]>
Commit | Line | Data |
---|---|---|
f7ab97f7 OH |
1 | ============================================================================ |
2 | ||
3 | can.txt | |
4 | ||
5 | Readme file for the Controller Area Network Protocol Family (aka Socket CAN) | |
6 | ||
7 | This file contains | |
8 | ||
9 | 1 Overview / What is Socket CAN | |
10 | ||
11 | 2 Motivation / Why using the socket API | |
12 | ||
13 | 3 Socket CAN concept | |
14 | 3.1 receive lists | |
15 | 3.2 local loopback of sent frames | |
16 | 3.3 network security issues (capabilities) | |
17 | 3.4 network problem notifications | |
18 | ||
19 | 4 How to use Socket CAN | |
20 | 4.1 RAW protocol sockets with can_filters (SOCK_RAW) | |
21 | 4.1.1 RAW socket option CAN_RAW_FILTER | |
22 | 4.1.2 RAW socket option CAN_RAW_ERR_FILTER | |
23 | 4.1.3 RAW socket option CAN_RAW_LOOPBACK | |
24 | 4.1.4 RAW socket option CAN_RAW_RECV_OWN_MSGS | |
25 | 4.2 Broadcast Manager protocol sockets (SOCK_DGRAM) | |
26 | 4.3 connected transport protocols (SOCK_SEQPACKET) | |
27 | 4.4 unconnected transport protocols (SOCK_DGRAM) | |
28 | ||
29 | 5 Socket CAN core module | |
30 | 5.1 can.ko module params | |
31 | 5.2 procfs content | |
32 | 5.3 writing own CAN protocol modules | |
33 | ||
34 | 6 CAN network drivers | |
35 | 6.1 general settings | |
36 | 6.2 local loopback of sent frames | |
37 | 6.3 CAN controller hardware filters | |
e5d23048 | 38 | 6.4 The virtual CAN driver (vcan) |
e20dad96 WG |
39 | 6.5 The CAN network device driver interface |
40 | 6.5.1 Netlink interface to set/get devices properties | |
41 | 6.5.2 Setting the CAN bit-timing | |
42 | 6.5.3 Starting and stopping the CAN network device | |
43 | 6.6 supported CAN hardware | |
f7ab97f7 | 44 | |
e20dad96 WG |
45 | 7 Socket CAN resources |
46 | ||
47 | 8 Credits | |
f7ab97f7 OH |
48 | |
49 | ============================================================================ | |
50 | ||
51 | 1. Overview / What is Socket CAN | |
52 | -------------------------------- | |
53 | ||
54 | The socketcan package is an implementation of CAN protocols | |
55 | (Controller Area Network) for Linux. CAN is a networking technology | |
56 | which has widespread use in automation, embedded devices, and | |
57 | automotive fields. While there have been other CAN implementations | |
58 | for Linux based on character devices, Socket CAN uses the Berkeley | |
59 | socket API, the Linux network stack and implements the CAN device | |
60 | drivers as network interfaces. The CAN socket API has been designed | |
61 | as similar as possible to the TCP/IP protocols to allow programmers, | |
62 | familiar with network programming, to easily learn how to use CAN | |
63 | sockets. | |
64 | ||
65 | 2. Motivation / Why using the socket API | |
66 | ---------------------------------------- | |
67 | ||
68 | There have been CAN implementations for Linux before Socket CAN so the | |
69 | question arises, why we have started another project. Most existing | |
70 | implementations come as a device driver for some CAN hardware, they | |
71 | are based on character devices and provide comparatively little | |
72 | functionality. Usually, there is only a hardware-specific device | |
73 | driver which provides a character device interface to send and | |
74 | receive raw CAN frames, directly to/from the controller hardware. | |
75 | Queueing of frames and higher-level transport protocols like ISO-TP | |
76 | have to be implemented in user space applications. Also, most | |
77 | character-device implementations support only one single process to | |
78 | open the device at a time, similar to a serial interface. Exchanging | |
79 | the CAN controller requires employment of another device driver and | |
80 | often the need for adaption of large parts of the application to the | |
81 | new driver's API. | |
82 | ||
83 | Socket CAN was designed to overcome all of these limitations. A new | |
84 | protocol family has been implemented which provides a socket interface | |
85 | to user space applications and which builds upon the Linux network | |
86 | layer, so to use all of the provided queueing functionality. A device | |
87 | driver for CAN controller hardware registers itself with the Linux | |
88 | network layer as a network device, so that CAN frames from the | |
89 | controller can be passed up to the network layer and on to the CAN | |
90 | protocol family module and also vice-versa. Also, the protocol family | |
91 | module provides an API for transport protocol modules to register, so | |
92 | that any number of transport protocols can be loaded or unloaded | |
93 | dynamically. In fact, the can core module alone does not provide any | |
94 | protocol and cannot be used without loading at least one additional | |
95 | protocol module. Multiple sockets can be opened at the same time, | |
96 | on different or the same protocol module and they can listen/send | |
97 | frames on different or the same CAN IDs. Several sockets listening on | |
98 | the same interface for frames with the same CAN ID are all passed the | |
99 | same received matching CAN frames. An application wishing to | |
100 | communicate using a specific transport protocol, e.g. ISO-TP, just | |
101 | selects that protocol when opening the socket, and then can read and | |
102 | write application data byte streams, without having to deal with | |
103 | CAN-IDs, frames, etc. | |
104 | ||
105 | Similar functionality visible from user-space could be provided by a | |
106 | character device, too, but this would lead to a technically inelegant | |
107 | solution for a couple of reasons: | |
108 | ||
109 | * Intricate usage. Instead of passing a protocol argument to | |
110 | socket(2) and using bind(2) to select a CAN interface and CAN ID, an | |
111 | application would have to do all these operations using ioctl(2)s. | |
112 | ||
113 | * Code duplication. A character device cannot make use of the Linux | |
114 | network queueing code, so all that code would have to be duplicated | |
115 | for CAN networking. | |
116 | ||
117 | * Abstraction. In most existing character-device implementations, the | |
118 | hardware-specific device driver for a CAN controller directly | |
119 | provides the character device for the application to work with. | |
120 | This is at least very unusual in Unix systems for both, char and | |
121 | block devices. For example you don't have a character device for a | |
122 | certain UART of a serial interface, a certain sound chip in your | |
123 | computer, a SCSI or IDE controller providing access to your hard | |
124 | disk or tape streamer device. Instead, you have abstraction layers | |
125 | which provide a unified character or block device interface to the | |
126 | application on the one hand, and a interface for hardware-specific | |
127 | device drivers on the other hand. These abstractions are provided | |
128 | by subsystems like the tty layer, the audio subsystem or the SCSI | |
129 | and IDE subsystems for the devices mentioned above. | |
130 | ||
131 | The easiest way to implement a CAN device driver is as a character | |
132 | device without such a (complete) abstraction layer, as is done by most | |
133 | existing drivers. The right way, however, would be to add such a | |
134 | layer with all the functionality like registering for certain CAN | |
135 | IDs, supporting several open file descriptors and (de)multiplexing | |
136 | CAN frames between them, (sophisticated) queueing of CAN frames, and | |
137 | providing an API for device drivers to register with. However, then | |
138 | it would be no more difficult, or may be even easier, to use the | |
139 | networking framework provided by the Linux kernel, and this is what | |
140 | Socket CAN does. | |
141 | ||
142 | The use of the networking framework of the Linux kernel is just the | |
143 | natural and most appropriate way to implement CAN for Linux. | |
144 | ||
145 | 3. Socket CAN concept | |
146 | --------------------- | |
147 | ||
148 | As described in chapter 2 it is the main goal of Socket CAN to | |
149 | provide a socket interface to user space applications which builds | |
150 | upon the Linux network layer. In contrast to the commonly known | |
151 | TCP/IP and ethernet networking, the CAN bus is a broadcast-only(!) | |
152 | medium that has no MAC-layer addressing like ethernet. The CAN-identifier | |
153 | (can_id) is used for arbitration on the CAN-bus. Therefore the CAN-IDs | |
154 | have to be chosen uniquely on the bus. When designing a CAN-ECU | |
155 | network the CAN-IDs are mapped to be sent by a specific ECU. | |
156 | For this reason a CAN-ID can be treated best as a kind of source address. | |
157 | ||
158 | 3.1 receive lists | |
159 | ||
160 | The network transparent access of multiple applications leads to the | |
161 | problem that different applications may be interested in the same | |
162 | CAN-IDs from the same CAN network interface. The Socket CAN core | |
163 | module - which implements the protocol family CAN - provides several | |
164 | high efficient receive lists for this reason. If e.g. a user space | |
165 | application opens a CAN RAW socket, the raw protocol module itself | |
166 | requests the (range of) CAN-IDs from the Socket CAN core that are | |
167 | requested by the user. The subscription and unsubscription of | |
168 | CAN-IDs can be done for specific CAN interfaces or for all(!) known | |
169 | CAN interfaces with the can_rx_(un)register() functions provided to | |
170 | CAN protocol modules by the SocketCAN core (see chapter 5). | |
171 | To optimize the CPU usage at runtime the receive lists are split up | |
172 | into several specific lists per device that match the requested | |
173 | filter complexity for a given use-case. | |
174 | ||
175 | 3.2 local loopback of sent frames | |
176 | ||
177 | As known from other networking concepts the data exchanging | |
178 | applications may run on the same or different nodes without any | |
179 | change (except for the according addressing information): | |
180 | ||
181 | ___ ___ ___ _______ ___ | |
182 | | _ | | _ | | _ | | _ _ | | _ | | |
183 | ||A|| ||B|| ||C|| ||A| |B|| ||C|| | |
184 | |___| |___| |___| |_______| |___| | |
185 | | | | | | | |
186 | -----------------(1)- CAN bus -(2)--------------- | |
187 | ||
188 | To ensure that application A receives the same information in the | |
189 | example (2) as it would receive in example (1) there is need for | |
190 | some kind of local loopback of the sent CAN frames on the appropriate | |
191 | node. | |
192 | ||
193 | The Linux network devices (by default) just can handle the | |
194 | transmission and reception of media dependent frames. Due to the | |
d9195881 | 195 | arbitration on the CAN bus the transmission of a low prio CAN-ID |
f7ab97f7 OH |
196 | may be delayed by the reception of a high prio CAN frame. To |
197 | reflect the correct* traffic on the node the loopback of the sent | |
198 | data has to be performed right after a successful transmission. If | |
199 | the CAN network interface is not capable of performing the loopback for | |
200 | some reason the SocketCAN core can do this task as a fallback solution. | |
201 | See chapter 6.2 for details (recommended). | |
202 | ||
203 | The loopback functionality is enabled by default to reflect standard | |
204 | networking behaviour for CAN applications. Due to some requests from | |
205 | the RT-SocketCAN group the loopback optionally may be disabled for each | |
206 | separate socket. See sockopts from the CAN RAW sockets in chapter 4.1. | |
207 | ||
208 | * = you really like to have this when you're running analyser tools | |
209 | like 'candump' or 'cansniffer' on the (same) node. | |
210 | ||
211 | 3.3 network security issues (capabilities) | |
212 | ||
213 | The Controller Area Network is a local field bus transmitting only | |
214 | broadcast messages without any routing and security concepts. | |
215 | In the majority of cases the user application has to deal with | |
216 | raw CAN frames. Therefore it might be reasonable NOT to restrict | |
217 | the CAN access only to the user root, as known from other networks. | |
218 | Since the currently implemented CAN_RAW and CAN_BCM sockets can only | |
219 | send and receive frames to/from CAN interfaces it does not affect | |
220 | security of others networks to allow all users to access the CAN. | |
221 | To enable non-root users to access CAN_RAW and CAN_BCM protocol | |
222 | sockets the Kconfig options CAN_RAW_USER and/or CAN_BCM_USER may be | |
223 | selected at kernel compile time. | |
224 | ||
225 | 3.4 network problem notifications | |
226 | ||
227 | The use of the CAN bus may lead to several problems on the physical | |
228 | and media access control layer. Detecting and logging of these lower | |
229 | layer problems is a vital requirement for CAN users to identify | |
230 | hardware issues on the physical transceiver layer as well as | |
231 | arbitration problems and error frames caused by the different | |
232 | ECUs. The occurrence of detected errors are important for diagnosis | |
233 | and have to be logged together with the exact timestamp. For this | |
234 | reason the CAN interface driver can generate so called Error Frames | |
235 | that can optionally be passed to the user application in the same | |
236 | way as other CAN frames. Whenever an error on the physical layer | |
237 | or the MAC layer is detected (e.g. by the CAN controller) the driver | |
238 | creates an appropriate error frame. Error frames can be requested by | |
239 | the user application using the common CAN filter mechanisms. Inside | |
240 | this filter definition the (interested) type of errors may be | |
241 | selected. The reception of error frames is disabled by default. | |
e20dad96 WG |
242 | The format of the CAN error frame is briefly decribed in the Linux |
243 | header file "include/linux/can/error.h". | |
f7ab97f7 OH |
244 | |
245 | 4. How to use Socket CAN | |
246 | ------------------------ | |
247 | ||
248 | Like TCP/IP, you first need to open a socket for communicating over a | |
249 | CAN network. Since Socket CAN implements a new protocol family, you | |
250 | need to pass PF_CAN as the first argument to the socket(2) system | |
251 | call. Currently, there are two CAN protocols to choose from, the raw | |
252 | socket protocol and the broadcast manager (BCM). So to open a socket, | |
253 | you would write | |
254 | ||
255 | s = socket(PF_CAN, SOCK_RAW, CAN_RAW); | |
256 | ||
257 | and | |
258 | ||
259 | s = socket(PF_CAN, SOCK_DGRAM, CAN_BCM); | |
260 | ||
261 | respectively. After the successful creation of the socket, you would | |
262 | normally use the bind(2) system call to bind the socket to a CAN | |
263 | interface (which is different from TCP/IP due to different addressing | |
264 | - see chapter 3). After binding (CAN_RAW) or connecting (CAN_BCM) | |
265 | the socket, you can read(2) and write(2) from/to the socket or use | |
266 | send(2), sendto(2), sendmsg(2) and the recv* counterpart operations | |
267 | on the socket as usual. There are also CAN specific socket options | |
268 | described below. | |
269 | ||
270 | The basic CAN frame structure and the sockaddr structure are defined | |
271 | in include/linux/can.h: | |
272 | ||
273 | struct can_frame { | |
274 | canid_t can_id; /* 32 bit CAN_ID + EFF/RTR/ERR flags */ | |
275 | __u8 can_dlc; /* data length code: 0 .. 8 */ | |
276 | __u8 data[8] __attribute__((aligned(8))); | |
277 | }; | |
278 | ||
279 | The alignment of the (linear) payload data[] to a 64bit boundary | |
280 | allows the user to define own structs and unions to easily access the | |
281 | CAN payload. There is no given byteorder on the CAN bus by | |
282 | default. A read(2) system call on a CAN_RAW socket transfers a | |
283 | struct can_frame to the user space. | |
284 | ||
285 | The sockaddr_can structure has an interface index like the | |
286 | PF_PACKET socket, that also binds to a specific interface: | |
287 | ||
288 | struct sockaddr_can { | |
289 | sa_family_t can_family; | |
290 | int can_ifindex; | |
291 | union { | |
56690c21 OH |
292 | /* transport protocol class address info (e.g. ISOTP) */ |
293 | struct { canid_t rx_id, tx_id; } tp; | |
294 | ||
295 | /* reserved for future CAN protocols address information */ | |
f7ab97f7 OH |
296 | } can_addr; |
297 | }; | |
298 | ||
299 | To determine the interface index an appropriate ioctl() has to | |
300 | be used (example for CAN_RAW sockets without error checking): | |
301 | ||
302 | int s; | |
303 | struct sockaddr_can addr; | |
304 | struct ifreq ifr; | |
305 | ||
306 | s = socket(PF_CAN, SOCK_RAW, CAN_RAW); | |
307 | ||
308 | strcpy(ifr.ifr_name, "can0" ); | |
309 | ioctl(s, SIOCGIFINDEX, &ifr); | |
310 | ||
311 | addr.can_family = AF_CAN; | |
312 | addr.can_ifindex = ifr.ifr_ifindex; | |
313 | ||
314 | bind(s, (struct sockaddr *)&addr, sizeof(addr)); | |
315 | ||
316 | (..) | |
317 | ||
318 | To bind a socket to all(!) CAN interfaces the interface index must | |
319 | be 0 (zero). In this case the socket receives CAN frames from every | |
320 | enabled CAN interface. To determine the originating CAN interface | |
321 | the system call recvfrom(2) may be used instead of read(2). To send | |
322 | on a socket that is bound to 'any' interface sendto(2) is needed to | |
323 | specify the outgoing interface. | |
324 | ||
325 | Reading CAN frames from a bound CAN_RAW socket (see above) consists | |
326 | of reading a struct can_frame: | |
327 | ||
328 | struct can_frame frame; | |
329 | ||
330 | nbytes = read(s, &frame, sizeof(struct can_frame)); | |
331 | ||
332 | if (nbytes < 0) { | |
333 | perror("can raw socket read"); | |
334 | return 1; | |
335 | } | |
336 | ||
19f59460 | 337 | /* paranoid check ... */ |
f7ab97f7 OH |
338 | if (nbytes < sizeof(struct can_frame)) { |
339 | fprintf(stderr, "read: incomplete CAN frame\n"); | |
340 | return 1; | |
341 | } | |
342 | ||
343 | /* do something with the received CAN frame */ | |
344 | ||
345 | Writing CAN frames can be done similarly, with the write(2) system call: | |
346 | ||
347 | nbytes = write(s, &frame, sizeof(struct can_frame)); | |
348 | ||
349 | When the CAN interface is bound to 'any' existing CAN interface | |
350 | (addr.can_ifindex = 0) it is recommended to use recvfrom(2) if the | |
351 | information about the originating CAN interface is needed: | |
352 | ||
353 | struct sockaddr_can addr; | |
354 | struct ifreq ifr; | |
355 | socklen_t len = sizeof(addr); | |
356 | struct can_frame frame; | |
357 | ||
358 | nbytes = recvfrom(s, &frame, sizeof(struct can_frame), | |
359 | 0, (struct sockaddr*)&addr, &len); | |
360 | ||
361 | /* get interface name of the received CAN frame */ | |
362 | ifr.ifr_ifindex = addr.can_ifindex; | |
363 | ioctl(s, SIOCGIFNAME, &ifr); | |
364 | printf("Received a CAN frame from interface %s", ifr.ifr_name); | |
365 | ||
366 | To write CAN frames on sockets bound to 'any' CAN interface the | |
367 | outgoing interface has to be defined certainly. | |
368 | ||
369 | strcpy(ifr.ifr_name, "can0"); | |
370 | ioctl(s, SIOCGIFINDEX, &ifr); | |
371 | addr.can_ifindex = ifr.ifr_ifindex; | |
372 | addr.can_family = AF_CAN; | |
373 | ||
374 | nbytes = sendto(s, &frame, sizeof(struct can_frame), | |
375 | 0, (struct sockaddr*)&addr, sizeof(addr)); | |
376 | ||
377 | 4.1 RAW protocol sockets with can_filters (SOCK_RAW) | |
378 | ||
379 | Using CAN_RAW sockets is extensively comparable to the commonly | |
380 | known access to CAN character devices. To meet the new possibilities | |
381 | provided by the multi user SocketCAN approach, some reasonable | |
382 | defaults are set at RAW socket binding time: | |
383 | ||
384 | - The filters are set to exactly one filter receiving everything | |
385 | - The socket only receives valid data frames (=> no error frames) | |
386 | - The loopback of sent CAN frames is enabled (see chapter 3.2) | |
387 | - The socket does not receive its own sent frames (in loopback mode) | |
388 | ||
389 | These default settings may be changed before or after binding the socket. | |
390 | To use the referenced definitions of the socket options for CAN_RAW | |
391 | sockets, include <linux/can/raw.h>. | |
392 | ||
393 | 4.1.1 RAW socket option CAN_RAW_FILTER | |
394 | ||
395 | The reception of CAN frames using CAN_RAW sockets can be controlled | |
396 | by defining 0 .. n filters with the CAN_RAW_FILTER socket option. | |
397 | ||
398 | The CAN filter structure is defined in include/linux/can.h: | |
399 | ||
400 | struct can_filter { | |
401 | canid_t can_id; | |
402 | canid_t can_mask; | |
403 | }; | |
404 | ||
405 | A filter matches, when | |
406 | ||
407 | <received_can_id> & mask == can_id & mask | |
408 | ||
409 | which is analogous to known CAN controllers hardware filter semantics. | |
410 | The filter can be inverted in this semantic, when the CAN_INV_FILTER | |
411 | bit is set in can_id element of the can_filter structure. In | |
412 | contrast to CAN controller hardware filters the user may set 0 .. n | |
413 | receive filters for each open socket separately: | |
414 | ||
415 | struct can_filter rfilter[2]; | |
416 | ||
417 | rfilter[0].can_id = 0x123; | |
418 | rfilter[0].can_mask = CAN_SFF_MASK; | |
419 | rfilter[1].can_id = 0x200; | |
420 | rfilter[1].can_mask = 0x700; | |
421 | ||
422 | setsockopt(s, SOL_CAN_RAW, CAN_RAW_FILTER, &rfilter, sizeof(rfilter)); | |
423 | ||
424 | To disable the reception of CAN frames on the selected CAN_RAW socket: | |
425 | ||
426 | setsockopt(s, SOL_CAN_RAW, CAN_RAW_FILTER, NULL, 0); | |
427 | ||
428 | To set the filters to zero filters is quite obsolete as not read | |
429 | data causes the raw socket to discard the received CAN frames. But | |
430 | having this 'send only' use-case we may remove the receive list in the | |
431 | Kernel to save a little (really a very little!) CPU usage. | |
432 | ||
433 | 4.1.2 RAW socket option CAN_RAW_ERR_FILTER | |
434 | ||
435 | As described in chapter 3.4 the CAN interface driver can generate so | |
436 | called Error Frames that can optionally be passed to the user | |
437 | application in the same way as other CAN frames. The possible | |
438 | errors are divided into different error classes that may be filtered | |
439 | using the appropriate error mask. To register for every possible | |
440 | error condition CAN_ERR_MASK can be used as value for the error mask. | |
441 | The values for the error mask are defined in linux/can/error.h . | |
442 | ||
443 | can_err_mask_t err_mask = ( CAN_ERR_TX_TIMEOUT | CAN_ERR_BUSOFF ); | |
444 | ||
445 | setsockopt(s, SOL_CAN_RAW, CAN_RAW_ERR_FILTER, | |
446 | &err_mask, sizeof(err_mask)); | |
447 | ||
448 | 4.1.3 RAW socket option CAN_RAW_LOOPBACK | |
449 | ||
450 | To meet multi user needs the local loopback is enabled by default | |
451 | (see chapter 3.2 for details). But in some embedded use-cases | |
452 | (e.g. when only one application uses the CAN bus) this loopback | |
453 | functionality can be disabled (separately for each socket): | |
454 | ||
455 | int loopback = 0; /* 0 = disabled, 1 = enabled (default) */ | |
456 | ||
457 | setsockopt(s, SOL_CAN_RAW, CAN_RAW_LOOPBACK, &loopback, sizeof(loopback)); | |
458 | ||
459 | 4.1.4 RAW socket option CAN_RAW_RECV_OWN_MSGS | |
460 | ||
461 | When the local loopback is enabled, all the sent CAN frames are | |
462 | looped back to the open CAN sockets that registered for the CAN | |
463 | frames' CAN-ID on this given interface to meet the multi user | |
464 | needs. The reception of the CAN frames on the same socket that was | |
465 | sending the CAN frame is assumed to be unwanted and therefore | |
466 | disabled by default. This default behaviour may be changed on | |
467 | demand: | |
468 | ||
469 | int recv_own_msgs = 1; /* 0 = disabled (default), 1 = enabled */ | |
470 | ||
471 | setsockopt(s, SOL_CAN_RAW, CAN_RAW_RECV_OWN_MSGS, | |
472 | &recv_own_msgs, sizeof(recv_own_msgs)); | |
473 | ||
474 | 4.2 Broadcast Manager protocol sockets (SOCK_DGRAM) | |
475 | 4.3 connected transport protocols (SOCK_SEQPACKET) | |
476 | 4.4 unconnected transport protocols (SOCK_DGRAM) | |
477 | ||
478 | ||
479 | 5. Socket CAN core module | |
480 | ------------------------- | |
481 | ||
482 | The Socket CAN core module implements the protocol family | |
483 | PF_CAN. CAN protocol modules are loaded by the core module at | |
484 | runtime. The core module provides an interface for CAN protocol | |
485 | modules to subscribe needed CAN IDs (see chapter 3.1). | |
486 | ||
487 | 5.1 can.ko module params | |
488 | ||
489 | - stats_timer: To calculate the Socket CAN core statistics | |
490 | (e.g. current/maximum frames per second) this 1 second timer is | |
491 | invoked at can.ko module start time by default. This timer can be | |
d9195881 | 492 | disabled by using stattimer=0 on the module commandline. |
f7ab97f7 OH |
493 | |
494 | - debug: (removed since SocketCAN SVN r546) | |
495 | ||
496 | 5.2 procfs content | |
497 | ||
498 | As described in chapter 3.1 the Socket CAN core uses several filter | |
499 | lists to deliver received CAN frames to CAN protocol modules. These | |
500 | receive lists, their filters and the count of filter matches can be | |
501 | checked in the appropriate receive list. All entries contain the | |
502 | device and a protocol module identifier: | |
503 | ||
504 | foo@bar:~$ cat /proc/net/can/rcvlist_all | |
505 | ||
506 | receive list 'rx_all': | |
507 | (vcan3: no entry) | |
508 | (vcan2: no entry) | |
509 | (vcan1: no entry) | |
510 | device can_id can_mask function userdata matches ident | |
511 | vcan0 000 00000000 f88e6370 f6c6f400 0 raw | |
512 | (any: no entry) | |
513 | ||
514 | In this example an application requests any CAN traffic from vcan0. | |
515 | ||
516 | rcvlist_all - list for unfiltered entries (no filter operations) | |
517 | rcvlist_eff - list for single extended frame (EFF) entries | |
518 | rcvlist_err - list for error frames masks | |
519 | rcvlist_fil - list for mask/value filters | |
520 | rcvlist_inv - list for mask/value filters (inverse semantic) | |
521 | rcvlist_sff - list for single standard frame (SFF) entries | |
522 | ||
523 | Additional procfs files in /proc/net/can | |
524 | ||
525 | stats - Socket CAN core statistics (rx/tx frames, match ratios, ...) | |
526 | reset_stats - manual statistic reset | |
527 | version - prints the Socket CAN core version and the ABI version | |
528 | ||
529 | 5.3 writing own CAN protocol modules | |
530 | ||
531 | To implement a new protocol in the protocol family PF_CAN a new | |
532 | protocol has to be defined in include/linux/can.h . | |
533 | The prototypes and definitions to use the Socket CAN core can be | |
534 | accessed by including include/linux/can/core.h . | |
535 | In addition to functions that register the CAN protocol and the | |
536 | CAN device notifier chain there are functions to subscribe CAN | |
537 | frames received by CAN interfaces and to send CAN frames: | |
538 | ||
539 | can_rx_register - subscribe CAN frames from a specific interface | |
540 | can_rx_unregister - unsubscribe CAN frames from a specific interface | |
541 | can_send - transmit a CAN frame (optional with local loopback) | |
542 | ||
543 | For details see the kerneldoc documentation in net/can/af_can.c or | |
544 | the source code of net/can/raw.c or net/can/bcm.c . | |
545 | ||
546 | 6. CAN network drivers | |
547 | ---------------------- | |
548 | ||
549 | Writing a CAN network device driver is much easier than writing a | |
550 | CAN character device driver. Similar to other known network device | |
551 | drivers you mainly have to deal with: | |
552 | ||
553 | - TX: Put the CAN frame from the socket buffer to the CAN controller. | |
554 | - RX: Put the CAN frame from the CAN controller to the socket buffer. | |
555 | ||
556 | See e.g. at Documentation/networking/netdevices.txt . The differences | |
557 | for writing CAN network device driver are described below: | |
558 | ||
559 | 6.1 general settings | |
560 | ||
561 | dev->type = ARPHRD_CAN; /* the netdevice hardware type */ | |
562 | dev->flags = IFF_NOARP; /* CAN has no arp */ | |
563 | ||
564 | dev->mtu = sizeof(struct can_frame); | |
565 | ||
566 | The struct can_frame is the payload of each socket buffer in the | |
567 | protocol family PF_CAN. | |
568 | ||
569 | 6.2 local loopback of sent frames | |
570 | ||
571 | As described in chapter 3.2 the CAN network device driver should | |
572 | support a local loopback functionality similar to the local echo | |
573 | e.g. of tty devices. In this case the driver flag IFF_ECHO has to be | |
574 | set to prevent the PF_CAN core from locally echoing sent frames | |
575 | (aka loopback) as fallback solution: | |
576 | ||
577 | dev->flags = (IFF_NOARP | IFF_ECHO); | |
578 | ||
579 | 6.3 CAN controller hardware filters | |
580 | ||
581 | To reduce the interrupt load on deep embedded systems some CAN | |
582 | controllers support the filtering of CAN IDs or ranges of CAN IDs. | |
583 | These hardware filter capabilities vary from controller to | |
584 | controller and have to be identified as not feasible in a multi-user | |
585 | networking approach. The use of the very controller specific | |
586 | hardware filters could make sense in a very dedicated use-case, as a | |
587 | filter on driver level would affect all users in the multi-user | |
588 | system. The high efficient filter sets inside the PF_CAN core allow | |
589 | to set different multiple filters for each socket separately. | |
590 | Therefore the use of hardware filters goes to the category 'handmade | |
591 | tuning on deep embedded systems'. The author is running a MPC603e | |
592 | @133MHz with four SJA1000 CAN controllers from 2002 under heavy bus | |
593 | load without any problems ... | |
594 | ||
e5d23048 OH |
595 | 6.4 The virtual CAN driver (vcan) |
596 | ||
597 | Similar to the network loopback devices, vcan offers a virtual local | |
598 | CAN interface. A full qualified address on CAN consists of | |
599 | ||
600 | - a unique CAN Identifier (CAN ID) | |
601 | - the CAN bus this CAN ID is transmitted on (e.g. can0) | |
602 | ||
603 | so in common use cases more than one virtual CAN interface is needed. | |
604 | ||
605 | The virtual CAN interfaces allow the transmission and reception of CAN | |
606 | frames without real CAN controller hardware. Virtual CAN network | |
607 | devices are usually named 'vcanX', like vcan0 vcan1 vcan2 ... | |
608 | When compiled as a module the virtual CAN driver module is called vcan.ko | |
609 | ||
610 | Since Linux Kernel version 2.6.24 the vcan driver supports the Kernel | |
611 | netlink interface to create vcan network devices. The creation and | |
612 | removal of vcan network devices can be managed with the ip(8) tool: | |
613 | ||
614 | - Create a virtual CAN network interface: | |
e20dad96 | 615 | $ ip link add type vcan |
e5d23048 OH |
616 | |
617 | - Create a virtual CAN network interface with a specific name 'vcan42': | |
e20dad96 | 618 | $ ip link add dev vcan42 type vcan |
e5d23048 OH |
619 | |
620 | - Remove a (virtual CAN) network interface 'vcan42': | |
e20dad96 WG |
621 | $ ip link del vcan42 |
622 | ||
623 | 6.5 The CAN network device driver interface | |
624 | ||
625 | The CAN network device driver interface provides a generic interface | |
626 | to setup, configure and monitor CAN network devices. The user can then | |
627 | configure the CAN device, like setting the bit-timing parameters, via | |
628 | the netlink interface using the program "ip" from the "IPROUTE2" | |
629 | utility suite. The following chapter describes briefly how to use it. | |
630 | Furthermore, the interface uses a common data structure and exports a | |
631 | set of common functions, which all real CAN network device drivers | |
632 | should use. Please have a look to the SJA1000 or MSCAN driver to | |
633 | understand how to use them. The name of the module is can-dev.ko. | |
634 | ||
635 | 6.5.1 Netlink interface to set/get devices properties | |
636 | ||
637 | The CAN device must be configured via netlink interface. The supported | |
638 | netlink message types are defined and briefly described in | |
639 | "include/linux/can/netlink.h". CAN link support for the program "ip" | |
640 | of the IPROUTE2 utility suite is avaiable and it can be used as shown | |
641 | below: | |
642 | ||
643 | - Setting CAN device properties: | |
644 | ||
645 | $ ip link set can0 type can help | |
646 | Usage: ip link set DEVICE type can | |
647 | [ bitrate BITRATE [ sample-point SAMPLE-POINT] ] | | |
648 | [ tq TQ prop-seg PROP_SEG phase-seg1 PHASE-SEG1 | |
649 | phase-seg2 PHASE-SEG2 [ sjw SJW ] ] | |
650 | ||
651 | [ loopback { on | off } ] | |
652 | [ listen-only { on | off } ] | |
653 | [ triple-sampling { on | off } ] | |
654 | ||
655 | [ restart-ms TIME-MS ] | |
656 | [ restart ] | |
657 | ||
658 | Where: BITRATE := { 1..1000000 } | |
659 | SAMPLE-POINT := { 0.000..0.999 } | |
660 | TQ := { NUMBER } | |
661 | PROP-SEG := { 1..8 } | |
662 | PHASE-SEG1 := { 1..8 } | |
663 | PHASE-SEG2 := { 1..8 } | |
664 | SJW := { 1..4 } | |
665 | RESTART-MS := { 0 | NUMBER } | |
666 | ||
667 | - Display CAN device details and statistics: | |
668 | ||
669 | $ ip -details -statistics link show can0 | |
670 | 2: can0: <NOARP,UP,LOWER_UP,ECHO> mtu 16 qdisc pfifo_fast state UP qlen 10 | |
671 | link/can | |
672 | can <TRIPLE-SAMPLING> state ERROR-ACTIVE restart-ms 100 | |
673 | bitrate 125000 sample_point 0.875 | |
674 | tq 125 prop-seg 6 phase-seg1 7 phase-seg2 2 sjw 1 | |
675 | sja1000: tseg1 1..16 tseg2 1..8 sjw 1..4 brp 1..64 brp-inc 1 | |
676 | clock 8000000 | |
677 | re-started bus-errors arbit-lost error-warn error-pass bus-off | |
678 | 41 17457 0 41 42 41 | |
679 | RX: bytes packets errors dropped overrun mcast | |
680 | 140859 17608 17457 0 0 0 | |
681 | TX: bytes packets errors dropped carrier collsns | |
682 | 861 112 0 41 0 0 | |
683 | ||
684 | More info to the above output: | |
685 | ||
686 | "<TRIPLE-SAMPLING>" | |
687 | Shows the list of selected CAN controller modes: LOOPBACK, | |
688 | LISTEN-ONLY, or TRIPLE-SAMPLING. | |
689 | ||
690 | "state ERROR-ACTIVE" | |
691 | The current state of the CAN controller: "ERROR-ACTIVE", | |
692 | "ERROR-WARNING", "ERROR-PASSIVE", "BUS-OFF" or "STOPPED" | |
693 | ||
694 | "restart-ms 100" | |
695 | Automatic restart delay time. If set to a non-zero value, a | |
696 | restart of the CAN controller will be triggered automatically | |
697 | in case of a bus-off condition after the specified delay time | |
698 | in milliseconds. By default it's off. | |
699 | ||
700 | "bitrate 125000 sample_point 0.875" | |
701 | Shows the real bit-rate in bits/sec and the sample-point in the | |
702 | range 0.000..0.999. If the calculation of bit-timing parameters | |
703 | is enabled in the kernel (CONFIG_CAN_CALC_BITTIMING=y), the | |
704 | bit-timing can be defined by setting the "bitrate" argument. | |
705 | Optionally the "sample-point" can be specified. By default it's | |
706 | 0.000 assuming CIA-recommended sample-points. | |
707 | ||
708 | "tq 125 prop-seg 6 phase-seg1 7 phase-seg2 2 sjw 1" | |
709 | Shows the time quanta in ns, propagation segment, phase buffer | |
710 | segment 1 and 2 and the synchronisation jump width in units of | |
711 | tq. They allow to define the CAN bit-timing in a hardware | |
712 | independent format as proposed by the Bosch CAN 2.0 spec (see | |
713 | chapter 8 of http://www.semiconductors.bosch.de/pdf/can2spec.pdf). | |
714 | ||
715 | "sja1000: tseg1 1..16 tseg2 1..8 sjw 1..4 brp 1..64 brp-inc 1 | |
716 | clock 8000000" | |
717 | Shows the bit-timing constants of the CAN controller, here the | |
718 | "sja1000". The minimum and maximum values of the time segment 1 | |
719 | and 2, the synchronisation jump width in units of tq, the | |
720 | bitrate pre-scaler and the CAN system clock frequency in Hz. | |
721 | These constants could be used for user-defined (non-standard) | |
722 | bit-timing calculation algorithms in user-space. | |
723 | ||
724 | "re-started bus-errors arbit-lost error-warn error-pass bus-off" | |
725 | Shows the number of restarts, bus and arbitration lost errors, | |
726 | and the state changes to the error-warning, error-passive and | |
727 | bus-off state. RX overrun errors are listed in the "overrun" | |
728 | field of the standard network statistics. | |
729 | ||
730 | 6.5.2 Setting the CAN bit-timing | |
731 | ||
732 | The CAN bit-timing parameters can always be defined in a hardware | |
733 | independent format as proposed in the Bosch CAN 2.0 specification | |
734 | specifying the arguments "tq", "prop_seg", "phase_seg1", "phase_seg2" | |
735 | and "sjw": | |
736 | ||
737 | $ ip link set canX type can tq 125 prop-seg 6 \ | |
738 | phase-seg1 7 phase-seg2 2 sjw 1 | |
739 | ||
740 | If the kernel option CONFIG_CAN_CALC_BITTIMING is enabled, CIA | |
741 | recommended CAN bit-timing parameters will be calculated if the bit- | |
742 | rate is specified with the argument "bitrate": | |
743 | ||
744 | $ ip link set canX type can bitrate 125000 | |
745 | ||
746 | Note that this works fine for the most common CAN controllers with | |
747 | standard bit-rates but may *fail* for exotic bit-rates or CAN system | |
748 | clock frequencies. Disabling CONFIG_CAN_CALC_BITTIMING saves some | |
749 | space and allows user-space tools to solely determine and set the | |
750 | bit-timing parameters. The CAN controller specific bit-timing | |
751 | constants can be used for that purpose. They are listed by the | |
752 | following command: | |
753 | ||
754 | $ ip -details link show can0 | |
755 | ... | |
756 | sja1000: clock 8000000 tseg1 1..16 tseg2 1..8 sjw 1..4 brp 1..64 brp-inc 1 | |
757 | ||
758 | 6.5.3 Starting and stopping the CAN network device | |
759 | ||
760 | A CAN network device is started or stopped as usual with the command | |
761 | "ifconfig canX up/down" or "ip link set canX up/down". Be aware that | |
762 | you *must* define proper bit-timing parameters for real CAN devices | |
763 | before you can start it to avoid error-prone default settings: | |
764 | ||
765 | $ ip link set canX up type can bitrate 125000 | |
766 | ||
767 | A device may enter the "bus-off" state if too much errors occurred on | |
768 | the CAN bus. Then no more messages are received or sent. An automatic | |
769 | bus-off recovery can be enabled by setting the "restart-ms" to a | |
770 | non-zero value, e.g.: | |
771 | ||
772 | $ ip link set canX type can restart-ms 100 | |
773 | ||
774 | Alternatively, the application may realize the "bus-off" condition | |
775 | by monitoring CAN error frames and do a restart when appropriate with | |
776 | the command: | |
777 | ||
778 | $ ip link set canX type can restart | |
779 | ||
780 | Note that a restart will also create a CAN error frame (see also | |
781 | chapter 3.4). | |
f7ab97f7 | 782 | |
e20dad96 | 783 | 6.6 Supported CAN hardware |
f7ab97f7 | 784 | |
e20dad96 WG |
785 | Please check the "Kconfig" file in "drivers/net/can" to get an actual |
786 | list of the support CAN hardware. On the Socket CAN project website | |
787 | (see chapter 7) there might be further drivers available, also for | |
788 | older kernel versions. | |
f7ab97f7 | 789 | |
e20dad96 WG |
790 | 7. Socket CAN resources |
791 | ----------------------- | |
f7ab97f7 | 792 | |
e20dad96 WG |
793 | You can find further resources for Socket CAN like user space tools, |
794 | support for old kernel versions, more drivers, mailing lists, etc. | |
795 | at the BerliOS OSS project website for Socket CAN: | |
f7ab97f7 | 796 | |
e20dad96 | 797 | http://developer.berlios.de/projects/socketcan |
f7ab97f7 | 798 | |
e20dad96 WG |
799 | If you have questions, bug fixes, etc., don't hesitate to post them to |
800 | the Socketcan-Users mailing list. But please search the archives first. | |
f7ab97f7 | 801 | |
e20dad96 | 802 | 8. Credits |
f7ab97f7 OH |
803 | ---------- |
804 | ||
e20dad96 | 805 | Oliver Hartkopp (PF_CAN core, filters, drivers, bcm, SJA1000 driver) |
f7ab97f7 OH |
806 | Urs Thuermann (PF_CAN core, kernel integration, socket interfaces, raw, vcan) |
807 | Jan Kizka (RT-SocketCAN core, Socket-API reconciliation) | |
e20dad96 WG |
808 | Wolfgang Grandegger (RT-SocketCAN core & drivers, Raw Socket-API reviews, |
809 | CAN device driver interface, MSCAN driver) | |
f7ab97f7 OH |
810 | Robert Schwebel (design reviews, PTXdist integration) |
811 | Marc Kleine-Budde (design reviews, Kernel 2.6 cleanups, drivers) | |
812 | Benedikt Spranger (reviews) | |
813 | Thomas Gleixner (LKML reviews, coding style, posting hints) | |
e20dad96 | 814 | Andrey Volkov (kernel subtree structure, ioctls, MSCAN driver) |
f7ab97f7 OH |
815 | Matthias Brukner (first SJA1000 CAN netdevice implementation Q2/2003) |
816 | Klaus Hitschler (PEAK driver integration) | |
817 | Uwe Koppe (CAN netdevices with PF_PACKET approach) | |
818 | Michael Schulze (driver layer loopback requirement, RT CAN drivers review) | |
e20dad96 WG |
819 | Pavel Pisa (Bit-timing calculation) |
820 | Sascha Hauer (SJA1000 platform driver) | |
821 | Sebastian Haas (SJA1000 EMS PCI driver) | |
822 | Markus Plessing (SJA1000 EMS PCI driver) | |
823 | Per Dalen (SJA1000 Kvaser PCI driver) | |
824 | Sam Ravnborg (reviews, coding style, kbuild help) |