1===================================
2SocketCAN - Controller Area Network
3===================================
4
5Overview / What is SocketCAN
6============================
7
8The socketcan package is an implementation of CAN protocols
9(Controller Area Network) for Linux.  CAN is a networking technology
10which has widespread use in automation, embedded devices, and
11automotive fields.  While there have been other CAN implementations
12for Linux based on character devices, SocketCAN uses the Berkeley
13socket API, the Linux network stack and implements the CAN device
14drivers as network interfaces.  The CAN socket API has been designed
15as similar as possible to the TCP/IP protocols to allow programmers,
16familiar with network programming, to easily learn how to use CAN
17sockets.
18
19
20.. _socketcan-motivation:
21
22Motivation / Why Using the Socket API
23=====================================
24
25There have been CAN implementations for Linux before SocketCAN so the
26question arises, why we have started another project.  Most existing
27implementations come as a device driver for some CAN hardware, they
28are based on character devices and provide comparatively little
29functionality.  Usually, there is only a hardware-specific device
30driver which provides a character device interface to send and
31receive raw CAN frames, directly to/from the controller hardware.
32Queueing of frames and higher-level transport protocols like ISO-TP
33have to be implemented in user space applications.  Also, most
34character-device implementations support only one single process to
35open the device at a time, similar to a serial interface.  Exchanging
36the CAN controller requires employment of another device driver and
37often the need for adaption of large parts of the application to the
38new driver's API.
39
40SocketCAN was designed to overcome all of these limitations.  A new
41protocol family has been implemented which provides a socket interface
42to user space applications and which builds upon the Linux network
43layer, enabling use all of the provided queueing functionality.  A device
44driver for CAN controller hardware registers itself with the Linux
45network layer as a network device, so that CAN frames from the
46controller can be passed up to the network layer and on to the CAN
47protocol family module and also vice-versa.  Also, the protocol family
48module provides an API for transport protocol modules to register, so
49that any number of transport protocols can be loaded or unloaded
50dynamically.  In fact, the can core module alone does not provide any
51protocol and cannot be used without loading at least one additional
52protocol module.  Multiple sockets can be opened at the same time,
53on different or the same protocol module and they can listen/send
54frames on different or the same CAN IDs.  Several sockets listening on
55the same interface for frames with the same CAN ID are all passed the
56same received matching CAN frames.  An application wishing to
57communicate using a specific transport protocol, e.g. ISO-TP, just
58selects that protocol when opening the socket, and then can read and
59write application data byte streams, without having to deal with
60CAN-IDs, frames, etc.
61
62Similar functionality visible from user-space could be provided by a
63character device, too, but this would lead to a technically inelegant
64solution for a couple of reasons:
65
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.
69
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
72  for CAN networking.
73
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.
87
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
97  SocketCAN does.
98
99The use of the networking framework of the Linux kernel is just the
100natural and most appropriate way to implement CAN for Linux.
101
102
103.. _socketcan-concept:
104
105SocketCAN Concept
106=================
107
108As described in :ref:`socketcan-motivation` the main goal of SocketCAN is to
109provide a socket interface to user space applications which builds
110upon the Linux network layer. In contrast to the commonly known
111TCP/IP and ethernet networking, the CAN bus is a broadcast-only(!)
112medium 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
114have to be chosen uniquely on the bus. When designing a CAN-ECU
115network the CAN-IDs are mapped to be sent by a specific ECU.
116For this reason a CAN-ID can be treated best as a kind of source address.
117
118
119.. _socketcan-receive-lists:
120
121Receive Lists
122-------------
123
124The network transparent access of multiple applications leads to the
125problem that different applications may be interested in the same
126CAN-IDs from the same CAN network interface. The SocketCAN core
127module - which implements the protocol family CAN - provides several
128high efficient receive lists for this reason. If e.g. a user space
129application opens a CAN RAW socket, the raw protocol module itself
130requests the (range of) CAN-IDs from the SocketCAN core that are
131requested by the user. The subscription and unsubscription of
132CAN-IDs can be done for specific CAN interfaces or for all(!) known
133CAN interfaces with the can_rx_(un)register() functions provided to
134CAN protocol modules by the SocketCAN core (see :ref:`socketcan-core-module`).
135To optimize the CPU usage at runtime the receive lists are split up
136into several specific lists per device that match the requested
137filter complexity for a given use-case.
138
139
140.. _socketcan-local-loopback1:
141
142Local Loopback of Sent Frames
143-----------------------------
144
145As known from other networking concepts the data exchanging
146applications may run on the same or different nodes without any
147change (except for the according addressing information):
148
149.. code::
150
151	 ___   ___   ___                   _______   ___
152	| _ | | _ | | _ |                 | _   _ | | _ |
153	||A|| ||B|| ||C||                 ||A| |B|| ||C||
154	|___| |___| |___|                 |_______| |___|
155	  |     |     |                       |       |
156	-----------------(1)- CAN bus -(2)---------------
157
158To ensure that application A receives the same information in the
159example (2) as it would receive in example (1) there is need for
160some kind of local loopback of the sent CAN frames on the appropriate
161node.
162
163The Linux network devices (by default) just can handle the
164transmission and reception of media dependent frames. Due to the
165arbitration on the CAN bus the transmission of a low prio CAN-ID
166may be delayed by the reception of a high prio CAN frame. To
167reflect the correct [#f1]_ traffic on the node the loopback of the sent
168data has to be performed right after a successful transmission. If
169the CAN network interface is not capable of performing the loopback for
170some reason the SocketCAN core can do this task as a fallback solution.
171See :ref:`socketcan-local-loopback1` for details (recommended).
172
173The loopback functionality is enabled by default to reflect standard
174networking behaviour for CAN applications. Due to some requests from
175the RT-SocketCAN group the loopback optionally may be disabled for each
176separate socket. See sockopts from the CAN RAW sockets in :ref:`socketcan-raw-sockets`.
177
178.. [#f1] you really like to have this when you're running analyser
179       tools like 'candump' or 'cansniffer' on the (same) node.
180
181
182.. _socketcan-network-problem-notifications:
183
184Network Problem Notifications
185-----------------------------
186
187The use of the CAN bus may lead to several problems on the physical
188and media access control layer. Detecting and logging of these lower
189layer problems is a vital requirement for CAN users to identify
190hardware issues on the physical transceiver layer as well as
191arbitration problems and error frames caused by the different
192ECUs. The occurrence of detected errors are important for diagnosis
193and have to be logged together with the exact timestamp. For this
194reason the CAN interface driver can generate so called Error Message
195Frames that can optionally be passed to the user application in the
196same way as other CAN frames. Whenever an error on the physical layer
197or the MAC layer is detected (e.g. by the CAN controller) the driver
198creates an appropriate error message frame. Error messages frames can
199be requested by the user application using the common CAN filter
200mechanisms. Inside this filter definition the (interested) type of
201errors may be selected. The reception of error messages is disabled
202by default. The format of the CAN error message frame is briefly
203described in the Linux header file "include/uapi/linux/can/error.h".
204
205
206How to use SocketCAN
207====================
208
209Like TCP/IP, you first need to open a socket for communicating over a
210CAN network. Since SocketCAN implements a new protocol family, you
211need to pass PF_CAN as the first argument to the socket(2) system
212call. Currently, there are two CAN protocols to choose from, the raw
213socket protocol and the broadcast manager (BCM). So to open a socket,
214you would write::
215
216    s = socket(PF_CAN, SOCK_RAW, CAN_RAW);
217
218and::
219
220    s = socket(PF_CAN, SOCK_DGRAM, CAN_BCM);
221
222respectively.  After the successful creation of the socket, you would
223normally use the bind(2) system call to bind the socket to a CAN
224interface (which is different from TCP/IP due to different addressing
225- see :ref:`socketcan-concept`). After binding (CAN_RAW) or connecting (CAN_BCM)
226the socket, you can read(2) and write(2) from/to the socket or use
227send(2), sendto(2), sendmsg(2) and the recv* counterpart operations
228on the socket as usual. There are also CAN specific socket options
229described below.
230
231The Classical CAN frame structure (aka CAN 2.0B), the CAN FD frame structure
232and the sockaddr structure are defined in include/linux/can.h:
233
234.. code-block:: C
235
236    struct can_frame {
237            canid_t can_id;  /* 32 bit CAN_ID + EFF/RTR/ERR flags */
238            union {
239                    /* CAN frame payload length in byte (0 .. CAN_MAX_DLEN)
240                     * was previously named can_dlc so we need to carry that
241                     * name for legacy support
242                     */
243                    __u8 len;
244                    __u8 can_dlc; /* deprecated */
245            };
246            __u8    __pad;   /* padding */
247            __u8    __res0;  /* reserved / padding */
248            __u8    len8_dlc; /* optional DLC for 8 byte payload length (9 .. 15) */
249            __u8    data[8] __attribute__((aligned(8)));
250    };
251
252Remark: The len element contains the payload length in bytes and should be
253used instead of can_dlc. The deprecated can_dlc was misleadingly named as
254it always contained the plain payload length in bytes and not the so called
255'data length code' (DLC).
256
257To pass the raw DLC from/to a Classical CAN network device the len8_dlc
258element can contain values 9 .. 15 when the len element is 8 (the real
259payload length for all DLC values greater or equal to 8).
260
261The alignment of the (linear) payload data[] to a 64bit boundary
262allows the user to define their own structs and unions to easily access
263the CAN payload. There is no given byteorder on the CAN bus by
264default. A read(2) system call on a CAN_RAW socket transfers a
265struct can_frame to the user space.
266
267The sockaddr_can structure has an interface index like the
268PF_PACKET socket, that also binds to a specific interface:
269
270.. code-block:: C
271
272    struct sockaddr_can {
273            sa_family_t can_family;
274            int         can_ifindex;
275            union {
276                    /* transport protocol class address info (e.g. ISOTP) */
277                    struct { canid_t rx_id, tx_id; } tp;
278
279                    /* J1939 address information */
280                    struct {
281                            /* 8 byte name when using dynamic addressing */
282                            __u64 name;
283
284                            /* pgn:
285                             * 8 bit: PS in PDU2 case, else 0
286                             * 8 bit: PF
287                             * 1 bit: DP
288                             * 1 bit: reserved
289                             */
290                            __u32 pgn;
291
292                            /* 1 byte address */
293                            __u8 addr;
294                    } j1939;
295
296                    /* reserved for future CAN protocols address information */
297            } can_addr;
298    };
299
300To determine the interface index an appropriate ioctl() has to
301be used (example for CAN_RAW sockets without error checking):
302
303.. code-block:: C
304
305    int s;
306    struct sockaddr_can addr;
307    struct ifreq ifr;
308
309    s = socket(PF_CAN, SOCK_RAW, CAN_RAW);
310
311    strcpy(ifr.ifr_name, "can0" );
312    ioctl(s, SIOCGIFINDEX, &ifr);
313
314    addr.can_family = AF_CAN;
315    addr.can_ifindex = ifr.ifr_ifindex;
316
317    bind(s, (struct sockaddr *)&addr, sizeof(addr));
318
319    (..)
320
321To bind a socket to all(!) CAN interfaces the interface index must
322be 0 (zero). In this case the socket receives CAN frames from every
323enabled CAN interface. To determine the originating CAN interface
324the system call recvfrom(2) may be used instead of read(2). To send
325on a socket that is bound to 'any' interface sendto(2) is needed to
326specify the outgoing interface.
327
328Reading CAN frames from a bound CAN_RAW socket (see above) consists
329of reading a struct can_frame:
330
331.. code-block:: C
332
333    struct can_frame frame;
334
335    nbytes = read(s, &frame, sizeof(struct can_frame));
336
337    if (nbytes < 0) {
338            perror("can raw socket read");
339            return 1;
340    }
341
342    /* paranoid check ... */
343    if (nbytes < sizeof(struct can_frame)) {
344            fprintf(stderr, "read: incomplete CAN frame\n");
345            return 1;
346    }
347
348    /* do something with the received CAN frame */
349
350Writing CAN frames can be done similarly, with the write(2) system call::
351
352    nbytes = write(s, &frame, sizeof(struct can_frame));
353
354When the CAN interface is bound to 'any' existing CAN interface
355(addr.can_ifindex = 0) it is recommended to use recvfrom(2) if the
356information about the originating CAN interface is needed:
357
358.. code-block:: C
359
360    struct sockaddr_can addr;
361    struct ifreq ifr;
362    socklen_t len = sizeof(addr);
363    struct can_frame frame;
364
365    nbytes = recvfrom(s, &frame, sizeof(struct can_frame),
366                      0, (struct sockaddr*)&addr, &len);
367
368    /* get interface name of the received CAN frame */
369    ifr.ifr_ifindex = addr.can_ifindex;
370    ioctl(s, SIOCGIFNAME, &ifr);
371    printf("Received a CAN frame from interface %s", ifr.ifr_name);
372
373To write CAN frames on sockets bound to 'any' CAN interface the
374outgoing interface has to be defined certainly:
375
376.. code-block:: C
377
378    strcpy(ifr.ifr_name, "can0");
379    ioctl(s, SIOCGIFINDEX, &ifr);
380    addr.can_ifindex = ifr.ifr_ifindex;
381    addr.can_family  = AF_CAN;
382
383    nbytes = sendto(s, &frame, sizeof(struct can_frame),
384                    0, (struct sockaddr*)&addr, sizeof(addr));
385
386An accurate timestamp can be obtained with an ioctl(2) call after reading
387a message from the socket:
388
389.. code-block:: C
390
391    struct timeval tv;
392    ioctl(s, SIOCGSTAMP, &tv);
393
394The timestamp has a resolution of one microsecond and is set automatically
395at the reception of a CAN frame.
396
397Remark about CAN FD (flexible data rate) support:
398
399Generally the handling of CAN FD is very similar to the formerly described
400examples. The new CAN FD capable CAN controllers support two different
401bitrates for the arbitration phase and the payload phase of the CAN FD frame
402and up to 64 bytes of payload. This extended payload length breaks all the
403kernel interfaces (ABI) which heavily rely on the CAN frame with fixed eight
404bytes of payload (struct can_frame) like the CAN_RAW socket. Therefore e.g.
405the CAN_RAW socket supports a new socket option CAN_RAW_FD_FRAMES that
406switches the socket into a mode that allows the handling of CAN FD frames
407and Classical CAN frames simultaneously (see :ref:`socketcan-rawfd`).
408
409The struct canfd_frame is defined in include/linux/can.h:
410
411.. code-block:: C
412
413    struct canfd_frame {
414            canid_t can_id;  /* 32 bit CAN_ID + EFF/RTR/ERR flags */
415            __u8    len;     /* frame payload length in byte (0 .. 64) */
416            __u8    flags;   /* additional flags for CAN FD */
417            __u8    __res0;  /* reserved / padding */
418            __u8    __res1;  /* reserved / padding */
419            __u8    data[64] __attribute__((aligned(8)));
420    };
421
422The struct canfd_frame and the existing struct can_frame have the can_id,
423the payload length and the payload data at the same offset inside their
424structures. This allows to handle the different structures very similar.
425When the content of a struct can_frame is copied into a struct canfd_frame
426all structure elements can be used as-is - only the data[] becomes extended.
427
428When introducing the struct canfd_frame it turned out that the data length
429code (DLC) of the struct can_frame was used as a length information as the
430length and the DLC has a 1:1 mapping in the range of 0 .. 8. To preserve
431the easy handling of the length information the canfd_frame.len element
432contains a plain length value from 0 .. 64. So both canfd_frame.len and
433can_frame.len are equal and contain a length information and no DLC.
434For details about the distinction of CAN and CAN FD capable devices and
435the mapping to the bus-relevant data length code (DLC), see :ref:`socketcan-can-fd-driver`.
436
437The length of the two CAN(FD) frame structures define the maximum transfer
438unit (MTU) of the CAN(FD) network interface and skbuff data length. Two
439definitions are specified for CAN specific MTUs in include/linux/can.h:
440
441.. code-block:: C
442
443  #define CAN_MTU   (sizeof(struct can_frame))   == 16  => Classical CAN frame
444  #define CANFD_MTU (sizeof(struct canfd_frame)) == 72  => CAN FD frame
445
446
447.. _socketcan-raw-sockets:
448
449RAW Protocol Sockets with can_filters (SOCK_RAW)
450------------------------------------------------
451
452Using CAN_RAW sockets is extensively comparable to the commonly
453known access to CAN character devices. To meet the new possibilities
454provided by the multi user SocketCAN approach, some reasonable
455defaults are set at RAW socket binding time:
456
457- The filters are set to exactly one filter receiving everything
458- The socket only receives valid data frames (=> no error message frames)
459- The loopback of sent CAN frames is enabled (see :ref:`socketcan-local-loopback2`)
460- The socket does not receive its own sent frames (in loopback mode)
461
462These default settings may be changed before or after binding the socket.
463To use the referenced definitions of the socket options for CAN_RAW
464sockets, include <linux/can/raw.h>.
465
466
467.. _socketcan-rawfilter:
468
469RAW socket option CAN_RAW_FILTER
470~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
471
472The reception of CAN frames using CAN_RAW sockets can be controlled
473by defining 0 .. n filters with the CAN_RAW_FILTER socket option.
474
475The CAN filter structure is defined in include/linux/can.h:
476
477.. code-block:: C
478
479    struct can_filter {
480            canid_t can_id;
481            canid_t can_mask;
482    };
483
484A filter matches, when:
485
486.. code-block:: C
487
488    <received_can_id> & mask == can_id & mask
489
490which is analogous to known CAN controllers hardware filter semantics.
491The filter can be inverted in this semantic, when the CAN_INV_FILTER
492bit is set in can_id element of the can_filter structure. In
493contrast to CAN controller hardware filters the user may set 0 .. n
494receive filters for each open socket separately:
495
496.. code-block:: C
497
498    struct can_filter rfilter[2];
499
500    rfilter[0].can_id   = 0x123;
501    rfilter[0].can_mask = CAN_SFF_MASK;
502    rfilter[1].can_id   = 0x200;
503    rfilter[1].can_mask = 0x700;
504
505    setsockopt(s, SOL_CAN_RAW, CAN_RAW_FILTER, &rfilter, sizeof(rfilter));
506
507To disable the reception of CAN frames on the selected CAN_RAW socket:
508
509.. code-block:: C
510
511    setsockopt(s, SOL_CAN_RAW, CAN_RAW_FILTER, NULL, 0);
512
513To set the filters to zero filters is quite obsolete as to not read
514data causes the raw socket to discard the received CAN frames. But
515having this 'send only' use-case we may remove the receive list in the
516Kernel to save a little (really a very little!) CPU usage.
517
518CAN Filter Usage Optimisation
519.............................
520
521The CAN filters are processed in per-device filter lists at CAN frame
522reception time. To reduce the number of checks that need to be performed
523while walking through the filter lists the CAN core provides an optimized
524filter handling when the filter subscription focusses on a single CAN ID.
525
526For the possible 2048 SFF CAN identifiers the identifier is used as an index
527to access the corresponding subscription list without any further checks.
528For the 2^29 possible EFF CAN identifiers a 10 bit XOR folding is used as
529hash function to retrieve the EFF table index.
530
531To benefit from the optimized filters for single CAN identifiers the
532CAN_SFF_MASK or CAN_EFF_MASK have to be set into can_filter.mask together
533with set CAN_EFF_FLAG and CAN_RTR_FLAG bits. A set CAN_EFF_FLAG bit in the
534can_filter.mask makes clear that it matters whether a SFF or EFF CAN ID is
535subscribed. E.g. in the example from above:
536
537.. code-block:: C
538
539    rfilter[0].can_id   = 0x123;
540    rfilter[0].can_mask = CAN_SFF_MASK;
541
542both SFF frames with CAN ID 0x123 and EFF frames with 0xXXXXX123 can pass.
543
544To filter for only 0x123 (SFF) and 0x12345678 (EFF) CAN identifiers the
545filter has to be defined in this way to benefit from the optimized filters:
546
547.. code-block:: C
548
549    struct can_filter rfilter[2];
550
551    rfilter[0].can_id   = 0x123;
552    rfilter[0].can_mask = (CAN_EFF_FLAG | CAN_RTR_FLAG | CAN_SFF_MASK);
553    rfilter[1].can_id   = 0x12345678 | CAN_EFF_FLAG;
554    rfilter[1].can_mask = (CAN_EFF_FLAG | CAN_RTR_FLAG | CAN_EFF_MASK);
555
556    setsockopt(s, SOL_CAN_RAW, CAN_RAW_FILTER, &rfilter, sizeof(rfilter));
557
558
559RAW Socket Option CAN_RAW_ERR_FILTER
560~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
561
562As described in :ref:`socketcan-network-problem-notifications` the CAN interface driver can generate so
563called Error Message Frames that can optionally be passed to the user
564application in the same way as other CAN frames. The possible
565errors are divided into different error classes that may be filtered
566using the appropriate error mask. To register for every possible
567error condition CAN_ERR_MASK can be used as value for the error mask.
568The values for the error mask are defined in linux/can/error.h:
569
570.. code-block:: C
571
572    can_err_mask_t err_mask = ( CAN_ERR_TX_TIMEOUT | CAN_ERR_BUSOFF );
573
574    setsockopt(s, SOL_CAN_RAW, CAN_RAW_ERR_FILTER,
575               &err_mask, sizeof(err_mask));
576
577
578RAW Socket Option CAN_RAW_LOOPBACK
579~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
580
581To meet multi user needs the local loopback is enabled by default
582(see :ref:`socketcan-local-loopback1` for details). But in some embedded use-cases
583(e.g. when only one application uses the CAN bus) this loopback
584functionality can be disabled (separately for each socket):
585
586.. code-block:: C
587
588    int loopback = 0; /* 0 = disabled, 1 = enabled (default) */
589
590    setsockopt(s, SOL_CAN_RAW, CAN_RAW_LOOPBACK, &loopback, sizeof(loopback));
591
592
593RAW socket option CAN_RAW_RECV_OWN_MSGS
594~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
595
596When the local loopback is enabled, all the sent CAN frames are
597looped back to the open CAN sockets that registered for the CAN
598frames' CAN-ID on this given interface to meet the multi user
599needs. The reception of the CAN frames on the same socket that was
600sending the CAN frame is assumed to be unwanted and therefore
601disabled by default. This default behaviour may be changed on
602demand:
603
604.. code-block:: C
605
606    int recv_own_msgs = 1; /* 0 = disabled (default), 1 = enabled */
607
608    setsockopt(s, SOL_CAN_RAW, CAN_RAW_RECV_OWN_MSGS,
609               &recv_own_msgs, sizeof(recv_own_msgs));
610
611Note that reception of a socket's own CAN frames are subject to the same
612filtering as other CAN frames (see :ref:`socketcan-rawfilter`).
613
614.. _socketcan-rawfd:
615
616RAW Socket Option CAN_RAW_FD_FRAMES
617~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
618
619CAN FD support in CAN_RAW sockets can be enabled with a new socket option
620CAN_RAW_FD_FRAMES which is off by default. When the new socket option is
621not supported by the CAN_RAW socket (e.g. on older kernels), switching the
622CAN_RAW_FD_FRAMES option returns the error -ENOPROTOOPT.
623
624Once CAN_RAW_FD_FRAMES is enabled the application can send both CAN frames
625and CAN FD frames. OTOH the application has to handle CAN and CAN FD frames
626when reading from the socket:
627
628.. code-block:: C
629
630    CAN_RAW_FD_FRAMES enabled:  CAN_MTU and CANFD_MTU are allowed
631    CAN_RAW_FD_FRAMES disabled: only CAN_MTU is allowed (default)
632
633Example:
634
635.. code-block:: C
636
637    [ remember: CANFD_MTU == sizeof(struct canfd_frame) ]
638
639    struct canfd_frame cfd;
640
641    nbytes = read(s, &cfd, CANFD_MTU);
642
643    if (nbytes == CANFD_MTU) {
644            printf("got CAN FD frame with length %d\n", cfd.len);
645            /* cfd.flags contains valid data */
646    } else if (nbytes == CAN_MTU) {
647            printf("got Classical CAN frame with length %d\n", cfd.len);
648            /* cfd.flags is undefined */
649    } else {
650            fprintf(stderr, "read: invalid CAN(FD) frame\n");
651            return 1;
652    }
653
654    /* the content can be handled independently from the received MTU size */
655
656    printf("can_id: %X data length: %d data: ", cfd.can_id, cfd.len);
657    for (i = 0; i < cfd.len; i++)
658            printf("%02X ", cfd.data[i]);
659
660When reading with size CANFD_MTU only returns CAN_MTU bytes that have
661been received from the socket a Classical CAN frame has been read into the
662provided CAN FD structure. Note that the canfd_frame.flags data field is
663not specified in the struct can_frame and therefore it is only valid in
664CANFD_MTU sized CAN FD frames.
665
666Implementation hint for new CAN applications:
667
668To build a CAN FD aware application use struct canfd_frame as basic CAN
669data structure for CAN_RAW based applications. When the application is
670executed on an older Linux kernel and switching the CAN_RAW_FD_FRAMES
671socket option returns an error: No problem. You'll get Classical CAN frames
672or CAN FD frames and can process them the same way.
673
674When sending to CAN devices make sure that the device is capable to handle
675CAN FD frames by checking if the device maximum transfer unit is CANFD_MTU.
676The CAN device MTU can be retrieved e.g. with a SIOCGIFMTU ioctl() syscall.
677
678
679RAW socket option CAN_RAW_JOIN_FILTERS
680~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
681
682The CAN_RAW socket can set multiple CAN identifier specific filters that
683lead to multiple filters in the af_can.c filter processing. These filters
684are indenpendent from each other which leads to logical OR'ed filters when
685applied (see :ref:`socketcan-rawfilter`).
686
687This socket option joines the given CAN filters in the way that only CAN
688frames are passed to user space that matched *all* given CAN filters. The
689semantic for the applied filters is therefore changed to a logical AND.
690
691This is useful especially when the filterset is a combination of filters
692where the CAN_INV_FILTER flag is set in order to notch single CAN IDs or
693CAN ID ranges from the incoming traffic.
694
695
696RAW Socket Returned Message Flags
697~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
698
699When using recvmsg() call, the msg->msg_flags may contain following flags:
700
701MSG_DONTROUTE:
702	set when the received frame was created on the local host.
703
704MSG_CONFIRM:
705	set when the frame was sent via the socket it is received on.
706	This flag can be interpreted as a 'transmission confirmation' when the
707	CAN driver supports the echo of frames on driver level, see
708	:ref:`socketcan-local-loopback1` and :ref:`socketcan-local-loopback2`.
709	In order to receive such messages, CAN_RAW_RECV_OWN_MSGS must be set.
710
711
712Broadcast Manager Protocol Sockets (SOCK_DGRAM)
713-----------------------------------------------
714
715The Broadcast Manager protocol provides a command based configuration
716interface to filter and send (e.g. cyclic) CAN messages in kernel space.
717
718Receive filters can be used to down sample frequent messages; detect events
719such as message contents changes, packet length changes, and do time-out
720monitoring of received messages.
721
722Periodic transmission tasks of CAN frames or a sequence of CAN frames can be
723created and modified at runtime; both the message content and the two
724possible transmit intervals can be altered.
725
726A BCM socket is not intended for sending individual CAN frames using the
727struct can_frame as known from the CAN_RAW socket. Instead a special BCM
728configuration message is defined. The basic BCM configuration message used
729to communicate with the broadcast manager and the available operations are
730defined in the linux/can/bcm.h include. The BCM message consists of a
731message header with a command ('opcode') followed by zero or more CAN frames.
732The broadcast manager sends responses to user space in the same form:
733
734.. code-block:: C
735
736    struct bcm_msg_head {
737            __u32 opcode;                   /* command */
738            __u32 flags;                    /* special flags */
739            __u32 count;                    /* run 'count' times with ival1 */
740            struct timeval ival1, ival2;    /* count and subsequent interval */
741            canid_t can_id;                 /* unique can_id for task */
742            __u32 nframes;                  /* number of can_frames following */
743            struct can_frame frames[0];
744    };
745
746The aligned payload 'frames' uses the same basic CAN frame structure defined
747at the beginning of :ref:`socketcan-rawfd` and in the include/linux/can.h include. All
748messages to the broadcast manager from user space have this structure.
749
750Note a CAN_BCM socket must be connected instead of bound after socket
751creation (example without error checking):
752
753.. code-block:: C
754
755    int s;
756    struct sockaddr_can addr;
757    struct ifreq ifr;
758
759    s = socket(PF_CAN, SOCK_DGRAM, CAN_BCM);
760
761    strcpy(ifr.ifr_name, "can0");
762    ioctl(s, SIOCGIFINDEX, &ifr);
763
764    addr.can_family = AF_CAN;
765    addr.can_ifindex = ifr.ifr_ifindex;
766
767    connect(s, (struct sockaddr *)&addr, sizeof(addr));
768
769    (..)
770
771The broadcast manager socket is able to handle any number of in flight
772transmissions or receive filters concurrently. The different RX/TX jobs are
773distinguished by the unique can_id in each BCM message. However additional
774CAN_BCM sockets are recommended to communicate on multiple CAN interfaces.
775When the broadcast manager socket is bound to 'any' CAN interface (=> the
776interface index is set to zero) the configured receive filters apply to any
777CAN interface unless the sendto() syscall is used to overrule the 'any' CAN
778interface index. When using recvfrom() instead of read() to retrieve BCM
779socket messages the originating CAN interface is provided in can_ifindex.
780
781
782Broadcast Manager Operations
783~~~~~~~~~~~~~~~~~~~~~~~~~~~~
784
785The opcode defines the operation for the broadcast manager to carry out,
786or details the broadcast managers response to several events, including
787user requests.
788
789Transmit Operations (user space to broadcast manager):
790
791TX_SETUP:
792	Create (cyclic) transmission task.
793
794TX_DELETE:
795	Remove (cyclic) transmission task, requires only can_id.
796
797TX_READ:
798	Read properties of (cyclic) transmission task for can_id.
799
800TX_SEND:
801	Send one CAN frame.
802
803Transmit Responses (broadcast manager to user space):
804
805TX_STATUS:
806	Reply to TX_READ request (transmission task configuration).
807
808TX_EXPIRED:
809	Notification when counter finishes sending at initial interval
810	'ival1'. Requires the TX_COUNTEVT flag to be set at TX_SETUP.
811
812Receive Operations (user space to broadcast manager):
813
814RX_SETUP:
815	Create RX content filter subscription.
816
817RX_DELETE:
818	Remove RX content filter subscription, requires only can_id.
819
820RX_READ:
821	Read properties of RX content filter subscription for can_id.
822
823Receive Responses (broadcast manager to user space):
824
825RX_STATUS:
826	Reply to RX_READ request (filter task configuration).
827
828RX_TIMEOUT:
829	Cyclic message is detected to be absent (timer ival1 expired).
830
831RX_CHANGED:
832	BCM message with updated CAN frame (detected content change).
833	Sent on first message received or on receipt of revised CAN messages.
834
835
836Broadcast Manager Message Flags
837~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
838
839When sending a message to the broadcast manager the 'flags' element may
840contain the following flag definitions which influence the behaviour:
841
842SETTIMER:
843	Set the values of ival1, ival2 and count
844
845STARTTIMER:
846	Start the timer with the actual values of ival1, ival2
847	and count. Starting the timer leads simultaneously to emit a CAN frame.
848
849TX_COUNTEVT:
850	Create the message TX_EXPIRED when count expires
851
852TX_ANNOUNCE:
853	A change of data by the process is emitted immediately.
854
855TX_CP_CAN_ID:
856	Copies the can_id from the message header to each
857	subsequent frame in frames. This is intended as usage simplification. For
858	TX tasks the unique can_id from the message header may differ from the
859	can_id(s) stored for transmission in the subsequent struct can_frame(s).
860
861RX_FILTER_ID:
862	Filter by can_id alone, no frames required (nframes=0).
863
864RX_CHECK_DLC:
865	A change of the DLC leads to an RX_CHANGED.
866
867RX_NO_AUTOTIMER:
868	Prevent automatically starting the timeout monitor.
869
870RX_ANNOUNCE_RESUME:
871	If passed at RX_SETUP and a receive timeout occurred, a
872	RX_CHANGED message will be generated when the (cyclic) receive restarts.
873
874TX_RESET_MULTI_IDX:
875	Reset the index for the multiple frame transmission.
876
877RX_RTR_FRAME:
878	Send reply for RTR-request (placed in op->frames[0]).
879
880CAN_FD_FRAME:
881	The CAN frames following the bcm_msg_head are struct canfd_frame's
882
883Broadcast Manager Transmission Timers
884~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
885
886Periodic transmission configurations may use up to two interval timers.
887In this case the BCM sends a number of messages ('count') at an interval
888'ival1', then continuing to send at another given interval 'ival2'. When
889only one timer is needed 'count' is set to zero and only 'ival2' is used.
890When SET_TIMER and START_TIMER flag were set the timers are activated.
891The timer values can be altered at runtime when only SET_TIMER is set.
892
893
894Broadcast Manager message sequence transmission
895~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
896
897Up to 256 CAN frames can be transmitted in a sequence in the case of a cyclic
898TX task configuration. The number of CAN frames is provided in the 'nframes'
899element of the BCM message head. The defined number of CAN frames are added
900as array to the TX_SETUP BCM configuration message:
901
902.. code-block:: C
903
904    /* create a struct to set up a sequence of four CAN frames */
905    struct {
906            struct bcm_msg_head msg_head;
907            struct can_frame frame[4];
908    } mytxmsg;
909
910    (..)
911    mytxmsg.msg_head.nframes = 4;
912    (..)
913
914    write(s, &mytxmsg, sizeof(mytxmsg));
915
916With every transmission the index in the array of CAN frames is increased
917and set to zero at index overflow.
918
919
920Broadcast Manager Receive Filter Timers
921~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
922
923The timer values ival1 or ival2 may be set to non-zero values at RX_SETUP.
924When the SET_TIMER flag is set the timers are enabled:
925
926ival1:
927	Send RX_TIMEOUT when a received message is not received again within
928	the given time. When START_TIMER is set at RX_SETUP the timeout detection
929	is activated directly - even without a former CAN frame reception.
930
931ival2:
932	Throttle the received message rate down to the value of ival2. This
933	is useful to reduce messages for the application when the signal inside the
934	CAN frame is stateless as state changes within the ival2 periode may get
935	lost.
936
937Broadcast Manager Multiplex Message Receive Filter
938~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
939
940To filter for content changes in multiplex message sequences an array of more
941than one CAN frames can be passed in a RX_SETUP configuration message. The
942data bytes of the first CAN frame contain the mask of relevant bits that
943have to match in the subsequent CAN frames with the received CAN frame.
944If one of the subsequent CAN frames is matching the bits in that frame data
945mark the relevant content to be compared with the previous received content.
946Up to 257 CAN frames (multiplex filter bit mask CAN frame plus 256 CAN
947filters) can be added as array to the TX_SETUP BCM configuration message:
948
949.. code-block:: C
950
951    /* usually used to clear CAN frame data[] - beware of endian problems! */
952    #define U64_DATA(p) (*(unsigned long long*)(p)->data)
953
954    struct {
955            struct bcm_msg_head msg_head;
956            struct can_frame frame[5];
957    } msg;
958
959    msg.msg_head.opcode  = RX_SETUP;
960    msg.msg_head.can_id  = 0x42;
961    msg.msg_head.flags   = 0;
962    msg.msg_head.nframes = 5;
963    U64_DATA(&msg.frame[0]) = 0xFF00000000000000ULL; /* MUX mask */
964    U64_DATA(&msg.frame[1]) = 0x01000000000000FFULL; /* data mask (MUX 0x01) */
965    U64_DATA(&msg.frame[2]) = 0x0200FFFF000000FFULL; /* data mask (MUX 0x02) */
966    U64_DATA(&msg.frame[3]) = 0x330000FFFFFF0003ULL; /* data mask (MUX 0x33) */
967    U64_DATA(&msg.frame[4]) = 0x4F07FC0FF0000000ULL; /* data mask (MUX 0x4F) */
968
969    write(s, &msg, sizeof(msg));
970
971
972Broadcast Manager CAN FD Support
973~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
974
975The programming API of the CAN_BCM depends on struct can_frame which is
976given as array directly behind the bcm_msg_head structure. To follow this
977schema for the CAN FD frames a new flag 'CAN_FD_FRAME' in the bcm_msg_head
978flags indicates that the concatenated CAN frame structures behind the
979bcm_msg_head are defined as struct canfd_frame:
980
981.. code-block:: C
982
983    struct {
984            struct bcm_msg_head msg_head;
985            struct canfd_frame frame[5];
986    } msg;
987
988    msg.msg_head.opcode  = RX_SETUP;
989    msg.msg_head.can_id  = 0x42;
990    msg.msg_head.flags   = CAN_FD_FRAME;
991    msg.msg_head.nframes = 5;
992    (..)
993
994When using CAN FD frames for multiplex filtering the MUX mask is still
995expected in the first 64 bit of the struct canfd_frame data section.
996
997
998Connected Transport Protocols (SOCK_SEQPACKET)
999----------------------------------------------
1000
1001(to be written)
1002
1003
1004Unconnected Transport Protocols (SOCK_DGRAM)
1005--------------------------------------------
1006
1007(to be written)
1008
1009
1010.. _socketcan-core-module:
1011
1012SocketCAN Core Module
1013=====================
1014
1015The SocketCAN core module implements the protocol family
1016PF_CAN. CAN protocol modules are loaded by the core module at
1017runtime. The core module provides an interface for CAN protocol
1018modules to subscribe needed CAN IDs (see :ref:`socketcan-receive-lists`).
1019
1020
1021can.ko Module Params
1022--------------------
1023
1024- **stats_timer**:
1025  To calculate the SocketCAN core statistics
1026  (e.g. current/maximum frames per second) this 1 second timer is
1027  invoked at can.ko module start time by default. This timer can be
1028  disabled by using stattimer=0 on the module commandline.
1029
1030- **debug**:
1031  (removed since SocketCAN SVN r546)
1032
1033
1034procfs content
1035--------------
1036
1037As described in :ref:`socketcan-receive-lists` the SocketCAN core uses several filter
1038lists to deliver received CAN frames to CAN protocol modules. These
1039receive lists, their filters and the count of filter matches can be
1040checked in the appropriate receive list. All entries contain the
1041device and a protocol module identifier::
1042
1043    foo@bar:~$ cat /proc/net/can/rcvlist_all
1044
1045    receive list 'rx_all':
1046      (vcan3: no entry)
1047      (vcan2: no entry)
1048      (vcan1: no entry)
1049      device   can_id   can_mask  function  userdata   matches  ident
1050       vcan0     000    00000000  f88e6370  f6c6f400         0  raw
1051      (any: no entry)
1052
1053In this example an application requests any CAN traffic from vcan0::
1054
1055    rcvlist_all - list for unfiltered entries (no filter operations)
1056    rcvlist_eff - list for single extended frame (EFF) entries
1057    rcvlist_err - list for error message frames masks
1058    rcvlist_fil - list for mask/value filters
1059    rcvlist_inv - list for mask/value filters (inverse semantic)
1060    rcvlist_sff - list for single standard frame (SFF) entries
1061
1062Additional procfs files in /proc/net/can::
1063
1064    stats       - SocketCAN core statistics (rx/tx frames, match ratios, ...)
1065    reset_stats - manual statistic reset
1066    version     - prints SocketCAN core and ABI version (removed in Linux 5.10)
1067
1068
1069Writing Own CAN Protocol Modules
1070--------------------------------
1071
1072To implement a new protocol in the protocol family PF_CAN a new
1073protocol has to be defined in include/linux/can.h .
1074The prototypes and definitions to use the SocketCAN core can be
1075accessed by including include/linux/can/core.h .
1076In addition to functions that register the CAN protocol and the
1077CAN device notifier chain there are functions to subscribe CAN
1078frames received by CAN interfaces and to send CAN frames::
1079
1080    can_rx_register   - subscribe CAN frames from a specific interface
1081    can_rx_unregister - unsubscribe CAN frames from a specific interface
1082    can_send          - transmit a CAN frame (optional with local loopback)
1083
1084For details see the kerneldoc documentation in net/can/af_can.c or
1085the source code of net/can/raw.c or net/can/bcm.c .
1086
1087
1088CAN Network Drivers
1089===================
1090
1091Writing a CAN network device driver is much easier than writing a
1092CAN character device driver. Similar to other known network device
1093drivers you mainly have to deal with:
1094
1095- TX: Put the CAN frame from the socket buffer to the CAN controller.
1096- RX: Put the CAN frame from the CAN controller to the socket buffer.
1097
1098See e.g. at Documentation/networking/netdevices.rst . The differences
1099for writing CAN network device driver are described below:
1100
1101
1102General Settings
1103----------------
1104
1105.. code-block:: C
1106
1107    dev->type  = ARPHRD_CAN; /* the netdevice hardware type */
1108    dev->flags = IFF_NOARP;  /* CAN has no arp */
1109
1110    dev->mtu = CAN_MTU; /* sizeof(struct can_frame) -> Classical CAN interface */
1111
1112    or alternative, when the controller supports CAN with flexible data rate:
1113    dev->mtu = CANFD_MTU; /* sizeof(struct canfd_frame) -> CAN FD interface */
1114
1115The struct can_frame or struct canfd_frame is the payload of each socket
1116buffer (skbuff) in the protocol family PF_CAN.
1117
1118
1119.. _socketcan-local-loopback2:
1120
1121Local Loopback of Sent Frames
1122-----------------------------
1123
1124As described in :ref:`socketcan-local-loopback1` the CAN network device driver should
1125support a local loopback functionality similar to the local echo
1126e.g. of tty devices. In this case the driver flag IFF_ECHO has to be
1127set to prevent the PF_CAN core from locally echoing sent frames
1128(aka loopback) as fallback solution::
1129
1130    dev->flags = (IFF_NOARP | IFF_ECHO);
1131
1132
1133CAN Controller Hardware Filters
1134-------------------------------
1135
1136To reduce the interrupt load on deep embedded systems some CAN
1137controllers support the filtering of CAN IDs or ranges of CAN IDs.
1138These hardware filter capabilities vary from controller to
1139controller and have to be identified as not feasible in a multi-user
1140networking approach. The use of the very controller specific
1141hardware filters could make sense in a very dedicated use-case, as a
1142filter on driver level would affect all users in the multi-user
1143system. The high efficient filter sets inside the PF_CAN core allow
1144to set different multiple filters for each socket separately.
1145Therefore the use of hardware filters goes to the category 'handmade
1146tuning on deep embedded systems'. The author is running a MPC603e
1147@133MHz with four SJA1000 CAN controllers from 2002 under heavy bus
1148load without any problems ...
1149
1150
1151The Virtual CAN Driver (vcan)
1152-----------------------------
1153
1154Similar to the network loopback devices, vcan offers a virtual local
1155CAN interface. A full qualified address on CAN consists of
1156
1157- a unique CAN Identifier (CAN ID)
1158- the CAN bus this CAN ID is transmitted on (e.g. can0)
1159
1160so in common use cases more than one virtual CAN interface is needed.
1161
1162The virtual CAN interfaces allow the transmission and reception of CAN
1163frames without real CAN controller hardware. Virtual CAN network
1164devices are usually named 'vcanX', like vcan0 vcan1 vcan2 ...
1165When compiled as a module the virtual CAN driver module is called vcan.ko
1166
1167Since Linux Kernel version 2.6.24 the vcan driver supports the Kernel
1168netlink interface to create vcan network devices. The creation and
1169removal of vcan network devices can be managed with the ip(8) tool::
1170
1171  - Create a virtual CAN network interface:
1172       $ ip link add type vcan
1173
1174  - Create a virtual CAN network interface with a specific name 'vcan42':
1175       $ ip link add dev vcan42 type vcan
1176
1177  - Remove a (virtual CAN) network interface 'vcan42':
1178       $ ip link del vcan42
1179
1180
1181The CAN Network Device Driver Interface
1182---------------------------------------
1183
1184The CAN network device driver interface provides a generic interface
1185to setup, configure and monitor CAN network devices. The user can then
1186configure the CAN device, like setting the bit-timing parameters, via
1187the netlink interface using the program "ip" from the "IPROUTE2"
1188utility suite. The following chapter describes briefly how to use it.
1189Furthermore, the interface uses a common data structure and exports a
1190set of common functions, which all real CAN network device drivers
1191should use. Please have a look to the SJA1000 or MSCAN driver to
1192understand how to use them. The name of the module is can-dev.ko.
1193
1194
1195Netlink interface to set/get devices properties
1196~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1197
1198The CAN device must be configured via netlink interface. The supported
1199netlink message types are defined and briefly described in
1200"include/linux/can/netlink.h". CAN link support for the program "ip"
1201of the IPROUTE2 utility suite is available and it can be used as shown
1202below:
1203
1204Setting CAN device properties::
1205
1206    $ ip link set can0 type can help
1207    Usage: ip link set DEVICE type can
1208        [ bitrate BITRATE [ sample-point SAMPLE-POINT] ] |
1209        [ tq TQ prop-seg PROP_SEG phase-seg1 PHASE-SEG1
1210          phase-seg2 PHASE-SEG2 [ sjw SJW ] ]
1211
1212        [ dbitrate BITRATE [ dsample-point SAMPLE-POINT] ] |
1213        [ dtq TQ dprop-seg PROP_SEG dphase-seg1 PHASE-SEG1
1214          dphase-seg2 PHASE-SEG2 [ dsjw SJW ] ]
1215
1216        [ loopback { on | off } ]
1217        [ listen-only { on | off } ]
1218        [ triple-sampling { on | off } ]
1219        [ one-shot { on | off } ]
1220        [ berr-reporting { on | off } ]
1221        [ fd { on | off } ]
1222        [ fd-non-iso { on | off } ]
1223        [ presume-ack { on | off } ]
1224        [ cc-len8-dlc { on | off } ]
1225
1226        [ restart-ms TIME-MS ]
1227        [ restart ]
1228
1229        Where: BITRATE       := { 1..1000000 }
1230               SAMPLE-POINT  := { 0.000..0.999 }
1231               TQ            := { NUMBER }
1232               PROP-SEG      := { 1..8 }
1233               PHASE-SEG1    := { 1..8 }
1234               PHASE-SEG2    := { 1..8 }
1235               SJW           := { 1..4 }
1236               RESTART-MS    := { 0 | NUMBER }
1237
1238Display CAN device details and statistics::
1239
1240    $ ip -details -statistics link show can0
1241    2: can0: <NOARP,UP,LOWER_UP,ECHO> mtu 16 qdisc pfifo_fast state UP qlen 10
1242      link/can
1243      can <TRIPLE-SAMPLING> state ERROR-ACTIVE restart-ms 100
1244      bitrate 125000 sample_point 0.875
1245      tq 125 prop-seg 6 phase-seg1 7 phase-seg2 2 sjw 1
1246      sja1000: tseg1 1..16 tseg2 1..8 sjw 1..4 brp 1..64 brp-inc 1
1247      clock 8000000
1248      re-started bus-errors arbit-lost error-warn error-pass bus-off
1249      41         17457      0          41         42         41
1250      RX: bytes  packets  errors  dropped overrun mcast
1251      140859     17608    17457   0       0       0
1252      TX: bytes  packets  errors  dropped carrier collsns
1253      861        112      0       41      0       0
1254
1255More info to the above output:
1256
1257"<TRIPLE-SAMPLING>"
1258	Shows the list of selected CAN controller modes: LOOPBACK,
1259	LISTEN-ONLY, or TRIPLE-SAMPLING.
1260
1261"state ERROR-ACTIVE"
1262	The current state of the CAN controller: "ERROR-ACTIVE",
1263	"ERROR-WARNING", "ERROR-PASSIVE", "BUS-OFF" or "STOPPED"
1264
1265"restart-ms 100"
1266	Automatic restart delay time. If set to a non-zero value, a
1267	restart of the CAN controller will be triggered automatically
1268	in case of a bus-off condition after the specified delay time
1269	in milliseconds. By default it's off.
1270
1271"bitrate 125000 sample-point 0.875"
1272	Shows the real bit-rate in bits/sec and the sample-point in the
1273	range 0.000..0.999. If the calculation of bit-timing parameters
1274	is enabled in the kernel (CONFIG_CAN_CALC_BITTIMING=y), the
1275	bit-timing can be defined by setting the "bitrate" argument.
1276	Optionally the "sample-point" can be specified. By default it's
1277	0.000 assuming CIA-recommended sample-points.
1278
1279"tq 125 prop-seg 6 phase-seg1 7 phase-seg2 2 sjw 1"
1280	Shows the time quanta in ns, propagation segment, phase buffer
1281	segment 1 and 2 and the synchronisation jump width in units of
1282	tq. They allow to define the CAN bit-timing in a hardware
1283	independent format as proposed by the Bosch CAN 2.0 spec (see
1284	chapter 8 of http://www.semiconductors.bosch.de/pdf/can2spec.pdf).
1285
1286"sja1000: tseg1 1..16 tseg2 1..8 sjw 1..4 brp 1..64 brp-inc 1 clock 8000000"
1287	Shows the bit-timing constants of the CAN controller, here the
1288	"sja1000". The minimum and maximum values of the time segment 1
1289	and 2, the synchronisation jump width in units of tq, the
1290	bitrate pre-scaler and the CAN system clock frequency in Hz.
1291	These constants could be used for user-defined (non-standard)
1292	bit-timing calculation algorithms in user-space.
1293
1294"re-started bus-errors arbit-lost error-warn error-pass bus-off"
1295	Shows the number of restarts, bus and arbitration lost errors,
1296	and the state changes to the error-warning, error-passive and
1297	bus-off state. RX overrun errors are listed in the "overrun"
1298	field of the standard network statistics.
1299
1300Setting the CAN Bit-Timing
1301~~~~~~~~~~~~~~~~~~~~~~~~~~
1302
1303The CAN bit-timing parameters can always be defined in a hardware
1304independent format as proposed in the Bosch CAN 2.0 specification
1305specifying the arguments "tq", "prop_seg", "phase_seg1", "phase_seg2"
1306and "sjw"::
1307
1308    $ ip link set canX type can tq 125 prop-seg 6 \
1309				phase-seg1 7 phase-seg2 2 sjw 1
1310
1311If the kernel option CONFIG_CAN_CALC_BITTIMING is enabled, CIA
1312recommended CAN bit-timing parameters will be calculated if the bit-
1313rate is specified with the argument "bitrate"::
1314
1315    $ ip link set canX type can bitrate 125000
1316
1317Note that this works fine for the most common CAN controllers with
1318standard bit-rates but may *fail* for exotic bit-rates or CAN system
1319clock frequencies. Disabling CONFIG_CAN_CALC_BITTIMING saves some
1320space and allows user-space tools to solely determine and set the
1321bit-timing parameters. The CAN controller specific bit-timing
1322constants can be used for that purpose. They are listed by the
1323following command::
1324
1325    $ ip -details link show can0
1326    ...
1327      sja1000: clock 8000000 tseg1 1..16 tseg2 1..8 sjw 1..4 brp 1..64 brp-inc 1
1328
1329
1330Starting and Stopping the CAN Network Device
1331~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1332
1333A CAN network device is started or stopped as usual with the command
1334"ifconfig canX up/down" or "ip link set canX up/down". Be aware that
1335you *must* define proper bit-timing parameters for real CAN devices
1336before you can start it to avoid error-prone default settings::
1337
1338    $ ip link set canX up type can bitrate 125000
1339
1340A device may enter the "bus-off" state if too many errors occurred on
1341the CAN bus. Then no more messages are received or sent. An automatic
1342bus-off recovery can be enabled by setting the "restart-ms" to a
1343non-zero value, e.g.::
1344
1345    $ ip link set canX type can restart-ms 100
1346
1347Alternatively, the application may realize the "bus-off" condition
1348by monitoring CAN error message frames and do a restart when
1349appropriate with the command::
1350
1351    $ ip link set canX type can restart
1352
1353Note that a restart will also create a CAN error message frame (see
1354also :ref:`socketcan-network-problem-notifications`).
1355
1356
1357.. _socketcan-can-fd-driver:
1358
1359CAN FD (Flexible Data Rate) Driver Support
1360------------------------------------------
1361
1362CAN FD capable CAN controllers support two different bitrates for the
1363arbitration phase and the payload phase of the CAN FD frame. Therefore a
1364second bit timing has to be specified in order to enable the CAN FD bitrate.
1365
1366Additionally CAN FD capable CAN controllers support up to 64 bytes of
1367payload. The representation of this length in can_frame.len and
1368canfd_frame.len for userspace applications and inside the Linux network
1369layer is a plain value from 0 .. 64 instead of the CAN 'data length code'.
1370The data length code was a 1:1 mapping to the payload length in the Classical
1371CAN frames anyway. The payload length to the bus-relevant DLC mapping is
1372only performed inside the CAN drivers, preferably with the helper
1373functions can_fd_dlc2len() and can_fd_len2dlc().
1374
1375The CAN netdevice driver capabilities can be distinguished by the network
1376devices maximum transfer unit (MTU)::
1377
1378  MTU = 16 (CAN_MTU)   => sizeof(struct can_frame)   => Classical CAN device
1379  MTU = 72 (CANFD_MTU) => sizeof(struct canfd_frame) => CAN FD capable device
1380
1381The CAN device MTU can be retrieved e.g. with a SIOCGIFMTU ioctl() syscall.
1382N.B. CAN FD capable devices can also handle and send Classical CAN frames.
1383
1384When configuring CAN FD capable CAN controllers an additional 'data' bitrate
1385has to be set. This bitrate for the data phase of the CAN FD frame has to be
1386at least the bitrate which was configured for the arbitration phase. This
1387second bitrate is specified analogue to the first bitrate but the bitrate
1388setting keywords for the 'data' bitrate start with 'd' e.g. dbitrate,
1389dsample-point, dsjw or dtq and similar settings. When a data bitrate is set
1390within the configuration process the controller option "fd on" can be
1391specified to enable the CAN FD mode in the CAN controller. This controller
1392option also switches the device MTU to 72 (CANFD_MTU).
1393
1394The first CAN FD specification presented as whitepaper at the International
1395CAN Conference 2012 needed to be improved for data integrity reasons.
1396Therefore two CAN FD implementations have to be distinguished today:
1397
1398- ISO compliant:     The ISO 11898-1:2015 CAN FD implementation (default)
1399- non-ISO compliant: The CAN FD implementation following the 2012 whitepaper
1400
1401Finally there are three types of CAN FD controllers:
1402
14031. ISO compliant (fixed)
14042. non-ISO compliant (fixed, like the M_CAN IP core v3.0.1 in m_can.c)
14053. ISO/non-ISO CAN FD controllers (switchable, like the PEAK PCAN-USB FD)
1406
1407The current ISO/non-ISO mode is announced by the CAN controller driver via
1408netlink and displayed by the 'ip' tool (controller option FD-NON-ISO).
1409The ISO/non-ISO-mode can be altered by setting 'fd-non-iso {on|off}' for
1410switchable CAN FD controllers only.
1411
1412Example configuring 500 kbit/s arbitration bitrate and 4 Mbit/s data bitrate::
1413
1414    $ ip link set can0 up type can bitrate 500000 sample-point 0.75 \
1415                                   dbitrate 4000000 dsample-point 0.8 fd on
1416    $ ip -details link show can0
1417    5: can0: <NOARP,UP,LOWER_UP,ECHO> mtu 72 qdisc pfifo_fast state UNKNOWN \
1418             mode DEFAULT group default qlen 10
1419    link/can  promiscuity 0
1420    can <FD> state ERROR-ACTIVE (berr-counter tx 0 rx 0) restart-ms 0
1421          bitrate 500000 sample-point 0.750
1422          tq 50 prop-seg 14 phase-seg1 15 phase-seg2 10 sjw 1
1423          pcan_usb_pro_fd: tseg1 1..64 tseg2 1..16 sjw 1..16 brp 1..1024 \
1424          brp-inc 1
1425          dbitrate 4000000 dsample-point 0.800
1426          dtq 12 dprop-seg 7 dphase-seg1 8 dphase-seg2 4 dsjw 1
1427          pcan_usb_pro_fd: dtseg1 1..16 dtseg2 1..8 dsjw 1..4 dbrp 1..1024 \
1428          dbrp-inc 1
1429          clock 80000000
1430
1431Example when 'fd-non-iso on' is added on this switchable CAN FD adapter::
1432
1433   can <FD,FD-NON-ISO> state ERROR-ACTIVE (berr-counter tx 0 rx 0) restart-ms 0
1434
1435
1436Supported CAN Hardware
1437----------------------
1438
1439Please check the "Kconfig" file in "drivers/net/can" to get an actual
1440list of the support CAN hardware. On the SocketCAN project website
1441(see :ref:`socketcan-resources`) there might be further drivers available, also for
1442older kernel versions.
1443
1444
1445.. _socketcan-resources:
1446
1447SocketCAN Resources
1448===================
1449
1450The Linux CAN / SocketCAN project resources (project site / mailing list)
1451are referenced in the MAINTAINERS file in the Linux source tree.
1452Search for CAN NETWORK [LAYERS|DRIVERS].
1453
1454Credits
1455=======
1456
1457- Oliver Hartkopp (PF_CAN core, filters, drivers, bcm, SJA1000 driver)
1458- Urs Thuermann (PF_CAN core, kernel integration, socket interfaces, raw, vcan)
1459- Jan Kizka (RT-SocketCAN core, Socket-API reconciliation)
1460- Wolfgang Grandegger (RT-SocketCAN core & drivers, Raw Socket-API reviews, CAN device driver interface, MSCAN driver)
1461- Robert Schwebel (design reviews, PTXdist integration)
1462- Marc Kleine-Budde (design reviews, Kernel 2.6 cleanups, drivers)
1463- Benedikt Spranger (reviews)
1464- Thomas Gleixner (LKML reviews, coding style, posting hints)
1465- Andrey Volkov (kernel subtree structure, ioctls, MSCAN driver)
1466- Matthias Brukner (first SJA1000 CAN netdevice implementation Q2/2003)
1467- Klaus Hitschler (PEAK driver integration)
1468- Uwe Koppe (CAN netdevices with PF_PACKET approach)
1469- Michael Schulze (driver layer loopback requirement, RT CAN drivers review)
1470- Pavel Pisa (Bit-timing calculation)
1471- Sascha Hauer (SJA1000 platform driver)
1472- Sebastian Haas (SJA1000 EMS PCI driver)
1473- Markus Plessing (SJA1000 EMS PCI driver)
1474- Per Dalen (SJA1000 Kvaser PCI driver)
1475- Sam Ravnborg (reviews, coding style, kbuild help)
1476