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Based on kernel version 4.7.2. Page generated on 2016-08-22 22:47 EST.

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