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 basic CAN frame structure and the sockaddr structure are defined
232in 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            __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)));
243    };
244
245The alignment of the (linear) payload data[] to a 64bit boundary
246allows the user to define their own structs and unions to easily access
247the CAN payload. There is no given byteorder on the CAN bus by
248default. A read(2) system call on a CAN_RAW socket transfers a
249struct can_frame to the user space.
250
251The sockaddr_can structure has an interface index like the
252PF_PACKET socket, that also binds to a specific interface:
253
254.. code-block:: C
255
256    struct sockaddr_can {
257            sa_family_t can_family;
258            int         can_ifindex;
259            union {
260                    /* transport protocol class address info (e.g. ISOTP) */
261                    struct { canid_t rx_id, tx_id; } tp;
262
263                    /* reserved for future CAN protocols address information */
264            } can_addr;
265    };
266
267To determine the interface index an appropriate ioctl() has to
268be used (example for CAN_RAW sockets without error checking):
269
270.. code-block:: C
271
272    int s;
273    struct sockaddr_can addr;
274    struct ifreq ifr;
275
276    s = socket(PF_CAN, SOCK_RAW, CAN_RAW);
277
278    strcpy(ifr.ifr_name, "can0" );
279    ioctl(s, SIOCGIFINDEX, &ifr);
280
281    addr.can_family = AF_CAN;
282    addr.can_ifindex = ifr.ifr_ifindex;
283
284    bind(s, (struct sockaddr *)&addr, sizeof(addr));
285
286    (..)
287
288To bind a socket to all(!) CAN interfaces the interface index must
289be 0 (zero). In this case the socket receives CAN frames from every
290enabled CAN interface. To determine the originating CAN interface
291the system call recvfrom(2) may be used instead of read(2). To send
292on a socket that is bound to 'any' interface sendto(2) is needed to
293specify the outgoing interface.
294
295Reading CAN frames from a bound CAN_RAW socket (see above) consists
296of reading a struct can_frame:
297
298.. code-block:: C
299
300    struct can_frame frame;
301
302    nbytes = read(s, &frame, sizeof(struct can_frame));
303
304    if (nbytes < 0) {
305            perror("can raw socket read");
306            return 1;
307    }
308
309    /* paranoid check ... */
310    if (nbytes < sizeof(struct can_frame)) {
311            fprintf(stderr, "read: incomplete CAN frame\n");
312            return 1;
313    }
314
315    /* do something with the received CAN frame */
316
317Writing CAN frames can be done similarly, with the write(2) system call::
318
319    nbytes = write(s, &frame, sizeof(struct can_frame));
320
321When the CAN interface is bound to 'any' existing CAN interface
322(addr.can_ifindex = 0) it is recommended to use recvfrom(2) if the
323information about the originating CAN interface is needed:
324
325.. code-block:: C
326
327    struct sockaddr_can addr;
328    struct ifreq ifr;
329    socklen_t len = sizeof(addr);
330    struct can_frame frame;
331
332    nbytes = recvfrom(s, &frame, sizeof(struct can_frame),
333                      0, (struct sockaddr*)&addr, &len);
334
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);
339
340To write CAN frames on sockets bound to 'any' CAN interface the
341outgoing interface has to be defined certainly:
342
343.. code-block:: C
344
345    strcpy(ifr.ifr_name, "can0");
346    ioctl(s, SIOCGIFINDEX, &ifr);
347    addr.can_ifindex = ifr.ifr_ifindex;
348    addr.can_family  = AF_CAN;
349
350    nbytes = sendto(s, &frame, sizeof(struct can_frame),
351                    0, (struct sockaddr*)&addr, sizeof(addr));
352
353An accurate timestamp can be obtained with an ioctl(2) call after reading
354a message from the socket:
355
356.. code-block:: C
357
358    struct timeval tv;
359    ioctl(s, SIOCGSTAMP, &tv);
360
361The timestamp has a resolution of one microsecond and is set automatically
362at the reception of a CAN frame.
363
364Remark about CAN FD (flexible data rate) support:
365
366Generally the handling of CAN FD is very similar to the formerly described
367examples. The new CAN FD capable CAN controllers support two different
368bitrates for the arbitration phase and the payload phase of the CAN FD frame
369and up to 64 bytes of payload. This extended payload length breaks all the
370kernel interfaces (ABI) which heavily rely on the CAN frame with fixed eight
371bytes of payload (struct can_frame) like the CAN_RAW socket. Therefore e.g.
372the CAN_RAW socket supports a new socket option CAN_RAW_FD_FRAMES that
373switches the socket into a mode that allows the handling of CAN FD frames
374and (legacy) CAN frames simultaneously (see :ref:`socketcan-rawfd`).
375
376The struct canfd_frame is defined in include/linux/can.h:
377
378.. code-block:: C
379
380    struct canfd_frame {
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)));
387    };
388
389The struct canfd_frame and the existing struct can_frame have the can_id,
390the payload length and the payload data at the same offset inside their
391structures. This allows to handle the different structures very similar.
392When the content of a struct can_frame is copied into a struct canfd_frame
393all structure elements can be used as-is - only the data[] becomes extended.
394
395When introducing the struct canfd_frame it turned out that the data length
396code (DLC) of the struct can_frame was used as a length information as the
397length and the DLC has a 1:1 mapping in the range of 0 .. 8. To preserve
398the easy handling of the length information the canfd_frame.len element
399contains a plain length value from 0 .. 64. So both canfd_frame.len and
400can_frame.can_dlc are equal and contain a length information and no DLC.
401For details about the distinction of CAN and CAN FD capable devices and
402the mapping to the bus-relevant data length code (DLC), see :ref:`socketcan-can-fd-driver`.
403
404The length of the two CAN(FD) frame structures define the maximum transfer
405unit (MTU) of the CAN(FD) network interface and skbuff data length. Two
406definitions are specified for CAN specific MTUs in include/linux/can.h:
407
408.. code-block:: C
409
410  #define CAN_MTU   (sizeof(struct can_frame))   == 16  => 'legacy' CAN frame
411  #define CANFD_MTU (sizeof(struct canfd_frame)) == 72  => CAN FD frame
412
413
414.. _socketcan-raw-sockets:
415
416RAW Protocol Sockets with can_filters (SOCK_RAW)
417------------------------------------------------
418
419Using CAN_RAW sockets is extensively comparable to the commonly
420known access to CAN character devices. To meet the new possibilities
421provided by the multi user SocketCAN approach, some reasonable
422defaults are set at RAW socket binding time:
423
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)
428
429These default settings may be changed before or after binding the socket.
430To use the referenced definitions of the socket options for CAN_RAW
431sockets, include <linux/can/raw.h>.
432
433
434.. _socketcan-rawfilter:
435
436RAW socket option CAN_RAW_FILTER
437~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
438
439The reception of CAN frames using CAN_RAW sockets can be controlled
440by defining 0 .. n filters with the CAN_RAW_FILTER socket option.
441
442The CAN filter structure is defined in include/linux/can.h:
443
444.. code-block:: C
445
446    struct can_filter {
447            canid_t can_id;
448            canid_t can_mask;
449    };
450
451A filter matches, when:
452
453.. code-block:: C
454
455    <received_can_id> & mask == can_id & mask
456
457which is analogous to known CAN controllers hardware filter semantics.
458The filter can be inverted in this semantic, when the CAN_INV_FILTER
459bit is set in can_id element of the can_filter structure. In
460contrast to CAN controller hardware filters the user may set 0 .. n
461receive filters for each open socket separately:
462
463.. code-block:: C
464
465    struct can_filter rfilter[2];
466
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;
471
472    setsockopt(s, SOL_CAN_RAW, CAN_RAW_FILTER, &rfilter, sizeof(rfilter));
473
474To disable the reception of CAN frames on the selected CAN_RAW socket:
475
476.. code-block:: C
477
478    setsockopt(s, SOL_CAN_RAW, CAN_RAW_FILTER, NULL, 0);
479
480To set the filters to zero filters is quite obsolete as to not read
481data causes the raw socket to discard the received CAN frames. But
482having this 'send only' use-case we may remove the receive list in the
483Kernel to save a little (really a very little!) CPU usage.
484
485CAN Filter Usage Optimisation
486.............................
487
488The CAN filters are processed in per-device filter lists at CAN frame
489reception time. To reduce the number of checks that need to be performed
490while walking through the filter lists the CAN core provides an optimized
491filter handling when the filter subscription focusses on a single CAN ID.
492
493For the possible 2048 SFF CAN identifiers the identifier is used as an index
494to access the corresponding subscription list without any further checks.
495For the 2^29 possible EFF CAN identifiers a 10 bit XOR folding is used as
496hash function to retrieve the EFF table index.
497
498To benefit from the optimized filters for single CAN identifiers the
499CAN_SFF_MASK or CAN_EFF_MASK have to be set into can_filter.mask together
500with set CAN_EFF_FLAG and CAN_RTR_FLAG bits. A set CAN_EFF_FLAG bit in the
501can_filter.mask makes clear that it matters whether a SFF or EFF CAN ID is
502subscribed. E.g. in the example from above:
503
504.. code-block:: C
505
506    rfilter[0].can_id   = 0x123;
507    rfilter[0].can_mask = CAN_SFF_MASK;
508
509both SFF frames with CAN ID 0x123 and EFF frames with 0xXXXXX123 can pass.
510
511To filter for only 0x123 (SFF) and 0x12345678 (EFF) CAN identifiers the
512filter has to be defined in this way to benefit from the optimized filters:
513
514.. code-block:: C
515
516    struct can_filter rfilter[2];
517
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);
522
523    setsockopt(s, SOL_CAN_RAW, CAN_RAW_FILTER, &rfilter, sizeof(rfilter));
524
525
526RAW Socket Option CAN_RAW_ERR_FILTER
527~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
528
529As described in :ref:`socketcan-network-problem-notifications` the CAN interface driver can generate so
530called Error Message Frames that can optionally be passed to the user
531application in the same way as other CAN frames. The possible
532errors are divided into different error classes that may be filtered
533using the appropriate error mask. To register for every possible
534error condition CAN_ERR_MASK can be used as value for the error mask.
535The values for the error mask are defined in linux/can/error.h:
536
537.. code-block:: C
538
539    can_err_mask_t err_mask = ( CAN_ERR_TX_TIMEOUT | CAN_ERR_BUSOFF );
540
541    setsockopt(s, SOL_CAN_RAW, CAN_RAW_ERR_FILTER,
542               &err_mask, sizeof(err_mask));
543
544
545RAW Socket Option CAN_RAW_LOOPBACK
546~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
547
548To 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
551functionality can be disabled (separately for each socket):
552
553.. code-block:: C
554
555    int loopback = 0; /* 0 = disabled, 1 = enabled (default) */
556
557    setsockopt(s, SOL_CAN_RAW, CAN_RAW_LOOPBACK, &loopback, sizeof(loopback));
558
559
560RAW socket option CAN_RAW_RECV_OWN_MSGS
561~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
562
563When the local loopback is enabled, all the sent CAN frames are
564looped back to the open CAN sockets that registered for the CAN
565frames' CAN-ID on this given interface to meet the multi user
566needs. The reception of the CAN frames on the same socket that was
567sending the CAN frame is assumed to be unwanted and therefore
568disabled by default. This default behaviour may be changed on
569demand:
570
571.. code-block:: C
572
573    int recv_own_msgs = 1; /* 0 = disabled (default), 1 = enabled */
574
575    setsockopt(s, SOL_CAN_RAW, CAN_RAW_RECV_OWN_MSGS,
576               &recv_own_msgs, sizeof(recv_own_msgs));
577
578
579.. _socketcan-rawfd:
580
581RAW Socket Option CAN_RAW_FD_FRAMES
582~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
583
584CAN FD support in CAN_RAW sockets can be enabled with a new socket option
585CAN_RAW_FD_FRAMES which is off by default. When the new socket option is
586not supported by the CAN_RAW socket (e.g. on older kernels), switching the
587CAN_RAW_FD_FRAMES option returns the error -ENOPROTOOPT.
588
589Once CAN_RAW_FD_FRAMES is enabled the application can send both CAN frames
590and CAN FD frames. OTOH the application has to handle CAN and CAN FD frames
591when reading from the socket:
592
593.. code-block:: C
594
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)
597
598Example:
599
600.. code-block:: C
601
602    [ remember: CANFD_MTU == sizeof(struct canfd_frame) ]
603
604    struct canfd_frame cfd;
605
606    nbytes = read(s, &cfd, CANFD_MTU);
607
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 */
614    } else {
615            fprintf(stderr, "read: invalid CAN(FD) frame\n");
616            return 1;
617    }
618
619    /* the content can be handled independently from the received MTU size */
620
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]);
624
625When reading with size CANFD_MTU only returns CAN_MTU bytes that have
626been received from the socket a legacy CAN frame has been read into the
627provided CAN FD structure. Note that the canfd_frame.flags data field is
628not specified in the struct can_frame and therefore it is only valid in
629CANFD_MTU sized CAN FD frames.
630
631Implementation hint for new CAN applications:
632
633To build a CAN FD aware application use struct canfd_frame as basic CAN
634data structure for CAN_RAW based applications. When the application is
635executed on an older Linux kernel and switching the CAN_RAW_FD_FRAMES
636socket option returns an error: No problem. You'll get legacy CAN frames
637or CAN FD frames and can process them the same way.
638
639When sending to CAN devices make sure that the device is capable to handle
640CAN FD frames by checking if the device maximum transfer unit is CANFD_MTU.
641The CAN device MTU can be retrieved e.g. with a SIOCGIFMTU ioctl() syscall.
642
643
644RAW socket option CAN_RAW_JOIN_FILTERS
645~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
646
647The CAN_RAW socket can set multiple CAN identifier specific filters that
648lead to multiple filters in the af_can.c filter processing. These filters
649are indenpendent from each other which leads to logical OR'ed filters when
650applied (see :ref:`socketcan-rawfilter`).
651
652This socket option joines the given CAN filters in the way that only CAN
653frames are passed to user space that matched *all* given CAN filters. The
654semantic for the applied filters is therefore changed to a logical AND.
655
656This is useful especially when the filterset is a combination of filters
657where the CAN_INV_FILTER flag is set in order to notch single CAN IDs or
658CAN ID ranges from the incoming traffic.
659
660
661RAW Socket Returned Message Flags
662~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
663
664When using recvmsg() call, the msg->msg_flags may contain following flags:
665
666MSG_DONTROUTE:
667	set when the received frame was created on the local host.
668
669MSG_CONFIRM:
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.
675
676
677Broadcast Manager Protocol Sockets (SOCK_DGRAM)
678-----------------------------------------------
679
680The Broadcast Manager protocol provides a command based configuration
681interface to filter and send (e.g. cyclic) CAN messages in kernel space.
682
683Receive filters can be used to down sample frequent messages; detect events
684such as message contents changes, packet length changes, and do time-out
685monitoring of received messages.
686
687Periodic transmission tasks of CAN frames or a sequence of CAN frames can be
688created and modified at runtime; both the message content and the two
689possible transmit intervals can be altered.
690
691A BCM socket is not intended for sending individual CAN frames using the
692struct can_frame as known from the CAN_RAW socket. Instead a special BCM
693configuration message is defined. The basic BCM configuration message used
694to communicate with the broadcast manager and the available operations are
695defined in the linux/can/bcm.h include. The BCM message consists of a
696message header with a command ('opcode') followed by zero or more CAN frames.
697The broadcast manager sends responses to user space in the same form:
698
699.. code-block:: C
700
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];
709    };
710
711The aligned payload 'frames' uses the same basic CAN frame structure defined
712at the beginning of :ref:`socketcan-rawfd` and in the include/linux/can.h include. All
713messages to the broadcast manager from user space have this structure.
714
715Note a CAN_BCM socket must be connected instead of bound after socket
716creation (example without error checking):
717
718.. code-block:: C
719
720    int s;
721    struct sockaddr_can addr;
722    struct ifreq ifr;
723
724    s = socket(PF_CAN, SOCK_DGRAM, CAN_BCM);
725
726    strcpy(ifr.ifr_name, "can0");
727    ioctl(s, SIOCGIFINDEX, &ifr);
728
729    addr.can_family = AF_CAN;
730    addr.can_ifindex = ifr.ifr_ifindex;
731
732    connect(s, (struct sockaddr *)&addr, sizeof(addr));
733
734    (..)
735
736The broadcast manager socket is able to handle any number of in flight
737transmissions or receive filters concurrently. The different RX/TX jobs are
738distinguished by the unique can_id in each BCM message. However additional
739CAN_BCM sockets are recommended to communicate on multiple CAN interfaces.
740When the broadcast manager socket is bound to 'any' CAN interface (=> the
741interface index is set to zero) the configured receive filters apply to any
742CAN interface unless the sendto() syscall is used to overrule the 'any' CAN
743interface index. When using recvfrom() instead of read() to retrieve BCM
744socket messages the originating CAN interface is provided in can_ifindex.
745
746
747Broadcast Manager Operations
748~~~~~~~~~~~~~~~~~~~~~~~~~~~~
749
750The opcode defines the operation for the broadcast manager to carry out,
751or details the broadcast managers response to several events, including
752user requests.
753
754Transmit Operations (user space to broadcast manager):
755
756TX_SETUP:
757	Create (cyclic) transmission task.
758
759TX_DELETE:
760	Remove (cyclic) transmission task, requires only can_id.
761
762TX_READ:
763	Read properties of (cyclic) transmission task for can_id.
764
765TX_SEND:
766	Send one CAN frame.
767
768Transmit Responses (broadcast manager to user space):
769
770TX_STATUS:
771	Reply to TX_READ request (transmission task configuration).
772
773TX_EXPIRED:
774	Notification when counter finishes sending at initial interval
775	'ival1'. Requires the TX_COUNTEVT flag to be set at TX_SETUP.
776
777Receive Operations (user space to broadcast manager):
778
779RX_SETUP:
780	Create RX content filter subscription.
781
782RX_DELETE:
783	Remove RX content filter subscription, requires only can_id.
784
785RX_READ:
786	Read properties of RX content filter subscription for can_id.
787
788Receive Responses (broadcast manager to user space):
789
790RX_STATUS:
791	Reply to RX_READ request (filter task configuration).
792
793RX_TIMEOUT:
794	Cyclic message is detected to be absent (timer ival1 expired).
795
796RX_CHANGED:
797	BCM message with updated CAN frame (detected content change).
798	Sent on first message received or on receipt of revised CAN messages.
799
800
801Broadcast Manager Message Flags
802~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
803
804When sending a message to the broadcast manager the 'flags' element may
805contain the following flag definitions which influence the behaviour:
806
807SETTIMER:
808	Set the values of ival1, ival2 and count
809
810STARTTIMER:
811	Start the timer with the actual values of ival1, ival2
812	and count. Starting the timer leads simultaneously to emit a CAN frame.
813
814TX_COUNTEVT:
815	Create the message TX_EXPIRED when count expires
816
817TX_ANNOUNCE:
818	A change of data by the process is emitted immediately.
819
820TX_CP_CAN_ID:
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).
825
826RX_FILTER_ID:
827	Filter by can_id alone, no frames required (nframes=0).
828
829RX_CHECK_DLC:
830	A change of the DLC leads to an RX_CHANGED.
831
832RX_NO_AUTOTIMER:
833	Prevent automatically starting the timeout monitor.
834
835RX_ANNOUNCE_RESUME:
836	If passed at RX_SETUP and a receive timeout occurred, a
837	RX_CHANGED message will be generated when the (cyclic) receive restarts.
838
839TX_RESET_MULTI_IDX:
840	Reset the index for the multiple frame transmission.
841
842RX_RTR_FRAME:
843	Send reply for RTR-request (placed in op->frames[0]).
844
845
846Broadcast Manager Transmission Timers
847~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
848
849Periodic transmission configurations may use up to two interval timers.
850In 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
852only one timer is needed 'count' is set to zero and only 'ival2' is used.
853When SET_TIMER and START_TIMER flag were set the timers are activated.
854The timer values can be altered at runtime when only SET_TIMER is set.
855
856
857Broadcast Manager message sequence transmission
858~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
859
860Up to 256 CAN frames can be transmitted in a sequence in the case of a cyclic
861TX task configuration. The number of CAN frames is provided in the 'nframes'
862element of the BCM message head. The defined number of CAN frames are added
863as array to the TX_SETUP BCM configuration message:
864
865.. code-block:: C
866
867    /* create a struct to set up a sequence of four CAN frames */
868    struct {
869            struct bcm_msg_head msg_head;
870            struct can_frame frame[4];
871    } mytxmsg;
872
873    (..)
874    mytxmsg.msg_head.nframes = 4;
875    (..)
876
877    write(s, &mytxmsg, sizeof(mytxmsg));
878
879With every transmission the index in the array of CAN frames is increased
880and set to zero at index overflow.
881
882
883Broadcast Manager Receive Filter Timers
884~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
885
886The timer values ival1 or ival2 may be set to non-zero values at RX_SETUP.
887When the SET_TIMER flag is set the timers are enabled:
888
889ival1:
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.
893
894ival2:
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
898	lost.
899
900Broadcast Manager Multiplex Message Receive Filter
901~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
902
903To filter for content changes in multiplex message sequences an array of more
904than one CAN frames can be passed in a RX_SETUP configuration message. The
905data bytes of the first CAN frame contain the mask of relevant bits that
906have to match in the subsequent CAN frames with the received CAN frame.
907If one of the subsequent CAN frames is matching the bits in that frame data
908mark the relevant content to be compared with the previous received content.
909Up to 257 CAN frames (multiplex filter bit mask CAN frame plus 256 CAN
910filters) can be added as array to the TX_SETUP BCM configuration message:
911
912.. code-block:: C
913
914    /* usually used to clear CAN frame data[] - beware of endian problems! */
915    #define U64_DATA(p) (*(unsigned long long*)(p)->data)
916
917    struct {
918            struct bcm_msg_head msg_head;
919            struct can_frame frame[5];
920    } msg;
921
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) */
931
932    write(s, &msg, sizeof(msg));
933
934
935Broadcast Manager CAN FD Support
936~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
937
938The programming API of the CAN_BCM depends on struct can_frame which is
939given as array directly behind the bcm_msg_head structure. To follow this
940schema for the CAN FD frames a new flag 'CAN_FD_FRAME' in the bcm_msg_head
941flags indicates that the concatenated CAN frame structures behind the
942bcm_msg_head are defined as struct canfd_frame:
943
944.. code-block:: C
945
946    struct {
947            struct bcm_msg_head msg_head;
948            struct canfd_frame frame[5];
949    } msg;
950
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;
955    (..)
956
957When using CAN FD frames for multiplex filtering the MUX mask is still
958expected in the first 64 bit of the struct canfd_frame data section.
959
960
961Connected Transport Protocols (SOCK_SEQPACKET)
962----------------------------------------------
963
964(to be written)
965
966
967Unconnected Transport Protocols (SOCK_DGRAM)
968--------------------------------------------
969
970(to be written)
971
972
973.. _socketcan-core-module:
974
975SocketCAN Core Module
976=====================
977
978The SocketCAN core module implements the protocol family
979PF_CAN. CAN protocol modules are loaded by the core module at
980runtime. The core module provides an interface for CAN protocol
981modules to subscribe needed CAN IDs (see :ref:`socketcan-receive-lists`).
982
983
984can.ko Module Params
985--------------------
986
987- **stats_timer**:
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.
992
993- **debug**:
994  (removed since SocketCAN SVN r546)
995
996
997procfs content
998--------------
999
1000As described in :ref:`socketcan-receive-lists` the SocketCAN core uses several filter
1001lists to deliver received CAN frames to CAN protocol modules. These
1002receive lists, their filters and the count of filter matches can be
1003checked in the appropriate receive list. All entries contain the
1004device and a protocol module identifier::
1005
1006    foo@bar:~$ cat /proc/net/can/rcvlist_all
1007
1008    receive list 'rx_all':
1009      (vcan3: no entry)
1010      (vcan2: no entry)
1011      (vcan1: no entry)
1012      device   can_id   can_mask  function  userdata   matches  ident
1013       vcan0     000    00000000  f88e6370  f6c6f400         0  raw
1014      (any: no entry)
1015
1016In this example an application requests any CAN traffic from vcan0::
1017
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
1024
1025Additional procfs files in /proc/net/can::
1026
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
1030
1031
1032Writing Own CAN Protocol Modules
1033--------------------------------
1034
1035To implement a new protocol in the protocol family PF_CAN a new
1036protocol has to be defined in include/linux/can.h .
1037The prototypes and definitions to use the SocketCAN core can be
1038accessed by including include/linux/can/core.h .
1039In addition to functions that register the CAN protocol and the
1040CAN device notifier chain there are functions to subscribe CAN
1041frames received by CAN interfaces and to send CAN frames::
1042
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)
1046
1047For details see the kerneldoc documentation in net/can/af_can.c or
1048the source code of net/can/raw.c or net/can/bcm.c .
1049
1050
1051CAN Network Drivers
1052===================
1053
1054Writing a CAN network device driver is much easier than writing a
1055CAN character device driver. Similar to other known network device
1056drivers you mainly have to deal with:
1057
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.
1060
1061See e.g. at Documentation/networking/netdevices.txt . The differences
1062for writing CAN network device driver are described below:
1063
1064
1065General Settings
1066----------------
1067
1068.. code-block:: C
1069
1070    dev->type  = ARPHRD_CAN; /* the netdevice hardware type */
1071    dev->flags = IFF_NOARP;  /* CAN has no arp */
1072
1073    dev->mtu = CAN_MTU; /* sizeof(struct can_frame) -> legacy CAN interface */
1074
1075    or alternative, when the controller supports CAN with flexible data rate:
1076    dev->mtu = CANFD_MTU; /* sizeof(struct canfd_frame) -> CAN FD interface */
1077
1078The struct can_frame or struct canfd_frame is the payload of each socket
1079buffer (skbuff) in the protocol family PF_CAN.
1080
1081
1082.. _socketcan-local-loopback2:
1083
1084Local Loopback of Sent Frames
1085-----------------------------
1086
1087As described in :ref:`socketcan-local-loopback1` the CAN network device driver should
1088support a local loopback functionality similar to the local echo
1089e.g. of tty devices. In this case the driver flag IFF_ECHO has to be
1090set to prevent the PF_CAN core from locally echoing sent frames
1091(aka loopback) as fallback solution::
1092
1093    dev->flags = (IFF_NOARP | IFF_ECHO);
1094
1095
1096CAN Controller Hardware Filters
1097-------------------------------
1098
1099To reduce the interrupt load on deep embedded systems some CAN
1100controllers support the filtering of CAN IDs or ranges of CAN IDs.
1101These hardware filter capabilities vary from controller to
1102controller and have to be identified as not feasible in a multi-user
1103networking approach. The use of the very controller specific
1104hardware filters could make sense in a very dedicated use-case, as a
1105filter on driver level would affect all users in the multi-user
1106system. The high efficient filter sets inside the PF_CAN core allow
1107to set different multiple filters for each socket separately.
1108Therefore the use of hardware filters goes to the category 'handmade
1109tuning on deep embedded systems'. The author is running a MPC603e
1110@133MHz with four SJA1000 CAN controllers from 2002 under heavy bus
1111load without any problems ...
1112
1113
1114The Virtual CAN Driver (vcan)
1115-----------------------------
1116
1117Similar to the network loopback devices, vcan offers a virtual local
1118CAN interface. A full qualified address on CAN consists of
1119
1120- a unique CAN Identifier (CAN ID)
1121- the CAN bus this CAN ID is transmitted on (e.g. can0)
1122
1123so in common use cases more than one virtual CAN interface is needed.
1124
1125The virtual CAN interfaces allow the transmission and reception of CAN
1126frames without real CAN controller hardware. Virtual CAN network
1127devices are usually named 'vcanX', like vcan0 vcan1 vcan2 ...
1128When compiled as a module the virtual CAN driver module is called vcan.ko
1129
1130Since Linux Kernel version 2.6.24 the vcan driver supports the Kernel
1131netlink interface to create vcan network devices. The creation and
1132removal of vcan network devices can be managed with the ip(8) tool::
1133
1134  - Create a virtual CAN network interface:
1135       $ ip link add type vcan
1136
1137  - Create a virtual CAN network interface with a specific name 'vcan42':
1138       $ ip link add dev vcan42 type vcan
1139
1140  - Remove a (virtual CAN) network interface 'vcan42':
1141       $ ip link del vcan42
1142
1143
1144The CAN Network Device Driver Interface
1145---------------------------------------
1146
1147The CAN network device driver interface provides a generic interface
1148to setup, configure and monitor CAN network devices. The user can then
1149configure the CAN device, like setting the bit-timing parameters, via
1150the netlink interface using the program "ip" from the "IPROUTE2"
1151utility suite. The following chapter describes briefly how to use it.
1152Furthermore, the interface uses a common data structure and exports a
1153set of common functions, which all real CAN network device drivers
1154should use. Please have a look to the SJA1000 or MSCAN driver to
1155understand how to use them. The name of the module is can-dev.ko.
1156
1157
1158Netlink interface to set/get devices properties
1159~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1160
1161The CAN device must be configured via netlink interface. The supported
1162netlink message types are defined and briefly described in
1163"include/linux/can/netlink.h". CAN link support for the program "ip"
1164of the IPROUTE2 utility suite is available and it can be used as shown
1165below:
1166
1167Setting CAN device properties::
1168
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 ] ]
1174
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 ] ]
1178
1179        [ loopback { on | off } ]
1180        [ listen-only { on | off } ]
1181        [ triple-sampling { on | off } ]
1182        [ one-shot { on | off } ]
1183        [ berr-reporting { on | off } ]
1184        [ fd { on | off } ]
1185        [ fd-non-iso { on | off } ]
1186        [ presume-ack { on | off } ]
1187
1188        [ restart-ms TIME-MS ]
1189        [ restart ]
1190
1191        Where: BITRATE       := { 1..1000000 }
1192               SAMPLE-POINT  := { 0.000..0.999 }
1193               TQ            := { NUMBER }
1194               PROP-SEG      := { 1..8 }
1195               PHASE-SEG1    := { 1..8 }
1196               PHASE-SEG2    := { 1..8 }
1197               SJW           := { 1..4 }
1198               RESTART-MS    := { 0 | NUMBER }
1199
1200Display CAN device details and statistics::
1201
1202    $ ip -details -statistics link show can0
1203    2: can0: <NOARP,UP,LOWER_UP,ECHO> mtu 16 qdisc pfifo_fast state UP qlen 10
1204      link/can
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
1209      clock 8000000
1210      re-started bus-errors arbit-lost error-warn error-pass bus-off
1211      41         17457      0          41         42         41
1212      RX: bytes  packets  errors  dropped overrun mcast
1213      140859     17608    17457   0       0       0
1214      TX: bytes  packets  errors  dropped carrier collsns
1215      861        112      0       41      0       0
1216
1217More info to the above output:
1218
1219"<TRIPLE-SAMPLING>"
1220	Shows the list of selected CAN controller modes: LOOPBACK,
1221	LISTEN-ONLY, or TRIPLE-SAMPLING.
1222
1223"state ERROR-ACTIVE"
1224	The current state of the CAN controller: "ERROR-ACTIVE",
1225	"ERROR-WARNING", "ERROR-PASSIVE", "BUS-OFF" or "STOPPED"
1226
1227"restart-ms 100"
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.
1232
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.
1240
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).
1247
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.
1255
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.
1261
1262Setting the CAN Bit-Timing
1263~~~~~~~~~~~~~~~~~~~~~~~~~~
1264
1265The CAN bit-timing parameters can always be defined in a hardware
1266independent format as proposed in the Bosch CAN 2.0 specification
1267specifying the arguments "tq", "prop_seg", "phase_seg1", "phase_seg2"
1268and "sjw"::
1269
1270    $ ip link set canX type can tq 125 prop-seg 6 \
1271				phase-seg1 7 phase-seg2 2 sjw 1
1272
1273If the kernel option CONFIG_CAN_CALC_BITTIMING is enabled, CIA
1274recommended CAN bit-timing parameters will be calculated if the bit-
1275rate is specified with the argument "bitrate"::
1276
1277    $ ip link set canX type can bitrate 125000
1278
1279Note that this works fine for the most common CAN controllers with
1280standard bit-rates but may *fail* for exotic bit-rates or CAN system
1281clock frequencies. Disabling CONFIG_CAN_CALC_BITTIMING saves some
1282space and allows user-space tools to solely determine and set the
1283bit-timing parameters. The CAN controller specific bit-timing
1284constants can be used for that purpose. They are listed by the
1285following command::
1286
1287    $ ip -details link show can0
1288    ...
1289      sja1000: clock 8000000 tseg1 1..16 tseg2 1..8 sjw 1..4 brp 1..64 brp-inc 1
1290
1291
1292Starting and Stopping the CAN Network Device
1293~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1294
1295A 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
1297you *must* define proper bit-timing parameters for real CAN devices
1298before you can start it to avoid error-prone default settings::
1299
1300    $ ip link set canX up type can bitrate 125000
1301
1302A device may enter the "bus-off" state if too many errors occurred on
1303the CAN bus. Then no more messages are received or sent. An automatic
1304bus-off recovery can be enabled by setting the "restart-ms" to a
1305non-zero value, e.g.::
1306
1307    $ ip link set canX type can restart-ms 100
1308
1309Alternatively, the application may realize the "bus-off" condition
1310by monitoring CAN error message frames and do a restart when
1311appropriate with the command::
1312
1313    $ ip link set canX type can restart
1314
1315Note that a restart will also create a CAN error message frame (see
1316also :ref:`socketcan-network-problem-notifications`).
1317
1318
1319.. _socketcan-can-fd-driver:
1320
1321CAN FD (Flexible Data Rate) Driver Support
1322------------------------------------------
1323
1324CAN FD capable CAN controllers support two different bitrates for the
1325arbitration phase and the payload phase of the CAN FD frame. Therefore a
1326second bit timing has to be specified in order to enable the CAN FD bitrate.
1327
1328Additionally CAN FD capable CAN controllers support up to 64 bytes of
1329payload. The representation of this length in can_frame.can_dlc and
1330canfd_frame.len for userspace applications and inside the Linux network
1331layer is a plain value from 0 .. 64 instead of the CAN 'data length code'.
1332The data length code was a 1:1 mapping to the payload length in the legacy
1333CAN frames anyway. The payload length to the bus-relevant DLC mapping is
1334only performed inside the CAN drivers, preferably with the helper
1335functions can_dlc2len() and can_len2dlc().
1336
1337The CAN netdevice driver capabilities can be distinguished by the network
1338devices maximum transfer unit (MTU)::
1339
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
1342
1343The CAN device MTU can be retrieved e.g. with a SIOCGIFMTU ioctl() syscall.
1344N.B. CAN FD capable devices can also handle and send legacy CAN frames.
1345
1346When configuring CAN FD capable CAN controllers an additional 'data' bitrate
1347has to be set. This bitrate for the data phase of the CAN FD frame has to be
1348at least the bitrate which was configured for the arbitration phase. This
1349second bitrate is specified analogue to the first bitrate but the bitrate
1350setting keywords for the 'data' bitrate start with 'd' e.g. dbitrate,
1351dsample-point, dsjw or dtq and similar settings. When a data bitrate is set
1352within the configuration process the controller option "fd on" can be
1353specified to enable the CAN FD mode in the CAN controller. This controller
1354option also switches the device MTU to 72 (CANFD_MTU).
1355
1356The first CAN FD specification presented as whitepaper at the International
1357CAN Conference 2012 needed to be improved for data integrity reasons.
1358Therefore two CAN FD implementations have to be distinguished today:
1359
1360- ISO compliant:     The ISO 11898-1:2015 CAN FD implementation (default)
1361- non-ISO compliant: The CAN FD implementation following the 2012 whitepaper
1362
1363Finally there are three types of CAN FD controllers:
1364
13651. ISO compliant (fixed)
13662. non-ISO compliant (fixed, like the M_CAN IP core v3.0.1 in m_can.c)
13673. ISO/non-ISO CAN FD controllers (switchable, like the PEAK PCAN-USB FD)
1368
1369The current ISO/non-ISO mode is announced by the CAN controller driver via
1370netlink and displayed by the 'ip' tool (controller option FD-NON-ISO).
1371The ISO/non-ISO-mode can be altered by setting 'fd-non-iso {on|off}' for
1372switchable CAN FD controllers only.
1373
1374Example configuring 500 kbit/s arbitration bitrate and 4 Mbit/s data bitrate::
1375
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 \
1386          brp-inc 1
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 \
1390          dbrp-inc 1
1391          clock 80000000
1392
1393Example when 'fd-non-iso on' is added on this switchable CAN FD adapter::
1394
1395   can <FD,FD-NON-ISO> state ERROR-ACTIVE (berr-counter tx 0 rx 0) restart-ms 0
1396
1397
1398Supported CAN Hardware
1399----------------------
1400
1401Please check the "Kconfig" file in "drivers/net/can" to get an actual
1402list of the support CAN hardware. On the SocketCAN project website
1403(see :ref:`socketcan-resources`) there might be further drivers available, also for
1404older kernel versions.
1405
1406
1407.. _socketcan-resources:
1408
1409SocketCAN Resources
1410===================
1411
1412The Linux CAN / SocketCAN project resources (project site / mailing list)
1413are referenced in the MAINTAINERS file in the Linux source tree.
1414Search for CAN NETWORK [LAYERS|DRIVERS].
1415
1416Credits
1417=======
1418
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)
1438