (RT-SocketCAN core & drivers, Raw Socket-API reviews,
843 CAN device driver interface, MSCAN driver)
844 Robert Schwebel (design reviews, PTXdist integration)
845 Marc Kleine-Budde (design reviews, Kernel 2.6 cleanups, drivers)
846 Benedikt Spranger (reviews)
847 Thomas Gleixner (LKML reviews, coding style, posting hints)
848 Andrey Volkov (kernel subtree structure, ioctls, MSCAN driver)
849 Matthias Brukner (first SJA1000 CAN netdevice implementation Q2/2003)
850 Klaus Hitschler (PEAK driver integration)
851 Uwe Koppe (CAN netdevices with PF_PACKET approach)
852 Michael Schulze (driver layer loopback requirement, RT CAN drivers review)
853 Pavel Pisa (Bit-timing calculation)
854 Sascha Hauer (SJA1000 platform driver)
855 Sebastian Haas (SJA1000 EMS PCI driver)
856 Markus Plessing (SJA1000 EMS PCI driver)
857 Per Dalen (SJA1000 Kvaser PCI driver)
858 Sam Ravnborg (reviews, coding style, kbuild help)