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1============================================================================
2
3can.txt
4
5Readme file for the Controller Area Network Protocol Family (aka SocketCAN)
6
7This file contains
8
9 1 Overview / What is SocketCAN
10
11 2 Motivation / Why using the socket API
12
13 3 SocketCAN concept
14 3.1 receive lists
15 3.2 local loopback of sent frames
16 3.3 network problem notifications
17
18 4 How to use SocketCAN
19 4.1 RAW protocol sockets with can_filters (SOCK_RAW)
20 4.1.1 RAW socket option CAN_RAW_FILTER
21 4.1.2 RAW socket option CAN_RAW_ERR_FILTER
22 4.1.3 RAW socket option CAN_RAW_LOOPBACK
23 4.1.4 RAW socket option CAN_RAW_RECV_OWN_MSGS
24 4.1.5 RAW socket option CAN_RAW_FD_FRAMES
25 4.1.6 RAW socket option CAN_RAW_JOIN_FILTERS
26 4.1.7 RAW socket returned message flags
27 4.2 Broadcast Manager protocol sockets (SOCK_DGRAM)
28 4.2.1 Broadcast Manager operations
29 4.2.2 Broadcast Manager message flags
30 4.2.3 Broadcast Manager transmission timers
31 4.2.4 Broadcast Manager message sequence transmission
32 4.2.5 Broadcast Manager receive filter timers
33 4.2.6 Broadcast Manager multiplex message receive filter
34 4.3 connected transport protocols (SOCK_SEQPACKET)
35 4.4 unconnected transport protocols (SOCK_DGRAM)
36
37 5 SocketCAN core module
38 5.1 can.ko module params
39 5.2 procfs content
40 5.3 writing own CAN protocol modules
41
42 6 CAN network drivers
43 6.1 general settings
44 6.2 local loopback of sent frames
45 6.3 CAN controller hardware filters
46 6.4 The virtual CAN driver (vcan)
47 6.5 The CAN network device driver interface
48 6.5.1 Netlink interface to set/get devices properties
49 6.5.2 Setting the CAN bit-timing
50 6.5.3 Starting and stopping the CAN network device
51 6.6 CAN FD (flexible data rate) driver support
52 6.7 supported CAN hardware
53
54 7 SocketCAN resources
55
56 8 Credits
57
58============================================================================
59
601. Overview / What is SocketCAN
61--------------------------------
62
63The socketcan package is an implementation of CAN protocols
64(Controller Area Network) for Linux. CAN is a networking technology
65which has widespread use in automation, embedded devices, and
66automotive fields. While there have been other CAN implementations
67for Linux based on character devices, SocketCAN uses the Berkeley
68socket API, the Linux network stack and implements the CAN device
69drivers as network interfaces. The CAN socket API has been designed
70as similar as possible to the TCP/IP protocols to allow programmers,
71familiar with network programming, to easily learn how to use CAN
72sockets.
73
742. Motivation / Why using the socket API
75----------------------------------------
76
77There have been CAN implementations for Linux before SocketCAN so the
78question arises, why we have started another project. Most existing
79implementations come as a device driver for some CAN hardware, they
80are based on character devices and provide comparatively little
81functionality. Usually, there is only a hardware-specific device
82driver which provides a character device interface to send and
83receive raw CAN frames, directly to/from the controller hardware.
84Queueing of frames and higher-level transport protocols like ISO-TP
85have to be implemented in user space applications. Also, most
86character-device implementations support only one single process to
87open the device at a time, similar to a serial interface. Exchanging
88the CAN controller requires employment of another device driver and
89often the need for adaption of large parts of the application to the
90new driver's API.
91
92SocketCAN was designed to overcome all of these limitations. A new
93protocol family has been implemented which provides a socket interface
94to user space applications and which builds upon the Linux network
95layer, enabling use all of the provided queueing functionality. A device
96driver for CAN controller hardware registers itself with the Linux
97network layer as a network device, so that CAN frames from the
98controller can be passed up to the network layer and on to the CAN
99protocol family module and also vice-versa. Also, the protocol family
100module provides an API for transport protocol modules to register, so
101that any number of transport protocols can be loaded or unloaded
102dynamically. In fact, the can core module alone does not provide any
103protocol and cannot be used without loading at least one additional
104protocol module. Multiple sockets can be opened at the same time,
105on different or the same protocol module and they can listen/send
106frames on different or the same CAN IDs. Several sockets listening on
107the same interface for frames with the same CAN ID are all passed the
108same received matching CAN frames. An application wishing to
109communicate using a specific transport protocol, e.g. ISO-TP, just
110selects that protocol when opening the socket, and then can read and
111write application data byte streams, without having to deal with
112CAN-IDs, frames, etc.
113
114Similar functionality visible from user-space could be provided by a
115character device, too, but this would lead to a technically inelegant
116solution for a couple of reasons:
117
118* Intricate usage. Instead of passing a protocol argument to
119 socket(2) and using bind(2) to select a CAN interface and CAN ID, an
120 application would have to do all these operations using ioctl(2)s.
121
122* Code duplication. A character device cannot make use of the Linux
123 network queueing code, so all that code would have to be duplicated
124 for CAN networking.
125
126* Abstraction. In most existing character-device implementations, the
127 hardware-specific device driver for a CAN controller directly
128 provides the character device for the application to work with.
129 This is at least very unusual in Unix systems for both, char and
130 block devices. For example you don't have a character device for a
131 certain UART of a serial interface, a certain sound chip in your
132 computer, a SCSI or IDE controller providing access to your hard
133 disk or tape streamer device. Instead, you have abstraction layers
134 which provide a unified character or block device interface to the
135 application on the one hand, and a interface for hardware-specific
136 device drivers on the other hand. These abstractions are provided
137 by subsystems like the tty layer, the audio subsystem or the SCSI
138 and IDE subsystems for the devices mentioned above.
139
140 The easiest way to implement a CAN device driver is as a character
141 device without such a (complete) abstraction layer, as is done by most
142 existing drivers. The right way, however, would be to add such a
143 layer with all the functionality like registering for certain CAN
144 IDs, supporting several open file descriptors and (de)multiplexing
145 CAN frames between them, (sophisticated) queueing of CAN frames, and
146 providing an API for device drivers to register with. However, then
147 it would be no more difficult, or may be even easier, to use the
148 networking framework provided by the Linux kernel, and this is what
149 SocketCAN does.
150
151 The use of the networking framework of the Linux kernel is just the
152 natural and most appropriate way to implement CAN for Linux.
153
1543. SocketCAN concept
155---------------------
156
157 As described in chapter 2 it is the main goal of SocketCAN to
158 provide a socket interface to user space applications which builds
159 upon the Linux network layer. In contrast to the commonly known
160 TCP/IP and ethernet networking, the CAN bus is a broadcast-only(!)
161 medium that has no MAC-layer addressing like ethernet. The CAN-identifier
162 (can_id) is used for arbitration on the CAN-bus. Therefore the CAN-IDs
163 have to be chosen uniquely on the bus. When designing a CAN-ECU
164 network the CAN-IDs are mapped to be sent by a specific ECU.
165 For this reason a CAN-ID can be treated best as a kind of source address.
166
167 3.1 receive lists
168
169 The network transparent access of multiple applications leads to the
170 problem that different applications may be interested in the same
171 CAN-IDs from the same CAN network interface. The SocketCAN core
172 module - which implements the protocol family CAN - provides several
173 high efficient receive lists for this reason. If e.g. a user space
174 application opens a CAN RAW socket, the raw protocol module itself
175 requests the (range of) CAN-IDs from the SocketCAN core that are
176 requested by the user. The subscription and unsubscription of
177 CAN-IDs can be done for specific CAN interfaces or for all(!) known
178 CAN interfaces with the can_rx_(un)register() functions provided to
179 CAN protocol modules by the SocketCAN core (see chapter 5).
180 To optimize the CPU usage at runtime the receive lists are split up
181 into several specific lists per device that match the requested
182 filter complexity for a given use-case.
183
184 3.2 local loopback of sent frames
185
186 As known from other networking concepts the data exchanging
187 applications may run on the same or different nodes without any
188 change (except for the according addressing information):
189
190 ___ ___ ___ _______ ___
191 | _ | | _ | | _ | | _ _ | | _ |
192 ||A|| ||B|| ||C|| ||A| |B|| ||C||
193 |___| |___| |___| |_______| |___|
194 | | | | |
195 -----------------(1)- CAN bus -(2)---------------
196
197 To ensure that application A receives the same information in the
198 example (2) as it would receive in example (1) there is need for
199 some kind of local loopback of the sent CAN frames on the appropriate
200 node.
201
202 The Linux network devices (by default) just can handle the
203 transmission and reception of media dependent frames. Due to the
204 arbitration on the CAN bus the transmission of a low prio CAN-ID
205 may be delayed by the reception of a high prio CAN frame. To
206 reflect the correct* traffic on the node the loopback of the sent
207 data has to be performed right after a successful transmission. If
208 the CAN network interface is not capable of performing the loopback for
209 some reason the SocketCAN core can do this task as a fallback solution.
210 See chapter 6.2 for details (recommended).
211
212 The loopback functionality is enabled by default to reflect standard
213 networking behaviour for CAN applications. Due to some requests from
214 the RT-SocketCAN group the loopback optionally may be disabled for each
215 separate socket. See sockopts from the CAN RAW sockets in chapter 4.1.
216
217 * = you really like to have this when you're running analyser tools
218 like 'candump' or 'cansniffer' on the (same) node.
219
220 3.3 network problem notifications
221
222 The use of the CAN bus may lead to several problems on the physical
223 and media access control layer. Detecting and logging of these lower
224 layer problems is a vital requirement for CAN users to identify
225 hardware issues on the physical transceiver layer as well as
226 arbitration problems and error frames caused by the different
227 ECUs. The occurrence of detected errors are important for diagnosis
228 and have to be logged together with the exact timestamp. For this
229 reason the CAN interface driver can generate so called Error Message
230 Frames that can optionally be passed to the user application in the
231 same way as other CAN frames. Whenever an error on the physical layer
232 or the MAC layer is detected (e.g. by the CAN controller) the driver
233 creates an appropriate error message frame. Error messages frames can
234 be requested by the user application using the common CAN filter
235 mechanisms. Inside this filter definition the (interested) type of
236 errors may be selected. The reception of error messages is disabled
237 by default. The format of the CAN error message frame is briefly
238 described in the Linux header file "include/uapi/linux/can/error.h".
239
2404. How to use SocketCAN
241------------------------
242
243 Like TCP/IP, you first need to open a socket for communicating over a
244 CAN network. Since SocketCAN implements a new protocol family, you
245 need to pass PF_CAN as the first argument to the socket(2) system
246 call. Currently, there are two CAN protocols to choose from, the raw
247 socket protocol and the broadcast manager (BCM). So to open a socket,
248 you would write
249
250 s = socket(PF_CAN, SOCK_RAW, CAN_RAW);
251
252 and
253
254 s = socket(PF_CAN, SOCK_DGRAM, CAN_BCM);
255
256 respectively. After the successful creation of the socket, you would
257 normally use the bind(2) system call to bind the socket to a CAN
258 interface (which is different from TCP/IP due to different addressing
259 - see chapter 3). After binding (CAN_RAW) or connecting (CAN_BCM)
260 the socket, you can read(2) and write(2) from/to the socket or use
261 send(2), sendto(2), sendmsg(2) and the recv* counterpart operations
262 on the socket as usual. There are also CAN specific socket options
263 described below.
264
265 The basic CAN frame structure and the sockaddr structure are defined
266 in include/linux/can.h:
267
268 struct can_frame {
269 canid_t can_id; /* 32 bit CAN_ID + EFF/RTR/ERR flags */
270 __u8 can_dlc; /* frame payload length in byte (0 .. 8) */
271 __u8 __pad; /* padding */
272 __u8 __res0; /* reserved / padding */
273 __u8 __res1; /* reserved / padding */
274 __u8 data[8] __attribute__((aligned(8)));
275 };
276
277 The alignment of the (linear) payload data[] to a 64bit boundary
278 allows the user to define their own structs and unions to easily access
279 the CAN payload. There is no given byteorder on the CAN bus by
280 default. A read(2) system call on a CAN_RAW socket transfers a
281 struct can_frame to the user space.
282
283 The sockaddr_can structure has an interface index like the
284 PF_PACKET socket, that also binds to a specific interface:
285
286 struct sockaddr_can {
287 sa_family_t can_family;
288 int can_ifindex;
289 union {
290 /* transport protocol class address info (e.g. ISOTP) */
291 struct { canid_t rx_id, tx_id; } tp;
292
293 /* reserved for future CAN protocols address information */
294 } can_addr;
295 };
296
297 To determine the interface index an appropriate ioctl() has to
298 be used (example for CAN_RAW sockets without error checking):
299
300 int s;
301 struct sockaddr_can addr;
302 struct ifreq ifr;
303
304 s = socket(PF_CAN, SOCK_RAW, CAN_RAW);
305
306 strcpy(ifr.ifr_name, "can0" );
307 ioctl(s, SIOCGIFINDEX, &ifr);
308
309 addr.can_family = AF_CAN;
310 addr.can_ifindex = ifr.ifr_ifindex;
311
312 bind(s, (struct sockaddr *)&addr, sizeof(addr));
313
314 (..)
315
316 To bind a socket to all(!) CAN interfaces the interface index must
317 be 0 (zero). In this case the socket receives CAN frames from every
318 enabled CAN interface. To determine the originating CAN interface
319 the system call recvfrom(2) may be used instead of read(2). To send
320 on a socket that is bound to 'any' interface sendto(2) is needed to
321 specify the outgoing interface.
322
323 Reading CAN frames from a bound CAN_RAW socket (see above) consists
324 of reading a struct can_frame:
325
326 struct can_frame frame;
327
328 nbytes = read(s, &frame, sizeof(struct can_frame));
329
330 if (nbytes < 0) {
331 perror("can raw socket read");
332 return 1;
333 }
334
335 /* paranoid check ... */
336 if (nbytes < sizeof(struct can_frame)) {
337 fprintf(stderr, "read: incomplete CAN frame\n");
338 return 1;
339 }
340
341 /* do something with the received CAN frame */
342
343 Writing CAN frames can be done similarly, with the write(2) system call:
344
345 nbytes = write(s, &frame, sizeof(struct can_frame));
346
347 When the CAN interface is bound to 'any' existing CAN interface
348 (addr.can_ifindex = 0) it is recommended to use recvfrom(2) if the
349 information about the originating CAN interface is needed:
350
351 struct sockaddr_can addr;
352 struct ifreq ifr;
353 socklen_t len = sizeof(addr);
354 struct can_frame frame;
355
356 nbytes = recvfrom(s, &frame, sizeof(struct can_frame),
357 0, (struct sockaddr*)&addr, &len);
358
359 /* get interface name of the received CAN frame */
360 ifr.ifr_ifindex = addr.can_ifindex;
361 ioctl(s, SIOCGIFNAME, &ifr);
362 printf("Received a CAN frame from interface %s", ifr.ifr_name);
363
364 To write CAN frames on sockets bound to 'any' CAN interface the
365 outgoing interface has to be defined certainly.
366
367 strcpy(ifr.ifr_name, "can0");
368 ioctl(s, SIOCGIFINDEX, &ifr);
369 addr.can_ifindex = ifr.ifr_ifindex;
370 addr.can_family = AF_CAN;
371
372 nbytes = sendto(s, &frame, sizeof(struct can_frame),
373 0, (struct sockaddr*)&addr, sizeof(addr));
374
375 An accurate timestamp can be obtained with an ioctl(2) call after reading
376 a message from the socket:
377
378 struct timeval tv;
379 ioctl(s, SIOCGSTAMP, &tv);
380
381 The timestamp has a resolution of one microsecond and is set automatically
382 at the reception of a CAN frame.
383
384 Remark about CAN FD (flexible data rate) support:
385
386 Generally the handling of CAN FD is very similar to the formerly described
387 examples. The new CAN FD capable CAN controllers support two different
388 bitrates for the arbitration phase and the payload phase of the CAN FD frame
389 and up to 64 bytes of payload. This extended payload length breaks all the
390 kernel interfaces (ABI) which heavily rely on the CAN frame with fixed eight
391 bytes of payload (struct can_frame) like the CAN_RAW socket. Therefore e.g.
392 the CAN_RAW socket supports a new socket option CAN_RAW_FD_FRAMES that
393 switches the socket into a mode that allows the handling of CAN FD frames
394 and (legacy) CAN frames simultaneously (see section 4.1.5).
395
396 The struct canfd_frame is defined in include/linux/can.h:
397
398 struct canfd_frame {
399 canid_t can_id; /* 32 bit CAN_ID + EFF/RTR/ERR flags */
400 __u8 len; /* frame payload length in byte (0 .. 64) */
401 __u8 flags; /* additional flags for CAN FD */
402 __u8 __res0; /* reserved / padding */
403 __u8 __res1; /* reserved / padding */
404 __u8 data[64] __attribute__((aligned(8)));
405 };
406
407 The struct canfd_frame and the existing struct can_frame have the can_id,
408 the payload length and the payload data at the same offset inside their
409 structures. This allows to handle the different structures very similar.
410 When the content of a struct can_frame is copied into a struct canfd_frame
411 all structure elements can be used as-is - only the data[] becomes extended.
412
413 When introducing the struct canfd_frame it turned out that the data length
414 code (DLC) of the struct can_frame was used as a length information as the
415 length and the DLC has a 1:1 mapping in the range of 0 .. 8. To preserve
416 the easy handling of the length information the canfd_frame.len element
417 contains a plain length value from 0 .. 64. So both canfd_frame.len and
418 can_frame.can_dlc are equal and contain a length information and no DLC.
419 For details about the distinction of CAN and CAN FD capable devices and
420 the mapping to the bus-relevant data length code (DLC), see chapter 6.6.
421
422 The length of the two CAN(FD) frame structures define the maximum transfer
423 unit (MTU) of the CAN(FD) network interface and skbuff data length. Two
424 definitions are specified for CAN specific MTUs in include/linux/can.h :
425
426 #define CAN_MTU (sizeof(struct can_frame)) == 16 => 'legacy' CAN frame
427 #define CANFD_MTU (sizeof(struct canfd_frame)) == 72 => CAN FD frame
428
429 4.1 RAW protocol sockets with can_filters (SOCK_RAW)
430
431 Using CAN_RAW sockets is extensively comparable to the commonly
432 known access to CAN character devices. To meet the new possibilities
433 provided by the multi user SocketCAN approach, some reasonable
434 defaults are set at RAW socket binding time:
435
436 - The filters are set to exactly one filter receiving everything
437 - The socket only receives valid data frames (=> no error message frames)
438 - The loopback of sent CAN frames is enabled (see chapter 3.2)
439 - The socket does not receive its own sent frames (in loopback mode)
440
441 These default settings may be changed before or after binding the socket.
442 To use the referenced definitions of the socket options for CAN_RAW
443 sockets, include <linux/can/raw.h>.
444
445 4.1.1 RAW socket option CAN_RAW_FILTER
446
447 The reception of CAN frames using CAN_RAW sockets can be controlled
448 by defining 0 .. n filters with the CAN_RAW_FILTER socket option.
449
450 The CAN filter structure is defined in include/linux/can.h:
451
452 struct can_filter {
453 canid_t can_id;
454 canid_t can_mask;
455 };
456
457 A filter matches, when
458
459 <received_can_id> & mask == can_id & mask
460
461 which is analogous to known CAN controllers hardware filter semantics.
462 The filter can be inverted in this semantic, when the CAN_INV_FILTER
463 bit is set in can_id element of the can_filter structure. In
464 contrast to CAN controller hardware filters the user may set 0 .. n
465 receive filters for each open socket separately:
466
467 struct can_filter rfilter[2];
468
469 rfilter[0].can_id = 0x123;
470 rfilter[0].can_mask = CAN_SFF_MASK;
471 rfilter[1].can_id = 0x200;
472 rfilter[1].can_mask = 0x700;
473
474 setsockopt(s, SOL_CAN_RAW, CAN_RAW_FILTER, &rfilter, sizeof(rfilter));
475
476 To disable the reception of CAN frames on the selected CAN_RAW socket:
477
478 setsockopt(s, SOL_CAN_RAW, CAN_RAW_FILTER, NULL, 0);
479
480 To set the filters to zero filters is quite obsolete as to not read
481 data causes the raw socket to discard the received CAN frames. But
482 having this 'send only' use-case we may remove the receive list in the
483 Kernel to save a little (really a very little!) CPU usage.
484
485 4.1.1.1 CAN filter usage optimisation
486
487 The CAN filters are processed in per-device filter lists at CAN frame
488 reception time. To reduce the number of checks that need to be performed
489 while walking through the filter lists the CAN core provides an optimized
490 filter handling when the filter subscription focusses on a single CAN ID.
491
492 For the possible 2048 SFF CAN identifiers the identifier is used as an index
493 to access the corresponding subscription list without any further checks.
494 For the 2^29 possible EFF CAN identifiers a 10 bit XOR folding is used as
495 hash function to retrieve the EFF table index.
496
497 To benefit from the optimized filters for single CAN identifiers the
498 CAN_SFF_MASK or CAN_EFF_MASK have to be set into can_filter.mask together
499 with set CAN_EFF_FLAG and CAN_RTR_FLAG bits. A set CAN_EFF_FLAG bit in the
500 can_filter.mask makes clear that it matters whether a SFF or EFF CAN ID is
501 subscribed. E.g. in the example from above
502
503 rfilter[0].can_id = 0x123;
504 rfilter[0].can_mask = CAN_SFF_MASK;
505
506 both SFF frames with CAN ID 0x123 and EFF frames with 0xXXXXX123 can pass.
507
508 To filter for only 0x123 (SFF) and 0x12345678 (EFF) CAN identifiers the
509 filter has to be defined in this way to benefit from the optimized filters:
510
511 struct can_filter rfilter[2];
512
513 rfilter[0].can_id = 0x123;
514 rfilter[0].can_mask = (CAN_EFF_FLAG | CAN_RTR_FLAG | CAN_SFF_MASK);
515 rfilter[1].can_id = 0x12345678 | CAN_EFF_FLAG;
516 rfilter[1].can_mask = (CAN_EFF_FLAG | CAN_RTR_FLAG | CAN_EFF_MASK);
517
518 setsockopt(s, SOL_CAN_RAW, CAN_RAW_FILTER, &rfilter, sizeof(rfilter));
519
520 4.1.2 RAW socket option CAN_RAW_ERR_FILTER
521
522 As described in chapter 3.3 the CAN interface driver can generate so
523 called Error Message Frames that can optionally be passed to the user
524 application in the same way as other CAN frames. The possible
525 errors are divided into different error classes that may be filtered
526 using the appropriate error mask. To register for every possible
527 error condition CAN_ERR_MASK can be used as value for the error mask.
528 The values for the error mask are defined in linux/can/error.h .
529
530 can_err_mask_t err_mask = ( CAN_ERR_TX_TIMEOUT | CAN_ERR_BUSOFF );
531
532 setsockopt(s, SOL_CAN_RAW, CAN_RAW_ERR_FILTER,
533 &err_mask, sizeof(err_mask));
534
535 4.1.3 RAW socket option CAN_RAW_LOOPBACK
536
537 To meet multi user needs the local loopback is enabled by default
538 (see chapter 3.2 for details). But in some embedded use-cases
539 (e.g. when only one application uses the CAN bus) this loopback
540 functionality can be disabled (separately for each socket):
541
542 int loopback = 0; /* 0 = disabled, 1 = enabled (default) */
543
544 setsockopt(s, SOL_CAN_RAW, CAN_RAW_LOOPBACK, &loopback, sizeof(loopback));
545
546 4.1.4 RAW socket option CAN_RAW_RECV_OWN_MSGS
547
548 When the local loopback is enabled, all the sent CAN frames are
549 looped back to the open CAN sockets that registered for the CAN
550 frames' CAN-ID on this given interface to meet the multi user
551 needs. The reception of the CAN frames on the same socket that was
552 sending the CAN frame is assumed to be unwanted and therefore
553 disabled by default. This default behaviour may be changed on
554 demand:
555
556 int recv_own_msgs = 1; /* 0 = disabled (default), 1 = enabled */
557
558 setsockopt(s, SOL_CAN_RAW, CAN_RAW_RECV_OWN_MSGS,
559 &recv_own_msgs, sizeof(recv_own_msgs));
560
561 4.1.5 RAW socket option CAN_RAW_FD_FRAMES
562
563 CAN FD support in CAN_RAW sockets can be enabled with a new socket option
564 CAN_RAW_FD_FRAMES which is off by default. When the new socket option is
565 not supported by the CAN_RAW socket (e.g. on older kernels), switching the
566 CAN_RAW_FD_FRAMES option returns the error -ENOPROTOOPT.
567
568 Once CAN_RAW_FD_FRAMES is enabled the application can send both CAN frames
569 and CAN FD frames. OTOH the application has to handle CAN and CAN FD frames
570 when reading from the socket.
571
572 CAN_RAW_FD_FRAMES enabled: CAN_MTU and CANFD_MTU are allowed
573 CAN_RAW_FD_FRAMES disabled: only CAN_MTU is allowed (default)
574
575 Example:
576 [ remember: CANFD_MTU == sizeof(struct canfd_frame) ]
577
578 struct canfd_frame cfd;
579
580 nbytes = read(s, &cfd, CANFD_MTU);
581
582 if (nbytes == CANFD_MTU) {
583 printf("got CAN FD frame with length %d\n", cfd.len);
584 /* cfd.flags contains valid data */
585 } else if (nbytes == CAN_MTU) {
586 printf("got legacy CAN frame with length %d\n", cfd.len);
587 /* cfd.flags is undefined */
588 } else {
589 fprintf(stderr, "read: invalid CAN(FD) frame\n");
590 return 1;
591 }
592
593 /* the content can be handled independently from the received MTU size */
594
595 printf("can_id: %X data length: %d data: ", cfd.can_id, cfd.len);
596 for (i = 0; i < cfd.len; i++)
597 printf("%02X ", cfd.data[i]);
598
599 When reading with size CANFD_MTU only returns CAN_MTU bytes that have
600 been received from the socket a legacy CAN frame has been read into the
601 provided CAN FD structure. Note that the canfd_frame.flags data field is
602 not specified in the struct can_frame and therefore it is only valid in
603 CANFD_MTU sized CAN FD frames.
604
605 Implementation hint for new CAN applications:
606
607 To build a CAN FD aware application use struct canfd_frame as basic CAN
608 data structure for CAN_RAW based applications. When the application is
609 executed on an older Linux kernel and switching the CAN_RAW_FD_FRAMES
610 socket option returns an error: No problem. You'll get legacy CAN frames
611 or CAN FD frames and can process them the same way.
612
613 When sending to CAN devices make sure that the device is capable to handle
614 CAN FD frames by checking if the device maximum transfer unit is CANFD_MTU.
615 The CAN device MTU can be retrieved e.g. with a SIOCGIFMTU ioctl() syscall.
616
617 4.1.6 RAW socket option CAN_RAW_JOIN_FILTERS
618
619 The CAN_RAW socket can set multiple CAN identifier specific filters that
620 lead to multiple filters in the af_can.c filter processing. These filters
621 are indenpendent from each other which leads to logical OR'ed filters when
622 applied (see 4.1.1).
623
624 This socket option joines the given CAN filters in the way that only CAN
625 frames are passed to user space that matched *all* given CAN filters. The
626 semantic for the applied filters is therefore changed to a logical AND.
627
628 This is useful especially when the filterset is a combination of filters
629 where the CAN_INV_FILTER flag is set in order to notch single CAN IDs or
630 CAN ID ranges from the incoming traffic.
631
632 4.1.7 RAW socket returned message flags
633
634 When using recvmsg() call, the msg->msg_flags may contain following flags:
635
636 MSG_DONTROUTE: set when the received frame was created on the local host.
637
638 MSG_CONFIRM: set when the frame was sent via the socket it is received on.
639 This flag can be interpreted as a 'transmission confirmation' when the
640 CAN driver supports the echo of frames on driver level, see 3.2 and 6.2.
641 In order to receive such messages, CAN_RAW_RECV_OWN_MSGS must be set.
642
643 4.2 Broadcast Manager protocol sockets (SOCK_DGRAM)
644
645 The Broadcast Manager protocol provides a command based configuration
646 interface to filter and send (e.g. cyclic) CAN messages in kernel space.
647
648 Receive filters can be used to down sample frequent messages; detect events
649 such as message contents changes, packet length changes, and do time-out
650 monitoring of received messages.
651
652 Periodic transmission tasks of CAN frames or a sequence of CAN frames can be
653 created and modified at runtime; both the message content and the two
654 possible transmit intervals can be altered.
655
656 A BCM socket is not intended for sending individual CAN frames using the
657 struct can_frame as known from the CAN_RAW socket. Instead a special BCM
658 configuration message is defined. The basic BCM configuration message used
659 to communicate with the broadcast manager and the available operations are
660 defined in the linux/can/bcm.h include. The BCM message consists of a
661 message header with a command ('opcode') followed by zero or more CAN frames.
662 The broadcast manager sends responses to user space in the same form:
663
664 struct bcm_msg_head {
665 __u32 opcode; /* command */
666 __u32 flags; /* special flags */
667 __u32 count; /* run 'count' times with ival1 */
668 struct timeval ival1, ival2; /* count and subsequent interval */
669 canid_t can_id; /* unique can_id for task */
670 __u32 nframes; /* number of can_frames following */
671 struct can_frame frames[0];
672 };
673
674 The aligned payload 'frames' uses the same basic CAN frame structure defined
675 at the beginning of section 4 and in the include/linux/can.h include. All
676 messages to the broadcast manager from user space have this structure.
677
678 Note a CAN_BCM socket must be connected instead of bound after socket
679 creation (example without error checking):
680
681 int s;
682 struct sockaddr_can addr;
683 struct ifreq ifr;
684
685 s = socket(PF_CAN, SOCK_DGRAM, CAN_BCM);
686
687 strcpy(ifr.ifr_name, "can0");
688 ioctl(s, SIOCGIFINDEX, &ifr);
689
690 addr.can_family = AF_CAN;
691 addr.can_ifindex = ifr.ifr_ifindex;
692
693 connect(s, (struct sockaddr *)&addr, sizeof(addr));
694
695 (..)
696
697 The broadcast manager socket is able to handle any number of in flight
698 transmissions or receive filters concurrently. The different RX/TX jobs are
699 distinguished by the unique can_id in each BCM message. However additional
700 CAN_BCM sockets are recommended to communicate on multiple CAN interfaces.
701 When the broadcast manager socket is bound to 'any' CAN interface (=> the
702 interface index is set to zero) the configured receive filters apply to any
703 CAN interface unless the sendto() syscall is used to overrule the 'any' CAN
704 interface index. When using recvfrom() instead of read() to retrieve BCM
705 socket messages the originating CAN interface is provided in can_ifindex.
706
707 4.2.1 Broadcast Manager operations
708
709 The opcode defines the operation for the broadcast manager to carry out,
710 or details the broadcast managers response to several events, including
711 user requests.
712
713 Transmit Operations (user space to broadcast manager):
714
715 TX_SETUP: Create (cyclic) transmission task.
716
717 TX_DELETE: Remove (cyclic) transmission task, requires only can_id.
718
719 TX_READ: Read properties of (cyclic) transmission task for can_id.
720
721 TX_SEND: Send one CAN frame.
722
723 Transmit Responses (broadcast manager to user space):
724
725 TX_STATUS: Reply to TX_READ request (transmission task configuration).
726
727 TX_EXPIRED: Notification when counter finishes sending at initial interval
728 'ival1'. Requires the TX_COUNTEVT flag to be set at TX_SETUP.
729
730 Receive Operations (user space to broadcast manager):
731
732 RX_SETUP: Create RX content filter subscription.
733
734 RX_DELETE: Remove RX content filter subscription, requires only can_id.
735
736 RX_READ: Read properties of RX content filter subscription for can_id.
737
738 Receive Responses (broadcast manager to user space):
739
740 RX_STATUS: Reply to RX_READ request (filter task configuration).
741
742 RX_TIMEOUT: Cyclic message is detected to be absent (timer ival1 expired).
743
744 RX_CHANGED: BCM message with updated CAN frame (detected content change).
745 Sent on first message received or on receipt of revised CAN messages.
746
747 4.2.2 Broadcast Manager message flags
748
749 When sending a message to the broadcast manager the 'flags' element may
750 contain the following flag definitions which influence the behaviour:
751
752 SETTIMER: Set the values of ival1, ival2 and count
753
754 STARTTIMER: Start the timer with the actual values of ival1, ival2
755 and count. Starting the timer leads simultaneously to emit a CAN frame.
756
757 TX_COUNTEVT: Create the message TX_EXPIRED when count expires
758
759 TX_ANNOUNCE: A change of data by the process is emitted immediately.
760
761 TX_CP_CAN_ID: Copies the can_id from the message header to each
762 subsequent frame in frames. This is intended as usage simplification. For
763 TX tasks the unique can_id from the message header may differ from the
764 can_id(s) stored for transmission in the subsequent struct can_frame(s).
765
766 RX_FILTER_ID: Filter by can_id alone, no frames required (nframes=0).
767
768 RX_CHECK_DLC: A change of the DLC leads to an RX_CHANGED.
769
770 RX_NO_AUTOTIMER: Prevent automatically starting the timeout monitor.
771
772 RX_ANNOUNCE_RESUME: If passed at RX_SETUP and a receive timeout occurred, a
773 RX_CHANGED message will be generated when the (cyclic) receive restarts.
774
775 TX_RESET_MULTI_IDX: Reset the index for the multiple frame transmission.
776
777 RX_RTR_FRAME: Send reply for RTR-request (placed in op->frames[0]).
778
779 4.2.3 Broadcast Manager transmission timers
780
781 Periodic transmission configurations may use up to two interval timers.
782 In this case the BCM sends a number of messages ('count') at an interval
783 'ival1', then continuing to send at another given interval 'ival2'. When
784 only one timer is needed 'count' is set to zero and only 'ival2' is used.
785 When SET_TIMER and START_TIMER flag were set the timers are activated.
786 The timer values can be altered at runtime when only SET_TIMER is set.
787
788 4.2.4 Broadcast Manager message sequence transmission
789
790 Up to 256 CAN frames can be transmitted in a sequence in the case of a cyclic
791 TX task configuration. The number of CAN frames is provided in the 'nframes'
792 element of the BCM message head. The defined number of CAN frames are added
793 as array to the TX_SETUP BCM configuration message.
794
795 /* create a struct to set up a sequence of four CAN frames */
796 struct {
797 struct bcm_msg_head msg_head;
798 struct can_frame frame[4];
799 } mytxmsg;
800
801 (..)
802 mytxmsg.nframes = 4;
803 (..)
804
805 write(s, &mytxmsg, sizeof(mytxmsg));
806
807 With every transmission the index in the array of CAN frames is increased
808 and set to zero at index overflow.
809
810 4.2.5 Broadcast Manager receive filter timers
811
812 The timer values ival1 or ival2 may be set to non-zero values at RX_SETUP.
813 When the SET_TIMER flag is set the timers are enabled:
814
815 ival1: Send RX_TIMEOUT when a received message is not received again within
816 the given time. When START_TIMER is set at RX_SETUP the timeout detection
817 is activated directly - even without a former CAN frame reception.
818
819 ival2: Throttle the received message rate down to the value of ival2. This
820 is useful to reduce messages for the application when the signal inside the
821 CAN frame is stateless as state changes within the ival2 periode may get
822 lost.
823
824 4.2.6 Broadcast Manager multiplex message receive filter
825
826 To filter for content changes in multiplex message sequences an array of more
827 than one CAN frames can be passed in a RX_SETUP configuration message. The
828 data bytes of the first CAN frame contain the mask of relevant bits that
829 have to match in the subsequent CAN frames with the received CAN frame.
830 If one of the subsequent CAN frames is matching the bits in that frame data
831 mark the relevant content to be compared with the previous received content.
832 Up to 257 CAN frames (multiplex filter bit mask CAN frame plus 256 CAN
833 filters) can be added as array to the TX_SETUP BCM configuration message.
834
835 /* usually used to clear CAN frame data[] - beware of endian problems! */
836 #define U64_DATA(p) (*(unsigned long long*)(p)->data)
837
838 struct {
839 struct bcm_msg_head msg_head;
840 struct can_frame frame[5];
841 } msg;
842
843 msg.msg_head.opcode = RX_SETUP;
844 msg.msg_head.can_id = 0x42;
845 msg.msg_head.flags = 0;
846 msg.msg_head.nframes = 5;
847 U64_DATA(&msg.frame[0]) = 0xFF00000000000000ULL; /* MUX mask */
848 U64_DATA(&msg.frame[1]) = 0x01000000000000FFULL; /* data mask (MUX 0x01) */
849 U64_DATA(&msg.frame[2]) = 0x0200FFFF000000FFULL; /* data mask (MUX 0x02) */
850 U64_DATA(&msg.frame[3]) = 0x330000FFFFFF0003ULL; /* data mask (MUX 0x33) */
851 U64_DATA(&msg.frame[4]) = 0x4F07FC0FF0000000ULL; /* data mask (MUX 0x4F) */
852
853 write(s, &msg, sizeof(msg));
854
855 4.3 connected transport protocols (SOCK_SEQPACKET)
856 4.4 unconnected transport protocols (SOCK_DGRAM)
857
858
8595. SocketCAN core module
860-------------------------
861
862 The SocketCAN core module implements the protocol family
863 PF_CAN. CAN protocol modules are loaded by the core module at
864 runtime. The core module provides an interface for CAN protocol
865 modules to subscribe needed CAN IDs (see chapter 3.1).
866
867 5.1 can.ko module params
868
869 - stats_timer: To calculate the SocketCAN core statistics
870 (e.g. current/maximum frames per second) this 1 second timer is
871 invoked at can.ko module start time by default. This timer can be
872 disabled by using stattimer=0 on the module commandline.
873
874 - debug: (removed since SocketCAN SVN r546)
875
876 5.2 procfs content
877
878 As described in chapter 3.1 the SocketCAN core uses several filter
879 lists to deliver received CAN frames to CAN protocol modules. These
880 receive lists, their filters and the count of filter matches can be
881 checked in the appropriate receive list. All entries contain the
882 device and a protocol module identifier:
883
884 foo@bar:~$ cat /proc/net/can/rcvlist_all
885
886 receive list 'rx_all':
887 (vcan3: no entry)
888 (vcan2: no entry)
889 (vcan1: no entry)
890 device can_id can_mask function userdata matches ident
891 vcan0 000 00000000 f88e6370 f6c6f400 0 raw
892 (any: no entry)
893
894 In this example an application requests any CAN traffic from vcan0.
895
896 rcvlist_all - list for unfiltered entries (no filter operations)
897 rcvlist_eff - list for single extended frame (EFF) entries
898 rcvlist_err - list for error message frames masks
899 rcvlist_fil - list for mask/value filters
900 rcvlist_inv - list for mask/value filters (inverse semantic)
901 rcvlist_sff - list for single standard frame (SFF) entries
902
903 Additional procfs files in /proc/net/can
904
905 stats - SocketCAN core statistics (rx/tx frames, match ratios, ...)
906 reset_stats - manual statistic reset
907 version - prints the SocketCAN core version and the ABI version
908
909 5.3 writing own CAN protocol modules
910
911 To implement a new protocol in the protocol family PF_CAN a new
912 protocol has to be defined in include/linux/can.h .
913 The prototypes and definitions to use the SocketCAN core can be
914 accessed by including include/linux/can/core.h .
915 In addition to functions that register the CAN protocol and the
916 CAN device notifier chain there are functions to subscribe CAN
917 frames received by CAN interfaces and to send CAN frames:
918
919 can_rx_register - subscribe CAN frames from a specific interface
920 can_rx_unregister - unsubscribe CAN frames from a specific interface
921 can_send - transmit a CAN frame (optional with local loopback)
922
923 For details see the kerneldoc documentation in net/can/af_can.c or
924 the source code of net/can/raw.c or net/can/bcm.c .
925
9266. CAN network drivers
927----------------------
928
929 Writing a CAN network device driver is much easier than writing a
930 CAN character device driver. Similar to other known network device
931 drivers you mainly have to deal with:
932
933 - TX: Put the CAN frame from the socket buffer to the CAN controller.
934 - RX: Put the CAN frame from the CAN controller to the socket buffer.
935
936 See e.g. at Documentation/networking/netdevices.txt . The differences
937 for writing CAN network device driver are described below:
938
939 6.1 general settings
940
941 dev->type = ARPHRD_CAN; /* the netdevice hardware type */
942 dev->flags = IFF_NOARP; /* CAN has no arp */
943
944 dev->mtu = CAN_MTU; /* sizeof(struct can_frame) -> legacy CAN interface */
945
946 or alternative, when the controller supports CAN with flexible data rate:
947 dev->mtu = CANFD_MTU; /* sizeof(struct canfd_frame) -> CAN FD interface */
948
949 The struct can_frame or struct canfd_frame is the payload of each socket
950 buffer (skbuff) in the protocol family PF_CAN.
951
952 6.2 local loopback of sent frames
953
954 As described in chapter 3.2 the CAN network device driver should
955 support a local loopback functionality similar to the local echo
956 e.g. of tty devices. In this case the driver flag IFF_ECHO has to be
957 set to prevent the PF_CAN core from locally echoing sent frames
958 (aka loopback) as fallback solution:
959
960 dev->flags = (IFF_NOARP | IFF_ECHO);
961
962 6.3 CAN controller hardware filters
963
964 To reduce the interrupt load on deep embedded systems some CAN
965 controllers support the filtering of CAN IDs or ranges of CAN IDs.
966 These hardware filter capabilities vary from controller to
967 controller and have to be identified as not feasible in a multi-user
968 networking approach. The use of the very controller specific
969 hardware filters could make sense in a very dedicated use-case, as a
970 filter on driver level would affect all users in the multi-user
971 system. The high efficient filter sets inside the PF_CAN core allow
972 to set different multiple filters for each socket separately.
973 Therefore the use of hardware filters goes to the category 'handmade
974 tuning on deep embedded systems'. The author is running a MPC603e
975 @133MHz with four SJA1000 CAN controllers from 2002 under heavy bus
976 load without any problems ...
977
978 6.4 The virtual CAN driver (vcan)
979
980 Similar to the network loopback devices, vcan offers a virtual local
981 CAN interface. A full qualified address on CAN consists of
982
983 - a unique CAN Identifier (CAN ID)
984 - the CAN bus this CAN ID is transmitted on (e.g. can0)
985
986 so in common use cases more than one virtual CAN interface is needed.
987
988 The virtual CAN interfaces allow the transmission and reception of CAN
989 frames without real CAN controller hardware. Virtual CAN network
990 devices are usually named 'vcanX', like vcan0 vcan1 vcan2 ...
991 When compiled as a module the virtual CAN driver module is called vcan.ko
992
993 Since Linux Kernel version 2.6.24 the vcan driver supports the Kernel
994 netlink interface to create vcan network devices. The creation and
995 removal of vcan network devices can be managed with the ip(8) tool:
996
997 - Create a virtual CAN network interface:
998 $ ip link add type vcan
999
1000 - Create a virtual CAN network interface with a specific name 'vcan42':
1001 $ ip link add dev vcan42 type vcan
1002
1003 - Remove a (virtual CAN) network interface 'vcan42':
1004 $ ip link del vcan42
1005
1006 6.5 The CAN network device driver interface
1007
1008 The CAN network device driver interface provides a generic interface
1009 to setup, configure and monitor CAN network devices. The user can then
1010 configure the CAN device, like setting the bit-timing parameters, via
1011 the netlink interface using the program "ip" from the "IPROUTE2"
1012 utility suite. The following chapter describes briefly how to use it.
1013 Furthermore, the interface uses a common data structure and exports a
1014 set of common functions, which all real CAN network device drivers
1015 should use. Please have a look to the SJA1000 or MSCAN driver to
1016 understand how to use them. The name of the module is can-dev.ko.
1017
1018 6.5.1 Netlink interface to set/get devices properties
1019
1020 The CAN device must be configured via netlink interface. The supported
1021 netlink message types are defined and briefly described in
1022 "include/linux/can/netlink.h". CAN link support for the program "ip"
1023 of the IPROUTE2 utility suite is available and it can be used as shown
1024 below:
1025
1026 - Setting CAN device properties:
1027
1028 $ ip link set can0 type can help
1029 Usage: ip link set DEVICE type can
1030 [ bitrate BITRATE [ sample-point SAMPLE-POINT] ] |
1031 [ tq TQ prop-seg PROP_SEG phase-seg1 PHASE-SEG1
1032 phase-seg2 PHASE-SEG2 [ sjw SJW ] ]
1033
1034 [ dbitrate BITRATE [ dsample-point SAMPLE-POINT] ] |
1035 [ dtq TQ dprop-seg PROP_SEG dphase-seg1 PHASE-SEG1
1036 dphase-seg2 PHASE-SEG2 [ dsjw SJW ] ]
1037
1038 [ loopback { on | off } ]
1039 [ listen-only { on | off } ]
1040 [ triple-sampling { on | off } ]
1041 [ one-shot { on | off } ]
1042 [ berr-reporting { on | off } ]
1043 [ fd { on | off } ]
1044 [ fd-non-iso { on | off } ]
1045 [ presume-ack { on | off } ]
1046
1047 [ restart-ms TIME-MS ]
1048 [ restart ]
1049
1050 Where: BITRATE := { 1..1000000 }
1051 SAMPLE-POINT := { 0.000..0.999 }
1052 TQ := { NUMBER }
1053 PROP-SEG := { 1..8 }
1054 PHASE-SEG1 := { 1..8 }
1055 PHASE-SEG2 := { 1..8 }
1056 SJW := { 1..4 }
1057 RESTART-MS := { 0 | NUMBER }
1058
1059 - Display CAN device details and statistics:
1060
1061 $ ip -details -statistics link show can0
1062 2: can0: <NOARP,UP,LOWER_UP,ECHO> mtu 16 qdisc pfifo_fast state UP qlen 10
1063 link/can
1064 can <TRIPLE-SAMPLING> state ERROR-ACTIVE restart-ms 100
1065 bitrate 125000 sample_point 0.875
1066 tq 125 prop-seg 6 phase-seg1 7 phase-seg2 2 sjw 1
1067 sja1000: tseg1 1..16 tseg2 1..8 sjw 1..4 brp 1..64 brp-inc 1
1068 clock 8000000
1069 re-started bus-errors arbit-lost error-warn error-pass bus-off
1070 41 17457 0 41 42 41
1071 RX: bytes packets errors dropped overrun mcast
1072 140859 17608 17457 0 0 0
1073 TX: bytes packets errors dropped carrier collsns
1074 861 112 0 41 0 0
1075
1076 More info to the above output:
1077
1078 "<TRIPLE-SAMPLING>"
1079 Shows the list of selected CAN controller modes: LOOPBACK,
1080 LISTEN-ONLY, or TRIPLE-SAMPLING.
1081
1082 "state ERROR-ACTIVE"
1083 The current state of the CAN controller: "ERROR-ACTIVE",
1084 "ERROR-WARNING", "ERROR-PASSIVE", "BUS-OFF" or "STOPPED"
1085
1086 "restart-ms 100"
1087 Automatic restart delay time. If set to a non-zero value, a
1088 restart of the CAN controller will be triggered automatically
1089 in case of a bus-off condition after the specified delay time
1090 in milliseconds. By default it's off.
1091
1092 "bitrate 125000 sample-point 0.875"
1093 Shows the real bit-rate in bits/sec and the sample-point in the
1094 range 0.000..0.999. If the calculation of bit-timing parameters
1095 is enabled in the kernel (CONFIG_CAN_CALC_BITTIMING=y), the
1096 bit-timing can be defined by setting the "bitrate" argument.
1097 Optionally the "sample-point" can be specified. By default it's
1098 0.000 assuming CIA-recommended sample-points.
1099
1100 "tq 125 prop-seg 6 phase-seg1 7 phase-seg2 2 sjw 1"
1101 Shows the time quanta in ns, propagation segment, phase buffer
1102 segment 1 and 2 and the synchronisation jump width in units of
1103 tq. They allow to define the CAN bit-timing in a hardware
1104 independent format as proposed by the Bosch CAN 2.0 spec (see
1105 chapter 8 of http://www.semiconductors.bosch.de/pdf/can2spec.pdf).
1106
1107 "sja1000: tseg1 1..16 tseg2 1..8 sjw 1..4 brp 1..64 brp-inc 1
1108 clock 8000000"
1109 Shows the bit-timing constants of the CAN controller, here the
1110 "sja1000". The minimum and maximum values of the time segment 1
1111 and 2, the synchronisation jump width in units of tq, the
1112 bitrate pre-scaler and the CAN system clock frequency in Hz.
1113 These constants could be used for user-defined (non-standard)
1114 bit-timing calculation algorithms in user-space.
1115
1116 "re-started bus-errors arbit-lost error-warn error-pass bus-off"
1117 Shows the number of restarts, bus and arbitration lost errors,
1118 and the state changes to the error-warning, error-passive and
1119 bus-off state. RX overrun errors are listed in the "overrun"
1120 field of the standard network statistics.
1121
1122 6.5.2 Setting the CAN bit-timing
1123
1124 The CAN bit-timing parameters can always be defined in a hardware
1125 independent format as proposed in the Bosch CAN 2.0 specification
1126 specifying the arguments "tq", "prop_seg", "phase_seg1", "phase_seg2"
1127 and "sjw":
1128
1129 $ ip link set canX type can tq 125 prop-seg 6 \
1130 phase-seg1 7 phase-seg2 2 sjw 1
1131
1132 If the kernel option CONFIG_CAN_CALC_BITTIMING is enabled, CIA
1133 recommended CAN bit-timing parameters will be calculated if the bit-
1134 rate is specified with the argument "bitrate":
1135
1136 $ ip link set canX type can bitrate 125000
1137
1138 Note that this works fine for the most common CAN controllers with
1139 standard bit-rates but may *fail* for exotic bit-rates or CAN system
1140 clock frequencies. Disabling CONFIG_CAN_CALC_BITTIMING saves some
1141 space and allows user-space tools to solely determine and set the
1142 bit-timing parameters. The CAN controller specific bit-timing
1143 constants can be used for that purpose. They are listed by the
1144 following command:
1145
1146 $ ip -details link show can0
1147 ...
1148 sja1000: clock 8000000 tseg1 1..16 tseg2 1..8 sjw 1..4 brp 1..64 brp-inc 1
1149
1150 6.5.3 Starting and stopping the CAN network device
1151
1152 A CAN network device is started or stopped as usual with the command
1153 "ifconfig canX up/down" or "ip link set canX up/down". Be aware that
1154 you *must* define proper bit-timing parameters for real CAN devices
1155 before you can start it to avoid error-prone default settings:
1156
1157 $ ip link set canX up type can bitrate 125000
1158
1159 A device may enter the "bus-off" state if too many errors occurred on
1160 the CAN bus. Then no more messages are received or sent. An automatic
1161 bus-off recovery can be enabled by setting the "restart-ms" to a
1162 non-zero value, e.g.:
1163
1164 $ ip link set canX type can restart-ms 100
1165
1166 Alternatively, the application may realize the "bus-off" condition
1167 by monitoring CAN error message frames and do a restart when
1168 appropriate with the command:
1169
1170 $ ip link set canX type can restart
1171
1172 Note that a restart will also create a CAN error message frame (see
1173 also chapter 3.3).
1174
1175 6.6 CAN FD (flexible data rate) driver support
1176
1177 CAN FD capable CAN controllers support two different bitrates for the
1178 arbitration phase and the payload phase of the CAN FD frame. Therefore a
1179 second bit timing has to be specified in order to enable the CAN FD bitrate.
1180
1181 Additionally CAN FD capable CAN controllers support up to 64 bytes of
1182 payload. The representation of this length in can_frame.can_dlc and
1183 canfd_frame.len for userspace applications and inside the Linux network
1184 layer is a plain value from 0 .. 64 instead of the CAN 'data length code'.
1185 The data length code was a 1:1 mapping to the payload length in the legacy
1186 CAN frames anyway. The payload length to the bus-relevant DLC mapping is
1187 only performed inside the CAN drivers, preferably with the helper
1188 functions can_dlc2len() and can_len2dlc().
1189
1190 The CAN netdevice driver capabilities can be distinguished by the network
1191 devices maximum transfer unit (MTU):
1192
1193 MTU = 16 (CAN_MTU) => sizeof(struct can_frame) => 'legacy' CAN device
1194 MTU = 72 (CANFD_MTU) => sizeof(struct canfd_frame) => CAN FD capable device
1195
1196 The CAN device MTU can be retrieved e.g. with a SIOCGIFMTU ioctl() syscall.
1197 N.B. CAN FD capable devices can also handle and send legacy CAN frames.
1198
1199 When configuring CAN FD capable CAN controllers an additional 'data' bitrate
1200 has to be set. This bitrate for the data phase of the CAN FD frame has to be
1201 at least the bitrate which was configured for the arbitration phase. This
1202 second bitrate is specified analogue to the first bitrate but the bitrate
1203 setting keywords for the 'data' bitrate start with 'd' e.g. dbitrate,
1204 dsample-point, dsjw or dtq and similar settings. When a data bitrate is set
1205 within the configuration process the controller option "fd on" can be
1206 specified to enable the CAN FD mode in the CAN controller. This controller
1207 option also switches the device MTU to 72 (CANFD_MTU).
1208
1209 The first CAN FD specification presented as whitepaper at the International
1210 CAN Conference 2012 needed to be improved for data integrity reasons.
1211 Therefore two CAN FD implementations have to be distinguished today:
1212
1213 - ISO compliant: The ISO 11898-1:2015 CAN FD implementation (default)
1214 - non-ISO compliant: The CAN FD implementation following the 2012 whitepaper
1215
1216 Finally there are three types of CAN FD controllers:
1217
1218 1. ISO compliant (fixed)
1219 2. non-ISO compliant (fixed, like the M_CAN IP core v3.0.1 in m_can.c)
1220 3. ISO/non-ISO CAN FD controllers (switchable, like the PEAK PCAN-USB FD)
1221
1222 The current ISO/non-ISO mode is announced by the CAN controller driver via
1223 netlink and displayed by the 'ip' tool (controller option FD-NON-ISO).
1224 The ISO/non-ISO-mode can be altered by setting 'fd-non-iso {on|off}' for
1225 switchable CAN FD controllers only.
1226
1227 Example configuring 500 kbit/s arbitration bitrate and 4 Mbit/s data bitrate:
1228
1229 $ ip link set can0 up type can bitrate 500000 sample-point 0.75 \
1230 dbitrate 4000000 dsample-point 0.8 fd on
1231 $ ip -details link show can0
1232 5: can0: <NOARP,UP,LOWER_UP,ECHO> mtu 72 qdisc pfifo_fast state UNKNOWN \
1233 mode DEFAULT group default qlen 10
1234 link/can promiscuity 0
1235 can <FD> state ERROR-ACTIVE (berr-counter tx 0 rx 0) restart-ms 0
1236 bitrate 500000 sample-point 0.750
1237 tq 50 prop-seg 14 phase-seg1 15 phase-seg2 10 sjw 1
1238 pcan_usb_pro_fd: tseg1 1..64 tseg2 1..16 sjw 1..16 brp 1..1024 \
1239 brp-inc 1
1240 dbitrate 4000000 dsample-point 0.800
1241 dtq 12 dprop-seg 7 dphase-seg1 8 dphase-seg2 4 dsjw 1
1242 pcan_usb_pro_fd: dtseg1 1..16 dtseg2 1..8 dsjw 1..4 dbrp 1..1024 \
1243 dbrp-inc 1
1244 clock 80000000
1245
1246 Example when 'fd-non-iso on' is added on this switchable CAN FD adapter:
1247 can <FD,FD-NON-ISO> state ERROR-ACTIVE (berr-counter tx 0 rx 0) restart-ms 0
1248
1249 6.7 Supported CAN hardware
1250
1251 Please check the "Kconfig" file in "drivers/net/can" to get an actual
1252 list of the support CAN hardware. On the SocketCAN project website
1253 (see chapter 7) there might be further drivers available, also for
1254 older kernel versions.
1255
12567. SocketCAN resources
1257-----------------------
1258
1259 The Linux CAN / SocketCAN project ressources (project site / mailing list)
1260 are referenced in the MAINTAINERS file in the Linux source tree.
1261 Search for CAN NETWORK [LAYERS|DRIVERS].
1262
12638. Credits
1264----------
1265
1266 Oliver Hartkopp (PF_CAN core, filters, drivers, bcm, SJA1000 driver)
1267 Urs Thuermann (PF_CAN core, kernel integration, socket interfaces, raw, vcan)
1268 Jan Kizka (RT-SocketCAN core, Socket-API reconciliation)
1269 Wolfgang Grandegger (RT-SocketCAN core & drivers, Raw Socket-API reviews,
1270 CAN device driver interface, MSCAN driver)
1271 Robert Schwebel (design reviews, PTXdist integration)
1272 Marc Kleine-Budde (design reviews, Kernel 2.6 cleanups, drivers)
1273 Benedikt Spranger (reviews)
1274 Thomas Gleixner (LKML reviews, coding style, posting hints)
1275 Andrey Volkov (kernel subtree structure, ioctls, MSCAN driver)
1276 Matthias Brukner (first SJA1000 CAN netdevice implementation Q2/2003)
1277 Klaus Hitschler (PEAK driver integration)
1278 Uwe Koppe (CAN netdevices with PF_PACKET approach)
1279 Michael Schulze (driver layer loopback requirement, RT CAN drivers review)
1280 Pavel Pisa (Bit-timing calculation)
1281 Sascha Hauer (SJA1000 platform driver)
1282 Sebastian Haas (SJA1000 EMS PCI driver)
1283 Markus Plessing (SJA1000 EMS PCI driver)
1284 Per Dalen (SJA1000 Kvaser PCI driver)
1285 Sam Ravnborg (reviews, coding style, kbuild help)