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Linux/Documentation/networking/can.txt

  1 ============================================================================
  2 
  3 can.txt
  4 
  5 Readme file for the Controller Area Network Protocol Family (aka SocketCAN)
  6 
  7 This file contains
  8 
  9   1 Overview / What is SocketCAN
 10 
 11   2 Motivation / Why using the socket API
 12 
 13   3 SocketCAN concept
 14     3.1 receive lists
 15     3.2 local loopback of sent frames
 16     3.3 network problem notifications
 17 
 18   4 How to use SocketCAN
 19     4.1 RAW protocol sockets with can_filters (SOCK_RAW)
 20       4.1.1 RAW socket option CAN_RAW_FILTER
 21       4.1.2 RAW socket option CAN_RAW_ERR_FILTER
 22       4.1.3 RAW socket option CAN_RAW_LOOPBACK
 23       4.1.4 RAW socket option CAN_RAW_RECV_OWN_MSGS
 24       4.1.5 RAW socket option CAN_RAW_FD_FRAMES
 25       4.1.6 RAW socket option CAN_RAW_JOIN_FILTERS
 26       4.1.7 RAW socket returned message flags
 27     4.2 Broadcast Manager protocol sockets (SOCK_DGRAM)
 28       4.2.1 Broadcast Manager operations
 29       4.2.2 Broadcast Manager message flags
 30       4.2.3 Broadcast Manager transmission timers
 31       4.2.4 Broadcast Manager message sequence transmission
 32       4.2.5 Broadcast Manager receive filter timers
 33       4.2.6 Broadcast Manager multiplex message receive filter
 34       4.2.7 Broadcast Manager CAN FD support
 35     4.3 connected transport protocols (SOCK_SEQPACKET)
 36     4.4 unconnected transport protocols (SOCK_DGRAM)
 37 
 38   5 SocketCAN core module
 39     5.1 can.ko module params
 40     5.2 procfs content
 41     5.3 writing own CAN protocol modules
 42 
 43   6 CAN network drivers
 44     6.1 general settings
 45     6.2 local loopback of sent frames
 46     6.3 CAN controller hardware filters
 47     6.4 The virtual CAN driver (vcan)
 48     6.5 The CAN network device driver interface
 49       6.5.1 Netlink interface to set/get devices properties
 50       6.5.2 Setting the CAN bit-timing
 51       6.5.3 Starting and stopping the CAN network device
 52     6.6 CAN FD (flexible data rate) driver support
 53     6.7 supported CAN hardware
 54 
 55   7 SocketCAN resources
 56 
 57   8 Credits
 58 
 59 ============================================================================
 60 
 61 1. Overview / What is SocketCAN
 62 --------------------------------
 63 
 64 The socketcan package is an implementation of CAN protocols
 65 (Controller Area Network) for Linux.  CAN is a networking technology
 66 which has widespread use in automation, embedded devices, and
 67 automotive fields.  While there have been other CAN implementations
 68 for Linux based on character devices, SocketCAN uses the Berkeley
 69 socket API, the Linux network stack and implements the CAN device
 70 drivers as network interfaces.  The CAN socket API has been designed
 71 as similar as possible to the TCP/IP protocols to allow programmers,
 72 familiar with network programming, to easily learn how to use CAN
 73 sockets.
 74 
 75 2. Motivation / Why using the socket API
 76 ----------------------------------------
 77 
 78 There have been CAN implementations for Linux before SocketCAN so the
 79 question arises, why we have started another project.  Most existing
 80 implementations come as a device driver for some CAN hardware, they
 81 are based on character devices and provide comparatively little
 82 functionality.  Usually, there is only a hardware-specific device
 83 driver which provides a character device interface to send and
 84 receive raw CAN frames, directly to/from the controller hardware.
 85 Queueing of frames and higher-level transport protocols like ISO-TP
 86 have to be implemented in user space applications.  Also, most
 87 character-device implementations support only one single process to
 88 open the device at a time, similar to a serial interface.  Exchanging
 89 the CAN controller requires employment of another device driver and
 90 often the need for adaption of large parts of the application to the
 91 new driver's API.
 92 
 93 SocketCAN was designed to overcome all of these limitations.  A new
 94 protocol family has been implemented which provides a socket interface
 95 to user space applications and which builds upon the Linux network
 96 layer, enabling use all of the provided queueing functionality.  A device
 97 driver for CAN controller hardware registers itself with the Linux
 98 network layer as a network device, so that CAN frames from the
 99 controller can be passed up to the network layer and on to the CAN
100 protocol family module and also vice-versa.  Also, the protocol family
101 module provides an API for transport protocol modules to register, so
102 that any number of transport protocols can be loaded or unloaded
103 dynamically.  In fact, the can core module alone does not provide any
104 protocol and cannot be used without loading at least one additional
105 protocol module.  Multiple sockets can be opened at the same time,
106 on different or the same protocol module and they can listen/send
107 frames on different or the same CAN IDs.  Several sockets listening on
108 the same interface for frames with the same CAN ID are all passed the
109 same received matching CAN frames.  An application wishing to
110 communicate using a specific transport protocol, e.g. ISO-TP, just
111 selects that protocol when opening the socket, and then can read and
112 write application data byte streams, without having to deal with
113 CAN-IDs, frames, etc.
114 
115 Similar functionality visible from user-space could be provided by a
116 character device, too, but this would lead to a technically inelegant
117 solution for a couple of reasons:
118 
119 * Intricate usage.  Instead of passing a protocol argument to
120   socket(2) and using bind(2) to select a CAN interface and CAN ID, an
121   application would have to do all these operations using ioctl(2)s.
122 
123 * Code duplication.  A character device cannot make use of the Linux
124   network queueing code, so all that code would have to be duplicated
125   for CAN networking.
126 
127 * Abstraction.  In most existing character-device implementations, the
128   hardware-specific device driver for a CAN controller directly
129   provides the character device for the application to work with.
130   This is at least very unusual in Unix systems for both, char and
131   block devices.  For example you don't have a character device for a
132   certain UART of a serial interface, a certain sound chip in your
133   computer, a SCSI or IDE controller providing access to your hard
134   disk or tape streamer device.  Instead, you have abstraction layers
135   which provide a unified character or block device interface to the
136   application on the one hand, and a interface for hardware-specific
137   device drivers on the other hand.  These abstractions are provided
138   by subsystems like the tty layer, the audio subsystem or the SCSI
139   and IDE subsystems for the devices mentioned above.
140 
141   The easiest way to implement a CAN device driver is as a character
142   device without such a (complete) abstraction layer, as is done by most
143   existing drivers.  The right way, however, would be to add such a
144   layer with all the functionality like registering for certain CAN
145   IDs, supporting several open file descriptors and (de)multiplexing
146   CAN frames between them, (sophisticated) queueing of CAN frames, and
147   providing an API for device drivers to register with.  However, then
148   it would be no more difficult, or may be even easier, to use the
149   networking framework provided by the Linux kernel, and this is what
150   SocketCAN does.
151 
152   The use of the networking framework of the Linux kernel is just the
153   natural and most appropriate way to implement CAN for Linux.
154 
155 3. SocketCAN concept
156 ---------------------
157 
158   As described in chapter 2 it is the main goal of SocketCAN to
159   provide a socket interface to user space applications which builds
160   upon the Linux network layer. In contrast to the commonly known
161   TCP/IP and ethernet networking, the CAN bus is a broadcast-only(!)
162   medium that has no MAC-layer addressing like ethernet. The CAN-identifier
163   (can_id) is used for arbitration on the CAN-bus. Therefore the CAN-IDs
164   have to be chosen uniquely on the bus. When designing a CAN-ECU
165   network the CAN-IDs are mapped to be sent by a specific ECU.
166   For this reason a CAN-ID can be treated best as a kind of source address.
167 
168   3.1 receive lists
169 
170   The network transparent access of multiple applications leads to the
171   problem that different applications may be interested in the same
172   CAN-IDs from the same CAN network interface. The SocketCAN core
173   module - which implements the protocol family CAN - provides several
174   high efficient receive lists for this reason. If e.g. a user space
175   application opens a CAN RAW socket, the raw protocol module itself
176   requests the (range of) CAN-IDs from the SocketCAN core that are
177   requested by the user. The subscription and unsubscription of
178   CAN-IDs can be done for specific CAN interfaces or for all(!) known
179   CAN interfaces with the can_rx_(un)register() functions provided to
180   CAN protocol modules by the SocketCAN core (see chapter 5).
181   To optimize the CPU usage at runtime the receive lists are split up
182   into several specific lists per device that match the requested
183   filter complexity for a given use-case.
184 
185   3.2 local loopback of sent frames
186 
187   As known from other networking concepts the data exchanging
188   applications may run on the same or different nodes without any
189   change (except for the according addressing information):
190 
191          ___   ___   ___                   _______   ___
192         | _ | | _ | | _ |                 | _   _ | | _ |
193         ||A|| ||B|| ||C||                 ||A| |B|| ||C||
194         |___| |___| |___|                 |_______| |___|
195           |     |     |                       |       |
196         -----------------(1)- CAN bus -(2)---------------
197 
198   To ensure that application A receives the same information in the
199   example (2) as it would receive in example (1) there is need for
200   some kind of local loopback of the sent CAN frames on the appropriate
201   node.
202 
203   The Linux network devices (by default) just can handle the
204   transmission and reception of media dependent frames. Due to the
205   arbitration on the CAN bus the transmission of a low prio CAN-ID
206   may be delayed by the reception of a high prio CAN frame. To
207   reflect the correct* traffic on the node the loopback of the sent
208   data has to be performed right after a successful transmission. If
209   the CAN network interface is not capable of performing the loopback for
210   some reason the SocketCAN core can do this task as a fallback solution.
211   See chapter 6.2 for details (recommended).
212 
213   The loopback functionality is enabled by default to reflect standard
214   networking behaviour for CAN applications. Due to some requests from
215   the RT-SocketCAN group the loopback optionally may be disabled for each
216   separate socket. See sockopts from the CAN RAW sockets in chapter 4.1.
217 
218   * = you really like to have this when you're running analyser tools
219       like 'candump' or 'cansniffer' on the (same) node.
220 
221   3.3 network problem notifications
222 
223   The use of the CAN bus may lead to several problems on the physical
224   and media access control layer. Detecting and logging of these lower
225   layer problems is a vital requirement for CAN users to identify
226   hardware issues on the physical transceiver layer as well as
227   arbitration problems and error frames caused by the different
228   ECUs. The occurrence of detected errors are important for diagnosis
229   and have to be logged together with the exact timestamp. For this
230   reason the CAN interface driver can generate so called Error Message
231   Frames that can optionally be passed to the user application in the
232   same way as other CAN frames. Whenever an error on the physical layer
233   or the MAC layer is detected (e.g. by the CAN controller) the driver
234   creates an appropriate error message frame. Error messages frames can
235   be requested by the user application using the common CAN filter
236   mechanisms. Inside this filter definition the (interested) type of
237   errors may be selected. The reception of error messages is disabled
238   by default. The format of the CAN error message frame is briefly
239   described in the Linux header file "include/uapi/linux/can/error.h".
240 
241 4. How to use SocketCAN
242 ------------------------
243 
244   Like TCP/IP, you first need to open a socket for communicating over a
245   CAN network. Since SocketCAN implements a new protocol family, you
246   need to pass PF_CAN as the first argument to the socket(2) system
247   call. Currently, there are two CAN protocols to choose from, the raw
248   socket protocol and the broadcast manager (BCM). So to open a socket,
249   you would write
250 
251     s = socket(PF_CAN, SOCK_RAW, CAN_RAW);
252 
253   and
254 
255     s = socket(PF_CAN, SOCK_DGRAM, CAN_BCM);
256 
257   respectively.  After the successful creation of the socket, you would
258   normally use the bind(2) system call to bind the socket to a CAN
259   interface (which is different from TCP/IP due to different addressing
260   - see chapter 3). After binding (CAN_RAW) or connecting (CAN_BCM)
261   the socket, you can read(2) and write(2) from/to the socket or use
262   send(2), sendto(2), sendmsg(2) and the recv* counterpart operations
263   on the socket as usual. There are also CAN specific socket options
264   described below.
265 
266   The basic CAN frame structure and the sockaddr structure are defined
267   in include/linux/can.h:
268 
269     struct can_frame {
270             canid_t can_id;  /* 32 bit CAN_ID + EFF/RTR/ERR flags */
271             __u8    can_dlc; /* frame payload length in byte (0 .. 8) */
272             __u8    __pad;   /* padding */
273             __u8    __res0;  /* reserved / padding */
274             __u8    __res1;  /* reserved / padding */
275             __u8    data[8] __attribute__((aligned(8)));
276     };
277 
278   The alignment of the (linear) payload data[] to a 64bit boundary
279   allows the user to define their own structs and unions to easily access
280   the CAN payload. There is no given byteorder on the CAN bus by
281   default. A read(2) system call on a CAN_RAW socket transfers a
282   struct can_frame to the user space.
283 
284   The sockaddr_can structure has an interface index like the
285   PF_PACKET socket, that also binds to a specific interface:
286 
287     struct sockaddr_can {
288             sa_family_t can_family;
289             int         can_ifindex;
290             union {
291                     /* transport protocol class address info (e.g. ISOTP) */
292                     struct { canid_t rx_id, tx_id; } tp;
293 
294                     /* reserved for future CAN protocols address information */
295             } can_addr;
296     };
297 
298   To determine the interface index an appropriate ioctl() has to
299   be used (example for CAN_RAW sockets without error checking):
300 
301     int s;
302     struct sockaddr_can addr;
303     struct ifreq ifr;
304 
305     s = socket(PF_CAN, SOCK_RAW, CAN_RAW);
306 
307     strcpy(ifr.ifr_name, "can0" );
308     ioctl(s, SIOCGIFINDEX, &ifr);
309 
310     addr.can_family = AF_CAN;
311     addr.can_ifindex = ifr.ifr_ifindex;
312 
313     bind(s, (struct sockaddr *)&addr, sizeof(addr));
314 
315     (..)
316 
317   To bind a socket to all(!) CAN interfaces the interface index must
318   be 0 (zero). In this case the socket receives CAN frames from every
319   enabled CAN interface. To determine the originating CAN interface
320   the system call recvfrom(2) may be used instead of read(2). To send
321   on a socket that is bound to 'any' interface sendto(2) is needed to
322   specify the outgoing interface.
323 
324   Reading CAN frames from a bound CAN_RAW socket (see above) consists
325   of reading a struct can_frame:
326 
327     struct can_frame frame;
328 
329     nbytes = read(s, &frame, sizeof(struct can_frame));
330 
331     if (nbytes < 0) {
332             perror("can raw socket read");
333             return 1;
334     }
335 
336     /* paranoid check ... */
337     if (nbytes < sizeof(struct can_frame)) {
338             fprintf(stderr, "read: incomplete CAN frame\n");
339             return 1;
340     }
341 
342     /* do something with the received CAN frame */
343 
344   Writing CAN frames can be done similarly, with the write(2) system call:
345 
346     nbytes = write(s, &frame, sizeof(struct can_frame));
347 
348   When the CAN interface is bound to 'any' existing CAN interface
349   (addr.can_ifindex = 0) it is recommended to use recvfrom(2) if the
350   information about the originating CAN interface is needed:
351 
352     struct sockaddr_can addr;
353     struct ifreq ifr;
354     socklen_t len = sizeof(addr);
355     struct can_frame frame;
356 
357     nbytes = recvfrom(s, &frame, sizeof(struct can_frame),
358                       0, (struct sockaddr*)&addr, &len);
359 
360     /* get interface name of the received CAN frame */
361     ifr.ifr_ifindex = addr.can_ifindex;
362     ioctl(s, SIOCGIFNAME, &ifr);
363     printf("Received a CAN frame from interface %s", ifr.ifr_name);
364 
365   To write CAN frames on sockets bound to 'any' CAN interface the
366   outgoing interface has to be defined certainly.
367 
368     strcpy(ifr.ifr_name, "can0");
369     ioctl(s, SIOCGIFINDEX, &ifr);
370     addr.can_ifindex = ifr.ifr_ifindex;
371     addr.can_family  = AF_CAN;
372 
373     nbytes = sendto(s, &frame, sizeof(struct can_frame),
374                     0, (struct sockaddr*)&addr, sizeof(addr));
375 
376   An accurate timestamp can be obtained with an ioctl(2) call after reading
377   a message from the socket:
378 
379     struct timeval tv;
380     ioctl(s, SIOCGSTAMP, &tv);
381 
382   The timestamp has a resolution of one microsecond and is set automatically
383   at the reception of a CAN frame.
384 
385   Remark about CAN FD (flexible data rate) support:
386 
387   Generally the handling of CAN FD is very similar to the formerly described
388   examples. The new CAN FD capable CAN controllers support two different
389   bitrates for the arbitration phase and the payload phase of the CAN FD frame
390   and up to 64 bytes of payload. This extended payload length breaks all the
391   kernel interfaces (ABI) which heavily rely on the CAN frame with fixed eight
392   bytes of payload (struct can_frame) like the CAN_RAW socket. Therefore e.g.
393   the CAN_RAW socket supports a new socket option CAN_RAW_FD_FRAMES that
394   switches the socket into a mode that allows the handling of CAN FD frames
395   and (legacy) CAN frames simultaneously (see section 4.1.5).
396 
397   The struct canfd_frame is defined in include/linux/can.h:
398 
399     struct canfd_frame {
400             canid_t can_id;  /* 32 bit CAN_ID + EFF/RTR/ERR flags */
401             __u8    len;     /* frame payload length in byte (0 .. 64) */
402             __u8    flags;   /* additional flags for CAN FD */
403             __u8    __res0;  /* reserved / padding */
404             __u8    __res1;  /* reserved / padding */
405             __u8    data[64] __attribute__((aligned(8)));
406     };
407 
408   The struct canfd_frame and the existing struct can_frame have the can_id,
409   the payload length and the payload data at the same offset inside their
410   structures. This allows to handle the different structures very similar.
411   When the content of a struct can_frame is copied into a struct canfd_frame
412   all structure elements can be used as-is - only the data[] becomes extended.
413 
414   When introducing the struct canfd_frame it turned out that the data length
415   code (DLC) of the struct can_frame was used as a length information as the
416   length and the DLC has a 1:1 mapping in the range of 0 .. 8. To preserve
417   the easy handling of the length information the canfd_frame.len element
418   contains a plain length value from 0 .. 64. So both canfd_frame.len and
419   can_frame.can_dlc are equal and contain a length information and no DLC.
420   For details about the distinction of CAN and CAN FD capable devices and
421   the mapping to the bus-relevant data length code (DLC), see chapter 6.6.
422 
423   The length of the two CAN(FD) frame structures define the maximum transfer
424   unit (MTU) of the CAN(FD) network interface and skbuff data length. Two
425   definitions are specified for CAN specific MTUs in include/linux/can.h :
426 
427   #define CAN_MTU   (sizeof(struct can_frame))   == 16  => 'legacy' CAN frame
428   #define CANFD_MTU (sizeof(struct canfd_frame)) == 72  => CAN FD frame
429 
430   4.1 RAW protocol sockets with can_filters (SOCK_RAW)
431 
432   Using CAN_RAW sockets is extensively comparable to the commonly
433   known access to CAN character devices. To meet the new possibilities
434   provided by the multi user SocketCAN approach, some reasonable
435   defaults are set at RAW socket binding time:
436 
437   - The filters are set to exactly one filter receiving everything
438   - The socket only receives valid data frames (=> no error message frames)
439   - The loopback of sent CAN frames is enabled (see chapter 3.2)
440   - The socket does not receive its own sent frames (in loopback mode)
441 
442   These default settings may be changed before or after binding the socket.
443   To use the referenced definitions of the socket options for CAN_RAW
444   sockets, include <linux/can/raw.h>.
445 
446   4.1.1 RAW socket option CAN_RAW_FILTER
447 
448   The reception of CAN frames using CAN_RAW sockets can be controlled
449   by defining 0 .. n filters with the CAN_RAW_FILTER socket option.
450 
451   The CAN filter structure is defined in include/linux/can.h:
452 
453     struct can_filter {
454             canid_t can_id;
455             canid_t can_mask;
456     };
457 
458   A filter matches, when
459 
460     <received_can_id> & mask == can_id & mask
461 
462   which is analogous to known CAN controllers hardware filter semantics.
463   The filter can be inverted in this semantic, when the CAN_INV_FILTER
464   bit is set in can_id element of the can_filter structure. In
465   contrast to CAN controller hardware filters the user may set 0 .. n
466   receive filters for each open socket separately:
467 
468     struct can_filter rfilter[2];
469 
470     rfilter[0].can_id   = 0x123;
471     rfilter[0].can_mask = CAN_SFF_MASK;
472     rfilter[1].can_id   = 0x200;
473     rfilter[1].can_mask = 0x700;
474 
475     setsockopt(s, SOL_CAN_RAW, CAN_RAW_FILTER, &rfilter, sizeof(rfilter));
476 
477   To disable the reception of CAN frames on the selected CAN_RAW socket:
478 
479     setsockopt(s, SOL_CAN_RAW, CAN_RAW_FILTER, NULL, 0);
480 
481   To set the filters to zero filters is quite obsolete as to not read
482   data causes the raw socket to discard the received CAN frames. But
483   having this 'send only' use-case we may remove the receive list in the
484   Kernel to save a little (really a very little!) CPU usage.
485 
486   4.1.1.1 CAN filter usage optimisation
487 
488   The CAN filters are processed in per-device filter lists at CAN frame
489   reception time. To reduce the number of checks that need to be performed
490   while walking through the filter lists the CAN core provides an optimized
491   filter handling when the filter subscription focusses on a single CAN ID.
492 
493   For the possible 2048 SFF CAN identifiers the identifier is used as an index
494   to access the corresponding subscription list without any further checks.
495   For the 2^29 possible EFF CAN identifiers a 10 bit XOR folding is used as
496   hash function to retrieve the EFF table index.
497 
498   To benefit from the optimized filters for single CAN identifiers the
499   CAN_SFF_MASK or CAN_EFF_MASK have to be set into can_filter.mask together
500   with set CAN_EFF_FLAG and CAN_RTR_FLAG bits. A set CAN_EFF_FLAG bit in the
501   can_filter.mask makes clear that it matters whether a SFF or EFF CAN ID is
502   subscribed. E.g. in the example from above
503 
504     rfilter[0].can_id   = 0x123;
505     rfilter[0].can_mask = CAN_SFF_MASK;
506 
507   both SFF frames with CAN ID 0x123 and EFF frames with 0xXXXXX123 can pass.
508 
509   To filter for only 0x123 (SFF) and 0x12345678 (EFF) CAN identifiers the
510   filter has to be defined in this way to benefit from the optimized filters:
511 
512     struct can_filter rfilter[2];
513 
514     rfilter[0].can_id   = 0x123;
515     rfilter[0].can_mask = (CAN_EFF_FLAG | CAN_RTR_FLAG | CAN_SFF_MASK);
516     rfilter[1].can_id   = 0x12345678 | CAN_EFF_FLAG;
517     rfilter[1].can_mask = (CAN_EFF_FLAG | CAN_RTR_FLAG | CAN_EFF_MASK);
518 
519     setsockopt(s, SOL_CAN_RAW, CAN_RAW_FILTER, &rfilter, sizeof(rfilter));
520 
521   4.1.2 RAW socket option CAN_RAW_ERR_FILTER
522 
523   As described in chapter 3.3 the CAN interface driver can generate so
524   called Error Message Frames that can optionally be passed to the user
525   application in the same way as other CAN frames. The possible
526   errors are divided into different error classes that may be filtered
527   using the appropriate error mask. To register for every possible
528   error condition CAN_ERR_MASK can be used as value for the error mask.
529   The values for the error mask are defined in linux/can/error.h .
530 
531     can_err_mask_t err_mask = ( CAN_ERR_TX_TIMEOUT | CAN_ERR_BUSOFF );
532 
533     setsockopt(s, SOL_CAN_RAW, CAN_RAW_ERR_FILTER,
534                &err_mask, sizeof(err_mask));
535 
536   4.1.3 RAW socket option CAN_RAW_LOOPBACK
537 
538   To meet multi user needs the local loopback is enabled by default
539   (see chapter 3.2 for details). But in some embedded use-cases
540   (e.g. when only one application uses the CAN bus) this loopback
541   functionality can be disabled (separately for each socket):
542 
543     int loopback = 0; /* 0 = disabled, 1 = enabled (default) */
544 
545     setsockopt(s, SOL_CAN_RAW, CAN_RAW_LOOPBACK, &loopback, sizeof(loopback));
546 
547   4.1.4 RAW socket option CAN_RAW_RECV_OWN_MSGS
548 
549   When the local loopback is enabled, all the sent CAN frames are
550   looped back to the open CAN sockets that registered for the CAN
551   frames' CAN-ID on this given interface to meet the multi user
552   needs. The reception of the CAN frames on the same socket that was
553   sending the CAN frame is assumed to be unwanted and therefore
554   disabled by default. This default behaviour may be changed on
555   demand:
556 
557     int recv_own_msgs = 1; /* 0 = disabled (default), 1 = enabled */
558 
559     setsockopt(s, SOL_CAN_RAW, CAN_RAW_RECV_OWN_MSGS,
560                &recv_own_msgs, sizeof(recv_own_msgs));
561 
562   4.1.5 RAW socket option CAN_RAW_FD_FRAMES
563 
564   CAN FD support in CAN_RAW sockets can be enabled with a new socket option
565   CAN_RAW_FD_FRAMES which is off by default. When the new socket option is
566   not supported by the CAN_RAW socket (e.g. on older kernels), switching the
567   CAN_RAW_FD_FRAMES option returns the error -ENOPROTOOPT.
568 
569   Once CAN_RAW_FD_FRAMES is enabled the application can send both CAN frames
570   and CAN FD frames. OTOH the application has to handle CAN and CAN FD frames
571   when reading from the socket.
572 
573     CAN_RAW_FD_FRAMES enabled:  CAN_MTU and CANFD_MTU are allowed
574     CAN_RAW_FD_FRAMES disabled: only CAN_MTU is allowed (default)
575 
576   Example:
577     [ remember: CANFD_MTU == sizeof(struct canfd_frame) ]
578 
579     struct canfd_frame cfd;
580 
581     nbytes = read(s, &cfd, CANFD_MTU);
582 
583     if (nbytes == CANFD_MTU) {
584             printf("got CAN FD frame with length %d\n", cfd.len);
585             /* cfd.flags contains valid data */
586     } else if (nbytes == CAN_MTU) {
587             printf("got legacy CAN frame with length %d\n", cfd.len);
588             /* cfd.flags is undefined */
589     } else {
590             fprintf(stderr, "read: invalid CAN(FD) frame\n");
591             return 1;
592     }
593 
594     /* the content can be handled independently from the received MTU size */
595 
596     printf("can_id: %X data length: %d data: ", cfd.can_id, cfd.len);
597     for (i = 0; i < cfd.len; i++)
598             printf("%02X ", cfd.data[i]);
599 
600   When reading with size CANFD_MTU only returns CAN_MTU bytes that have
601   been received from the socket a legacy CAN frame has been read into the
602   provided CAN FD structure. Note that the canfd_frame.flags data field is
603   not specified in the struct can_frame and therefore it is only valid in
604   CANFD_MTU sized CAN FD frames.
605 
606   Implementation hint for new CAN applications:
607 
608   To build a CAN FD aware application use struct canfd_frame as basic CAN
609   data structure for CAN_RAW based applications. When the application is
610   executed on an older Linux kernel and switching the CAN_RAW_FD_FRAMES
611   socket option returns an error: No problem. You'll get legacy CAN frames
612   or CAN FD frames and can process them the same way.
613 
614   When sending to CAN devices make sure that the device is capable to handle
615   CAN FD frames by checking if the device maximum transfer unit is CANFD_MTU.
616   The CAN device MTU can be retrieved e.g. with a SIOCGIFMTU ioctl() syscall.
617 
618   4.1.6 RAW socket option CAN_RAW_JOIN_FILTERS
619 
620   The CAN_RAW socket can set multiple CAN identifier specific filters that
621   lead to multiple filters in the af_can.c filter processing. These filters
622   are indenpendent from each other which leads to logical OR'ed filters when
623   applied (see 4.1.1).
624 
625   This socket option joines the given CAN filters in the way that only CAN
626   frames are passed to user space that matched *all* given CAN filters. The
627   semantic for the applied filters is therefore changed to a logical AND.
628 
629   This is useful especially when the filterset is a combination of filters
630   where the CAN_INV_FILTER flag is set in order to notch single CAN IDs or
631   CAN ID ranges from the incoming traffic.
632 
633   4.1.7 RAW socket returned message flags
634 
635   When using recvmsg() call, the msg->msg_flags may contain following flags:
636 
637     MSG_DONTROUTE: set when the received frame was created on the local host.
638 
639     MSG_CONFIRM: set when the frame was sent via the socket it is received on.
640       This flag can be interpreted as a 'transmission confirmation' when the
641       CAN driver supports the echo of frames on driver level, see 3.2 and 6.2.
642       In order to receive such messages, CAN_RAW_RECV_OWN_MSGS must be set.
643 
644   4.2 Broadcast Manager protocol sockets (SOCK_DGRAM)
645 
646   The Broadcast Manager protocol provides a command based configuration
647   interface to filter and send (e.g. cyclic) CAN messages in kernel space.
648 
649   Receive filters can be used to down sample frequent messages; detect events
650   such as message contents changes, packet length changes, and do time-out
651   monitoring of received messages.
652 
653   Periodic transmission tasks of CAN frames or a sequence of CAN frames can be
654   created and modified at runtime; both the message content and the two
655   possible transmit intervals can be altered.
656 
657   A BCM socket is not intended for sending individual CAN frames using the
658   struct can_frame as known from the CAN_RAW socket. Instead a special BCM
659   configuration message is defined. The basic BCM configuration message used
660   to communicate with the broadcast manager and the available operations are
661   defined in the linux/can/bcm.h include. The BCM message consists of a
662   message header with a command ('opcode') followed by zero or more CAN frames.
663   The broadcast manager sends responses to user space in the same form:
664 
665     struct bcm_msg_head {
666             __u32 opcode;                   /* command */
667             __u32 flags;                    /* special flags */
668             __u32 count;                    /* run 'count' times with ival1 */
669             struct timeval ival1, ival2;    /* count and subsequent interval */
670             canid_t can_id;                 /* unique can_id for task */
671             __u32 nframes;                  /* number of can_frames following */
672             struct can_frame frames[0];
673     };
674 
675   The aligned payload 'frames' uses the same basic CAN frame structure defined
676   at the beginning of section 4 and in the include/linux/can.h include. All
677   messages to the broadcast manager from user space have this structure.
678 
679   Note a CAN_BCM socket must be connected instead of bound after socket
680   creation (example without error checking):
681 
682     int s;
683     struct sockaddr_can addr;
684     struct ifreq ifr;
685 
686     s = socket(PF_CAN, SOCK_DGRAM, CAN_BCM);
687 
688     strcpy(ifr.ifr_name, "can0");
689     ioctl(s, SIOCGIFINDEX, &ifr);
690 
691     addr.can_family = AF_CAN;
692     addr.can_ifindex = ifr.ifr_ifindex;
693 
694     connect(s, (struct sockaddr *)&addr, sizeof(addr));
695 
696     (..)
697 
698   The broadcast manager socket is able to handle any number of in flight
699   transmissions or receive filters concurrently. The different RX/TX jobs are
700   distinguished by the unique can_id in each BCM message. However additional
701   CAN_BCM sockets are recommended to communicate on multiple CAN interfaces.
702   When the broadcast manager socket is bound to 'any' CAN interface (=> the
703   interface index is set to zero) the configured receive filters apply to any
704   CAN interface unless the sendto() syscall is used to overrule the 'any' CAN
705   interface index. When using recvfrom() instead of read() to retrieve BCM
706   socket messages the originating CAN interface is provided in can_ifindex.
707 
708   4.2.1 Broadcast Manager operations
709 
710   The opcode defines the operation for the broadcast manager to carry out,
711   or details the broadcast managers response to several events, including
712   user requests.
713 
714   Transmit Operations (user space to broadcast manager):
715 
716     TX_SETUP:   Create (cyclic) transmission task.
717 
718     TX_DELETE:  Remove (cyclic) transmission task, requires only can_id.
719 
720     TX_READ:    Read properties of (cyclic) transmission task for can_id.
721 
722     TX_SEND:    Send one CAN frame.
723 
724   Transmit Responses (broadcast manager to user space):
725 
726     TX_STATUS:  Reply to TX_READ request (transmission task configuration).
727 
728     TX_EXPIRED: Notification when counter finishes sending at initial interval
729       'ival1'. Requires the TX_COUNTEVT flag to be set at TX_SETUP.
730 
731   Receive Operations (user space to broadcast manager):
732 
733     RX_SETUP:   Create RX content filter subscription.
734 
735     RX_DELETE:  Remove RX content filter subscription, requires only can_id.
736 
737     RX_READ:    Read properties of RX content filter subscription for can_id.
738 
739   Receive Responses (broadcast manager to user space):
740 
741     RX_STATUS:  Reply to RX_READ request (filter task configuration).
742 
743     RX_TIMEOUT: Cyclic message is detected to be absent (timer ival1 expired).
744 
745     RX_CHANGED: BCM message with updated CAN frame (detected content change).
746       Sent on first message received or on receipt of revised CAN messages.
747 
748   4.2.2 Broadcast Manager message flags
749 
750   When sending a message to the broadcast manager the 'flags' element may
751   contain the following flag definitions which influence the behaviour:
752 
753     SETTIMER:           Set the values of ival1, ival2 and count
754 
755     STARTTIMER:         Start the timer with the actual values of ival1, ival2
756       and count. Starting the timer leads simultaneously to emit a CAN frame.
757 
758     TX_COUNTEVT:        Create the message TX_EXPIRED when count expires
759 
760     TX_ANNOUNCE:        A change of data by the process is emitted immediately.
761 
762     TX_CP_CAN_ID:       Copies the can_id from the message header to each
763       subsequent frame in frames. This is intended as usage simplification. For
764       TX tasks the unique can_id from the message header may differ from the
765       can_id(s) stored for transmission in the subsequent struct can_frame(s).
766 
767     RX_FILTER_ID:       Filter by can_id alone, no frames required (nframes=0).
768 
769     RX_CHECK_DLC:       A change of the DLC leads to an RX_CHANGED.
770 
771     RX_NO_AUTOTIMER:    Prevent automatically starting the timeout monitor.
772 
773     RX_ANNOUNCE_RESUME: If passed at RX_SETUP and a receive timeout occurred, a
774       RX_CHANGED message will be generated when the (cyclic) receive restarts.
775 
776     TX_RESET_MULTI_IDX: Reset the index for the multiple frame transmission.
777 
778     RX_RTR_FRAME:       Send reply for RTR-request (placed in op->frames[0]).
779 
780   4.2.3 Broadcast Manager transmission timers
781 
782   Periodic transmission configurations may use up to two interval timers.
783   In this case the BCM sends a number of messages ('count') at an interval
784   'ival1', then continuing to send at another given interval 'ival2'. When
785   only one timer is needed 'count' is set to zero and only 'ival2' is used.
786   When SET_TIMER and START_TIMER flag were set the timers are activated.
787   The timer values can be altered at runtime when only SET_TIMER is set.
788 
789   4.2.4 Broadcast Manager message sequence transmission
790 
791   Up to 256 CAN frames can be transmitted in a sequence in the case of a cyclic
792   TX task configuration. The number of CAN frames is provided in the 'nframes'
793   element of the BCM message head. The defined number of CAN frames are added
794   as array to the TX_SETUP BCM configuration message.
795 
796     /* create a struct to set up a sequence of four CAN frames */
797     struct {
798             struct bcm_msg_head msg_head;
799             struct can_frame frame[4];
800     } mytxmsg;
801 
802     (..)
803     mytxmsg.msg_head.nframes = 4;
804     (..)
805 
806     write(s, &mytxmsg, sizeof(mytxmsg));
807 
808   With every transmission the index in the array of CAN frames is increased
809   and set to zero at index overflow.
810 
811   4.2.5 Broadcast Manager receive filter timers
812 
813   The timer values ival1 or ival2 may be set to non-zero values at RX_SETUP.
814   When the SET_TIMER flag is set the timers are enabled:
815 
816   ival1: Send RX_TIMEOUT when a received message is not received again within
817     the given time. When START_TIMER is set at RX_SETUP the timeout detection
818     is activated directly - even without a former CAN frame reception.
819 
820   ival2: Throttle the received message rate down to the value of ival2. This
821     is useful to reduce messages for the application when the signal inside the
822     CAN frame is stateless as state changes within the ival2 periode may get
823     lost.
824 
825   4.2.6 Broadcast Manager multiplex message receive filter
826 
827   To filter for content changes in multiplex message sequences an array of more
828   than one CAN frames can be passed in a RX_SETUP configuration message. The
829   data bytes of the first CAN frame contain the mask of relevant bits that
830   have to match in the subsequent CAN frames with the received CAN frame.
831   If one of the subsequent CAN frames is matching the bits in that frame data
832   mark the relevant content to be compared with the previous received content.
833   Up to 257 CAN frames (multiplex filter bit mask CAN frame plus 256 CAN
834   filters) can be added as array to the TX_SETUP BCM configuration message.
835 
836     /* usually used to clear CAN frame data[] - beware of endian problems! */
837     #define U64_DATA(p) (*(unsigned long long*)(p)->data)
838 
839     struct {
840             struct bcm_msg_head msg_head;
841             struct can_frame frame[5];
842     } msg;
843 
844     msg.msg_head.opcode  = RX_SETUP;
845     msg.msg_head.can_id  = 0x42;
846     msg.msg_head.flags   = 0;
847     msg.msg_head.nframes = 5;
848     U64_DATA(&msg.frame[0]) = 0xFF00000000000000ULL; /* MUX mask */
849     U64_DATA(&msg.frame[1]) = 0x01000000000000FFULL; /* data mask (MUX 0x01) */
850     U64_DATA(&msg.frame[2]) = 0x0200FFFF000000FFULL; /* data mask (MUX 0x02) */
851     U64_DATA(&msg.frame[3]) = 0x330000FFFFFF0003ULL; /* data mask (MUX 0x33) */
852     U64_DATA(&msg.frame[4]) = 0x4F07FC0FF0000000ULL; /* data mask (MUX 0x4F) */
853 
854     write(s, &msg, sizeof(msg));
855 
856   4.2.7 Broadcast Manager CAN FD support
857 
858   The programming API of the CAN_BCM depends on struct can_frame which is
859   given as array directly behind the bcm_msg_head structure. To follow this
860   schema for the CAN FD frames a new flag 'CAN_FD_FRAME' in the bcm_msg_head
861   flags indicates that the concatenated CAN frame structures behind the
862   bcm_msg_head are defined as struct canfd_frame.
863 
864     struct {
865             struct bcm_msg_head msg_head;
866             struct canfd_frame frame[5];
867     } msg;
868 
869     msg.msg_head.opcode  = RX_SETUP;
870     msg.msg_head.can_id  = 0x42;
871     msg.msg_head.flags   = CAN_FD_FRAME;
872     msg.msg_head.nframes = 5;
873     (..)
874 
875   When using CAN FD frames for multiplex filtering the MUX mask is still
876   expected in the first 64 bit of the struct canfd_frame data section.
877 
878   4.3 connected transport protocols (SOCK_SEQPACKET)
879   4.4 unconnected transport protocols (SOCK_DGRAM)
880 
881 
882 5. SocketCAN core module
883 -------------------------
884 
885   The SocketCAN core module implements the protocol family
886   PF_CAN. CAN protocol modules are loaded by the core module at
887   runtime. The core module provides an interface for CAN protocol
888   modules to subscribe needed CAN IDs (see chapter 3.1).
889 
890   5.1 can.ko module params
891 
892   - stats_timer: To calculate the SocketCAN core statistics
893     (e.g. current/maximum frames per second) this 1 second timer is
894     invoked at can.ko module start time by default. This timer can be
895     disabled by using stattimer=0 on the module commandline.
896 
897   - debug: (removed since SocketCAN SVN r546)
898 
899   5.2 procfs content
900 
901   As described in chapter 3.1 the SocketCAN core uses several filter
902   lists to deliver received CAN frames to CAN protocol modules. These
903   receive lists, their filters and the count of filter matches can be
904   checked in the appropriate receive list. All entries contain the
905   device and a protocol module identifier:
906 
907     foo@bar:~$ cat /proc/net/can/rcvlist_all
908 
909     receive list 'rx_all':
910       (vcan3: no entry)
911       (vcan2: no entry)
912       (vcan1: no entry)
913       device   can_id   can_mask  function  userdata   matches  ident
914        vcan0     000    00000000  f88e6370  f6c6f400         0  raw
915       (any: no entry)
916 
917   In this example an application requests any CAN traffic from vcan0.
918 
919     rcvlist_all - list for unfiltered entries (no filter operations)
920     rcvlist_eff - list for single extended frame (EFF) entries
921     rcvlist_err - list for error message frames masks
922     rcvlist_fil - list for mask/value filters
923     rcvlist_inv - list for mask/value filters (inverse semantic)
924     rcvlist_sff - list for single standard frame (SFF) entries
925 
926   Additional procfs files in /proc/net/can
927 
928     stats       - SocketCAN core statistics (rx/tx frames, match ratios, ...)
929     reset_stats - manual statistic reset
930     version     - prints the SocketCAN core version and the ABI version
931 
932   5.3 writing own CAN protocol modules
933 
934   To implement a new protocol in the protocol family PF_CAN a new
935   protocol has to be defined in include/linux/can.h .
936   The prototypes and definitions to use the SocketCAN core can be
937   accessed by including include/linux/can/core.h .
938   In addition to functions that register the CAN protocol and the
939   CAN device notifier chain there are functions to subscribe CAN
940   frames received by CAN interfaces and to send CAN frames:
941 
942     can_rx_register   - subscribe CAN frames from a specific interface
943     can_rx_unregister - unsubscribe CAN frames from a specific interface
944     can_send          - transmit a CAN frame (optional with local loopback)
945 
946   For details see the kerneldoc documentation in net/can/af_can.c or
947   the source code of net/can/raw.c or net/can/bcm.c .
948 
949 6. CAN network drivers
950 ----------------------
951 
952   Writing a CAN network device driver is much easier than writing a
953   CAN character device driver. Similar to other known network device
954   drivers you mainly have to deal with:
955 
956   - TX: Put the CAN frame from the socket buffer to the CAN controller.
957   - RX: Put the CAN frame from the CAN controller to the socket buffer.
958 
959   See e.g. at Documentation/networking/netdevices.txt . The differences
960   for writing CAN network device driver are described below:
961 
962   6.1 general settings
963 
964     dev->type  = ARPHRD_CAN; /* the netdevice hardware type */
965     dev->flags = IFF_NOARP;  /* CAN has no arp */
966 
967     dev->mtu = CAN_MTU; /* sizeof(struct can_frame) -> legacy CAN interface */
968 
969     or alternative, when the controller supports CAN with flexible data rate:
970     dev->mtu = CANFD_MTU; /* sizeof(struct canfd_frame) -> CAN FD interface */
971 
972   The struct can_frame or struct canfd_frame is the payload of each socket
973   buffer (skbuff) in the protocol family PF_CAN.
974 
975   6.2 local loopback of sent frames
976 
977   As described in chapter 3.2 the CAN network device driver should
978   support a local loopback functionality similar to the local echo
979   e.g. of tty devices. In this case the driver flag IFF_ECHO has to be
980   set to prevent the PF_CAN core from locally echoing sent frames
981   (aka loopback) as fallback solution:
982 
983     dev->flags = (IFF_NOARP | IFF_ECHO);
984 
985   6.3 CAN controller hardware filters
986 
987   To reduce the interrupt load on deep embedded systems some CAN
988   controllers support the filtering of CAN IDs or ranges of CAN IDs.
989   These hardware filter capabilities vary from controller to
990   controller and have to be identified as not feasible in a multi-user
991   networking approach. The use of the very controller specific
992   hardware filters could make sense in a very dedicated use-case, as a
993   filter on driver level would affect all users in the multi-user
994   system. The high efficient filter sets inside the PF_CAN core allow
995   to set different multiple filters for each socket separately.
996   Therefore the use of hardware filters goes to the category 'handmade
997   tuning on deep embedded systems'. The author is running a MPC603e
998   @133MHz with four SJA1000 CAN controllers from 2002 under heavy bus
999   load without any problems ...
1000 
1001   6.4 The virtual CAN driver (vcan)
1002 
1003   Similar to the network loopback devices, vcan offers a virtual local
1004   CAN interface. A full qualified address on CAN consists of
1005 
1006   - a unique CAN Identifier (CAN ID)
1007   - the CAN bus this CAN ID is transmitted on (e.g. can0)
1008 
1009   so in common use cases more than one virtual CAN interface is needed.
1010 
1011   The virtual CAN interfaces allow the transmission and reception of CAN
1012   frames without real CAN controller hardware. Virtual CAN network
1013   devices are usually named 'vcanX', like vcan0 vcan1 vcan2 ...
1014   When compiled as a module the virtual CAN driver module is called vcan.ko
1015 
1016   Since Linux Kernel version 2.6.24 the vcan driver supports the Kernel
1017   netlink interface to create vcan network devices. The creation and
1018   removal of vcan network devices can be managed with the ip(8) tool:
1019 
1020   - Create a virtual CAN network interface:
1021        $ ip link add type vcan
1022 
1023   - Create a virtual CAN network interface with a specific name 'vcan42':
1024        $ ip link add dev vcan42 type vcan
1025 
1026   - Remove a (virtual CAN) network interface 'vcan42':
1027        $ ip link del vcan42
1028 
1029   6.5 The CAN network device driver interface
1030 
1031   The CAN network device driver interface provides a generic interface
1032   to setup, configure and monitor CAN network devices. The user can then
1033   configure the CAN device, like setting the bit-timing parameters, via
1034   the netlink interface using the program "ip" from the "IPROUTE2"
1035   utility suite. The following chapter describes briefly how to use it.
1036   Furthermore, the interface uses a common data structure and exports a
1037   set of common functions, which all real CAN network device drivers
1038   should use. Please have a look to the SJA1000 or MSCAN driver to
1039   understand how to use them. The name of the module is can-dev.ko.
1040 
1041   6.5.1 Netlink interface to set/get devices properties
1042 
1043   The CAN device must be configured via netlink interface. The supported
1044   netlink message types are defined and briefly described in
1045   "include/linux/can/netlink.h". CAN link support for the program "ip"
1046   of the IPROUTE2 utility suite is available and it can be used as shown
1047   below:
1048 
1049   - Setting CAN device properties:
1050 
1051     $ ip link set can0 type can help
1052     Usage: ip link set DEVICE type can
1053         [ bitrate BITRATE [ sample-point SAMPLE-POINT] ] |
1054         [ tq TQ prop-seg PROP_SEG phase-seg1 PHASE-SEG1
1055           phase-seg2 PHASE-SEG2 [ sjw SJW ] ]
1056 
1057         [ dbitrate BITRATE [ dsample-point SAMPLE-POINT] ] |
1058         [ dtq TQ dprop-seg PROP_SEG dphase-seg1 PHASE-SEG1
1059           dphase-seg2 PHASE-SEG2 [ dsjw SJW ] ]
1060 
1061         [ loopback { on | off } ]
1062         [ listen-only { on | off } ]
1063         [ triple-sampling { on | off } ]
1064         [ one-shot { on | off } ]
1065         [ berr-reporting { on | off } ]
1066         [ fd { on | off } ]
1067         [ fd-non-iso { on | off } ]
1068         [ presume-ack { on | off } ]
1069 
1070         [ restart-ms TIME-MS ]
1071         [ restart ]
1072 
1073         Where: BITRATE       := { 1..1000000 }
1074                SAMPLE-POINT  := { 0.000..0.999 }
1075                TQ            := { NUMBER }
1076                PROP-SEG      := { 1..8 }
1077                PHASE-SEG1    := { 1..8 }
1078                PHASE-SEG2    := { 1..8 }
1079                SJW           := { 1..4 }
1080                RESTART-MS    := { 0 | NUMBER }
1081 
1082   - Display CAN device details and statistics:
1083 
1084     $ ip -details -statistics link show can0
1085     2: can0: <NOARP,UP,LOWER_UP,ECHO> mtu 16 qdisc pfifo_fast state UP qlen 10
1086       link/can
1087       can <TRIPLE-SAMPLING> state ERROR-ACTIVE restart-ms 100
1088       bitrate 125000 sample_point 0.875
1089       tq 125 prop-seg 6 phase-seg1 7 phase-seg2 2 sjw 1
1090       sja1000: tseg1 1..16 tseg2 1..8 sjw 1..4 brp 1..64 brp-inc 1
1091       clock 8000000
1092       re-started bus-errors arbit-lost error-warn error-pass bus-off
1093       41         17457      0          41         42         41
1094       RX: bytes  packets  errors  dropped overrun mcast
1095       140859     17608    17457   0       0       0
1096       TX: bytes  packets  errors  dropped carrier collsns
1097       861        112      0       41      0       0
1098 
1099   More info to the above output:
1100 
1101     "<TRIPLE-SAMPLING>"
1102         Shows the list of selected CAN controller modes: LOOPBACK,
1103         LISTEN-ONLY, or TRIPLE-SAMPLING.
1104 
1105     "state ERROR-ACTIVE"
1106         The current state of the CAN controller: "ERROR-ACTIVE",
1107         "ERROR-WARNING", "ERROR-PASSIVE", "BUS-OFF" or "STOPPED"
1108 
1109     "restart-ms 100"
1110         Automatic restart delay time. If set to a non-zero value, a
1111         restart of the CAN controller will be triggered automatically
1112         in case of a bus-off condition after the specified delay time
1113         in milliseconds. By default it's off.
1114 
1115     "bitrate 125000 sample-point 0.875"
1116         Shows the real bit-rate in bits/sec and the sample-point in the
1117         range 0.000..0.999. If the calculation of bit-timing parameters
1118         is enabled in the kernel (CONFIG_CAN_CALC_BITTIMING=y), the
1119         bit-timing can be defined by setting the "bitrate" argument.
1120         Optionally the "sample-point" can be specified. By default it's
1121         0.000 assuming CIA-recommended sample-points.
1122 
1123     "tq 125 prop-seg 6 phase-seg1 7 phase-seg2 2 sjw 1"
1124         Shows the time quanta in ns, propagation segment, phase buffer
1125         segment 1 and 2 and the synchronisation jump width in units of
1126         tq. They allow to define the CAN bit-timing in a hardware
1127         independent format as proposed by the Bosch CAN 2.0 spec (see
1128         chapter 8 of http://www.semiconductors.bosch.de/pdf/can2spec.pdf).
1129 
1130     "sja1000: tseg1 1..16 tseg2 1..8 sjw 1..4 brp 1..64 brp-inc 1
1131      clock 8000000"
1132         Shows the bit-timing constants of the CAN controller, here the
1133         "sja1000". The minimum and maximum values of the time segment 1
1134         and 2, the synchronisation jump width in units of tq, the
1135         bitrate pre-scaler and the CAN system clock frequency in Hz.
1136         These constants could be used for user-defined (non-standard)
1137         bit-timing calculation algorithms in user-space.
1138 
1139     "re-started bus-errors arbit-lost error-warn error-pass bus-off"
1140         Shows the number of restarts, bus and arbitration lost errors,
1141         and the state changes to the error-warning, error-passive and
1142         bus-off state. RX overrun errors are listed in the "overrun"
1143         field of the standard network statistics.
1144 
1145   6.5.2 Setting the CAN bit-timing
1146 
1147   The CAN bit-timing parameters can always be defined in a hardware
1148   independent format as proposed in the Bosch CAN 2.0 specification
1149   specifying the arguments "tq", "prop_seg", "phase_seg1", "phase_seg2"
1150   and "sjw":
1151 
1152     $ ip link set canX type can tq 125 prop-seg 6 \
1153                                 phase-seg1 7 phase-seg2 2 sjw 1
1154 
1155   If the kernel option CONFIG_CAN_CALC_BITTIMING is enabled, CIA
1156   recommended CAN bit-timing parameters will be calculated if the bit-
1157   rate is specified with the argument "bitrate":
1158 
1159     $ ip link set canX type can bitrate 125000
1160 
1161   Note that this works fine for the most common CAN controllers with
1162   standard bit-rates but may *fail* for exotic bit-rates or CAN system
1163   clock frequencies. Disabling CONFIG_CAN_CALC_BITTIMING saves some
1164   space and allows user-space tools to solely determine and set the
1165   bit-timing parameters. The CAN controller specific bit-timing
1166   constants can be used for that purpose. They are listed by the
1167   following command:
1168 
1169     $ ip -details link show can0
1170     ...
1171       sja1000: clock 8000000 tseg1 1..16 tseg2 1..8 sjw 1..4 brp 1..64 brp-inc 1
1172 
1173   6.5.3 Starting and stopping the CAN network device
1174 
1175   A CAN network device is started or stopped as usual with the command
1176   "ifconfig canX up/down" or "ip link set canX up/down". Be aware that
1177   you *must* define proper bit-timing parameters for real CAN devices
1178   before you can start it to avoid error-prone default settings:
1179 
1180     $ ip link set canX up type can bitrate 125000
1181 
1182   A device may enter the "bus-off" state if too many errors occurred on
1183   the CAN bus. Then no more messages are received or sent. An automatic
1184   bus-off recovery can be enabled by setting the "restart-ms" to a
1185   non-zero value, e.g.:
1186 
1187     $ ip link set canX type can restart-ms 100
1188 
1189   Alternatively, the application may realize the "bus-off" condition
1190   by monitoring CAN error message frames and do a restart when
1191   appropriate with the command:
1192 
1193     $ ip link set canX type can restart
1194 
1195   Note that a restart will also create a CAN error message frame (see
1196   also chapter 3.3).
1197 
1198   6.6 CAN FD (flexible data rate) driver support
1199 
1200   CAN FD capable CAN controllers support two different bitrates for the
1201   arbitration phase and the payload phase of the CAN FD frame. Therefore a
1202   second bit timing has to be specified in order to enable the CAN FD bitrate.
1203 
1204   Additionally CAN FD capable CAN controllers support up to 64 bytes of
1205   payload. The representation of this length in can_frame.can_dlc and
1206   canfd_frame.len for userspace applications and inside the Linux network
1207   layer is a plain value from 0 .. 64 instead of the CAN 'data length code'.
1208   The data length code was a 1:1 mapping to the payload length in the legacy
1209   CAN frames anyway. The payload length to the bus-relevant DLC mapping is
1210   only performed inside the CAN drivers, preferably with the helper
1211   functions can_dlc2len() and can_len2dlc().
1212 
1213   The CAN netdevice driver capabilities can be distinguished by the network
1214   devices maximum transfer unit (MTU):
1215 
1216   MTU = 16 (CAN_MTU)   => sizeof(struct can_frame)   => 'legacy' CAN device
1217   MTU = 72 (CANFD_MTU) => sizeof(struct canfd_frame) => CAN FD capable device
1218 
1219   The CAN device MTU can be retrieved e.g. with a SIOCGIFMTU ioctl() syscall.
1220   N.B. CAN FD capable devices can also handle and send legacy CAN frames.
1221 
1222   When configuring CAN FD capable CAN controllers an additional 'data' bitrate
1223   has to be set. This bitrate for the data phase of the CAN FD frame has to be
1224   at least the bitrate which was configured for the arbitration phase. This
1225   second bitrate is specified analogue to the first bitrate but the bitrate
1226   setting keywords for the 'data' bitrate start with 'd' e.g. dbitrate,
1227   dsample-point, dsjw or dtq and similar settings. When a data bitrate is set
1228   within the configuration process the controller option "fd on" can be
1229   specified to enable the CAN FD mode in the CAN controller. This controller
1230   option also switches the device MTU to 72 (CANFD_MTU).
1231 
1232   The first CAN FD specification presented as whitepaper at the International
1233   CAN Conference 2012 needed to be improved for data integrity reasons.
1234   Therefore two CAN FD implementations have to be distinguished today:
1235 
1236   - ISO compliant:     The ISO 11898-1:2015 CAN FD implementation (default)
1237   - non-ISO compliant: The CAN FD implementation following the 2012 whitepaper
1238 
1239   Finally there are three types of CAN FD controllers:
1240 
1241   1. ISO compliant (fixed)
1242   2. non-ISO compliant (fixed, like the M_CAN IP core v3.0.1 in m_can.c)
1243   3. ISO/non-ISO CAN FD controllers (switchable, like the PEAK PCAN-USB FD)
1244 
1245   The current ISO/non-ISO mode is announced by the CAN controller driver via
1246   netlink and displayed by the 'ip' tool (controller option FD-NON-ISO).
1247   The ISO/non-ISO-mode can be altered by setting 'fd-non-iso {on|off}' for
1248   switchable CAN FD controllers only.
1249 
1250   Example configuring 500 kbit/s arbitration bitrate and 4 Mbit/s data bitrate:
1251 
1252     $ ip link set can0 up type can bitrate 500000 sample-point 0.75 \
1253                                    dbitrate 4000000 dsample-point 0.8 fd on
1254     $ ip -details link show can0
1255     5: can0: <NOARP,UP,LOWER_UP,ECHO> mtu 72 qdisc pfifo_fast state UNKNOWN \
1256              mode DEFAULT group default qlen 10
1257     link/can  promiscuity 0
1258     can <FD> state ERROR-ACTIVE (berr-counter tx 0 rx 0) restart-ms 0
1259           bitrate 500000 sample-point 0.750
1260           tq 50 prop-seg 14 phase-seg1 15 phase-seg2 10 sjw 1
1261           pcan_usb_pro_fd: tseg1 1..64 tseg2 1..16 sjw 1..16 brp 1..1024 \
1262           brp-inc 1
1263           dbitrate 4000000 dsample-point 0.800
1264           dtq 12 dprop-seg 7 dphase-seg1 8 dphase-seg2 4 dsjw 1
1265           pcan_usb_pro_fd: dtseg1 1..16 dtseg2 1..8 dsjw 1..4 dbrp 1..1024 \
1266           dbrp-inc 1
1267           clock 80000000
1268 
1269   Example when 'fd-non-iso on' is added on this switchable CAN FD adapter:
1270    can <FD,FD-NON-ISO> state ERROR-ACTIVE (berr-counter tx 0 rx 0) restart-ms 0
1271 
1272   6.7 Supported CAN hardware
1273 
1274   Please check the "Kconfig" file in "drivers/net/can" to get an actual
1275   list of the support CAN hardware. On the SocketCAN project website
1276   (see chapter 7) there might be further drivers available, also for
1277   older kernel versions.
1278 
1279 7. SocketCAN resources
1280 -----------------------
1281 
1282   The Linux CAN / SocketCAN project resources (project site / mailing list)
1283   are referenced in the MAINTAINERS file in the Linux source tree.
1284   Search for CAN NETWORK [LAYERS|DRIVERS].
1285 
1286 8. Credits
1287 ----------
1288 
1289   Oliver Hartkopp (PF_CAN core, filters, drivers, bcm, SJA1000 driver)
1290   Urs Thuermann (PF_CAN core, kernel integration, socket interfaces, raw, vcan)
1291   Jan Kizka (RT-SocketCAN core, Socket-API reconciliation)
1292   Wolfgang Grandegger (RT-SocketCAN core & drivers, Raw Socket-API reviews,
1293                        CAN device driver interface, MSCAN driver)
1294   Robert Schwebel (design reviews, PTXdist integration)
1295   Marc Kleine-Budde (design reviews, Kernel 2.6 cleanups, drivers)
1296   Benedikt Spranger (reviews)
1297   Thomas Gleixner (LKML reviews, coding style, posting hints)
1298   Andrey Volkov (kernel subtree structure, ioctls, MSCAN driver)
1299   Matthias Brukner (first SJA1000 CAN netdevice implementation Q2/2003)
1300   Klaus Hitschler (PEAK driver integration)
1301   Uwe Koppe (CAN netdevices with PF_PACKET approach)
1302   Michael Schulze (driver layer loopback requirement, RT CAN drivers review)
1303   Pavel Pisa (Bit-timing calculation)
1304   Sascha Hauer (SJA1000 platform driver)
1305   Sebastian Haas (SJA1000 EMS PCI driver)
1306   Markus Plessing (SJA1000 EMS PCI driver)
1307   Per Dalen (SJA1000 Kvaser PCI driver)
1308   Sam Ravnborg (reviews, coding style, kbuild help)

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