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Oliver Hartkoppf7ab97f2007-11-16 16:09:28 -08001============================================================================
2
3can.txt
4
5Readme file for the Controller Area Network Protocol Family (aka Socket CAN)
6
7This file contains
8
9 1 Overview / What is Socket CAN
10
11 2 Motivation / Why using the socket API
12
13 3 Socket CAN concept
14 3.1 receive lists
15 3.2 local loopback of sent frames
16 3.3 network security issues (capabilities)
17 3.4 network problem notifications
18
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
Oliver Hartkopp1e556592010-10-19 09:32:04 +000025 4.1.5 RAW socket returned message flags
Oliver Hartkoppf7ab97f2007-11-16 16:09:28 -080026 4.2 Broadcast Manager protocol sockets (SOCK_DGRAM)
27 4.3 connected transport protocols (SOCK_SEQPACKET)
28 4.4 unconnected transport protocols (SOCK_DGRAM)
29
30 5 Socket CAN core module
31 5.1 can.ko module params
32 5.2 procfs content
33 5.3 writing own CAN protocol modules
34
35 6 CAN network drivers
36 6.1 general settings
37 6.2 local loopback of sent frames
38 6.3 CAN controller hardware filters
Oliver Hartkoppe5d23042008-09-23 14:53:14 -070039 6.4 The virtual CAN driver (vcan)
Wolfgang Grandeggere20dad92009-05-15 23:39:27 +000040 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
Oliver Hartkoppf7ab97f2007-11-16 16:09:28 -080045
Wolfgang Grandeggere20dad92009-05-15 23:39:27 +000046 7 Socket CAN resources
47
48 8 Credits
Oliver Hartkoppf7ab97f2007-11-16 16:09:28 -080049
50============================================================================
51
521. Overview / What is Socket CAN
53--------------------------------
54
55The socketcan package is an implementation of CAN protocols
56(Controller Area Network) for Linux. CAN is a networking technology
57which has widespread use in automation, embedded devices, and
58automotive fields. While there have been other CAN implementations
59for Linux based on character devices, Socket CAN uses the Berkeley
60socket API, the Linux network stack and implements the CAN device
61drivers as network interfaces. The CAN socket API has been designed
62as similar as possible to the TCP/IP protocols to allow programmers,
63familiar with network programming, to easily learn how to use CAN
64sockets.
65
662. Motivation / Why using the socket API
67----------------------------------------
68
69There have been CAN implementations for Linux before Socket CAN so the
70question arises, why we have started another project. Most existing
71implementations come as a device driver for some CAN hardware, they
72are based on character devices and provide comparatively little
73functionality. Usually, there is only a hardware-specific device
74driver which provides a character device interface to send and
75receive raw CAN frames, directly to/from the controller hardware.
76Queueing of frames and higher-level transport protocols like ISO-TP
77have to be implemented in user space applications. Also, most
78character-device implementations support only one single process to
79open the device at a time, similar to a serial interface. Exchanging
80the CAN controller requires employment of another device driver and
81often the need for adaption of large parts of the application to the
82new driver's API.
83
84Socket CAN was designed to overcome all of these limitations. A new
85protocol family has been implemented which provides a socket interface
86to user space applications and which builds upon the Linux network
87layer, so to use all of the provided queueing functionality. A device
88driver for CAN controller hardware registers itself with the Linux
89network layer as a network device, so that CAN frames from the
90controller can be passed up to the network layer and on to the CAN
91protocol family module and also vice-versa. Also, the protocol family
92module provides an API for transport protocol modules to register, so
93that any number of transport protocols can be loaded or unloaded
94dynamically. In fact, the can core module alone does not provide any
95protocol and cannot be used without loading at least one additional
96protocol module. Multiple sockets can be opened at the same time,
97on different or the same protocol module and they can listen/send
98frames on different or the same CAN IDs. Several sockets listening on
99the same interface for frames with the same CAN ID are all passed the
100same received matching CAN frames. An application wishing to
101communicate using a specific transport protocol, e.g. ISO-TP, just
102selects that protocol when opening the socket, and then can read and
103write application data byte streams, without having to deal with
104CAN-IDs, frames, etc.
105
106Similar functionality visible from user-space could be provided by a
107character device, too, but this would lead to a technically inelegant
108solution for a couple of reasons:
109
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.
113
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
116 for CAN networking.
117
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.
131
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
141 Socket CAN does.
142
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.
145
1463. Socket CAN concept
147---------------------
148
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.
158
159 3.1 receive lists
160
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.
175
176 3.2 local loopback of sent frames
177
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):
181
182 ___ ___ ___ _______ ___
183 | _ | | _ | | _ | | _ _ | | _ |
184 ||A|| ||B|| ||C|| ||A| |B|| ||C||
185 |___| |___| |___| |_______| |___|
186 | | | | |
187 -----------------(1)- CAN bus -(2)---------------
188
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
192 node.
193
194 The Linux network devices (by default) just can handle the
195 transmission and reception of media dependent frames. Due to the
Matt LaPlanted9195882008-07-25 19:45:33 -0700196 arbitration on the CAN bus the transmission of a low prio CAN-ID
Oliver Hartkoppf7ab97f2007-11-16 16:09:28 -0800197 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).
203
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.
208
209 * = you really like to have this when you're running analyser tools
210 like 'candump' or 'cansniffer' on the (same) node.
211
212 3.3 network security issues (capabilities)
213
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.
225
226 3.4 network problem notifications
227
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.
Lucas De Marchi25985ed2011-03-30 22:57:33 -0300243 The format of the CAN error frame is briefly described in the Linux
Wolfgang Grandeggere20dad92009-05-15 23:39:27 +0000244 header file "include/linux/can/error.h".
Oliver Hartkoppf7ab97f2007-11-16 16:09:28 -0800245
2464. How to use Socket CAN
247------------------------
248
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,
254 you would write
255
256 s = socket(PF_CAN, SOCK_RAW, CAN_RAW);
257
258 and
259
260 s = socket(PF_CAN, SOCK_DGRAM, CAN_BCM);
261
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
269 described below.
270
271 The basic CAN frame structure and the sockaddr structure are defined
272 in include/linux/can.h:
273
274 struct can_frame {
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)));
278 };
279
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.
285
286 The sockaddr_can structure has an interface index like the
287 PF_PACKET socket, that also binds to a specific interface:
288
289 struct sockaddr_can {
290 sa_family_t can_family;
291 int can_ifindex;
292 union {
Oliver Hartkopp56690c22008-04-15 00:46:38 -0700293 /* transport protocol class address info (e.g. ISOTP) */
294 struct { canid_t rx_id, tx_id; } tp;
295
296 /* reserved for future CAN protocols address information */
Oliver Hartkoppf7ab97f2007-11-16 16:09:28 -0800297 } can_addr;
298 };
299
300 To determine the interface index an appropriate ioctl() has to
301 be used (example for CAN_RAW sockets without error checking):
302
303 int s;
304 struct sockaddr_can addr;
305 struct ifreq ifr;
306
307 s = socket(PF_CAN, SOCK_RAW, CAN_RAW);
308
309 strcpy(ifr.ifr_name, "can0" );
310 ioctl(s, SIOCGIFINDEX, &ifr);
311
312 addr.can_family = AF_CAN;
313 addr.can_ifindex = ifr.ifr_ifindex;
314
315 bind(s, (struct sockaddr *)&addr, sizeof(addr));
316
317 (..)
318
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.
325
326 Reading CAN frames from a bound CAN_RAW socket (see above) consists
327 of reading a struct can_frame:
328
329 struct can_frame frame;
330
331 nbytes = read(s, &frame, sizeof(struct can_frame));
332
333 if (nbytes < 0) {
334 perror("can raw socket read");
335 return 1;
336 }
337
Matt LaPlante19f59462009-04-27 15:06:31 +0200338 /* paranoid check ... */
Oliver Hartkoppf7ab97f2007-11-16 16:09:28 -0800339 if (nbytes < sizeof(struct can_frame)) {
340 fprintf(stderr, "read: incomplete CAN frame\n");
341 return 1;
342 }
343
344 /* do something with the received CAN frame */
345
346 Writing CAN frames can be done similarly, with the write(2) system call:
347
348 nbytes = write(s, &frame, sizeof(struct can_frame));
349
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:
353
354 struct sockaddr_can addr;
355 struct ifreq ifr;
356 socklen_t len = sizeof(addr);
357 struct can_frame frame;
358
359 nbytes = recvfrom(s, &frame, sizeof(struct can_frame),
360 0, (struct sockaddr*)&addr, &len);
361
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);
366
367 To write CAN frames on sockets bound to 'any' CAN interface the
368 outgoing interface has to be defined certainly.
369
370 strcpy(ifr.ifr_name, "can0");
371 ioctl(s, SIOCGIFINDEX, &ifr);
372 addr.can_ifindex = ifr.ifr_ifindex;
373 addr.can_family = AF_CAN;
374
375 nbytes = sendto(s, &frame, sizeof(struct can_frame),
376 0, (struct sockaddr*)&addr, sizeof(addr));
377
378 4.1 RAW protocol sockets with can_filters (SOCK_RAW)
379
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:
384
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)
389
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>.
393
394 4.1.1 RAW socket option CAN_RAW_FILTER
395
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.
398
399 The CAN filter structure is defined in include/linux/can.h:
400
401 struct can_filter {
402 canid_t can_id;
403 canid_t can_mask;
404 };
405
406 A filter matches, when
407
408 <received_can_id> & mask == can_id & mask
409
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:
415
416 struct can_filter rfilter[2];
417
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;
422
423 setsockopt(s, SOL_CAN_RAW, CAN_RAW_FILTER, &rfilter, sizeof(rfilter));
424
425 To disable the reception of CAN frames on the selected CAN_RAW socket:
426
427 setsockopt(s, SOL_CAN_RAW, CAN_RAW_FILTER, NULL, 0);
428
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.
433
434 4.1.2 RAW socket option CAN_RAW_ERR_FILTER
435
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 .
443
444 can_err_mask_t err_mask = ( CAN_ERR_TX_TIMEOUT | CAN_ERR_BUSOFF );
445
446 setsockopt(s, SOL_CAN_RAW, CAN_RAW_ERR_FILTER,
447 &err_mask, sizeof(err_mask));
448
449 4.1.3 RAW socket option CAN_RAW_LOOPBACK
450
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):
455
456 int loopback = 0; /* 0 = disabled, 1 = enabled (default) */
457
458 setsockopt(s, SOL_CAN_RAW, CAN_RAW_LOOPBACK, &loopback, sizeof(loopback));
459
460 4.1.4 RAW socket option CAN_RAW_RECV_OWN_MSGS
461
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
468 demand:
469
470 int recv_own_msgs = 1; /* 0 = disabled (default), 1 = enabled */
471
472 setsockopt(s, SOL_CAN_RAW, CAN_RAW_RECV_OWN_MSGS,
473 &recv_own_msgs, sizeof(recv_own_msgs));
474
Oliver Hartkopp1e556592010-10-19 09:32:04 +0000475 4.1.5 RAW socket returned message flags
476
477 When using recvmsg() call, the msg->msg_flags may contain following flags:
478
479 MSG_DONTROUTE: set when the received frame was created on the local host.
480
481 MSG_CONFIRM: set when the frame was sent via the socket it is received on.
482 This flag can be interpreted as a 'transmission confirmation' when the
483 CAN driver supports the echo of frames on driver level, see 3.2 and 6.2.
484 In order to receive such messages, CAN_RAW_RECV_OWN_MSGS must be set.
485
Oliver Hartkoppf7ab97f2007-11-16 16:09:28 -0800486 4.2 Broadcast Manager protocol sockets (SOCK_DGRAM)
487 4.3 connected transport protocols (SOCK_SEQPACKET)
488 4.4 unconnected transport protocols (SOCK_DGRAM)
489
490
4915. Socket CAN core module
492-------------------------
493
494 The Socket CAN core module implements the protocol family
495 PF_CAN. CAN protocol modules are loaded by the core module at
496 runtime. The core module provides an interface for CAN protocol
497 modules to subscribe needed CAN IDs (see chapter 3.1).
498
499 5.1 can.ko module params
500
501 - stats_timer: To calculate the Socket CAN core statistics
502 (e.g. current/maximum frames per second) this 1 second timer is
503 invoked at can.ko module start time by default. This timer can be
Matt LaPlanted9195882008-07-25 19:45:33 -0700504 disabled by using stattimer=0 on the module commandline.
Oliver Hartkoppf7ab97f2007-11-16 16:09:28 -0800505
506 - debug: (removed since SocketCAN SVN r546)
507
508 5.2 procfs content
509
510 As described in chapter 3.1 the Socket CAN core uses several filter
511 lists to deliver received CAN frames to CAN protocol modules. These
512 receive lists, their filters and the count of filter matches can be
513 checked in the appropriate receive list. All entries contain the
514 device and a protocol module identifier:
515
516 foo@bar:~$ cat /proc/net/can/rcvlist_all
517
518 receive list 'rx_all':
519 (vcan3: no entry)
520 (vcan2: no entry)
521 (vcan1: no entry)
522 device can_id can_mask function userdata matches ident
523 vcan0 000 00000000 f88e6370 f6c6f400 0 raw
524 (any: no entry)
525
526 In this example an application requests any CAN traffic from vcan0.
527
528 rcvlist_all - list for unfiltered entries (no filter operations)
529 rcvlist_eff - list for single extended frame (EFF) entries
530 rcvlist_err - list for error frames masks
531 rcvlist_fil - list for mask/value filters
532 rcvlist_inv - list for mask/value filters (inverse semantic)
533 rcvlist_sff - list for single standard frame (SFF) entries
534
535 Additional procfs files in /proc/net/can
536
537 stats - Socket CAN core statistics (rx/tx frames, match ratios, ...)
538 reset_stats - manual statistic reset
539 version - prints the Socket CAN core version and the ABI version
540
541 5.3 writing own CAN protocol modules
542
543 To implement a new protocol in the protocol family PF_CAN a new
544 protocol has to be defined in include/linux/can.h .
545 The prototypes and definitions to use the Socket CAN core can be
546 accessed by including include/linux/can/core.h .
547 In addition to functions that register the CAN protocol and the
548 CAN device notifier chain there are functions to subscribe CAN
549 frames received by CAN interfaces and to send CAN frames:
550
551 can_rx_register - subscribe CAN frames from a specific interface
552 can_rx_unregister - unsubscribe CAN frames from a specific interface
553 can_send - transmit a CAN frame (optional with local loopback)
554
555 For details see the kerneldoc documentation in net/can/af_can.c or
556 the source code of net/can/raw.c or net/can/bcm.c .
557
5586. CAN network drivers
559----------------------
560
561 Writing a CAN network device driver is much easier than writing a
562 CAN character device driver. Similar to other known network device
563 drivers you mainly have to deal with:
564
565 - TX: Put the CAN frame from the socket buffer to the CAN controller.
566 - RX: Put the CAN frame from the CAN controller to the socket buffer.
567
568 See e.g. at Documentation/networking/netdevices.txt . The differences
569 for writing CAN network device driver are described below:
570
571 6.1 general settings
572
573 dev->type = ARPHRD_CAN; /* the netdevice hardware type */
574 dev->flags = IFF_NOARP; /* CAN has no arp */
575
576 dev->mtu = sizeof(struct can_frame);
577
578 The struct can_frame is the payload of each socket buffer in the
579 protocol family PF_CAN.
580
581 6.2 local loopback of sent frames
582
583 As described in chapter 3.2 the CAN network device driver should
584 support a local loopback functionality similar to the local echo
585 e.g. of tty devices. In this case the driver flag IFF_ECHO has to be
586 set to prevent the PF_CAN core from locally echoing sent frames
587 (aka loopback) as fallback solution:
588
589 dev->flags = (IFF_NOARP | IFF_ECHO);
590
591 6.3 CAN controller hardware filters
592
593 To reduce the interrupt load on deep embedded systems some CAN
594 controllers support the filtering of CAN IDs or ranges of CAN IDs.
595 These hardware filter capabilities vary from controller to
596 controller and have to be identified as not feasible in a multi-user
597 networking approach. The use of the very controller specific
598 hardware filters could make sense in a very dedicated use-case, as a
599 filter on driver level would affect all users in the multi-user
600 system. The high efficient filter sets inside the PF_CAN core allow
601 to set different multiple filters for each socket separately.
602 Therefore the use of hardware filters goes to the category 'handmade
603 tuning on deep embedded systems'. The author is running a MPC603e
604 @133MHz with four SJA1000 CAN controllers from 2002 under heavy bus
605 load without any problems ...
606
Oliver Hartkoppe5d23042008-09-23 14:53:14 -0700607 6.4 The virtual CAN driver (vcan)
608
609 Similar to the network loopback devices, vcan offers a virtual local
610 CAN interface. A full qualified address on CAN consists of
611
612 - a unique CAN Identifier (CAN ID)
613 - the CAN bus this CAN ID is transmitted on (e.g. can0)
614
615 so in common use cases more than one virtual CAN interface is needed.
616
617 The virtual CAN interfaces allow the transmission and reception of CAN
618 frames without real CAN controller hardware. Virtual CAN network
619 devices are usually named 'vcanX', like vcan0 vcan1 vcan2 ...
620 When compiled as a module the virtual CAN driver module is called vcan.ko
621
622 Since Linux Kernel version 2.6.24 the vcan driver supports the Kernel
623 netlink interface to create vcan network devices. The creation and
624 removal of vcan network devices can be managed with the ip(8) tool:
625
626 - Create a virtual CAN network interface:
Wolfgang Grandeggere20dad92009-05-15 23:39:27 +0000627 $ ip link add type vcan
Oliver Hartkoppe5d23042008-09-23 14:53:14 -0700628
629 - Create a virtual CAN network interface with a specific name 'vcan42':
Wolfgang Grandeggere20dad92009-05-15 23:39:27 +0000630 $ ip link add dev vcan42 type vcan
Oliver Hartkoppe5d23042008-09-23 14:53:14 -0700631
632 - Remove a (virtual CAN) network interface 'vcan42':
Wolfgang Grandeggere20dad92009-05-15 23:39:27 +0000633 $ ip link del vcan42
Oliver Hartkoppe5d23042008-09-23 14:53:14 -0700634
Wolfgang Grandeggere20dad92009-05-15 23:39:27 +0000635 6.5 The CAN network device driver interface
Oliver Hartkoppe5d23042008-09-23 14:53:14 -0700636
Wolfgang Grandeggere20dad92009-05-15 23:39:27 +0000637 The CAN network device driver interface provides a generic interface
638 to setup, configure and monitor CAN network devices. The user can then
639 configure the CAN device, like setting the bit-timing parameters, via
640 the netlink interface using the program "ip" from the "IPROUTE2"
641 utility suite. The following chapter describes briefly how to use it.
642 Furthermore, the interface uses a common data structure and exports a
643 set of common functions, which all real CAN network device drivers
644 should use. Please have a look to the SJA1000 or MSCAN driver to
645 understand how to use them. The name of the module is can-dev.ko.
Oliver Hartkoppe5d23042008-09-23 14:53:14 -0700646
Wolfgang Grandeggere20dad92009-05-15 23:39:27 +0000647 6.5.1 Netlink interface to set/get devices properties
Oliver Hartkoppf7ab97f2007-11-16 16:09:28 -0800648
Wolfgang Grandeggere20dad92009-05-15 23:39:27 +0000649 The CAN device must be configured via netlink interface. The supported
650 netlink message types are defined and briefly described in
651 "include/linux/can/netlink.h". CAN link support for the program "ip"
652 of the IPROUTE2 utility suite is avaiable and it can be used as shown
653 below:
Oliver Hartkoppf7ab97f2007-11-16 16:09:28 -0800654
Wolfgang Grandeggere20dad92009-05-15 23:39:27 +0000655 - Setting CAN device properties:
Oliver Hartkoppf7ab97f2007-11-16 16:09:28 -0800656
Wolfgang Grandeggere20dad92009-05-15 23:39:27 +0000657 $ ip link set can0 type can help
658 Usage: ip link set DEVICE type can
659 [ bitrate BITRATE [ sample-point SAMPLE-POINT] ] |
660 [ tq TQ prop-seg PROP_SEG phase-seg1 PHASE-SEG1
661 phase-seg2 PHASE-SEG2 [ sjw SJW ] ]
Oliver Hartkoppf7ab97f2007-11-16 16:09:28 -0800662
Wolfgang Grandeggere20dad92009-05-15 23:39:27 +0000663 [ loopback { on | off } ]
664 [ listen-only { on | off } ]
665 [ triple-sampling { on | off } ]
Oliver Hartkoppf7ab97f2007-11-16 16:09:28 -0800666
Wolfgang Grandeggere20dad92009-05-15 23:39:27 +0000667 [ restart-ms TIME-MS ]
668 [ restart ]
Oliver Hartkoppf7ab97f2007-11-16 16:09:28 -0800669
Wolfgang Grandeggere20dad92009-05-15 23:39:27 +0000670 Where: BITRATE := { 1..1000000 }
671 SAMPLE-POINT := { 0.000..0.999 }
672 TQ := { NUMBER }
673 PROP-SEG := { 1..8 }
674 PHASE-SEG1 := { 1..8 }
675 PHASE-SEG2 := { 1..8 }
676 SJW := { 1..4 }
677 RESTART-MS := { 0 | NUMBER }
Oliver Hartkoppf7ab97f2007-11-16 16:09:28 -0800678
Wolfgang Grandeggere20dad92009-05-15 23:39:27 +0000679 - Display CAN device details and statistics:
680
681 $ ip -details -statistics link show can0
682 2: can0: <NOARP,UP,LOWER_UP,ECHO> mtu 16 qdisc pfifo_fast state UP qlen 10
683 link/can
684 can <TRIPLE-SAMPLING> state ERROR-ACTIVE restart-ms 100
685 bitrate 125000 sample_point 0.875
686 tq 125 prop-seg 6 phase-seg1 7 phase-seg2 2 sjw 1
687 sja1000: tseg1 1..16 tseg2 1..8 sjw 1..4 brp 1..64 brp-inc 1
688 clock 8000000
689 re-started bus-errors arbit-lost error-warn error-pass bus-off
690 41 17457 0 41 42 41
691 RX: bytes packets errors dropped overrun mcast
692 140859 17608 17457 0 0 0
693 TX: bytes packets errors dropped carrier collsns
694 861 112 0 41 0 0
695
696 More info to the above output:
697
698 "<TRIPLE-SAMPLING>"
699 Shows the list of selected CAN controller modes: LOOPBACK,
700 LISTEN-ONLY, or TRIPLE-SAMPLING.
701
702 "state ERROR-ACTIVE"
703 The current state of the CAN controller: "ERROR-ACTIVE",
704 "ERROR-WARNING", "ERROR-PASSIVE", "BUS-OFF" or "STOPPED"
705
706 "restart-ms 100"
707 Automatic restart delay time. If set to a non-zero value, a
708 restart of the CAN controller will be triggered automatically
709 in case of a bus-off condition after the specified delay time
710 in milliseconds. By default it's off.
711
712 "bitrate 125000 sample_point 0.875"
713 Shows the real bit-rate in bits/sec and the sample-point in the
714 range 0.000..0.999. If the calculation of bit-timing parameters
715 is enabled in the kernel (CONFIG_CAN_CALC_BITTIMING=y), the
716 bit-timing can be defined by setting the "bitrate" argument.
717 Optionally the "sample-point" can be specified. By default it's
718 0.000 assuming CIA-recommended sample-points.
719
720 "tq 125 prop-seg 6 phase-seg1 7 phase-seg2 2 sjw 1"
721 Shows the time quanta in ns, propagation segment, phase buffer
722 segment 1 and 2 and the synchronisation jump width in units of
723 tq. They allow to define the CAN bit-timing in a hardware
724 independent format as proposed by the Bosch CAN 2.0 spec (see
725 chapter 8 of http://www.semiconductors.bosch.de/pdf/can2spec.pdf).
726
727 "sja1000: tseg1 1..16 tseg2 1..8 sjw 1..4 brp 1..64 brp-inc 1
728 clock 8000000"
729 Shows the bit-timing constants of the CAN controller, here the
730 "sja1000". The minimum and maximum values of the time segment 1
731 and 2, the synchronisation jump width in units of tq, the
732 bitrate pre-scaler and the CAN system clock frequency in Hz.
733 These constants could be used for user-defined (non-standard)
734 bit-timing calculation algorithms in user-space.
735
736 "re-started bus-errors arbit-lost error-warn error-pass bus-off"
737 Shows the number of restarts, bus and arbitration lost errors,
738 and the state changes to the error-warning, error-passive and
739 bus-off state. RX overrun errors are listed in the "overrun"
740 field of the standard network statistics.
741
742 6.5.2 Setting the CAN bit-timing
743
744 The CAN bit-timing parameters can always be defined in a hardware
745 independent format as proposed in the Bosch CAN 2.0 specification
746 specifying the arguments "tq", "prop_seg", "phase_seg1", "phase_seg2"
747 and "sjw":
748
749 $ ip link set canX type can tq 125 prop-seg 6 \
750 phase-seg1 7 phase-seg2 2 sjw 1
751
752 If the kernel option CONFIG_CAN_CALC_BITTIMING is enabled, CIA
753 recommended CAN bit-timing parameters will be calculated if the bit-
754 rate is specified with the argument "bitrate":
755
756 $ ip link set canX type can bitrate 125000
757
758 Note that this works fine for the most common CAN controllers with
759 standard bit-rates but may *fail* for exotic bit-rates or CAN system
760 clock frequencies. Disabling CONFIG_CAN_CALC_BITTIMING saves some
761 space and allows user-space tools to solely determine and set the
762 bit-timing parameters. The CAN controller specific bit-timing
763 constants can be used for that purpose. They are listed by the
764 following command:
765
766 $ ip -details link show can0
767 ...
768 sja1000: clock 8000000 tseg1 1..16 tseg2 1..8 sjw 1..4 brp 1..64 brp-inc 1
769
770 6.5.3 Starting and stopping the CAN network device
771
772 A CAN network device is started or stopped as usual with the command
773 "ifconfig canX up/down" or "ip link set canX up/down". Be aware that
774 you *must* define proper bit-timing parameters for real CAN devices
775 before you can start it to avoid error-prone default settings:
776
777 $ ip link set canX up type can bitrate 125000
778
779 A device may enter the "bus-off" state if too much errors occurred on
780 the CAN bus. Then no more messages are received or sent. An automatic
781 bus-off recovery can be enabled by setting the "restart-ms" to a
782 non-zero value, e.g.:
783
784 $ ip link set canX type can restart-ms 100
785
786 Alternatively, the application may realize the "bus-off" condition
787 by monitoring CAN error frames and do a restart when appropriate with
788 the command:
789
790 $ ip link set canX type can restart
791
792 Note that a restart will also create a CAN error frame (see also
793 chapter 3.4).
794
795 6.6 Supported CAN hardware
796
797 Please check the "Kconfig" file in "drivers/net/can" to get an actual
798 list of the support CAN hardware. On the Socket CAN project website
799 (see chapter 7) there might be further drivers available, also for
800 older kernel versions.
801
8027. Socket CAN resources
803-----------------------
804
805 You can find further resources for Socket CAN like user space tools,
806 support for old kernel versions, more drivers, mailing lists, etc.
807 at the BerliOS OSS project website for Socket CAN:
808
809 http://developer.berlios.de/projects/socketcan
810
811 If you have questions, bug fixes, etc., don't hesitate to post them to
812 the Socketcan-Users mailing list. But please search the archives first.
813
8148. Credits
Oliver Hartkoppf7ab97f2007-11-16 16:09:28 -0800815----------
816
Wolfgang Grandeggere20dad92009-05-15 23:39:27 +0000817 Oliver Hartkopp (PF_CAN core, filters, drivers, bcm, SJA1000 driver)
Oliver Hartkoppf7ab97f2007-11-16 16:09:28 -0800818 Urs Thuermann (PF_CAN core, kernel integration, socket interfaces, raw, vcan)
819 Jan Kizka (RT-SocketCAN core, Socket-API reconciliation)
Wolfgang Grandeggere20dad92009-05-15 23:39:27 +0000820 Wolfgang Grandegger (RT-SocketCAN core & drivers, Raw Socket-API reviews,
821 CAN device driver interface, MSCAN driver)
Oliver Hartkoppf7ab97f2007-11-16 16:09:28 -0800822 Robert Schwebel (design reviews, PTXdist integration)
823 Marc Kleine-Budde (design reviews, Kernel 2.6 cleanups, drivers)
824 Benedikt Spranger (reviews)
825 Thomas Gleixner (LKML reviews, coding style, posting hints)
Wolfgang Grandeggere20dad92009-05-15 23:39:27 +0000826 Andrey Volkov (kernel subtree structure, ioctls, MSCAN driver)
Oliver Hartkoppf7ab97f2007-11-16 16:09:28 -0800827 Matthias Brukner (first SJA1000 CAN netdevice implementation Q2/2003)
828 Klaus Hitschler (PEAK driver integration)
829 Uwe Koppe (CAN netdevices with PF_PACKET approach)
830 Michael Schulze (driver layer loopback requirement, RT CAN drivers review)
Wolfgang Grandeggere20dad92009-05-15 23:39:27 +0000831 Pavel Pisa (Bit-timing calculation)
832 Sascha Hauer (SJA1000 platform driver)
833 Sebastian Haas (SJA1000 EMS PCI driver)
834 Markus Plessing (SJA1000 EMS PCI driver)
835 Per Dalen (SJA1000 Kvaser PCI driver)
836 Sam Ravnborg (reviews, coding style, kbuild help)