1 ===================================
2 SocketCAN - Controller Area Network
3 ===================================
5 Overview / What is SocketCAN
6 ============================
8 The socketcan package is an implementation of CAN protocols
9 (Controller Area Network) for Linux. CAN is a networking technology
10 which has widespread use in automation, embedded devices, and
11 automotive fields. While there have been other CAN implementations
12 for Linux based on character devices, SocketCAN uses the Berkeley
13 socket API, the Linux network stack and implements the CAN device
14 drivers as network interfaces. The CAN socket API has been designed
15 as similar as possible to the TCP/IP protocols to allow programmers,
16 familiar with network programming, to easily learn how to use CAN
20 .. _socketcan-motivation:
22 Motivation / Why Using the Socket API
23 =====================================
25 There have been CAN implementations for Linux before SocketCAN so the
26 question arises, why we have started another project. Most existing
27 implementations come as a device driver for some CAN hardware, they
28 are based on character devices and provide comparatively little
29 functionality. Usually, there is only a hardware-specific device
30 driver which provides a character device interface to send and
31 receive raw CAN frames, directly to/from the controller hardware.
32 Queueing of frames and higher-level transport protocols like ISO-TP
33 have to be implemented in user space applications. Also, most
34 character-device implementations support only one single process to
35 open the device at a time, similar to a serial interface. Exchanging
36 the CAN controller requires employment of another device driver and
37 often the need for adaption of large parts of the application to the
40 SocketCAN was designed to overcome all of these limitations. A new
41 protocol family has been implemented which provides a socket interface
42 to user space applications and which builds upon the Linux network
43 layer, enabling use all of the provided queueing functionality. A device
44 driver for CAN controller hardware registers itself with the Linux
45 network layer as a network device, so that CAN frames from the
46 controller can be passed up to the network layer and on to the CAN
47 protocol family module and also vice-versa. Also, the protocol family
48 module provides an API for transport protocol modules to register, so
49 that any number of transport protocols can be loaded or unloaded
50 dynamically. In fact, the can core module alone does not provide any
51 protocol and cannot be used without loading at least one additional
52 protocol module. Multiple sockets can be opened at the same time,
53 on different or the same protocol module and they can listen/send
54 frames on different or the same CAN IDs. Several sockets listening on
55 the same interface for frames with the same CAN ID are all passed the
56 same received matching CAN frames. An application wishing to
57 communicate using a specific transport protocol, e.g. ISO-TP, just
58 selects that protocol when opening the socket, and then can read and
59 write application data byte streams, without having to deal with
62 Similar functionality visible from user-space could be provided by a
63 character device, too, but this would lead to a technically inelegant
64 solution for a couple of reasons:
66 * **Intricate usage:** Instead of passing a protocol argument to
67 socket(2) and using bind(2) to select a CAN interface and CAN ID, an
68 application would have to do all these operations using ioctl(2)s.
70 * **Code duplication:** A character device cannot make use of the Linux
71 network queueing code, so all that code would have to be duplicated
74 * **Abstraction:** In most existing character-device implementations, the
75 hardware-specific device driver for a CAN controller directly
76 provides the character device for the application to work with.
77 This is at least very unusual in Unix systems for both, char and
78 block devices. For example you don't have a character device for a
79 certain UART of a serial interface, a certain sound chip in your
80 computer, a SCSI or IDE controller providing access to your hard
81 disk or tape streamer device. Instead, you have abstraction layers
82 which provide a unified character or block device interface to the
83 application on the one hand, and a interface for hardware-specific
84 device drivers on the other hand. These abstractions are provided
85 by subsystems like the tty layer, the audio subsystem or the SCSI
86 and IDE subsystems for the devices mentioned above.
88 The easiest way to implement a CAN device driver is as a character
89 device without such a (complete) abstraction layer, as is done by most
90 existing drivers. The right way, however, would be to add such a
91 layer with all the functionality like registering for certain CAN
92 IDs, supporting several open file descriptors and (de)multiplexing
93 CAN frames between them, (sophisticated) queueing of CAN frames, and
94 providing an API for device drivers to register with. However, then
95 it would be no more difficult, or may be even easier, to use the
96 networking framework provided by the Linux kernel, and this is what
99 The use of the networking framework of the Linux kernel is just the
100 natural and most appropriate way to implement CAN for Linux.
103 .. _socketcan-concept:
108 As described in :ref:`socketcan-motivation` the main goal of SocketCAN is to
109 provide a socket interface to user space applications which builds
110 upon the Linux network layer. In contrast to the commonly known
111 TCP/IP and ethernet networking, the CAN bus is a broadcast-only(!)
112 medium that has no MAC-layer addressing like ethernet. The CAN-identifier
113 (can_id) is used for arbitration on the CAN-bus. Therefore the CAN-IDs
114 have to be chosen uniquely on the bus. When designing a CAN-ECU
115 network the CAN-IDs are mapped to be sent by a specific ECU.
116 For this reason a CAN-ID can be treated best as a kind of source address.
119 .. _socketcan-receive-lists:
124 The network transparent access of multiple applications leads to the
125 problem that different applications may be interested in the same
126 CAN-IDs from the same CAN network interface. The SocketCAN core
127 module - which implements the protocol family CAN - provides several
128 high efficient receive lists for this reason. If e.g. a user space
129 application opens a CAN RAW socket, the raw protocol module itself
130 requests the (range of) CAN-IDs from the SocketCAN core that are
131 requested by the user. The subscription and unsubscription of
132 CAN-IDs can be done for specific CAN interfaces or for all(!) known
133 CAN interfaces with the can_rx_(un)register() functions provided to
134 CAN protocol modules by the SocketCAN core (see :ref:`socketcan-core-module`).
135 To optimize the CPU usage at runtime the receive lists are split up
136 into several specific lists per device that match the requested
137 filter complexity for a given use-case.
140 .. _socketcan-local-loopback1:
142 Local Loopback of Sent Frames
143 -----------------------------
145 As known from other networking concepts the data exchanging
146 applications may run on the same or different nodes without any
147 change (except for the according addressing information):
151 ___ ___ ___ _______ ___
152 | _ | | _ | | _ | | _ _ | | _ |
153 ||A|| ||B|| ||C|| ||A| |B|| ||C||
154 |___| |___| |___| |_______| |___|
156 -----------------(1)- CAN bus -(2)---------------
158 To ensure that application A receives the same information in the
159 example (2) as it would receive in example (1) there is need for
160 some kind of local loopback of the sent CAN frames on the appropriate
163 The Linux network devices (by default) just can handle the
164 transmission and reception of media dependent frames. Due to the
165 arbitration on the CAN bus the transmission of a low prio CAN-ID
166 may be delayed by the reception of a high prio CAN frame. To
167 reflect the correct [#f1]_ traffic on the node the loopback of the sent
168 data has to be performed right after a successful transmission. If
169 the CAN network interface is not capable of performing the loopback for
170 some reason the SocketCAN core can do this task as a fallback solution.
171 See :ref:`socketcan-local-loopback1` for details (recommended).
173 The loopback functionality is enabled by default to reflect standard
174 networking behaviour for CAN applications. Due to some requests from
175 the RT-SocketCAN group the loopback optionally may be disabled for each
176 separate socket. See sockopts from the CAN RAW sockets in :ref:`socketcan-raw-sockets`.
178 .. [#f1] you really like to have this when you're running analyser
179 tools like 'candump' or 'cansniffer' on the (same) node.
182 .. _socketcan-network-problem-notifications:
184 Network Problem Notifications
185 -----------------------------
187 The use of the CAN bus may lead to several problems on the physical
188 and media access control layer. Detecting and logging of these lower
189 layer problems is a vital requirement for CAN users to identify
190 hardware issues on the physical transceiver layer as well as
191 arbitration problems and error frames caused by the different
192 ECUs. The occurrence of detected errors are important for diagnosis
193 and have to be logged together with the exact timestamp. For this
194 reason the CAN interface driver can generate so called Error Message
195 Frames that can optionally be passed to the user application in the
196 same way as other CAN frames. Whenever an error on the physical layer
197 or the MAC layer is detected (e.g. by the CAN controller) the driver
198 creates an appropriate error message frame. Error messages frames can
199 be requested by the user application using the common CAN filter
200 mechanisms. Inside this filter definition the (interested) type of
201 errors may be selected. The reception of error messages is disabled
202 by default. The format of the CAN error message frame is briefly
203 described in the Linux header file "include/uapi/linux/can/error.h".
209 Like TCP/IP, you first need to open a socket for communicating over a
210 CAN network. Since SocketCAN implements a new protocol family, you
211 need to pass PF_CAN as the first argument to the socket(2) system
212 call. Currently, there are two CAN protocols to choose from, the raw
213 socket protocol and the broadcast manager (BCM). So to open a socket,
216 s = socket(PF_CAN, SOCK_RAW, CAN_RAW);
220 s = socket(PF_CAN, SOCK_DGRAM, CAN_BCM);
222 respectively. After the successful creation of the socket, you would
223 normally use the bind(2) system call to bind the socket to a CAN
224 interface (which is different from TCP/IP due to different addressing
225 - see :ref:`socketcan-concept`). After binding (CAN_RAW) or connecting (CAN_BCM)
226 the socket, you can read(2) and write(2) from/to the socket or use
227 send(2), sendto(2), sendmsg(2) and the recv* counterpart operations
228 on the socket as usual. There are also CAN specific socket options
231 The basic CAN frame structure and the sockaddr structure are defined
232 in include/linux/can.h:
237 canid_t can_id; /* 32 bit CAN_ID + EFF/RTR/ERR flags */
238 __u8 can_dlc; /* frame payload length in byte (0 .. 8) */
239 __u8 __pad; /* padding */
240 __u8 __res0; /* reserved / padding */
241 __u8 __res1; /* reserved / padding */
242 __u8 data[8] __attribute__((aligned(8)));
245 The alignment of the (linear) payload data[] to a 64bit boundary
246 allows the user to define their own structs and unions to easily access
247 the CAN payload. There is no given byteorder on the CAN bus by
248 default. A read(2) system call on a CAN_RAW socket transfers a
249 struct can_frame to the user space.
251 The sockaddr_can structure has an interface index like the
252 PF_PACKET socket, that also binds to a specific interface:
256 struct sockaddr_can {
257 sa_family_t can_family;
260 /* transport protocol class address info (e.g. ISOTP) */
261 struct { canid_t rx_id, tx_id; } tp;
263 /* reserved for future CAN protocols address information */
267 To determine the interface index an appropriate ioctl() has to
268 be used (example for CAN_RAW sockets without error checking):
273 struct sockaddr_can addr;
276 s = socket(PF_CAN, SOCK_RAW, CAN_RAW);
278 strcpy(ifr.ifr_name, "can0" );
279 ioctl(s, SIOCGIFINDEX, &ifr);
281 addr.can_family = AF_CAN;
282 addr.can_ifindex = ifr.ifr_ifindex;
284 bind(s, (struct sockaddr *)&addr, sizeof(addr));
288 To bind a socket to all(!) CAN interfaces the interface index must
289 be 0 (zero). In this case the socket receives CAN frames from every
290 enabled CAN interface. To determine the originating CAN interface
291 the system call recvfrom(2) may be used instead of read(2). To send
292 on a socket that is bound to 'any' interface sendto(2) is needed to
293 specify the outgoing interface.
295 Reading CAN frames from a bound CAN_RAW socket (see above) consists
296 of reading a struct can_frame:
300 struct can_frame frame;
302 nbytes = read(s, &frame, sizeof(struct can_frame));
305 perror("can raw socket read");
309 /* paranoid check ... */
310 if (nbytes < sizeof(struct can_frame)) {
311 fprintf(stderr, "read: incomplete CAN frame\n");
315 /* do something with the received CAN frame */
317 Writing CAN frames can be done similarly, with the write(2) system call::
319 nbytes = write(s, &frame, sizeof(struct can_frame));
321 When the CAN interface is bound to 'any' existing CAN interface
322 (addr.can_ifindex = 0) it is recommended to use recvfrom(2) if the
323 information about the originating CAN interface is needed:
327 struct sockaddr_can addr;
329 socklen_t len = sizeof(addr);
330 struct can_frame frame;
332 nbytes = recvfrom(s, &frame, sizeof(struct can_frame),
333 0, (struct sockaddr*)&addr, &len);
335 /* get interface name of the received CAN frame */
336 ifr.ifr_ifindex = addr.can_ifindex;
337 ioctl(s, SIOCGIFNAME, &ifr);
338 printf("Received a CAN frame from interface %s", ifr.ifr_name);
340 To write CAN frames on sockets bound to 'any' CAN interface the
341 outgoing interface has to be defined certainly:
345 strcpy(ifr.ifr_name, "can0");
346 ioctl(s, SIOCGIFINDEX, &ifr);
347 addr.can_ifindex = ifr.ifr_ifindex;
348 addr.can_family = AF_CAN;
350 nbytes = sendto(s, &frame, sizeof(struct can_frame),
351 0, (struct sockaddr*)&addr, sizeof(addr));
353 An accurate timestamp can be obtained with an ioctl(2) call after reading
354 a message from the socket:
359 ioctl(s, SIOCGSTAMP, &tv);
361 The timestamp has a resolution of one microsecond and is set automatically
362 at the reception of a CAN frame.
364 Remark about CAN FD (flexible data rate) support:
366 Generally the handling of CAN FD is very similar to the formerly described
367 examples. The new CAN FD capable CAN controllers support two different
368 bitrates for the arbitration phase and the payload phase of the CAN FD frame
369 and up to 64 bytes of payload. This extended payload length breaks all the
370 kernel interfaces (ABI) which heavily rely on the CAN frame with fixed eight
371 bytes of payload (struct can_frame) like the CAN_RAW socket. Therefore e.g.
372 the CAN_RAW socket supports a new socket option CAN_RAW_FD_FRAMES that
373 switches the socket into a mode that allows the handling of CAN FD frames
374 and (legacy) CAN frames simultaneously (see :ref:`socketcan-rawfd`).
376 The struct canfd_frame is defined in include/linux/can.h:
381 canid_t can_id; /* 32 bit CAN_ID + EFF/RTR/ERR flags */
382 __u8 len; /* frame payload length in byte (0 .. 64) */
383 __u8 flags; /* additional flags for CAN FD */
384 __u8 __res0; /* reserved / padding */
385 __u8 __res1; /* reserved / padding */
386 __u8 data[64] __attribute__((aligned(8)));
389 The struct canfd_frame and the existing struct can_frame have the can_id,
390 the payload length and the payload data at the same offset inside their
391 structures. This allows to handle the different structures very similar.
392 When the content of a struct can_frame is copied into a struct canfd_frame
393 all structure elements can be used as-is - only the data[] becomes extended.
395 When introducing the struct canfd_frame it turned out that the data length
396 code (DLC) of the struct can_frame was used as a length information as the
397 length and the DLC has a 1:1 mapping in the range of 0 .. 8. To preserve
398 the easy handling of the length information the canfd_frame.len element
399 contains a plain length value from 0 .. 64. So both canfd_frame.len and
400 can_frame.can_dlc are equal and contain a length information and no DLC.
401 For details about the distinction of CAN and CAN FD capable devices and
402 the mapping to the bus-relevant data length code (DLC), see :ref:`socketcan-can-fd-driver`.
404 The length of the two CAN(FD) frame structures define the maximum transfer
405 unit (MTU) of the CAN(FD) network interface and skbuff data length. Two
406 definitions are specified for CAN specific MTUs in include/linux/can.h:
410 #define CAN_MTU (sizeof(struct can_frame)) == 16 => 'legacy' CAN frame
411 #define CANFD_MTU (sizeof(struct canfd_frame)) == 72 => CAN FD frame
414 .. _socketcan-raw-sockets:
416 RAW Protocol Sockets with can_filters (SOCK_RAW)
417 ------------------------------------------------
419 Using CAN_RAW sockets is extensively comparable to the commonly
420 known access to CAN character devices. To meet the new possibilities
421 provided by the multi user SocketCAN approach, some reasonable
422 defaults are set at RAW socket binding time:
424 - The filters are set to exactly one filter receiving everything
425 - The socket only receives valid data frames (=> no error message frames)
426 - The loopback of sent CAN frames is enabled (see :ref:`socketcan-local-loopback2`)
427 - The socket does not receive its own sent frames (in loopback mode)
429 These default settings may be changed before or after binding the socket.
430 To use the referenced definitions of the socket options for CAN_RAW
431 sockets, include <linux/can/raw.h>.
434 .. _socketcan-rawfilter:
436 RAW socket option CAN_RAW_FILTER
437 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
439 The reception of CAN frames using CAN_RAW sockets can be controlled
440 by defining 0 .. n filters with the CAN_RAW_FILTER socket option.
442 The CAN filter structure is defined in include/linux/can.h:
451 A filter matches, when:
455 <received_can_id> & mask == can_id & mask
457 which is analogous to known CAN controllers hardware filter semantics.
458 The filter can be inverted in this semantic, when the CAN_INV_FILTER
459 bit is set in can_id element of the can_filter structure. In
460 contrast to CAN controller hardware filters the user may set 0 .. n
461 receive filters for each open socket separately:
465 struct can_filter rfilter[2];
467 rfilter[0].can_id = 0x123;
468 rfilter[0].can_mask = CAN_SFF_MASK;
469 rfilter[1].can_id = 0x200;
470 rfilter[1].can_mask = 0x700;
472 setsockopt(s, SOL_CAN_RAW, CAN_RAW_FILTER, &rfilter, sizeof(rfilter));
474 To disable the reception of CAN frames on the selected CAN_RAW socket:
478 setsockopt(s, SOL_CAN_RAW, CAN_RAW_FILTER, NULL, 0);
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.
485 CAN Filter Usage Optimisation
486 .............................
488 The CAN filters are processed in per-device filter lists at CAN frame
489 reception time. To reduce the number of checks that need to be performed
490 while walking through the filter lists the CAN core provides an optimized
491 filter handling when the filter subscription focusses on a single CAN ID.
493 For the possible 2048 SFF CAN identifiers the identifier is used as an index
494 to access the corresponding subscription list without any further checks.
495 For the 2^29 possible EFF CAN identifiers a 10 bit XOR folding is used as
496 hash function to retrieve the EFF table index.
498 To benefit from the optimized filters for single CAN identifiers the
499 CAN_SFF_MASK or CAN_EFF_MASK have to be set into can_filter.mask together
500 with set CAN_EFF_FLAG and CAN_RTR_FLAG bits. A set CAN_EFF_FLAG bit in the
501 can_filter.mask makes clear that it matters whether a SFF or EFF CAN ID is
502 subscribed. E.g. in the example from above:
506 rfilter[0].can_id = 0x123;
507 rfilter[0].can_mask = CAN_SFF_MASK;
509 both SFF frames with CAN ID 0x123 and EFF frames with 0xXXXXX123 can pass.
511 To filter for only 0x123 (SFF) and 0x12345678 (EFF) CAN identifiers the
512 filter has to be defined in this way to benefit from the optimized filters:
516 struct can_filter rfilter[2];
518 rfilter[0].can_id = 0x123;
519 rfilter[0].can_mask = (CAN_EFF_FLAG | CAN_RTR_FLAG | CAN_SFF_MASK);
520 rfilter[1].can_id = 0x12345678 | CAN_EFF_FLAG;
521 rfilter[1].can_mask = (CAN_EFF_FLAG | CAN_RTR_FLAG | CAN_EFF_MASK);
523 setsockopt(s, SOL_CAN_RAW, CAN_RAW_FILTER, &rfilter, sizeof(rfilter));
526 RAW Socket Option CAN_RAW_ERR_FILTER
527 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
529 As described in :ref:`socketcan-network-problem-notifications` the CAN interface driver can generate so
530 called Error Message Frames that can optionally be passed to the user
531 application in the same way as other CAN frames. The possible
532 errors are divided into different error classes that may be filtered
533 using the appropriate error mask. To register for every possible
534 error condition CAN_ERR_MASK can be used as value for the error mask.
535 The values for the error mask are defined in linux/can/error.h:
539 can_err_mask_t err_mask = ( CAN_ERR_TX_TIMEOUT | CAN_ERR_BUSOFF );
541 setsockopt(s, SOL_CAN_RAW, CAN_RAW_ERR_FILTER,
542 &err_mask, sizeof(err_mask));
545 RAW Socket Option CAN_RAW_LOOPBACK
546 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
548 To meet multi user needs the local loopback is enabled by default
549 (see :ref:`socketcan-local-loopback1` for details). But in some embedded use-cases
550 (e.g. when only one application uses the CAN bus) this loopback
551 functionality can be disabled (separately for each socket):
555 int loopback = 0; /* 0 = disabled, 1 = enabled (default) */
557 setsockopt(s, SOL_CAN_RAW, CAN_RAW_LOOPBACK, &loopback, sizeof(loopback));
560 RAW socket option CAN_RAW_RECV_OWN_MSGS
561 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
563 When the local loopback is enabled, all the sent CAN frames are
564 looped back to the open CAN sockets that registered for the CAN
565 frames' CAN-ID on this given interface to meet the multi user
566 needs. The reception of the CAN frames on the same socket that was
567 sending the CAN frame is assumed to be unwanted and therefore
568 disabled by default. This default behaviour may be changed on
573 int recv_own_msgs = 1; /* 0 = disabled (default), 1 = enabled */
575 setsockopt(s, SOL_CAN_RAW, CAN_RAW_RECV_OWN_MSGS,
576 &recv_own_msgs, sizeof(recv_own_msgs));
581 RAW Socket Option CAN_RAW_FD_FRAMES
582 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
584 CAN FD support in CAN_RAW sockets can be enabled with a new socket option
585 CAN_RAW_FD_FRAMES which is off by default. When the new socket option is
586 not supported by the CAN_RAW socket (e.g. on older kernels), switching the
587 CAN_RAW_FD_FRAMES option returns the error -ENOPROTOOPT.
589 Once CAN_RAW_FD_FRAMES is enabled the application can send both CAN frames
590 and CAN FD frames. OTOH the application has to handle CAN and CAN FD frames
591 when reading from the socket:
595 CAN_RAW_FD_FRAMES enabled: CAN_MTU and CANFD_MTU are allowed
596 CAN_RAW_FD_FRAMES disabled: only CAN_MTU is allowed (default)
602 [ remember: CANFD_MTU == sizeof(struct canfd_frame) ]
604 struct canfd_frame cfd;
606 nbytes = read(s, &cfd, CANFD_MTU);
608 if (nbytes == CANFD_MTU) {
609 printf("got CAN FD frame with length %d\n", cfd.len);
610 /* cfd.flags contains valid data */
611 } else if (nbytes == CAN_MTU) {
612 printf("got legacy CAN frame with length %d\n", cfd.len);
613 /* cfd.flags is undefined */
615 fprintf(stderr, "read: invalid CAN(FD) frame\n");
619 /* the content can be handled independently from the received MTU size */
621 printf("can_id: %X data length: %d data: ", cfd.can_id, cfd.len);
622 for (i = 0; i < cfd.len; i++)
623 printf("%02X ", cfd.data[i]);
625 When reading with size CANFD_MTU only returns CAN_MTU bytes that have
626 been received from the socket a legacy CAN frame has been read into the
627 provided CAN FD structure. Note that the canfd_frame.flags data field is
628 not specified in the struct can_frame and therefore it is only valid in
629 CANFD_MTU sized CAN FD frames.
631 Implementation hint for new CAN applications:
633 To build a CAN FD aware application use struct canfd_frame as basic CAN
634 data structure for CAN_RAW based applications. When the application is
635 executed on an older Linux kernel and switching the CAN_RAW_FD_FRAMES
636 socket option returns an error: No problem. You'll get legacy CAN frames
637 or CAN FD frames and can process them the same way.
639 When sending to CAN devices make sure that the device is capable to handle
640 CAN FD frames by checking if the device maximum transfer unit is CANFD_MTU.
641 The CAN device MTU can be retrieved e.g. with a SIOCGIFMTU ioctl() syscall.
644 RAW socket option CAN_RAW_JOIN_FILTERS
645 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
647 The CAN_RAW socket can set multiple CAN identifier specific filters that
648 lead to multiple filters in the af_can.c filter processing. These filters
649 are indenpendent from each other which leads to logical OR'ed filters when
650 applied (see :ref:`socketcan-rawfilter`).
652 This socket option joines the given CAN filters in the way that only CAN
653 frames are passed to user space that matched *all* given CAN filters. The
654 semantic for the applied filters is therefore changed to a logical AND.
656 This is useful especially when the filterset is a combination of filters
657 where the CAN_INV_FILTER flag is set in order to notch single CAN IDs or
658 CAN ID ranges from the incoming traffic.
661 RAW Socket Returned Message Flags
662 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
664 When using recvmsg() call, the msg->msg_flags may contain following flags:
667 set when the received frame was created on the local host.
670 set when the frame was sent via the socket it is received on.
671 This flag can be interpreted as a 'transmission confirmation' when the
672 CAN driver supports the echo of frames on driver level, see
673 :ref:`socketcan-local-loopback1` and :ref:`socketcan-local-loopback2`.
674 In order to receive such messages, CAN_RAW_RECV_OWN_MSGS must be set.
677 Broadcast Manager Protocol Sockets (SOCK_DGRAM)
678 -----------------------------------------------
680 The Broadcast Manager protocol provides a command based configuration
681 interface to filter and send (e.g. cyclic) CAN messages in kernel space.
683 Receive filters can be used to down sample frequent messages; detect events
684 such as message contents changes, packet length changes, and do time-out
685 monitoring of received messages.
687 Periodic transmission tasks of CAN frames or a sequence of CAN frames can be
688 created and modified at runtime; both the message content and the two
689 possible transmit intervals can be altered.
691 A BCM socket is not intended for sending individual CAN frames using the
692 struct can_frame as known from the CAN_RAW socket. Instead a special BCM
693 configuration message is defined. The basic BCM configuration message used
694 to communicate with the broadcast manager and the available operations are
695 defined in the linux/can/bcm.h include. The BCM message consists of a
696 message header with a command ('opcode') followed by zero or more CAN frames.
697 The broadcast manager sends responses to user space in the same form:
701 struct bcm_msg_head {
702 __u32 opcode; /* command */
703 __u32 flags; /* special flags */
704 __u32 count; /* run 'count' times with ival1 */
705 struct timeval ival1, ival2; /* count and subsequent interval */
706 canid_t can_id; /* unique can_id for task */
707 __u32 nframes; /* number of can_frames following */
708 struct can_frame frames[0];
711 The aligned payload 'frames' uses the same basic CAN frame structure defined
712 at the beginning of :ref:`socketcan-rawfd` and in the include/linux/can.h include. All
713 messages to the broadcast manager from user space have this structure.
715 Note a CAN_BCM socket must be connected instead of bound after socket
716 creation (example without error checking):
721 struct sockaddr_can addr;
724 s = socket(PF_CAN, SOCK_DGRAM, CAN_BCM);
726 strcpy(ifr.ifr_name, "can0");
727 ioctl(s, SIOCGIFINDEX, &ifr);
729 addr.can_family = AF_CAN;
730 addr.can_ifindex = ifr.ifr_ifindex;
732 connect(s, (struct sockaddr *)&addr, sizeof(addr));
736 The broadcast manager socket is able to handle any number of in flight
737 transmissions or receive filters concurrently. The different RX/TX jobs are
738 distinguished by the unique can_id in each BCM message. However additional
739 CAN_BCM sockets are recommended to communicate on multiple CAN interfaces.
740 When the broadcast manager socket is bound to 'any' CAN interface (=> the
741 interface index is set to zero) the configured receive filters apply to any
742 CAN interface unless the sendto() syscall is used to overrule the 'any' CAN
743 interface index. When using recvfrom() instead of read() to retrieve BCM
744 socket messages the originating CAN interface is provided in can_ifindex.
747 Broadcast Manager Operations
748 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
750 The opcode defines the operation for the broadcast manager to carry out,
751 or details the broadcast managers response to several events, including
754 Transmit Operations (user space to broadcast manager):
757 Create (cyclic) transmission task.
760 Remove (cyclic) transmission task, requires only can_id.
763 Read properties of (cyclic) transmission task for can_id.
768 Transmit Responses (broadcast manager to user space):
771 Reply to TX_READ request (transmission task configuration).
774 Notification when counter finishes sending at initial interval
775 'ival1'. Requires the TX_COUNTEVT flag to be set at TX_SETUP.
777 Receive Operations (user space to broadcast manager):
780 Create RX content filter subscription.
783 Remove RX content filter subscription, requires only can_id.
786 Read properties of RX content filter subscription for can_id.
788 Receive Responses (broadcast manager to user space):
791 Reply to RX_READ request (filter task configuration).
794 Cyclic message is detected to be absent (timer ival1 expired).
797 BCM message with updated CAN frame (detected content change).
798 Sent on first message received or on receipt of revised CAN messages.
801 Broadcast Manager Message Flags
802 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
804 When sending a message to the broadcast manager the 'flags' element may
805 contain the following flag definitions which influence the behaviour:
808 Set the values of ival1, ival2 and count
811 Start the timer with the actual values of ival1, ival2
812 and count. Starting the timer leads simultaneously to emit a CAN frame.
815 Create the message TX_EXPIRED when count expires
818 A change of data by the process is emitted immediately.
821 Copies the can_id from the message header to each
822 subsequent frame in frames. This is intended as usage simplification. For
823 TX tasks the unique can_id from the message header may differ from the
824 can_id(s) stored for transmission in the subsequent struct can_frame(s).
827 Filter by can_id alone, no frames required (nframes=0).
830 A change of the DLC leads to an RX_CHANGED.
833 Prevent automatically starting the timeout monitor.
836 If passed at RX_SETUP and a receive timeout occurred, a
837 RX_CHANGED message will be generated when the (cyclic) receive restarts.
840 Reset the index for the multiple frame transmission.
843 Send reply for RTR-request (placed in op->frames[0]).
846 Broadcast Manager Transmission Timers
847 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
849 Periodic transmission configurations may use up to two interval timers.
850 In this case the BCM sends a number of messages ('count') at an interval
851 'ival1', then continuing to send at another given interval 'ival2'. When
852 only one timer is needed 'count' is set to zero and only 'ival2' is used.
853 When SET_TIMER and START_TIMER flag were set the timers are activated.
854 The timer values can be altered at runtime when only SET_TIMER is set.
857 Broadcast Manager message sequence transmission
858 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
860 Up to 256 CAN frames can be transmitted in a sequence in the case of a cyclic
861 TX task configuration. The number of CAN frames is provided in the 'nframes'
862 element of the BCM message head. The defined number of CAN frames are added
863 as array to the TX_SETUP BCM configuration message:
867 /* create a struct to set up a sequence of four CAN frames */
869 struct bcm_msg_head msg_head;
870 struct can_frame frame[4];
874 mytxmsg.msg_head.nframes = 4;
877 write(s, &mytxmsg, sizeof(mytxmsg));
879 With every transmission the index in the array of CAN frames is increased
880 and set to zero at index overflow.
883 Broadcast Manager Receive Filter Timers
884 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
886 The timer values ival1 or ival2 may be set to non-zero values at RX_SETUP.
887 When the SET_TIMER flag is set the timers are enabled:
890 Send RX_TIMEOUT when a received message is not received again within
891 the given time. When START_TIMER is set at RX_SETUP the timeout detection
892 is activated directly - even without a former CAN frame reception.
895 Throttle the received message rate down to the value of ival2. This
896 is useful to reduce messages for the application when the signal inside the
897 CAN frame is stateless as state changes within the ival2 periode may get
900 Broadcast Manager Multiplex Message Receive Filter
901 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
903 To filter for content changes in multiplex message sequences an array of more
904 than one CAN frames can be passed in a RX_SETUP configuration message. The
905 data bytes of the first CAN frame contain the mask of relevant bits that
906 have to match in the subsequent CAN frames with the received CAN frame.
907 If one of the subsequent CAN frames is matching the bits in that frame data
908 mark the relevant content to be compared with the previous received content.
909 Up to 257 CAN frames (multiplex filter bit mask CAN frame plus 256 CAN
910 filters) can be added as array to the TX_SETUP BCM configuration message:
914 /* usually used to clear CAN frame data[] - beware of endian problems! */
915 #define U64_DATA(p) (*(unsigned long long*)(p)->data)
918 struct bcm_msg_head msg_head;
919 struct can_frame frame[5];
922 msg.msg_head.opcode = RX_SETUP;
923 msg.msg_head.can_id = 0x42;
924 msg.msg_head.flags = 0;
925 msg.msg_head.nframes = 5;
926 U64_DATA(&msg.frame[0]) = 0xFF00000000000000ULL; /* MUX mask */
927 U64_DATA(&msg.frame[1]) = 0x01000000000000FFULL; /* data mask (MUX 0x01) */
928 U64_DATA(&msg.frame[2]) = 0x0200FFFF000000FFULL; /* data mask (MUX 0x02) */
929 U64_DATA(&msg.frame[3]) = 0x330000FFFFFF0003ULL; /* data mask (MUX 0x33) */
930 U64_DATA(&msg.frame[4]) = 0x4F07FC0FF0000000ULL; /* data mask (MUX 0x4F) */
932 write(s, &msg, sizeof(msg));
935 Broadcast Manager CAN FD Support
936 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
938 The programming API of the CAN_BCM depends on struct can_frame which is
939 given as array directly behind the bcm_msg_head structure. To follow this
940 schema for the CAN FD frames a new flag 'CAN_FD_FRAME' in the bcm_msg_head
941 flags indicates that the concatenated CAN frame structures behind the
942 bcm_msg_head are defined as struct canfd_frame:
947 struct bcm_msg_head msg_head;
948 struct canfd_frame frame[5];
951 msg.msg_head.opcode = RX_SETUP;
952 msg.msg_head.can_id = 0x42;
953 msg.msg_head.flags = CAN_FD_FRAME;
954 msg.msg_head.nframes = 5;
957 When using CAN FD frames for multiplex filtering the MUX mask is still
958 expected in the first 64 bit of the struct canfd_frame data section.
961 Connected Transport Protocols (SOCK_SEQPACKET)
962 ----------------------------------------------
967 Unconnected Transport Protocols (SOCK_DGRAM)
968 --------------------------------------------
973 .. _socketcan-core-module:
975 SocketCAN Core Module
976 =====================
978 The SocketCAN core module implements the protocol family
979 PF_CAN. CAN protocol modules are loaded by the core module at
980 runtime. The core module provides an interface for CAN protocol
981 modules to subscribe needed CAN IDs (see :ref:`socketcan-receive-lists`).
988 To calculate the SocketCAN core statistics
989 (e.g. current/maximum frames per second) this 1 second timer is
990 invoked at can.ko module start time by default. This timer can be
991 disabled by using stattimer=0 on the module commandline.
994 (removed since SocketCAN SVN r546)
1000 As described in :ref:`socketcan-receive-lists` the SocketCAN core uses several filter
1001 lists to deliver received CAN frames to CAN protocol modules. These
1002 receive lists, their filters and the count of filter matches can be
1003 checked in the appropriate receive list. All entries contain the
1004 device and a protocol module identifier::
1006 foo@bar:~$ cat /proc/net/can/rcvlist_all
1008 receive list 'rx_all':
1012 device can_id can_mask function userdata matches ident
1013 vcan0 000 00000000 f88e6370 f6c6f400 0 raw
1016 In this example an application requests any CAN traffic from vcan0::
1018 rcvlist_all - list for unfiltered entries (no filter operations)
1019 rcvlist_eff - list for single extended frame (EFF) entries
1020 rcvlist_err - list for error message frames masks
1021 rcvlist_fil - list for mask/value filters
1022 rcvlist_inv - list for mask/value filters (inverse semantic)
1023 rcvlist_sff - list for single standard frame (SFF) entries
1025 Additional procfs files in /proc/net/can::
1027 stats - SocketCAN core statistics (rx/tx frames, match ratios, ...)
1028 reset_stats - manual statistic reset
1029 version - prints the SocketCAN core version and the ABI version
1032 Writing Own CAN Protocol Modules
1033 --------------------------------
1035 To implement a new protocol in the protocol family PF_CAN a new
1036 protocol has to be defined in include/linux/can.h .
1037 The prototypes and definitions to use the SocketCAN core can be
1038 accessed by including include/linux/can/core.h .
1039 In addition to functions that register the CAN protocol and the
1040 CAN device notifier chain there are functions to subscribe CAN
1041 frames received by CAN interfaces and to send CAN frames::
1043 can_rx_register - subscribe CAN frames from a specific interface
1044 can_rx_unregister - unsubscribe CAN frames from a specific interface
1045 can_send - transmit a CAN frame (optional with local loopback)
1047 For details see the kerneldoc documentation in net/can/af_can.c or
1048 the source code of net/can/raw.c or net/can/bcm.c .
1054 Writing a CAN network device driver is much easier than writing a
1055 CAN character device driver. Similar to other known network device
1056 drivers you mainly have to deal with:
1058 - TX: Put the CAN frame from the socket buffer to the CAN controller.
1059 - RX: Put the CAN frame from the CAN controller to the socket buffer.
1061 See e.g. at Documentation/networking/netdevices.rst . The differences
1062 for writing CAN network device driver are described below:
1070 dev->type = ARPHRD_CAN; /* the netdevice hardware type */
1071 dev->flags = IFF_NOARP; /* CAN has no arp */
1073 dev->mtu = CAN_MTU; /* sizeof(struct can_frame) -> legacy CAN interface */
1075 or alternative, when the controller supports CAN with flexible data rate:
1076 dev->mtu = CANFD_MTU; /* sizeof(struct canfd_frame) -> CAN FD interface */
1078 The struct can_frame or struct canfd_frame is the payload of each socket
1079 buffer (skbuff) in the protocol family PF_CAN.
1082 .. _socketcan-local-loopback2:
1084 Local Loopback of Sent Frames
1085 -----------------------------
1087 As described in :ref:`socketcan-local-loopback1` the CAN network device driver should
1088 support a local loopback functionality similar to the local echo
1089 e.g. of tty devices. In this case the driver flag IFF_ECHO has to be
1090 set to prevent the PF_CAN core from locally echoing sent frames
1091 (aka loopback) as fallback solution::
1093 dev->flags = (IFF_NOARP | IFF_ECHO);
1096 CAN Controller Hardware Filters
1097 -------------------------------
1099 To reduce the interrupt load on deep embedded systems some CAN
1100 controllers support the filtering of CAN IDs or ranges of CAN IDs.
1101 These hardware filter capabilities vary from controller to
1102 controller and have to be identified as not feasible in a multi-user
1103 networking approach. The use of the very controller specific
1104 hardware filters could make sense in a very dedicated use-case, as a
1105 filter on driver level would affect all users in the multi-user
1106 system. The high efficient filter sets inside the PF_CAN core allow
1107 to set different multiple filters for each socket separately.
1108 Therefore the use of hardware filters goes to the category 'handmade
1109 tuning on deep embedded systems'. The author is running a MPC603e
1110 @133MHz with four SJA1000 CAN controllers from 2002 under heavy bus
1111 load without any problems ...
1114 The Virtual CAN Driver (vcan)
1115 -----------------------------
1117 Similar to the network loopback devices, vcan offers a virtual local
1118 CAN interface. A full qualified address on CAN consists of
1120 - a unique CAN Identifier (CAN ID)
1121 - the CAN bus this CAN ID is transmitted on (e.g. can0)
1123 so in common use cases more than one virtual CAN interface is needed.
1125 The virtual CAN interfaces allow the transmission and reception of CAN
1126 frames without real CAN controller hardware. Virtual CAN network
1127 devices are usually named 'vcanX', like vcan0 vcan1 vcan2 ...
1128 When compiled as a module the virtual CAN driver module is called vcan.ko
1130 Since Linux Kernel version 2.6.24 the vcan driver supports the Kernel
1131 netlink interface to create vcan network devices. The creation and
1132 removal of vcan network devices can be managed with the ip(8) tool::
1134 - Create a virtual CAN network interface:
1135 $ ip link add type vcan
1137 - Create a virtual CAN network interface with a specific name 'vcan42':
1138 $ ip link add dev vcan42 type vcan
1140 - Remove a (virtual CAN) network interface 'vcan42':
1141 $ ip link del vcan42
1144 The CAN Network Device Driver Interface
1145 ---------------------------------------
1147 The CAN network device driver interface provides a generic interface
1148 to setup, configure and monitor CAN network devices. The user can then
1149 configure the CAN device, like setting the bit-timing parameters, via
1150 the netlink interface using the program "ip" from the "IPROUTE2"
1151 utility suite. The following chapter describes briefly how to use it.
1152 Furthermore, the interface uses a common data structure and exports a
1153 set of common functions, which all real CAN network device drivers
1154 should use. Please have a look to the SJA1000 or MSCAN driver to
1155 understand how to use them. The name of the module is can-dev.ko.
1158 Netlink interface to set/get devices properties
1159 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1161 The CAN device must be configured via netlink interface. The supported
1162 netlink message types are defined and briefly described in
1163 "include/linux/can/netlink.h". CAN link support for the program "ip"
1164 of the IPROUTE2 utility suite is available and it can be used as shown
1167 Setting CAN device properties::
1169 $ ip link set can0 type can help
1170 Usage: ip link set DEVICE type can
1171 [ bitrate BITRATE [ sample-point SAMPLE-POINT] ] |
1172 [ tq TQ prop-seg PROP_SEG phase-seg1 PHASE-SEG1
1173 phase-seg2 PHASE-SEG2 [ sjw SJW ] ]
1175 [ dbitrate BITRATE [ dsample-point SAMPLE-POINT] ] |
1176 [ dtq TQ dprop-seg PROP_SEG dphase-seg1 PHASE-SEG1
1177 dphase-seg2 PHASE-SEG2 [ dsjw SJW ] ]
1179 [ loopback { on | off } ]
1180 [ listen-only { on | off } ]
1181 [ triple-sampling { on | off } ]
1182 [ one-shot { on | off } ]
1183 [ berr-reporting { on | off } ]
1185 [ fd-non-iso { on | off } ]
1186 [ presume-ack { on | off } ]
1188 [ restart-ms TIME-MS ]
1191 Where: BITRATE := { 1..1000000 }
1192 SAMPLE-POINT := { 0.000..0.999 }
1194 PROP-SEG := { 1..8 }
1195 PHASE-SEG1 := { 1..8 }
1196 PHASE-SEG2 := { 1..8 }
1198 RESTART-MS := { 0 | NUMBER }
1200 Display CAN device details and statistics::
1202 $ ip -details -statistics link show can0
1203 2: can0: <NOARP,UP,LOWER_UP,ECHO> mtu 16 qdisc pfifo_fast state UP qlen 10
1205 can <TRIPLE-SAMPLING> state ERROR-ACTIVE restart-ms 100
1206 bitrate 125000 sample_point 0.875
1207 tq 125 prop-seg 6 phase-seg1 7 phase-seg2 2 sjw 1
1208 sja1000: tseg1 1..16 tseg2 1..8 sjw 1..4 brp 1..64 brp-inc 1
1210 re-started bus-errors arbit-lost error-warn error-pass bus-off
1212 RX: bytes packets errors dropped overrun mcast
1213 140859 17608 17457 0 0 0
1214 TX: bytes packets errors dropped carrier collsns
1217 More info to the above output:
1220 Shows the list of selected CAN controller modes: LOOPBACK,
1221 LISTEN-ONLY, or TRIPLE-SAMPLING.
1223 "state ERROR-ACTIVE"
1224 The current state of the CAN controller: "ERROR-ACTIVE",
1225 "ERROR-WARNING", "ERROR-PASSIVE", "BUS-OFF" or "STOPPED"
1228 Automatic restart delay time. If set to a non-zero value, a
1229 restart of the CAN controller will be triggered automatically
1230 in case of a bus-off condition after the specified delay time
1231 in milliseconds. By default it's off.
1233 "bitrate 125000 sample-point 0.875"
1234 Shows the real bit-rate in bits/sec and the sample-point in the
1235 range 0.000..0.999. If the calculation of bit-timing parameters
1236 is enabled in the kernel (CONFIG_CAN_CALC_BITTIMING=y), the
1237 bit-timing can be defined by setting the "bitrate" argument.
1238 Optionally the "sample-point" can be specified. By default it's
1239 0.000 assuming CIA-recommended sample-points.
1241 "tq 125 prop-seg 6 phase-seg1 7 phase-seg2 2 sjw 1"
1242 Shows the time quanta in ns, propagation segment, phase buffer
1243 segment 1 and 2 and the synchronisation jump width in units of
1244 tq. They allow to define the CAN bit-timing in a hardware
1245 independent format as proposed by the Bosch CAN 2.0 spec (see
1246 chapter 8 of http://www.semiconductors.bosch.de/pdf/can2spec.pdf).
1248 "sja1000: tseg1 1..16 tseg2 1..8 sjw 1..4 brp 1..64 brp-inc 1 clock 8000000"
1249 Shows the bit-timing constants of the CAN controller, here the
1250 "sja1000". The minimum and maximum values of the time segment 1
1251 and 2, the synchronisation jump width in units of tq, the
1252 bitrate pre-scaler and the CAN system clock frequency in Hz.
1253 These constants could be used for user-defined (non-standard)
1254 bit-timing calculation algorithms in user-space.
1256 "re-started bus-errors arbit-lost error-warn error-pass bus-off"
1257 Shows the number of restarts, bus and arbitration lost errors,
1258 and the state changes to the error-warning, error-passive and
1259 bus-off state. RX overrun errors are listed in the "overrun"
1260 field of the standard network statistics.
1262 Setting the CAN Bit-Timing
1263 ~~~~~~~~~~~~~~~~~~~~~~~~~~
1265 The CAN bit-timing parameters can always be defined in a hardware
1266 independent format as proposed in the Bosch CAN 2.0 specification
1267 specifying the arguments "tq", "prop_seg", "phase_seg1", "phase_seg2"
1270 $ ip link set canX type can tq 125 prop-seg 6 \
1271 phase-seg1 7 phase-seg2 2 sjw 1
1273 If the kernel option CONFIG_CAN_CALC_BITTIMING is enabled, CIA
1274 recommended CAN bit-timing parameters will be calculated if the bit-
1275 rate is specified with the argument "bitrate"::
1277 $ ip link set canX type can bitrate 125000
1279 Note that this works fine for the most common CAN controllers with
1280 standard bit-rates but may *fail* for exotic bit-rates or CAN system
1281 clock frequencies. Disabling CONFIG_CAN_CALC_BITTIMING saves some
1282 space and allows user-space tools to solely determine and set the
1283 bit-timing parameters. The CAN controller specific bit-timing
1284 constants can be used for that purpose. They are listed by the
1287 $ ip -details link show can0
1289 sja1000: clock 8000000 tseg1 1..16 tseg2 1..8 sjw 1..4 brp 1..64 brp-inc 1
1292 Starting and Stopping the CAN Network Device
1293 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1295 A CAN network device is started or stopped as usual with the command
1296 "ifconfig canX up/down" or "ip link set canX up/down". Be aware that
1297 you *must* define proper bit-timing parameters for real CAN devices
1298 before you can start it to avoid error-prone default settings::
1300 $ ip link set canX up type can bitrate 125000
1302 A device may enter the "bus-off" state if too many errors occurred on
1303 the CAN bus. Then no more messages are received or sent. An automatic
1304 bus-off recovery can be enabled by setting the "restart-ms" to a
1305 non-zero value, e.g.::
1307 $ ip link set canX type can restart-ms 100
1309 Alternatively, the application may realize the "bus-off" condition
1310 by monitoring CAN error message frames and do a restart when
1311 appropriate with the command::
1313 $ ip link set canX type can restart
1315 Note that a restart will also create a CAN error message frame (see
1316 also :ref:`socketcan-network-problem-notifications`).
1319 .. _socketcan-can-fd-driver:
1321 CAN FD (Flexible Data Rate) Driver Support
1322 ------------------------------------------
1324 CAN FD capable CAN controllers support two different bitrates for the
1325 arbitration phase and the payload phase of the CAN FD frame. Therefore a
1326 second bit timing has to be specified in order to enable the CAN FD bitrate.
1328 Additionally CAN FD capable CAN controllers support up to 64 bytes of
1329 payload. The representation of this length in can_frame.can_dlc and
1330 canfd_frame.len for userspace applications and inside the Linux network
1331 layer is a plain value from 0 .. 64 instead of the CAN 'data length code'.
1332 The data length code was a 1:1 mapping to the payload length in the legacy
1333 CAN frames anyway. The payload length to the bus-relevant DLC mapping is
1334 only performed inside the CAN drivers, preferably with the helper
1335 functions can_dlc2len() and can_len2dlc().
1337 The CAN netdevice driver capabilities can be distinguished by the network
1338 devices maximum transfer unit (MTU)::
1340 MTU = 16 (CAN_MTU) => sizeof(struct can_frame) => 'legacy' CAN device
1341 MTU = 72 (CANFD_MTU) => sizeof(struct canfd_frame) => CAN FD capable device
1343 The CAN device MTU can be retrieved e.g. with a SIOCGIFMTU ioctl() syscall.
1344 N.B. CAN FD capable devices can also handle and send legacy CAN frames.
1346 When configuring CAN FD capable CAN controllers an additional 'data' bitrate
1347 has to be set. This bitrate for the data phase of the CAN FD frame has to be
1348 at least the bitrate which was configured for the arbitration phase. This
1349 second bitrate is specified analogue to the first bitrate but the bitrate
1350 setting keywords for the 'data' bitrate start with 'd' e.g. dbitrate,
1351 dsample-point, dsjw or dtq and similar settings. When a data bitrate is set
1352 within the configuration process the controller option "fd on" can be
1353 specified to enable the CAN FD mode in the CAN controller. This controller
1354 option also switches the device MTU to 72 (CANFD_MTU).
1356 The first CAN FD specification presented as whitepaper at the International
1357 CAN Conference 2012 needed to be improved for data integrity reasons.
1358 Therefore two CAN FD implementations have to be distinguished today:
1360 - ISO compliant: The ISO 11898-1:2015 CAN FD implementation (default)
1361 - non-ISO compliant: The CAN FD implementation following the 2012 whitepaper
1363 Finally there are three types of CAN FD controllers:
1365 1. ISO compliant (fixed)
1366 2. non-ISO compliant (fixed, like the M_CAN IP core v3.0.1 in m_can.c)
1367 3. ISO/non-ISO CAN FD controllers (switchable, like the PEAK PCAN-USB FD)
1369 The current ISO/non-ISO mode is announced by the CAN controller driver via
1370 netlink and displayed by the 'ip' tool (controller option FD-NON-ISO).
1371 The ISO/non-ISO-mode can be altered by setting 'fd-non-iso {on|off}' for
1372 switchable CAN FD controllers only.
1374 Example configuring 500 kbit/s arbitration bitrate and 4 Mbit/s data bitrate::
1376 $ ip link set can0 up type can bitrate 500000 sample-point 0.75 \
1377 dbitrate 4000000 dsample-point 0.8 fd on
1378 $ ip -details link show can0
1379 5: can0: <NOARP,UP,LOWER_UP,ECHO> mtu 72 qdisc pfifo_fast state UNKNOWN \
1380 mode DEFAULT group default qlen 10
1381 link/can promiscuity 0
1382 can <FD> state ERROR-ACTIVE (berr-counter tx 0 rx 0) restart-ms 0
1383 bitrate 500000 sample-point 0.750
1384 tq 50 prop-seg 14 phase-seg1 15 phase-seg2 10 sjw 1
1385 pcan_usb_pro_fd: tseg1 1..64 tseg2 1..16 sjw 1..16 brp 1..1024 \
1387 dbitrate 4000000 dsample-point 0.800
1388 dtq 12 dprop-seg 7 dphase-seg1 8 dphase-seg2 4 dsjw 1
1389 pcan_usb_pro_fd: dtseg1 1..16 dtseg2 1..8 dsjw 1..4 dbrp 1..1024 \
1393 Example when 'fd-non-iso on' is added on this switchable CAN FD adapter::
1395 can <FD,FD-NON-ISO> state ERROR-ACTIVE (berr-counter tx 0 rx 0) restart-ms 0
1398 Supported CAN Hardware
1399 ----------------------
1401 Please check the "Kconfig" file in "drivers/net/can" to get an actual
1402 list of the support CAN hardware. On the SocketCAN project website
1403 (see :ref:`socketcan-resources`) there might be further drivers available, also for
1404 older kernel versions.
1407 .. _socketcan-resources:
1412 The Linux CAN / SocketCAN project resources (project site / mailing list)
1413 are referenced in the MAINTAINERS file in the Linux source tree.
1414 Search for CAN NETWORK [LAYERS|DRIVERS].
1419 - Oliver Hartkopp (PF_CAN core, filters, drivers, bcm, SJA1000 driver)
1420 - Urs Thuermann (PF_CAN core, kernel integration, socket interfaces, raw, vcan)
1421 - Jan Kizka (RT-SocketCAN core, Socket-API reconciliation)
1422 - Wolfgang Grandegger (RT-SocketCAN core & drivers, Raw Socket-API reviews, CAN device driver interface, MSCAN driver)
1423 - Robert Schwebel (design reviews, PTXdist integration)
1424 - Marc Kleine-Budde (design reviews, Kernel 2.6 cleanups, drivers)
1425 - Benedikt Spranger (reviews)
1426 - Thomas Gleixner (LKML reviews, coding style, posting hints)
1427 - Andrey Volkov (kernel subtree structure, ioctls, MSCAN driver)
1428 - Matthias Brukner (first SJA1000 CAN netdevice implementation Q2/2003)
1429 - Klaus Hitschler (PEAK driver integration)
1430 - Uwe Koppe (CAN netdevices with PF_PACKET approach)
1431 - Michael Schulze (driver layer loopback requirement, RT CAN drivers review)
1432 - Pavel Pisa (Bit-timing calculation)
1433 - Sascha Hauer (SJA1000 platform driver)
1434 - Sebastian Haas (SJA1000 EMS PCI driver)
1435 - Markus Plessing (SJA1000 EMS PCI driver)
1436 - Per Dalen (SJA1000 Kvaser PCI driver)
1437 - Sam Ravnborg (reviews, coding style, kbuild help)