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Based on kernel version 4.16.1. Page generated on 2018-04-09 11:53 EST.

1	===================================
2	SocketCAN - Controller Area Network
3	===================================
4	
5	Overview / What is SocketCAN
6	============================
7	
8	The socketcan package is an implementation of CAN protocols
9	(Controller Area Network) for Linux.  CAN is a networking technology
10	which has widespread use in automation, embedded devices, and
11	automotive fields.  While there have been other CAN implementations
12	for Linux based on character devices, SocketCAN uses the Berkeley
13	socket API, the Linux network stack and implements the CAN device
14	drivers as network interfaces.  The CAN socket API has been designed
15	as similar as possible to the TCP/IP protocols to allow programmers,
16	familiar with network programming, to easily learn how to use CAN
17	sockets.
18	
19	
20	.. _socketcan-motivation:
21	
22	Motivation / Why Using the Socket API
23	=====================================
24	
25	There have been CAN implementations for Linux before SocketCAN so the
26	question arises, why we have started another project.  Most existing
27	implementations come as a device driver for some CAN hardware, they
28	are based on character devices and provide comparatively little
29	functionality.  Usually, there is only a hardware-specific device
30	driver which provides a character device interface to send and
31	receive raw CAN frames, directly to/from the controller hardware.
32	Queueing of frames and higher-level transport protocols like ISO-TP
33	have to be implemented in user space applications.  Also, most
34	character-device implementations support only one single process to
35	open the device at a time, similar to a serial interface.  Exchanging
36	the CAN controller requires employment of another device driver and
37	often the need for adaption of large parts of the application to the
38	new driver's API.
39	
40	SocketCAN was designed to overcome all of these limitations.  A new
41	protocol family has been implemented which provides a socket interface
42	to user space applications and which builds upon the Linux network
43	layer, enabling use all of the provided queueing functionality.  A device
44	driver for CAN controller hardware registers itself with the Linux
45	network layer as a network device, so that CAN frames from the
46	controller can be passed up to the network layer and on to the CAN
47	protocol family module and also vice-versa.  Also, the protocol family
48	module provides an API for transport protocol modules to register, so
49	that any number of transport protocols can be loaded or unloaded
50	dynamically.  In fact, the can core module alone does not provide any
51	protocol and cannot be used without loading at least one additional
52	protocol module.  Multiple sockets can be opened at the same time,
53	on different or the same protocol module and they can listen/send
54	frames on different or the same CAN IDs.  Several sockets listening on
55	the same interface for frames with the same CAN ID are all passed the
56	same received matching CAN frames.  An application wishing to
57	communicate using a specific transport protocol, e.g. ISO-TP, just
58	selects that protocol when opening the socket, and then can read and
59	write application data byte streams, without having to deal with
60	CAN-IDs, frames, etc.
61	
62	Similar functionality visible from user-space could be provided by a
63	character device, too, but this would lead to a technically inelegant
64	solution for a couple of reasons:
65	
66	* **Intricate usage:**  Instead of passing a protocol argument to
67	  socket(2) and using bind(2) to select a CAN interface and CAN ID, an
68	  application would have to do all these operations using ioctl(2)s.
69	
70	* **Code duplication:**  A character device cannot make use of the Linux
71	  network queueing code, so all that code would have to be duplicated
72	  for CAN networking.
73	
74	* **Abstraction:**  In most existing character-device implementations, the
75	  hardware-specific device driver for a CAN controller directly
76	  provides the character device for the application to work with.
77	  This is at least very unusual in Unix systems for both, char and
78	  block devices.  For example you don't have a character device for a
79	  certain UART of a serial interface, a certain sound chip in your
80	  computer, a SCSI or IDE controller providing access to your hard
81	  disk or tape streamer device.  Instead, you have abstraction layers
82	  which provide a unified character or block device interface to the
83	  application on the one hand, and a interface for hardware-specific
84	  device drivers on the other hand.  These abstractions are provided
85	  by subsystems like the tty layer, the audio subsystem or the SCSI
86	  and IDE subsystems for the devices mentioned above.
87	
88	  The easiest way to implement a CAN device driver is as a character
89	  device without such a (complete) abstraction layer, as is done by most
90	  existing drivers.  The right way, however, would be to add such a
91	  layer with all the functionality like registering for certain CAN
92	  IDs, supporting several open file descriptors and (de)multiplexing
93	  CAN frames between them, (sophisticated) queueing of CAN frames, and
94	  providing an API for device drivers to register with.  However, then
95	  it would be no more difficult, or may be even easier, to use the
96	  networking framework provided by the Linux kernel, and this is what
97	  SocketCAN does.
98	
99	The use of the networking framework of the Linux kernel is just the
100	natural and most appropriate way to implement CAN for Linux.
101	
102	
103	.. _socketcan-concept:
104	
105	SocketCAN Concept
106	=================
107	
108	As described in :ref:`socketcan-motivation` the main goal of SocketCAN is to
109	provide a socket interface to user space applications which builds
110	upon the Linux network layer. In contrast to the commonly known
111	TCP/IP and ethernet networking, the CAN bus is a broadcast-only(!)
112	medium that has no MAC-layer addressing like ethernet. The CAN-identifier
113	(can_id) is used for arbitration on the CAN-bus. Therefore the CAN-IDs
114	have to be chosen uniquely on the bus. When designing a CAN-ECU
115	network the CAN-IDs are mapped to be sent by a specific ECU.
116	For this reason a CAN-ID can be treated best as a kind of source address.
117	
118	
119	.. _socketcan-receive-lists:
120	
121	Receive Lists
122	-------------
123	
124	The network transparent access of multiple applications leads to the
125	problem that different applications may be interested in the same
126	CAN-IDs from the same CAN network interface. The SocketCAN core
127	module - which implements the protocol family CAN - provides several
128	high efficient receive lists for this reason. If e.g. a user space
129	application opens a CAN RAW socket, the raw protocol module itself
130	requests the (range of) CAN-IDs from the SocketCAN core that are
131	requested by the user. The subscription and unsubscription of
132	CAN-IDs can be done for specific CAN interfaces or for all(!) known
133	CAN interfaces with the can_rx_(un)register() functions provided to
134	CAN protocol modules by the SocketCAN core (see :ref:`socketcan-core-module`).
135	To optimize the CPU usage at runtime the receive lists are split up
136	into several specific lists per device that match the requested
137	filter complexity for a given use-case.
138	
139	
140	.. _socketcan-local-loopback1:
141	
142	Local Loopback of Sent Frames
143	-----------------------------
144	
145	As known from other networking concepts the data exchanging
146	applications may run on the same or different nodes without any
147	change (except for the according addressing information):
148	
149	.. code::
150	
151		 ___   ___   ___                   _______   ___
152		| _ | | _ | | _ |                 | _   _ | | _ |
153		||A|| ||B|| ||C||                 ||A| |B|| ||C||
154		|___| |___| |___|                 |_______| |___|
155		  |     |     |                       |       |
156		-----------------(1)- CAN bus -(2)---------------
157	
158	To ensure that application A receives the same information in the
159	example (2) as it would receive in example (1) there is need for
160	some kind of local loopback of the sent CAN frames on the appropriate
161	node.
162	
163	The Linux network devices (by default) just can handle the
164	transmission and reception of media dependent frames. Due to the
165	arbitration on the CAN bus the transmission of a low prio CAN-ID
166	may be delayed by the reception of a high prio CAN frame. To
167	reflect the correct [*]_ traffic on the node the loopback of the sent
168	data has to be performed right after a successful transmission. If
169	the CAN network interface is not capable of performing the loopback for
170	some reason the SocketCAN core can do this task as a fallback solution.
171	See :ref:`socketcan-local-loopback1` for details (recommended).
172	
173	The loopback functionality is enabled by default to reflect standard
174	networking behaviour for CAN applications. Due to some requests from
175	the RT-SocketCAN group the loopback optionally may be disabled for each
176	separate socket. See sockopts from the CAN RAW sockets in :ref:`socketcan-raw-sockets`.
177	
178	.. [*] you really like to have this when you're running analyser
179	       tools like 'candump' or 'cansniffer' on the (same) node.
180	
181	
182	.. _socketcan-network-problem-notifications:
183	
184	Network Problem Notifications
185	-----------------------------
186	
187	The use of the CAN bus may lead to several problems on the physical
188	and media access control layer. Detecting and logging of these lower
189	layer problems is a vital requirement for CAN users to identify
190	hardware issues on the physical transceiver layer as well as
191	arbitration problems and error frames caused by the different
192	ECUs. The occurrence of detected errors are important for diagnosis
193	and have to be logged together with the exact timestamp. For this
194	reason the CAN interface driver can generate so called Error Message
195	Frames that can optionally be passed to the user application in the
196	same way as other CAN frames. Whenever an error on the physical layer
197	or the MAC layer is detected (e.g. by the CAN controller) the driver
198	creates an appropriate error message frame. Error messages frames can
199	be requested by the user application using the common CAN filter
200	mechanisms. Inside this filter definition the (interested) type of
201	errors may be selected. The reception of error messages is disabled
202	by default. The format of the CAN error message frame is briefly
203	described in the Linux header file "include/uapi/linux/can/error.h".
204	
205	
206	How to use SocketCAN
207	====================
208	
209	Like TCP/IP, you first need to open a socket for communicating over a
210	CAN network. Since SocketCAN implements a new protocol family, you
211	need to pass PF_CAN as the first argument to the socket(2) system
212	call. Currently, there are two CAN protocols to choose from, the raw
213	socket protocol and the broadcast manager (BCM). So to open a socket,
214	you would write::
215	
216	    s = socket(PF_CAN, SOCK_RAW, CAN_RAW);
217	
218	and::
219	
220	    s = socket(PF_CAN, SOCK_DGRAM, CAN_BCM);
221	
222	respectively.  After the successful creation of the socket, you would
223	normally use the bind(2) system call to bind the socket to a CAN
224	interface (which is different from TCP/IP due to different addressing
225	- see :ref:`socketcan-concept`). After binding (CAN_RAW) or connecting (CAN_BCM)
226	the socket, you can read(2) and write(2) from/to the socket or use
227	send(2), sendto(2), sendmsg(2) and the recv* counterpart operations
228	on the socket as usual. There are also CAN specific socket options
229	described below.
230	
231	The basic CAN frame structure and the sockaddr structure are defined
232	in include/linux/can.h:
233	
234	.. code-block:: C
235	
236	    struct can_frame {
237	            canid_t can_id;  /* 32 bit CAN_ID + EFF/RTR/ERR flags */
238	            __u8    can_dlc; /* frame payload length in byte (0 .. 8) */
239	            __u8    __pad;   /* padding */
240	            __u8    __res0;  /* reserved / padding */
241	            __u8    __res1;  /* reserved / padding */
242	            __u8    data[8] __attribute__((aligned(8)));
243	    };
244	
245	The alignment of the (linear) payload data[] to a 64bit boundary
246	allows the user to define their own structs and unions to easily access
247	the CAN payload. There is no given byteorder on the CAN bus by
248	default. A read(2) system call on a CAN_RAW socket transfers a
249	struct can_frame to the user space.
250	
251	The sockaddr_can structure has an interface index like the
252	PF_PACKET socket, that also binds to a specific interface:
253	
254	.. code-block:: C
255	
256	    struct sockaddr_can {
257	            sa_family_t can_family;
258	            int         can_ifindex;
259	            union {
260	                    /* transport protocol class address info (e.g. ISOTP) */
261	                    struct { canid_t rx_id, tx_id; } tp;
262	
263	                    /* reserved for future CAN protocols address information */
264	            } can_addr;
265	    };
266	
267	To determine the interface index an appropriate ioctl() has to
268	be used (example for CAN_RAW sockets without error checking):
269	
270	.. code-block:: C
271	
272	    int s;
273	    struct sockaddr_can addr;
274	    struct ifreq ifr;
275	
276	    s = socket(PF_CAN, SOCK_RAW, CAN_RAW);
277	
278	    strcpy(ifr.ifr_name, "can0" );
279	    ioctl(s, SIOCGIFINDEX, &ifr);
280	
281	    addr.can_family = AF_CAN;
282	    addr.can_ifindex = ifr.ifr_ifindex;
283	
284	    bind(s, (struct sockaddr *)&addr, sizeof(addr));
285	
286	    (..)
287	
288	To bind a socket to all(!) CAN interfaces the interface index must
289	be 0 (zero). In this case the socket receives CAN frames from every
290	enabled CAN interface. To determine the originating CAN interface
291	the system call recvfrom(2) may be used instead of read(2). To send
292	on a socket that is bound to 'any' interface sendto(2) is needed to
293	specify the outgoing interface.
294	
295	Reading CAN frames from a bound CAN_RAW socket (see above) consists
296	of reading a struct can_frame:
297	
298	.. code-block:: C
299	
300	    struct can_frame frame;
301	
302	    nbytes = read(s, &frame, sizeof(struct can_frame));
303	
304	    if (nbytes < 0) {
305	            perror("can raw socket read");
306	            return 1;
307	    }
308	
309	    /* paranoid check ... */
310	    if (nbytes < sizeof(struct can_frame)) {
311	            fprintf(stderr, "read: incomplete CAN frame\n");
312	            return 1;
313	    }
314	
315	    /* do something with the received CAN frame */
316	
317	Writing CAN frames can be done similarly, with the write(2) system call::
318	
319	    nbytes = write(s, &frame, sizeof(struct can_frame));
320	
321	When the CAN interface is bound to 'any' existing CAN interface
322	(addr.can_ifindex = 0) it is recommended to use recvfrom(2) if the
323	information about the originating CAN interface is needed:
324	
325	.. code-block:: C
326	
327	    struct sockaddr_can addr;
328	    struct ifreq ifr;
329	    socklen_t len = sizeof(addr);
330	    struct can_frame frame;
331	
332	    nbytes = recvfrom(s, &frame, sizeof(struct can_frame),
333	                      0, (struct sockaddr*)&addr, &len);
334	
335	    /* get interface name of the received CAN frame */
336	    ifr.ifr_ifindex = addr.can_ifindex;
337	    ioctl(s, SIOCGIFNAME, &ifr);
338	    printf("Received a CAN frame from interface %s", ifr.ifr_name);
339	
340	To write CAN frames on sockets bound to 'any' CAN interface the
341	outgoing interface has to be defined certainly:
342	
343	.. code-block:: C
344	
345	    strcpy(ifr.ifr_name, "can0");
346	    ioctl(s, SIOCGIFINDEX, &ifr);
347	    addr.can_ifindex = ifr.ifr_ifindex;
348	    addr.can_family  = AF_CAN;
349	
350	    nbytes = sendto(s, &frame, sizeof(struct can_frame),
351	                    0, (struct sockaddr*)&addr, sizeof(addr));
352	
353	An accurate timestamp can be obtained with an ioctl(2) call after reading
354	a message from the socket:
355	
356	.. code-block:: C
357	
358	    struct timeval tv;
359	    ioctl(s, SIOCGSTAMP, &tv);
360	
361	The timestamp has a resolution of one microsecond and is set automatically
362	at the reception of a CAN frame.
363	
364	Remark about CAN FD (flexible data rate) support:
365	
366	Generally the handling of CAN FD is very similar to the formerly described
367	examples. The new CAN FD capable CAN controllers support two different
368	bitrates for the arbitration phase and the payload phase of the CAN FD frame
369	and up to 64 bytes of payload. This extended payload length breaks all the
370	kernel interfaces (ABI) which heavily rely on the CAN frame with fixed eight
371	bytes of payload (struct can_frame) like the CAN_RAW socket. Therefore e.g.
372	the CAN_RAW socket supports a new socket option CAN_RAW_FD_FRAMES that
373	switches the socket into a mode that allows the handling of CAN FD frames
374	and (legacy) CAN frames simultaneously (see :ref:`socketcan-rawfd`).
375	
376	The struct canfd_frame is defined in include/linux/can.h:
377	
378	.. code-block:: C
379	
380	    struct canfd_frame {
381	            canid_t can_id;  /* 32 bit CAN_ID + EFF/RTR/ERR flags */
382	            __u8    len;     /* frame payload length in byte (0 .. 64) */
383	            __u8    flags;   /* additional flags for CAN FD */
384	            __u8    __res0;  /* reserved / padding */
385	            __u8    __res1;  /* reserved / padding */
386	            __u8    data[64] __attribute__((aligned(8)));
387	    };
388	
389	The struct canfd_frame and the existing struct can_frame have the can_id,
390	the payload length and the payload data at the same offset inside their
391	structures. This allows to handle the different structures very similar.
392	When the content of a struct can_frame is copied into a struct canfd_frame
393	all structure elements can be used as-is - only the data[] becomes extended.
394	
395	When introducing the struct canfd_frame it turned out that the data length
396	code (DLC) of the struct can_frame was used as a length information as the
397	length and the DLC has a 1:1 mapping in the range of 0 .. 8. To preserve
398	the easy handling of the length information the canfd_frame.len element
399	contains a plain length value from 0 .. 64. So both canfd_frame.len and
400	can_frame.can_dlc are equal and contain a length information and no DLC.
401	For details about the distinction of CAN and CAN FD capable devices and
402	the mapping to the bus-relevant data length code (DLC), see :ref:`socketcan-can-fd-driver`.
403	
404	The length of the two CAN(FD) frame structures define the maximum transfer
405	unit (MTU) of the CAN(FD) network interface and skbuff data length. Two
406	definitions are specified for CAN specific MTUs in include/linux/can.h:
407	
408	.. code-block:: C
409	
410	  #define CAN_MTU   (sizeof(struct can_frame))   == 16  => 'legacy' CAN frame
411	  #define CANFD_MTU (sizeof(struct canfd_frame)) == 72  => CAN FD frame
412	
413	
414	.. _socketcan-raw-sockets:
415	
416	RAW Protocol Sockets with can_filters (SOCK_RAW)
417	------------------------------------------------
418	
419	Using CAN_RAW sockets is extensively comparable to the commonly
420	known access to CAN character devices. To meet the new possibilities
421	provided by the multi user SocketCAN approach, some reasonable
422	defaults are set at RAW socket binding time:
423	
424	- The filters are set to exactly one filter receiving everything
425	- The socket only receives valid data frames (=> no error message frames)
426	- The loopback of sent CAN frames is enabled (see :ref:`socketcan-local-loopback2`)
427	- The socket does not receive its own sent frames (in loopback mode)
428	
429	These default settings may be changed before or after binding the socket.
430	To use the referenced definitions of the socket options for CAN_RAW
431	sockets, include <linux/can/raw.h>.
432	
433	
434	.. _socketcan-rawfilter:
435	
436	RAW socket option CAN_RAW_FILTER
437	~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
438	
439	The reception of CAN frames using CAN_RAW sockets can be controlled
440	by defining 0 .. n filters with the CAN_RAW_FILTER socket option.
441	
442	The CAN filter structure is defined in include/linux/can.h:
443	
444	.. code-block:: C
445	
446	    struct can_filter {
447	            canid_t can_id;
448	            canid_t can_mask;
449	    };
450	
451	A filter matches, when:
452	
453	.. code-block:: C
454	
455	    <received_can_id> & mask == can_id & mask
456	
457	which is analogous to known CAN controllers hardware filter semantics.
458	The filter can be inverted in this semantic, when the CAN_INV_FILTER
459	bit is set in can_id element of the can_filter structure. In
460	contrast to CAN controller hardware filters the user may set 0 .. n
461	receive filters for each open socket separately:
462	
463	.. code-block:: C
464	
465	    struct can_filter rfilter[2];
466	
467	    rfilter[0].can_id   = 0x123;
468	    rfilter[0].can_mask = CAN_SFF_MASK;
469	    rfilter[1].can_id   = 0x200;
470	    rfilter[1].can_mask = 0x700;
471	
472	    setsockopt(s, SOL_CAN_RAW, CAN_RAW_FILTER, &rfilter, sizeof(rfilter));
473	
474	To disable the reception of CAN frames on the selected CAN_RAW socket:
475	
476	.. code-block:: C
477	
478	    setsockopt(s, SOL_CAN_RAW, CAN_RAW_FILTER, NULL, 0);
479	
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	CAN Filter Usage Optimisation
486	.............................
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	.. code-block:: C
505	
506	    rfilter[0].can_id   = 0x123;
507	    rfilter[0].can_mask = CAN_SFF_MASK;
508	
509	both SFF frames with CAN ID 0x123 and EFF frames with 0xXXXXX123 can pass.
510	
511	To filter for only 0x123 (SFF) and 0x12345678 (EFF) CAN identifiers the
512	filter has to be defined in this way to benefit from the optimized filters:
513	
514	.. code-block:: C
515	
516	    struct can_filter rfilter[2];
517	
518	    rfilter[0].can_id   = 0x123;
519	    rfilter[0].can_mask = (CAN_EFF_FLAG | CAN_RTR_FLAG | CAN_SFF_MASK);
520	    rfilter[1].can_id   = 0x12345678 | CAN_EFF_FLAG;
521	    rfilter[1].can_mask = (CAN_EFF_FLAG | CAN_RTR_FLAG | CAN_EFF_MASK);
522	
523	    setsockopt(s, SOL_CAN_RAW, CAN_RAW_FILTER, &rfilter, sizeof(rfilter));
524	
525	
526	RAW Socket Option CAN_RAW_ERR_FILTER
527	~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
528	
529	As described in :ref:`socketcan-network-problem-notifications` the CAN interface driver can generate so
530	called Error Message Frames that can optionally be passed to the user
531	application in the same way as other CAN frames. The possible
532	errors are divided into different error classes that may be filtered
533	using the appropriate error mask. To register for every possible
534	error condition CAN_ERR_MASK can be used as value for the error mask.
535	The values for the error mask are defined in linux/can/error.h:
536	
537	.. code-block:: C
538	
539	    can_err_mask_t err_mask = ( CAN_ERR_TX_TIMEOUT | CAN_ERR_BUSOFF );
540	
541	    setsockopt(s, SOL_CAN_RAW, CAN_RAW_ERR_FILTER,
542	               &err_mask, sizeof(err_mask));
543	
544	
545	RAW Socket Option CAN_RAW_LOOPBACK
546	~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
547	
548	To meet multi user needs the local loopback is enabled by default
549	(see :ref:`socketcan-local-loopback1` for details). But in some embedded use-cases
550	(e.g. when only one application uses the CAN bus) this loopback
551	functionality can be disabled (separately for each socket):
552	
553	.. code-block:: C
554	
555	    int loopback = 0; /* 0 = disabled, 1 = enabled (default) */
556	
557	    setsockopt(s, SOL_CAN_RAW, CAN_RAW_LOOPBACK, &loopback, sizeof(loopback));
558	
559	
560	RAW socket option CAN_RAW_RECV_OWN_MSGS
561	~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
562	
563	When the local loopback is enabled, all the sent CAN frames are
564	looped back to the open CAN sockets that registered for the CAN
565	frames' CAN-ID on this given interface to meet the multi user
566	needs. The reception of the CAN frames on the same socket that was
567	sending the CAN frame is assumed to be unwanted and therefore
568	disabled by default. This default behaviour may be changed on
569	demand:
570	
571	.. code-block:: C
572	
573	    int recv_own_msgs = 1; /* 0 = disabled (default), 1 = enabled */
574	
575	    setsockopt(s, SOL_CAN_RAW, CAN_RAW_RECV_OWN_MSGS,
576	               &recv_own_msgs, sizeof(recv_own_msgs));
577	
578	
579	.. _socketcan-rawfd:
580	
581	RAW Socket Option CAN_RAW_FD_FRAMES
582	~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
583	
584	CAN FD support in CAN_RAW sockets can be enabled with a new socket option
585	CAN_RAW_FD_FRAMES which is off by default. When the new socket option is
586	not supported by the CAN_RAW socket (e.g. on older kernels), switching the
587	CAN_RAW_FD_FRAMES option returns the error -ENOPROTOOPT.
588	
589	Once CAN_RAW_FD_FRAMES is enabled the application can send both CAN frames
590	and CAN FD frames. OTOH the application has to handle CAN and CAN FD frames
591	when reading from the socket:
592	
593	.. code-block:: C
594	
595	    CAN_RAW_FD_FRAMES enabled:  CAN_MTU and CANFD_MTU are allowed
596	    CAN_RAW_FD_FRAMES disabled: only CAN_MTU is allowed (default)
597	
598	Example:
599	
600	.. code-block:: C
601	
602	    [ remember: CANFD_MTU == sizeof(struct canfd_frame) ]
603	
604	    struct canfd_frame cfd;
605	
606	    nbytes = read(s, &cfd, CANFD_MTU);
607	
608	    if (nbytes == CANFD_MTU) {
609	            printf("got CAN FD frame with length %d\n", cfd.len);
610	            /* cfd.flags contains valid data */
611	    } else if (nbytes == CAN_MTU) {
612	            printf("got legacy CAN frame with length %d\n", cfd.len);
613	            /* cfd.flags is undefined */
614	    } else {
615	            fprintf(stderr, "read: invalid CAN(FD) frame\n");
616	            return 1;
617	    }
618	
619	    /* the content can be handled independently from the received MTU size */
620	
621	    printf("can_id: %X data length: %d data: ", cfd.can_id, cfd.len);
622	    for (i = 0; i < cfd.len; i++)
623	            printf("%02X ", cfd.data[i]);
624	
625	When reading with size CANFD_MTU only returns CAN_MTU bytes that have
626	been received from the socket a legacy CAN frame has been read into the
627	provided CAN FD structure. Note that the canfd_frame.flags data field is
628	not specified in the struct can_frame and therefore it is only valid in
629	CANFD_MTU sized CAN FD frames.
630	
631	Implementation hint for new CAN applications:
632	
633	To build a CAN FD aware application use struct canfd_frame as basic CAN
634	data structure for CAN_RAW based applications. When the application is
635	executed on an older Linux kernel and switching the CAN_RAW_FD_FRAMES
636	socket option returns an error: No problem. You'll get legacy CAN frames
637	or CAN FD frames and can process them the same way.
638	
639	When sending to CAN devices make sure that the device is capable to handle
640	CAN FD frames by checking if the device maximum transfer unit is CANFD_MTU.
641	The CAN device MTU can be retrieved e.g. with a SIOCGIFMTU ioctl() syscall.
642	
643	
644	RAW socket option CAN_RAW_JOIN_FILTERS
645	~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
646	
647	The CAN_RAW socket can set multiple CAN identifier specific filters that
648	lead to multiple filters in the af_can.c filter processing. These filters
649	are indenpendent from each other which leads to logical OR'ed filters when
650	applied (see :ref:`socketcan-rawfilter`).
651	
652	This socket option joines the given CAN filters in the way that only CAN
653	frames are passed to user space that matched *all* given CAN filters. The
654	semantic for the applied filters is therefore changed to a logical AND.
655	
656	This is useful especially when the filterset is a combination of filters
657	where the CAN_INV_FILTER flag is set in order to notch single CAN IDs or
658	CAN ID ranges from the incoming traffic.
659	
660	
661	RAW Socket Returned Message Flags
662	~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
663	
664	When using recvmsg() call, the msg->msg_flags may contain following flags:
665	
666	MSG_DONTROUTE:
667		set when the received frame was created on the local host.
668	
669	MSG_CONFIRM:
670		set when the frame was sent via the socket it is received on.
671		This flag can be interpreted as a 'transmission confirmation' when the
672		CAN driver supports the echo of frames on driver level, see
673		:ref:`socketcan-local-loopback1` and :ref:`socketcan-local-loopback2`.
674		In order to receive such messages, CAN_RAW_RECV_OWN_MSGS must be set.
675	
676	
677	Broadcast Manager Protocol Sockets (SOCK_DGRAM)
678	-----------------------------------------------
679	
680	The Broadcast Manager protocol provides a command based configuration
681	interface to filter and send (e.g. cyclic) CAN messages in kernel space.
682	
683	Receive filters can be used to down sample frequent messages; detect events
684	such as message contents changes, packet length changes, and do time-out
685	monitoring of received messages.
686	
687	Periodic transmission tasks of CAN frames or a sequence of CAN frames can be
688	created and modified at runtime; both the message content and the two
689	possible transmit intervals can be altered.
690	
691	A BCM socket is not intended for sending individual CAN frames using the
692	struct can_frame as known from the CAN_RAW socket. Instead a special BCM
693	configuration message is defined. The basic BCM configuration message used
694	to communicate with the broadcast manager and the available operations are
695	defined in the linux/can/bcm.h include. The BCM message consists of a
696	message header with a command ('opcode') followed by zero or more CAN frames.
697	The broadcast manager sends responses to user space in the same form:
698	
699	.. code-block:: C
700	
701	    struct bcm_msg_head {
702	            __u32 opcode;                   /* command */
703	            __u32 flags;                    /* special flags */
704	            __u32 count;                    /* run 'count' times with ival1 */
705	            struct timeval ival1, ival2;    /* count and subsequent interval */
706	            canid_t can_id;                 /* unique can_id for task */
707	            __u32 nframes;                  /* number of can_frames following */
708	            struct can_frame frames[0];
709	    };
710	
711	The aligned payload 'frames' uses the same basic CAN frame structure defined
712	at the beginning of :ref:`socketcan-rawfd` and in the include/linux/can.h include. All
713	messages to the broadcast manager from user space have this structure.
714	
715	Note a CAN_BCM socket must be connected instead of bound after socket
716	creation (example without error checking):
717	
718	.. code-block:: C
719	
720	    int s;
721	    struct sockaddr_can addr;
722	    struct ifreq ifr;
723	
724	    s = socket(PF_CAN, SOCK_DGRAM, CAN_BCM);
725	
726	    strcpy(ifr.ifr_name, "can0");
727	    ioctl(s, SIOCGIFINDEX, &ifr);
728	
729	    addr.can_family = AF_CAN;
730	    addr.can_ifindex = ifr.ifr_ifindex;
731	
732	    connect(s, (struct sockaddr *)&addr, sizeof(addr));
733	
734	    (..)
735	
736	The broadcast manager socket is able to handle any number of in flight
737	transmissions or receive filters concurrently. The different RX/TX jobs are
738	distinguished by the unique can_id in each BCM message. However additional
739	CAN_BCM sockets are recommended to communicate on multiple CAN interfaces.
740	When the broadcast manager socket is bound to 'any' CAN interface (=> the
741	interface index is set to zero) the configured receive filters apply to any
742	CAN interface unless the sendto() syscall is used to overrule the 'any' CAN
743	interface index. When using recvfrom() instead of read() to retrieve BCM
744	socket messages the originating CAN interface is provided in can_ifindex.
745	
746	
747	Broadcast Manager Operations
748	~~~~~~~~~~~~~~~~~~~~~~~~~~~~
749	
750	The opcode defines the operation for the broadcast manager to carry out,
751	or details the broadcast managers response to several events, including
752	user requests.
753	
754	Transmit Operations (user space to broadcast manager):
755	
756	TX_SETUP:
757		Create (cyclic) transmission task.
758	
759	TX_DELETE:
760		Remove (cyclic) transmission task, requires only can_id.
761	
762	TX_READ:
763		Read properties of (cyclic) transmission task for can_id.
764	
765	TX_SEND:
766		Send one CAN frame.
767	
768	Transmit Responses (broadcast manager to user space):
769	
770	TX_STATUS:
771		Reply to TX_READ request (transmission task configuration).
772	
773	TX_EXPIRED:
774		Notification when counter finishes sending at initial interval
775		'ival1'. Requires the TX_COUNTEVT flag to be set at TX_SETUP.
776	
777	Receive Operations (user space to broadcast manager):
778	
779	RX_SETUP:
780		Create RX content filter subscription.
781	
782	RX_DELETE:
783		Remove RX content filter subscription, requires only can_id.
784	
785	RX_READ:
786		Read properties of RX content filter subscription for can_id.
787	
788	Receive Responses (broadcast manager to user space):
789	
790	RX_STATUS:
791		Reply to RX_READ request (filter task configuration).
792	
793	RX_TIMEOUT:
794		Cyclic message is detected to be absent (timer ival1 expired).
795	
796	RX_CHANGED:
797		BCM message with updated CAN frame (detected content change).
798		Sent on first message received or on receipt of revised CAN messages.
799	
800	
801	Broadcast Manager Message Flags
802	~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
803	
804	When sending a message to the broadcast manager the 'flags' element may
805	contain the following flag definitions which influence the behaviour:
806	
807	SETTIMER:
808		Set the values of ival1, ival2 and count
809	
810	STARTTIMER:
811		Start the timer with the actual values of ival1, ival2
812		and count. Starting the timer leads simultaneously to emit a CAN frame.
813	
814	TX_COUNTEVT:
815		Create the message TX_EXPIRED when count expires
816	
817	TX_ANNOUNCE:
818		A change of data by the process is emitted immediately.
819	
820	TX_CP_CAN_ID:
821		Copies the can_id from the message header to each
822		subsequent frame in frames. This is intended as usage simplification. For
823		TX tasks the unique can_id from the message header may differ from the
824		can_id(s) stored for transmission in the subsequent struct can_frame(s).
825	
826	RX_FILTER_ID:
827		Filter by can_id alone, no frames required (nframes=0).
828	
829	RX_CHECK_DLC:
830		A change of the DLC leads to an RX_CHANGED.
831	
832	RX_NO_AUTOTIMER:
833		Prevent automatically starting the timeout monitor.
834	
835	RX_ANNOUNCE_RESUME:
836		If passed at RX_SETUP and a receive timeout occurred, a
837		RX_CHANGED message will be generated when the (cyclic) receive restarts.
838	
839	TX_RESET_MULTI_IDX:
840		Reset the index for the multiple frame transmission.
841	
842	RX_RTR_FRAME:
843		Send reply for RTR-request (placed in op->frames[0]).
844	
845	
846	Broadcast Manager Transmission Timers
847	~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
848	
849	Periodic transmission configurations may use up to two interval timers.
850	In this case the BCM sends a number of messages ('count') at an interval
851	'ival1', then continuing to send at another given interval 'ival2'. When
852	only one timer is needed 'count' is set to zero and only 'ival2' is used.
853	When SET_TIMER and START_TIMER flag were set the timers are activated.
854	The timer values can be altered at runtime when only SET_TIMER is set.
855	
856	
857	Broadcast Manager message sequence transmission
858	~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
859	
860	Up to 256 CAN frames can be transmitted in a sequence in the case of a cyclic
861	TX task configuration. The number of CAN frames is provided in the 'nframes'
862	element of the BCM message head. The defined number of CAN frames are added
863	as array to the TX_SETUP BCM configuration message:
864	
865	.. code-block:: C
866	
867	    /* create a struct to set up a sequence of four CAN frames */
868	    struct {
869	            struct bcm_msg_head msg_head;
870	            struct can_frame frame[4];
871	    } mytxmsg;
872	
873	    (..)
874	    mytxmsg.msg_head.nframes = 4;
875	    (..)
876	
877	    write(s, &mytxmsg, sizeof(mytxmsg));
878	
879	With every transmission the index in the array of CAN frames is increased
880	and set to zero at index overflow.
881	
882	
883	Broadcast Manager Receive Filter Timers
884	~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
885	
886	The timer values ival1 or ival2 may be set to non-zero values at RX_SETUP.
887	When the SET_TIMER flag is set the timers are enabled:
888	
889	ival1:
890		Send RX_TIMEOUT when a received message is not received again within
891		the given time. When START_TIMER is set at RX_SETUP the timeout detection
892		is activated directly - even without a former CAN frame reception.
893	
894	ival2:
895		Throttle the received message rate down to the value of ival2. This
896		is useful to reduce messages for the application when the signal inside the
897		CAN frame is stateless as state changes within the ival2 periode may get
898		lost.
899	
900	Broadcast Manager Multiplex Message Receive Filter
901	~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
902	
903	To filter for content changes in multiplex message sequences an array of more
904	than one CAN frames can be passed in a RX_SETUP configuration message. The
905	data bytes of the first CAN frame contain the mask of relevant bits that
906	have to match in the subsequent CAN frames with the received CAN frame.
907	If one of the subsequent CAN frames is matching the bits in that frame data
908	mark the relevant content to be compared with the previous received content.
909	Up to 257 CAN frames (multiplex filter bit mask CAN frame plus 256 CAN
910	filters) can be added as array to the TX_SETUP BCM configuration message:
911	
912	.. code-block:: C
913	
914	    /* usually used to clear CAN frame data[] - beware of endian problems! */
915	    #define U64_DATA(p) (*(unsigned long long*)(p)->data)
916	
917	    struct {
918	            struct bcm_msg_head msg_head;
919	            struct can_frame frame[5];
920	    } msg;
921	
922	    msg.msg_head.opcode  = RX_SETUP;
923	    msg.msg_head.can_id  = 0x42;
924	    msg.msg_head.flags   = 0;
925	    msg.msg_head.nframes = 5;
926	    U64_DATA(&msg.frame[0]) = 0xFF00000000000000ULL; /* MUX mask */
927	    U64_DATA(&msg.frame[1]) = 0x01000000000000FFULL; /* data mask (MUX 0x01) */
928	    U64_DATA(&msg.frame[2]) = 0x0200FFFF000000FFULL; /* data mask (MUX 0x02) */
929	    U64_DATA(&msg.frame[3]) = 0x330000FFFFFF0003ULL; /* data mask (MUX 0x33) */
930	    U64_DATA(&msg.frame[4]) = 0x4F07FC0FF0000000ULL; /* data mask (MUX 0x4F) */
931	
932	    write(s, &msg, sizeof(msg));
933	
934	
935	Broadcast Manager CAN FD Support
936	~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
937	
938	The programming API of the CAN_BCM depends on struct can_frame which is
939	given as array directly behind the bcm_msg_head structure. To follow this
940	schema for the CAN FD frames a new flag 'CAN_FD_FRAME' in the bcm_msg_head
941	flags indicates that the concatenated CAN frame structures behind the
942	bcm_msg_head are defined as struct canfd_frame:
943	
944	.. code-block:: C
945	
946	    struct {
947	            struct bcm_msg_head msg_head;
948	            struct canfd_frame frame[5];
949	    } msg;
950	
951	    msg.msg_head.opcode  = RX_SETUP;
952	    msg.msg_head.can_id  = 0x42;
953	    msg.msg_head.flags   = CAN_FD_FRAME;
954	    msg.msg_head.nframes = 5;
955	    (..)
956	
957	When using CAN FD frames for multiplex filtering the MUX mask is still
958	expected in the first 64 bit of the struct canfd_frame data section.
959	
960	
961	Connected Transport Protocols (SOCK_SEQPACKET)
962	----------------------------------------------
963	
964	(to be written)
965	
966	
967	Unconnected Transport Protocols (SOCK_DGRAM)
968	--------------------------------------------
969	
970	(to be written)
971	
972	
973	.. _socketcan-core-module:
974	
975	SocketCAN Core Module
976	=====================
977	
978	The SocketCAN core module implements the protocol family
979	PF_CAN. CAN protocol modules are loaded by the core module at
980	runtime. The core module provides an interface for CAN protocol
981	modules to subscribe needed CAN IDs (see :ref:`socketcan-receive-lists`).
982	
983	
984	can.ko Module Params
985	--------------------
986	
987	- **stats_timer**:
988	  To calculate the SocketCAN core statistics
989	  (e.g. current/maximum frames per second) this 1 second timer is
990	  invoked at can.ko module start time by default. This timer can be
991	  disabled by using stattimer=0 on the module commandline.
992	
993	- **debug**:
994	  (removed since SocketCAN SVN r546)
995	
996	
997	procfs content
998	--------------
999	
1000	As described in :ref:`socketcan-receive-lists` the SocketCAN core uses several filter
1001	lists to deliver received CAN frames to CAN protocol modules. These
1002	receive lists, their filters and the count of filter matches can be
1003	checked in the appropriate receive list. All entries contain the
1004	device and a protocol module identifier::
1005	
1006	    foo@bar:~$ cat /proc/net/can/rcvlist_all
1007	
1008	    receive list 'rx_all':
1009	      (vcan3: no entry)
1010	      (vcan2: no entry)
1011	      (vcan1: no entry)
1012	      device   can_id   can_mask  function  userdata   matches  ident
1013	       vcan0     000    00000000  f88e6370  f6c6f400         0  raw
1014	      (any: no entry)
1015	
1016	In this example an application requests any CAN traffic from vcan0::
1017	
1018	    rcvlist_all - list for unfiltered entries (no filter operations)
1019	    rcvlist_eff - list for single extended frame (EFF) entries
1020	    rcvlist_err - list for error message frames masks
1021	    rcvlist_fil - list for mask/value filters
1022	    rcvlist_inv - list for mask/value filters (inverse semantic)
1023	    rcvlist_sff - list for single standard frame (SFF) entries
1024	
1025	Additional procfs files in /proc/net/can::
1026	
1027	    stats       - SocketCAN core statistics (rx/tx frames, match ratios, ...)
1028	    reset_stats - manual statistic reset
1029	    version     - prints the SocketCAN core version and the ABI version
1030	
1031	
1032	Writing Own CAN Protocol Modules
1033	--------------------------------
1034	
1035	To implement a new protocol in the protocol family PF_CAN a new
1036	protocol has to be defined in include/linux/can.h .
1037	The prototypes and definitions to use the SocketCAN core can be
1038	accessed by including include/linux/can/core.h .
1039	In addition to functions that register the CAN protocol and the
1040	CAN device notifier chain there are functions to subscribe CAN
1041	frames received by CAN interfaces and to send CAN frames::
1042	
1043	    can_rx_register   - subscribe CAN frames from a specific interface
1044	    can_rx_unregister - unsubscribe CAN frames from a specific interface
1045	    can_send          - transmit a CAN frame (optional with local loopback)
1046	
1047	For details see the kerneldoc documentation in net/can/af_can.c or
1048	the source code of net/can/raw.c or net/can/bcm.c .
1049	
1050	
1051	CAN Network Drivers
1052	===================
1053	
1054	Writing a CAN network device driver is much easier than writing a
1055	CAN character device driver. Similar to other known network device
1056	drivers you mainly have to deal with:
1057	
1058	- TX: Put the CAN frame from the socket buffer to the CAN controller.
1059	- RX: Put the CAN frame from the CAN controller to the socket buffer.
1060	
1061	See e.g. at Documentation/networking/netdevices.txt . The differences
1062	for writing CAN network device driver are described below:
1063	
1064	
1065	General Settings
1066	----------------
1067	
1068	.. code-block:: C
1069	
1070	    dev->type  = ARPHRD_CAN; /* the netdevice hardware type */
1071	    dev->flags = IFF_NOARP;  /* CAN has no arp */
1072	
1073	    dev->mtu = CAN_MTU; /* sizeof(struct can_frame) -> legacy CAN interface */
1074	
1075	    or alternative, when the controller supports CAN with flexible data rate:
1076	    dev->mtu = CANFD_MTU; /* sizeof(struct canfd_frame) -> CAN FD interface */
1077	
1078	The struct can_frame or struct canfd_frame is the payload of each socket
1079	buffer (skbuff) in the protocol family PF_CAN.
1080	
1081	
1082	.. _socketcan-local-loopback2:
1083	
1084	Local Loopback of Sent Frames
1085	-----------------------------
1086	
1087	As described in :ref:`socketcan-local-loopback1` the CAN network device driver should
1088	support a local loopback functionality similar to the local echo
1089	e.g. of tty devices. In this case the driver flag IFF_ECHO has to be
1090	set to prevent the PF_CAN core from locally echoing sent frames
1091	(aka loopback) as fallback solution::
1092	
1093	    dev->flags = (IFF_NOARP | IFF_ECHO);
1094	
1095	
1096	CAN Controller Hardware Filters
1097	-------------------------------
1098	
1099	To reduce the interrupt load on deep embedded systems some CAN
1100	controllers support the filtering of CAN IDs or ranges of CAN IDs.
1101	These hardware filter capabilities vary from controller to
1102	controller and have to be identified as not feasible in a multi-user
1103	networking approach. The use of the very controller specific
1104	hardware filters could make sense in a very dedicated use-case, as a
1105	filter on driver level would affect all users in the multi-user
1106	system. The high efficient filter sets inside the PF_CAN core allow
1107	to set different multiple filters for each socket separately.
1108	Therefore the use of hardware filters goes to the category 'handmade
1109	tuning on deep embedded systems'. The author is running a MPC603e
1110	@133MHz with four SJA1000 CAN controllers from 2002 under heavy bus
1111	load without any problems ...
1112	
1113	
1114	The Virtual CAN Driver (vcan)
1115	-----------------------------
1116	
1117	Similar to the network loopback devices, vcan offers a virtual local
1118	CAN interface. A full qualified address on CAN consists of
1119	
1120	- a unique CAN Identifier (CAN ID)
1121	- the CAN bus this CAN ID is transmitted on (e.g. can0)
1122	
1123	so in common use cases more than one virtual CAN interface is needed.
1124	
1125	The virtual CAN interfaces allow the transmission and reception of CAN
1126	frames without real CAN controller hardware. Virtual CAN network
1127	devices are usually named 'vcanX', like vcan0 vcan1 vcan2 ...
1128	When compiled as a module the virtual CAN driver module is called vcan.ko
1129	
1130	Since Linux Kernel version 2.6.24 the vcan driver supports the Kernel
1131	netlink interface to create vcan network devices. The creation and
1132	removal of vcan network devices can be managed with the ip(8) tool::
1133	
1134	  - Create a virtual CAN network interface:
1135	       $ ip link add type vcan
1136	
1137	  - Create a virtual CAN network interface with a specific name 'vcan42':
1138	       $ ip link add dev vcan42 type vcan
1139	
1140	  - Remove a (virtual CAN) network interface 'vcan42':
1141	       $ ip link del vcan42
1142	
1143	
1144	The CAN Network Device Driver Interface
1145	---------------------------------------
1146	
1147	The CAN network device driver interface provides a generic interface
1148	to setup, configure and monitor CAN network devices. The user can then
1149	configure the CAN device, like setting the bit-timing parameters, via
1150	the netlink interface using the program "ip" from the "IPROUTE2"
1151	utility suite. The following chapter describes briefly how to use it.
1152	Furthermore, the interface uses a common data structure and exports a
1153	set of common functions, which all real CAN network device drivers
1154	should use. Please have a look to the SJA1000 or MSCAN driver to
1155	understand how to use them. The name of the module is can-dev.ko.
1156	
1157	
1158	Netlink interface to set/get devices properties
1159	~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1160	
1161	The CAN device must be configured via netlink interface. The supported
1162	netlink message types are defined and briefly described in
1163	"include/linux/can/netlink.h". CAN link support for the program "ip"
1164	of the IPROUTE2 utility suite is available and it can be used as shown
1165	below:
1166	
1167	Setting CAN device properties::
1168	
1169	    $ ip link set can0 type can help
1170	    Usage: ip link set DEVICE type can
1171	        [ bitrate BITRATE [ sample-point SAMPLE-POINT] ] |
1172	        [ tq TQ prop-seg PROP_SEG phase-seg1 PHASE-SEG1
1173	          phase-seg2 PHASE-SEG2 [ sjw SJW ] ]
1174	
1175	        [ dbitrate BITRATE [ dsample-point SAMPLE-POINT] ] |
1176	        [ dtq TQ dprop-seg PROP_SEG dphase-seg1 PHASE-SEG1
1177	          dphase-seg2 PHASE-SEG2 [ dsjw SJW ] ]
1178	
1179	        [ loopback { on | off } ]
1180	        [ listen-only { on | off } ]
1181	        [ triple-sampling { on | off } ]
1182	        [ one-shot { on | off } ]
1183	        [ berr-reporting { on | off } ]
1184	        [ fd { on | off } ]
1185	        [ fd-non-iso { on | off } ]
1186	        [ presume-ack { on | off } ]
1187	
1188	        [ restart-ms TIME-MS ]
1189	        [ restart ]
1190	
1191	        Where: BITRATE       := { 1..1000000 }
1192	               SAMPLE-POINT  := { 0.000..0.999 }
1193	               TQ            := { NUMBER }
1194	               PROP-SEG      := { 1..8 }
1195	               PHASE-SEG1    := { 1..8 }
1196	               PHASE-SEG2    := { 1..8 }
1197	               SJW           := { 1..4 }
1198	               RESTART-MS    := { 0 | NUMBER }
1199	
1200	Display CAN device details and statistics::
1201	
1202	    $ ip -details -statistics link show can0
1203	    2: can0: <NOARP,UP,LOWER_UP,ECHO> mtu 16 qdisc pfifo_fast state UP qlen 10
1204	      link/can
1205	      can <TRIPLE-SAMPLING> state ERROR-ACTIVE restart-ms 100
1206	      bitrate 125000 sample_point 0.875
1207	      tq 125 prop-seg 6 phase-seg1 7 phase-seg2 2 sjw 1
1208	      sja1000: tseg1 1..16 tseg2 1..8 sjw 1..4 brp 1..64 brp-inc 1
1209	      clock 8000000
1210	      re-started bus-errors arbit-lost error-warn error-pass bus-off
1211	      41         17457      0          41         42         41
1212	      RX: bytes  packets  errors  dropped overrun mcast
1213	      140859     17608    17457   0       0       0
1214	      TX: bytes  packets  errors  dropped carrier collsns
1215	      861        112      0       41      0       0
1216	
1217	More info to the above output:
1218	
1219	"<TRIPLE-SAMPLING>"
1220		Shows the list of selected CAN controller modes: LOOPBACK,
1221		LISTEN-ONLY, or TRIPLE-SAMPLING.
1222	
1223	"state ERROR-ACTIVE"
1224		The current state of the CAN controller: "ERROR-ACTIVE",
1225		"ERROR-WARNING", "ERROR-PASSIVE", "BUS-OFF" or "STOPPED"
1226	
1227	"restart-ms 100"
1228		Automatic restart delay time. If set to a non-zero value, a
1229		restart of the CAN controller will be triggered automatically
1230		in case of a bus-off condition after the specified delay time
1231		in milliseconds. By default it's off.
1232	
1233	"bitrate 125000 sample-point 0.875"
1234		Shows the real bit-rate in bits/sec and the sample-point in the
1235		range 0.000..0.999. If the calculation of bit-timing parameters
1236		is enabled in the kernel (CONFIG_CAN_CALC_BITTIMING=y), the
1237		bit-timing can be defined by setting the "bitrate" argument.
1238		Optionally the "sample-point" can be specified. By default it's
1239		0.000 assuming CIA-recommended sample-points.
1240	
1241	"tq 125 prop-seg 6 phase-seg1 7 phase-seg2 2 sjw 1"
1242		Shows the time quanta in ns, propagation segment, phase buffer
1243		segment 1 and 2 and the synchronisation jump width in units of
1244		tq. They allow to define the CAN bit-timing in a hardware
1245		independent format as proposed by the Bosch CAN 2.0 spec (see
1246		chapter 8 of http://www.semiconductors.bosch.de/pdf/can2spec.pdf).
1247	
1248	"sja1000: tseg1 1..16 tseg2 1..8 sjw 1..4 brp 1..64 brp-inc 1 clock 8000000"
1249		Shows the bit-timing constants of the CAN controller, here the
1250		"sja1000". The minimum and maximum values of the time segment 1
1251		and 2, the synchronisation jump width in units of tq, the
1252		bitrate pre-scaler and the CAN system clock frequency in Hz.
1253		These constants could be used for user-defined (non-standard)
1254		bit-timing calculation algorithms in user-space.
1255	
1256	"re-started bus-errors arbit-lost error-warn error-pass bus-off"
1257		Shows the number of restarts, bus and arbitration lost errors,
1258		and the state changes to the error-warning, error-passive and
1259		bus-off state. RX overrun errors are listed in the "overrun"
1260		field of the standard network statistics.
1261	
1262	Setting the CAN Bit-Timing
1263	~~~~~~~~~~~~~~~~~~~~~~~~~~
1264	
1265	The CAN bit-timing parameters can always be defined in a hardware
1266	independent format as proposed in the Bosch CAN 2.0 specification
1267	specifying the arguments "tq", "prop_seg", "phase_seg1", "phase_seg2"
1268	and "sjw"::
1269	
1270	    $ ip link set canX type can tq 125 prop-seg 6 \
1271					phase-seg1 7 phase-seg2 2 sjw 1
1272	
1273	If the kernel option CONFIG_CAN_CALC_BITTIMING is enabled, CIA
1274	recommended CAN bit-timing parameters will be calculated if the bit-
1275	rate is specified with the argument "bitrate"::
1276	
1277	    $ ip link set canX type can bitrate 125000
1278	
1279	Note that this works fine for the most common CAN controllers with
1280	standard bit-rates but may *fail* for exotic bit-rates or CAN system
1281	clock frequencies. Disabling CONFIG_CAN_CALC_BITTIMING saves some
1282	space and allows user-space tools to solely determine and set the
1283	bit-timing parameters. The CAN controller specific bit-timing
1284	constants can be used for that purpose. They are listed by the
1285	following command::
1286	
1287	    $ ip -details link show can0
1288	    ...
1289	      sja1000: clock 8000000 tseg1 1..16 tseg2 1..8 sjw 1..4 brp 1..64 brp-inc 1
1290	
1291	
1292	Starting and Stopping the CAN Network Device
1293	~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1294	
1295	A CAN network device is started or stopped as usual with the command
1296	"ifconfig canX up/down" or "ip link set canX up/down". Be aware that
1297	you *must* define proper bit-timing parameters for real CAN devices
1298	before you can start it to avoid error-prone default settings::
1299	
1300	    $ ip link set canX up type can bitrate 125000
1301	
1302	A device may enter the "bus-off" state if too many errors occurred on
1303	the CAN bus. Then no more messages are received or sent. An automatic
1304	bus-off recovery can be enabled by setting the "restart-ms" to a
1305	non-zero value, e.g.::
1306	
1307	    $ ip link set canX type can restart-ms 100
1308	
1309	Alternatively, the application may realize the "bus-off" condition
1310	by monitoring CAN error message frames and do a restart when
1311	appropriate with the command::
1312	
1313	    $ ip link set canX type can restart
1314	
1315	Note that a restart will also create a CAN error message frame (see
1316	also :ref:`socketcan-network-problem-notifications`).
1317	
1318	
1319	.. _socketcan-can-fd-driver:
1320	
1321	CAN FD (Flexible Data Rate) Driver Support
1322	------------------------------------------
1323	
1324	CAN FD capable CAN controllers support two different bitrates for the
1325	arbitration phase and the payload phase of the CAN FD frame. Therefore a
1326	second bit timing has to be specified in order to enable the CAN FD bitrate.
1327	
1328	Additionally CAN FD capable CAN controllers support up to 64 bytes of
1329	payload. The representation of this length in can_frame.can_dlc and
1330	canfd_frame.len for userspace applications and inside the Linux network
1331	layer is a plain value from 0 .. 64 instead of the CAN 'data length code'.
1332	The data length code was a 1:1 mapping to the payload length in the legacy
1333	CAN frames anyway. The payload length to the bus-relevant DLC mapping is
1334	only performed inside the CAN drivers, preferably with the helper
1335	functions can_dlc2len() and can_len2dlc().
1336	
1337	The CAN netdevice driver capabilities can be distinguished by the network
1338	devices maximum transfer unit (MTU)::
1339	
1340	  MTU = 16 (CAN_MTU)   => sizeof(struct can_frame)   => 'legacy' CAN device
1341	  MTU = 72 (CANFD_MTU) => sizeof(struct canfd_frame) => CAN FD capable device
1342	
1343	The CAN device MTU can be retrieved e.g. with a SIOCGIFMTU ioctl() syscall.
1344	N.B. CAN FD capable devices can also handle and send legacy CAN frames.
1345	
1346	When configuring CAN FD capable CAN controllers an additional 'data' bitrate
1347	has to be set. This bitrate for the data phase of the CAN FD frame has to be
1348	at least the bitrate which was configured for the arbitration phase. This
1349	second bitrate is specified analogue to the first bitrate but the bitrate
1350	setting keywords for the 'data' bitrate start with 'd' e.g. dbitrate,
1351	dsample-point, dsjw or dtq and similar settings. When a data bitrate is set
1352	within the configuration process the controller option "fd on" can be
1353	specified to enable the CAN FD mode in the CAN controller. This controller
1354	option also switches the device MTU to 72 (CANFD_MTU).
1355	
1356	The first CAN FD specification presented as whitepaper at the International
1357	CAN Conference 2012 needed to be improved for data integrity reasons.
1358	Therefore two CAN FD implementations have to be distinguished today:
1359	
1360	- ISO compliant:     The ISO 11898-1:2015 CAN FD implementation (default)
1361	- non-ISO compliant: The CAN FD implementation following the 2012 whitepaper
1362	
1363	Finally there are three types of CAN FD controllers:
1364	
1365	1. ISO compliant (fixed)
1366	2. non-ISO compliant (fixed, like the M_CAN IP core v3.0.1 in m_can.c)
1367	3. ISO/non-ISO CAN FD controllers (switchable, like the PEAK PCAN-USB FD)
1368	
1369	The current ISO/non-ISO mode is announced by the CAN controller driver via
1370	netlink and displayed by the 'ip' tool (controller option FD-NON-ISO).
1371	The ISO/non-ISO-mode can be altered by setting 'fd-non-iso {on|off}' for
1372	switchable CAN FD controllers only.
1373	
1374	Example configuring 500 kbit/s arbitration bitrate and 4 Mbit/s data bitrate::
1375	
1376	    $ ip link set can0 up type can bitrate 500000 sample-point 0.75 \
1377	                                   dbitrate 4000000 dsample-point 0.8 fd on
1378	    $ ip -details link show can0
1379	    5: can0: <NOARP,UP,LOWER_UP,ECHO> mtu 72 qdisc pfifo_fast state UNKNOWN \
1380	             mode DEFAULT group default qlen 10
1381	    link/can  promiscuity 0
1382	    can <FD> state ERROR-ACTIVE (berr-counter tx 0 rx 0) restart-ms 0
1383	          bitrate 500000 sample-point 0.750
1384	          tq 50 prop-seg 14 phase-seg1 15 phase-seg2 10 sjw 1
1385	          pcan_usb_pro_fd: tseg1 1..64 tseg2 1..16 sjw 1..16 brp 1..1024 \
1386	          brp-inc 1
1387	          dbitrate 4000000 dsample-point 0.800
1388	          dtq 12 dprop-seg 7 dphase-seg1 8 dphase-seg2 4 dsjw 1
1389	          pcan_usb_pro_fd: dtseg1 1..16 dtseg2 1..8 dsjw 1..4 dbrp 1..1024 \
1390	          dbrp-inc 1
1391	          clock 80000000
1392	
1393	Example when 'fd-non-iso on' is added on this switchable CAN FD adapter::
1394	
1395	   can <FD,FD-NON-ISO> state ERROR-ACTIVE (berr-counter tx 0 rx 0) restart-ms 0
1396	
1397	
1398	Supported CAN Hardware
1399	----------------------
1400	
1401	Please check the "Kconfig" file in "drivers/net/can" to get an actual
1402	list of the support CAN hardware. On the SocketCAN project website
1403	(see :ref:`socketcan-resources`) there might be further drivers available, also for
1404	older kernel versions.
1405	
1406	
1407	.. _socketcan-resources:
1408	
1409	SocketCAN Resources
1410	===================
1411	
1412	The Linux CAN / SocketCAN project resources (project site / mailing list)
1413	are referenced in the MAINTAINERS file in the Linux source tree.
1414	Search for CAN NETWORK [LAYERS|DRIVERS].
1415	
1416	Credits
1417	=======
1418	
1419	- Oliver Hartkopp (PF_CAN core, filters, drivers, bcm, SJA1000 driver)
1420	- Urs Thuermann (PF_CAN core, kernel integration, socket interfaces, raw, vcan)
1421	- Jan Kizka (RT-SocketCAN core, Socket-API reconciliation)
1422	- Wolfgang Grandegger (RT-SocketCAN core & drivers, Raw Socket-API reviews, CAN device driver interface, MSCAN driver)
1423	- Robert Schwebel (design reviews, PTXdist integration)
1424	- Marc Kleine-Budde (design reviews, Kernel 2.6 cleanups, drivers)
1425	- Benedikt Spranger (reviews)
1426	- Thomas Gleixner (LKML reviews, coding style, posting hints)
1427	- Andrey Volkov (kernel subtree structure, ioctls, MSCAN driver)
1428	- Matthias Brukner (first SJA1000 CAN netdevice implementation Q2/2003)
1429	- Klaus Hitschler (PEAK driver integration)
1430	- Uwe Koppe (CAN netdevices with PF_PACKET approach)
1431	- Michael Schulze (driver layer loopback requirement, RT CAN drivers review)
1432	- Pavel Pisa (Bit-timing calculation)
1433	- Sascha Hauer (SJA1000 platform driver)
1434	- Sebastian Haas (SJA1000 EMS PCI driver)
1435	- Markus Plessing (SJA1000 EMS PCI driver)
1436	- Per Dalen (SJA1000 Kvaser PCI driver)
1437	- Sam Ravnborg (reviews, coding style, kbuild help)
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