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diff --git a/kernel/Documentation/networking/can.txt b/kernel/Documentation/networking/can.txt new file mode 100644 index 000000000..5abad1e92 --- /dev/null +++ b/kernel/Documentation/networking/can.txt @@ -0,0 +1,1216 @@ +============================================================================ + +can.txt + +Readme file for the Controller Area Network Protocol Family (aka SocketCAN) + +This file contains + + 1 Overview / What is SocketCAN + + 2 Motivation / Why using the socket API + + 3 SocketCAN concept + 3.1 receive lists + 3.2 local loopback of sent frames + 3.3 network problem notifications + + 4 How to use SocketCAN + 4.1 RAW protocol sockets with can_filters (SOCK_RAW) + 4.1.1 RAW socket option CAN_RAW_FILTER + 4.1.2 RAW socket option CAN_RAW_ERR_FILTER + 4.1.3 RAW socket option CAN_RAW_LOOPBACK + 4.1.4 RAW socket option CAN_RAW_RECV_OWN_MSGS + 4.1.5 RAW socket option CAN_RAW_FD_FRAMES + 4.1.6 RAW socket option CAN_RAW_JOIN_FILTERS + 4.1.7 RAW socket returned message flags + 4.2 Broadcast Manager protocol sockets (SOCK_DGRAM) + 4.2.1 Broadcast Manager operations + 4.2.2 Broadcast Manager message flags + 4.2.3 Broadcast Manager transmission timers + 4.2.4 Broadcast Manager message sequence transmission + 4.2.5 Broadcast Manager receive filter timers + 4.2.6 Broadcast Manager multiplex message receive filter + 4.3 connected transport protocols (SOCK_SEQPACKET) + 4.4 unconnected transport protocols (SOCK_DGRAM) + + 5 SocketCAN core module + 5.1 can.ko module params + 5.2 procfs content + 5.3 writing own CAN protocol modules + + 6 CAN network drivers + 6.1 general settings + 6.2 local loopback of sent frames + 6.3 CAN controller hardware filters + 6.4 The virtual CAN driver (vcan) + 6.5 The CAN network device driver interface + 6.5.1 Netlink interface to set/get devices properties + 6.5.2 Setting the CAN bit-timing + 6.5.3 Starting and stopping the CAN network device + 6.6 CAN FD (flexible data rate) driver support + 6.7 supported CAN hardware + + 7 SocketCAN resources + + 8 Credits + +============================================================================ + +1. Overview / What is SocketCAN +-------------------------------- + +The socketcan package is an implementation of CAN protocols +(Controller Area Network) for Linux. CAN is a networking technology +which has widespread use in automation, embedded devices, and +automotive fields. While there have been other CAN implementations +for Linux based on character devices, SocketCAN uses the Berkeley +socket API, the Linux network stack and implements the CAN device +drivers as network interfaces. The CAN socket API has been designed +as similar as possible to the TCP/IP protocols to allow programmers, +familiar with network programming, to easily learn how to use CAN +sockets. + +2. Motivation / Why using the socket API +---------------------------------------- + +There have been CAN implementations for Linux before SocketCAN so the +question arises, why we have started another project. Most existing +implementations come as a device driver for some CAN hardware, they +are based on character devices and provide comparatively little +functionality. Usually, there is only a hardware-specific device +driver which provides a character device interface to send and +receive raw CAN frames, directly to/from the controller hardware. +Queueing of frames and higher-level transport protocols like ISO-TP +have to be implemented in user space applications. Also, most +character-device implementations support only one single process to +open the device at a time, similar to a serial interface. Exchanging +the CAN controller requires employment of another device driver and +often the need for adaption of large parts of the application to the +new driver's API. + +SocketCAN was designed to overcome all of these limitations. A new +protocol family has been implemented which provides a socket interface +to user space applications and which builds upon the Linux network +layer, enabling use all of the provided queueing functionality. A device +driver for CAN controller hardware registers itself with the Linux +network layer as a network device, so that CAN frames from the +controller can be passed up to the network layer and on to the CAN +protocol family module and also vice-versa. Also, the protocol family +module provides an API for transport protocol modules to register, so +that any number of transport protocols can be loaded or unloaded +dynamically. In fact, the can core module alone does not provide any +protocol and cannot be used without loading at least one additional +protocol module. Multiple sockets can be opened at the same time, +on different or the same protocol module and they can listen/send +frames on different or the same CAN IDs. Several sockets listening on +the same interface for frames with the same CAN ID are all passed the +same received matching CAN frames. An application wishing to +communicate using a specific transport protocol, e.g. ISO-TP, just +selects that protocol when opening the socket, and then can read and +write application data byte streams, without having to deal with +CAN-IDs, frames, etc. + +Similar functionality visible from user-space could be provided by a +character device, too, but this would lead to a technically inelegant +solution for a couple of reasons: + +* Intricate usage. Instead of passing a protocol argument to + socket(2) and using bind(2) to select a CAN interface and CAN ID, an + application would have to do all these operations using ioctl(2)s. + +* Code duplication. A character device cannot make use of the Linux + network queueing code, so all that code would have to be duplicated + for CAN networking. + +* Abstraction. In most existing character-device implementations, the + hardware-specific device driver for a CAN controller directly + provides the character device for the application to work with. + This is at least very unusual in Unix systems for both, char and + block devices. For example you don't have a character device for a + certain UART of a serial interface, a certain sound chip in your + computer, a SCSI or IDE controller providing access to your hard + disk or tape streamer device. Instead, you have abstraction layers + which provide a unified character or block device interface to the + application on the one hand, and a interface for hardware-specific + device drivers on the other hand. These abstractions are provided + by subsystems like the tty layer, the audio subsystem or the SCSI + and IDE subsystems for the devices mentioned above. + + The easiest way to implement a CAN device driver is as a character + device without such a (complete) abstraction layer, as is done by most + existing drivers. The right way, however, would be to add such a + layer with all the functionality like registering for certain CAN + IDs, supporting several open file descriptors and (de)multiplexing + CAN frames between them, (sophisticated) queueing of CAN frames, and + providing an API for device drivers to register with. However, then + it would be no more difficult, or may be even easier, to use the + networking framework provided by the Linux kernel, and this is what + SocketCAN does. + + The use of the networking framework of the Linux kernel is just the + natural and most appropriate way to implement CAN for Linux. + +3. SocketCAN concept +--------------------- + + As described in chapter 2 it is the main goal of SocketCAN to + provide a socket interface to user space applications which builds + upon the Linux network layer. In contrast to the commonly known + TCP/IP and ethernet networking, the CAN bus is a broadcast-only(!) + medium that has no MAC-layer addressing like ethernet. The CAN-identifier + (can_id) is used for arbitration on the CAN-bus. Therefore the CAN-IDs + have to be chosen uniquely on the bus. When designing a CAN-ECU + network the CAN-IDs are mapped to be sent by a specific ECU. + For this reason a CAN-ID can be treated best as a kind of source address. + + 3.1 receive lists + + The network transparent access of multiple applications leads to the + problem that different applications may be interested in the same + CAN-IDs from the same CAN network interface. The SocketCAN core + module - which implements the protocol family CAN - provides several + high efficient receive lists for this reason. If e.g. a user space + application opens a CAN RAW socket, the raw protocol module itself + requests the (range of) CAN-IDs from the SocketCAN core that are + requested by the user. The subscription and unsubscription of + CAN-IDs can be done for specific CAN interfaces or for all(!) known + CAN interfaces with the can_rx_(un)register() functions provided to + CAN protocol modules by the SocketCAN core (see chapter 5). + To optimize the CPU usage at runtime the receive lists are split up + into several specific lists per device that match the requested + filter complexity for a given use-case. + + 3.2 local loopback of sent frames + + As known from other networking concepts the data exchanging + applications may run on the same or different nodes without any + change (except for the according addressing information): + + ___ ___ ___ _______ ___ + | _ | | _ | | _ | | _ _ | | _ | + ||A|| ||B|| ||C|| ||A| |B|| ||C|| + |___| |___| |___| |_______| |___| + | | | | | + -----------------(1)- CAN bus -(2)--------------- + + To ensure that application A receives the same information in the + example (2) as it would receive in example (1) there is need for + some kind of local loopback of the sent CAN frames on the appropriate + node. + + The Linux network devices (by default) just can handle the + transmission and reception of media dependent frames. Due to the + arbitration on the CAN bus the transmission of a low prio CAN-ID + may be delayed by the reception of a high prio CAN frame. To + reflect the correct* traffic on the node the loopback of the sent + data has to be performed right after a successful transmission. If + the CAN network interface is not capable of performing the loopback for + some reason the SocketCAN core can do this task as a fallback solution. + See chapter 6.2 for details (recommended). + + The loopback functionality is enabled by default to reflect standard + networking behaviour for CAN applications. Due to some requests from + the RT-SocketCAN group the loopback optionally may be disabled for each + separate socket. See sockopts from the CAN RAW sockets in chapter 4.1. + + * = you really like to have this when you're running analyser tools + like 'candump' or 'cansniffer' on the (same) node. + + 3.3 network problem notifications + + The use of the CAN bus may lead to several problems on the physical + and media access control layer. Detecting and logging of these lower + layer problems is a vital requirement for CAN users to identify + hardware issues on the physical transceiver layer as well as + arbitration problems and error frames caused by the different + ECUs. The occurrence of detected errors are important for diagnosis + and have to be logged together with the exact timestamp. For this + reason the CAN interface driver can generate so called Error Message + Frames that can optionally be passed to the user application in the + same way as other CAN frames. Whenever an error on the physical layer + or the MAC layer is detected (e.g. by the CAN controller) the driver + creates an appropriate error message frame. Error messages frames can + be requested by the user application using the common CAN filter + mechanisms. Inside this filter definition the (interested) type of + errors may be selected. The reception of error messages is disabled + by default. The format of the CAN error message frame is briefly + described in the Linux header file "include/uapi/linux/can/error.h". + +4. How to use SocketCAN +------------------------ + + Like TCP/IP, you first need to open a socket for communicating over a + CAN network. Since SocketCAN implements a new protocol family, you + need to pass PF_CAN as the first argument to the socket(2) system + call. Currently, there are two CAN protocols to choose from, the raw + socket protocol and the broadcast manager (BCM). So to open a socket, + you would write + + s = socket(PF_CAN, SOCK_RAW, CAN_RAW); + + and + + s = socket(PF_CAN, SOCK_DGRAM, CAN_BCM); + + respectively. After the successful creation of the socket, you would + normally use the bind(2) system call to bind the socket to a CAN + interface (which is different from TCP/IP due to different addressing + - see chapter 3). After binding (CAN_RAW) or connecting (CAN_BCM) + the socket, you can read(2) and write(2) from/to the socket or use + send(2), sendto(2), sendmsg(2) and the recv* counterpart operations + on the socket as usual. There are also CAN specific socket options + described below. + + The basic CAN frame structure and the sockaddr structure are defined + in include/linux/can.h: + + struct can_frame { + canid_t can_id; /* 32 bit CAN_ID + EFF/RTR/ERR flags */ + __u8 can_dlc; /* frame payload length in byte (0 .. 8) */ + __u8 data[8] __attribute__((aligned(8))); + }; + + The alignment of the (linear) payload data[] to a 64bit boundary + allows the user to define their own structs and unions to easily access + the CAN payload. There is no given byteorder on the CAN bus by + default. A read(2) system call on a CAN_RAW socket transfers a + struct can_frame to the user space. + + The sockaddr_can structure has an interface index like the + PF_PACKET socket, that also binds to a specific interface: + + struct sockaddr_can { + sa_family_t can_family; + int can_ifindex; + union { + /* transport protocol class address info (e.g. ISOTP) */ + struct { canid_t rx_id, tx_id; } tp; + + /* reserved for future CAN protocols address information */ + } can_addr; + }; + + To determine the interface index an appropriate ioctl() has to + be used (example for CAN_RAW sockets without error checking): + + int s; + struct sockaddr_can addr; + struct ifreq ifr; + + s = socket(PF_CAN, SOCK_RAW, CAN_RAW); + + strcpy(ifr.ifr_name, "can0" ); + ioctl(s, SIOCGIFINDEX, &ifr); + + addr.can_family = AF_CAN; + addr.can_ifindex = ifr.ifr_ifindex; + + bind(s, (struct sockaddr *)&addr, sizeof(addr)); + + (..) + + To bind a socket to all(!) CAN interfaces the interface index must + be 0 (zero). In this case the socket receives CAN frames from every + enabled CAN interface. To determine the originating CAN interface + the system call recvfrom(2) may be used instead of read(2). To send + on a socket that is bound to 'any' interface sendto(2) is needed to + specify the outgoing interface. + + Reading CAN frames from a bound CAN_RAW socket (see above) consists + of reading a struct can_frame: + + struct can_frame frame; + + nbytes = read(s, &frame, sizeof(struct can_frame)); + + if (nbytes < 0) { + perror("can raw socket read"); + return 1; + } + + /* paranoid check ... */ + if (nbytes < sizeof(struct can_frame)) { + fprintf(stderr, "read: incomplete CAN frame\n"); + return 1; + } + + /* do something with the received CAN frame */ + + Writing CAN frames can be done similarly, with the write(2) system call: + + nbytes = write(s, &frame, sizeof(struct can_frame)); + + When the CAN interface is bound to 'any' existing CAN interface + (addr.can_ifindex = 0) it is recommended to use recvfrom(2) if the + information about the originating CAN interface is needed: + + struct sockaddr_can addr; + struct ifreq ifr; + socklen_t len = sizeof(addr); + struct can_frame frame; + + nbytes = recvfrom(s, &frame, sizeof(struct can_frame), + 0, (struct sockaddr*)&addr, &len); + + /* get interface name of the received CAN frame */ + ifr.ifr_ifindex = addr.can_ifindex; + ioctl(s, SIOCGIFNAME, &ifr); + printf("Received a CAN frame from interface %s", ifr.ifr_name); + + To write CAN frames on sockets bound to 'any' CAN interface the + outgoing interface has to be defined certainly. + + strcpy(ifr.ifr_name, "can0"); + ioctl(s, SIOCGIFINDEX, &ifr); + addr.can_ifindex = ifr.ifr_ifindex; + addr.can_family = AF_CAN; + + nbytes = sendto(s, &frame, sizeof(struct can_frame), + 0, (struct sockaddr*)&addr, sizeof(addr)); + + Remark about CAN FD (flexible data rate) support: + + Generally the handling of CAN FD is very similar to the formerly described + examples. The new CAN FD capable CAN controllers support two different + bitrates for the arbitration phase and the payload phase of the CAN FD frame + and up to 64 bytes of payload. This extended payload length breaks all the + kernel interfaces (ABI) which heavily rely on the CAN frame with fixed eight + bytes of payload (struct can_frame) like the CAN_RAW socket. Therefore e.g. + the CAN_RAW socket supports a new socket option CAN_RAW_FD_FRAMES that + switches the socket into a mode that allows the handling of CAN FD frames + and (legacy) CAN frames simultaneously (see section 4.1.5). + + The struct canfd_frame is defined in include/linux/can.h: + + struct canfd_frame { + canid_t can_id; /* 32 bit CAN_ID + EFF/RTR/ERR flags */ + __u8 len; /* frame payload length in byte (0 .. 64) */ + __u8 flags; /* additional flags for CAN FD */ + __u8 __res0; /* reserved / padding */ + __u8 __res1; /* reserved / padding */ + __u8 data[64] __attribute__((aligned(8))); + }; + + The struct canfd_frame and the existing struct can_frame have the can_id, + the payload length and the payload data at the same offset inside their + structures. This allows to handle the different structures very similar. + When the content of a struct can_frame is copied into a struct canfd_frame + all structure elements can be used as-is - only the data[] becomes extended. + + When introducing the struct canfd_frame it turned out that the data length + code (DLC) of the struct can_frame was used as a length information as the + length and the DLC has a 1:1 mapping in the range of 0 .. 8. To preserve + the easy handling of the length information the canfd_frame.len element + contains a plain length value from 0 .. 64. So both canfd_frame.len and + can_frame.can_dlc are equal and contain a length information and no DLC. + For details about the distinction of CAN and CAN FD capable devices and + the mapping to the bus-relevant data length code (DLC), see chapter 6.6. + + The length of the two CAN(FD) frame structures define the maximum transfer + unit (MTU) of the CAN(FD) network interface and skbuff data length. Two + definitions are specified for CAN specific MTUs in include/linux/can.h : + + #define CAN_MTU (sizeof(struct can_frame)) == 16 => 'legacy' CAN frame + #define CANFD_MTU (sizeof(struct canfd_frame)) == 72 => CAN FD frame + + 4.1 RAW protocol sockets with can_filters (SOCK_RAW) + + Using CAN_RAW sockets is extensively comparable to the commonly + known access to CAN character devices. To meet the new possibilities + provided by the multi user SocketCAN approach, some reasonable + defaults are set at RAW socket binding time: + + - The filters are set to exactly one filter receiving everything + - The socket only receives valid data frames (=> no error message frames) + - The loopback of sent CAN frames is enabled (see chapter 3.2) + - The socket does not receive its own sent frames (in loopback mode) + + These default settings may be changed before or after binding the socket. + To use the referenced definitions of the socket options for CAN_RAW + sockets, include <linux/can/raw.h>. + + 4.1.1 RAW socket option CAN_RAW_FILTER + + The reception of CAN frames using CAN_RAW sockets can be controlled + by defining 0 .. n filters with the CAN_RAW_FILTER socket option. + + The CAN filter structure is defined in include/linux/can.h: + + struct can_filter { + canid_t can_id; + canid_t can_mask; + }; + + A filter matches, when + + <received_can_id> & mask == can_id & mask + + which is analogous to known CAN controllers hardware filter semantics. + The filter can be inverted in this semantic, when the CAN_INV_FILTER + bit is set in can_id element of the can_filter structure. In + contrast to CAN controller hardware filters the user may set 0 .. n + receive filters for each open socket separately: + + struct can_filter rfilter[2]; + + rfilter[0].can_id = 0x123; + rfilter[0].can_mask = CAN_SFF_MASK; + rfilter[1].can_id = 0x200; + rfilter[1].can_mask = 0x700; + + setsockopt(s, SOL_CAN_RAW, CAN_RAW_FILTER, &rfilter, sizeof(rfilter)); + + To disable the reception of CAN frames on the selected CAN_RAW socket: + + setsockopt(s, SOL_CAN_RAW, CAN_RAW_FILTER, NULL, 0); + + To set the filters to zero filters is quite obsolete as to not read + data causes the raw socket to discard the received CAN frames. But + having this 'send only' use-case we may remove the receive list in the + Kernel to save a little (really a very little!) CPU usage. + + 4.1.1.1 CAN filter usage optimisation + + The CAN filters are processed in per-device filter lists at CAN frame + reception time. To reduce the number of checks that need to be performed + while walking through the filter lists the CAN core provides an optimized + filter handling when the filter subscription focusses on a single CAN ID. + + For the possible 2048 SFF CAN identifiers the identifier is used as an index + to access the corresponding subscription list without any further checks. + For the 2^29 possible EFF CAN identifiers a 10 bit XOR folding is used as + hash function to retrieve the EFF table index. + + To benefit from the optimized filters for single CAN identifiers the + CAN_SFF_MASK or CAN_EFF_MASK have to be set into can_filter.mask together + with set CAN_EFF_FLAG and CAN_RTR_FLAG bits. A set CAN_EFF_FLAG bit in the + can_filter.mask makes clear that it matters whether a SFF or EFF CAN ID is + subscribed. E.g. in the example from above + + rfilter[0].can_id = 0x123; + rfilter[0].can_mask = CAN_SFF_MASK; + + both SFF frames with CAN ID 0x123 and EFF frames with 0xXXXXX123 can pass. + + To filter for only 0x123 (SFF) and 0x12345678 (EFF) CAN identifiers the + filter has to be defined in this way to benefit from the optimized filters: + + struct can_filter rfilter[2]; + + rfilter[0].can_id = 0x123; + rfilter[0].can_mask = (CAN_EFF_FLAG | CAN_RTR_FLAG | CAN_SFF_MASK); + rfilter[1].can_id = 0x12345678 | CAN_EFF_FLAG; + rfilter[1].can_mask = (CAN_EFF_FLAG | CAN_RTR_FLAG | CAN_EFF_MASK); + + setsockopt(s, SOL_CAN_RAW, CAN_RAW_FILTER, &rfilter, sizeof(rfilter)); + + 4.1.2 RAW socket option CAN_RAW_ERR_FILTER + + As described in chapter 3.4 the CAN interface driver can generate so + called Error Message Frames that can optionally be passed to the user + application in the same way as other CAN frames. The possible + errors are divided into different error classes that may be filtered + using the appropriate error mask. To register for every possible + error condition CAN_ERR_MASK can be used as value for the error mask. + The values for the error mask are defined in linux/can/error.h . + + can_err_mask_t err_mask = ( CAN_ERR_TX_TIMEOUT | CAN_ERR_BUSOFF ); + + setsockopt(s, SOL_CAN_RAW, CAN_RAW_ERR_FILTER, + &err_mask, sizeof(err_mask)); + + 4.1.3 RAW socket option CAN_RAW_LOOPBACK + + To meet multi user needs the local loopback is enabled by default + (see chapter 3.2 for details). But in some embedded use-cases + (e.g. when only one application uses the CAN bus) this loopback + functionality can be disabled (separately for each socket): + + int loopback = 0; /* 0 = disabled, 1 = enabled (default) */ + + setsockopt(s, SOL_CAN_RAW, CAN_RAW_LOOPBACK, &loopback, sizeof(loopback)); + + 4.1.4 RAW socket option CAN_RAW_RECV_OWN_MSGS + + When the local loopback is enabled, all the sent CAN frames are + looped back to the open CAN sockets that registered for the CAN + frames' CAN-ID on this given interface to meet the multi user + needs. The reception of the CAN frames on the same socket that was + sending the CAN frame is assumed to be unwanted and therefore + disabled by default. This default behaviour may be changed on + demand: + + int recv_own_msgs = 1; /* 0 = disabled (default), 1 = enabled */ + + setsockopt(s, SOL_CAN_RAW, CAN_RAW_RECV_OWN_MSGS, + &recv_own_msgs, sizeof(recv_own_msgs)); + + 4.1.5 RAW socket option CAN_RAW_FD_FRAMES + + CAN FD support in CAN_RAW sockets can be enabled with a new socket option + CAN_RAW_FD_FRAMES which is off by default. When the new socket option is + not supported by the CAN_RAW socket (e.g. on older kernels), switching the + CAN_RAW_FD_FRAMES option returns the error -ENOPROTOOPT. + + Once CAN_RAW_FD_FRAMES is enabled the application can send both CAN frames + and CAN FD frames. OTOH the application has to handle CAN and CAN FD frames + when reading from the socket. + + CAN_RAW_FD_FRAMES enabled: CAN_MTU and CANFD_MTU are allowed + CAN_RAW_FD_FRAMES disabled: only CAN_MTU is allowed (default) + + Example: + [ remember: CANFD_MTU == sizeof(struct canfd_frame) ] + + struct canfd_frame cfd; + + nbytes = read(s, &cfd, CANFD_MTU); + + if (nbytes == CANFD_MTU) { + printf("got CAN FD frame with length %d\n", cfd.len); + /* cfd.flags contains valid data */ + } else if (nbytes == CAN_MTU) { + printf("got legacy CAN frame with length %d\n", cfd.len); + /* cfd.flags is undefined */ + } else { + fprintf(stderr, "read: invalid CAN(FD) frame\n"); + return 1; + } + + /* the content can be handled independently from the received MTU size */ + + printf("can_id: %X data length: %d data: ", cfd.can_id, cfd.len); + for (i = 0; i < cfd.len; i++) + printf("%02X ", cfd.data[i]); + + When reading with size CANFD_MTU only returns CAN_MTU bytes that have + been received from the socket a legacy CAN frame has been read into the + provided CAN FD structure. Note that the canfd_frame.flags data field is + not specified in the struct can_frame and therefore it is only valid in + CANFD_MTU sized CAN FD frames. + + Implementation hint for new CAN applications: + + To build a CAN FD aware application use struct canfd_frame as basic CAN + data structure for CAN_RAW based applications. When the application is + executed on an older Linux kernel and switching the CAN_RAW_FD_FRAMES + socket option returns an error: No problem. You'll get legacy CAN frames + or CAN FD frames and can process them the same way. + + When sending to CAN devices make sure that the device is capable to handle + CAN FD frames by checking if the device maximum transfer unit is CANFD_MTU. + The CAN device MTU can be retrieved e.g. with a SIOCGIFMTU ioctl() syscall. + + 4.1.6 RAW socket option CAN_RAW_JOIN_FILTERS + + The CAN_RAW socket can set multiple CAN identifier specific filters that + lead to multiple filters in the af_can.c filter processing. These filters + are indenpendent from each other which leads to logical OR'ed filters when + applied (see 4.1.1). + + This socket option joines the given CAN filters in the way that only CAN + frames are passed to user space that matched *all* given CAN filters. The + semantic for the applied filters is therefore changed to a logical AND. + + This is useful especially when the filterset is a combination of filters + where the CAN_INV_FILTER flag is set in order to notch single CAN IDs or + CAN ID ranges from the incoming traffic. + + 4.1.7 RAW socket returned message flags + + When using recvmsg() call, the msg->msg_flags may contain following flags: + + MSG_DONTROUTE: set when the received frame was created on the local host. + + MSG_CONFIRM: set when the frame was sent via the socket it is received on. + This flag can be interpreted as a 'transmission confirmation' when the + CAN driver supports the echo of frames on driver level, see 3.2 and 6.2. + In order to receive such messages, CAN_RAW_RECV_OWN_MSGS must be set. + + 4.2 Broadcast Manager protocol sockets (SOCK_DGRAM) + + The Broadcast Manager protocol provides a command based configuration + interface to filter and send (e.g. cyclic) CAN messages in kernel space. + + Receive filters can be used to down sample frequent messages; detect events + such as message contents changes, packet length changes, and do time-out + monitoring of received messages. + + Periodic transmission tasks of CAN frames or a sequence of CAN frames can be + created and modified at runtime; both the message content and the two + possible transmit intervals can be altered. + + A BCM socket is not intended for sending individual CAN frames using the + struct can_frame as known from the CAN_RAW socket. Instead a special BCM + configuration message is defined. The basic BCM configuration message used + to communicate with the broadcast manager and the available operations are + defined in the linux/can/bcm.h include. The BCM message consists of a + message header with a command ('opcode') followed by zero or more CAN frames. + The broadcast manager sends responses to user space in the same form: + + struct bcm_msg_head { + __u32 opcode; /* command */ + __u32 flags; /* special flags */ + __u32 count; /* run 'count' times with ival1 */ + struct timeval ival1, ival2; /* count and subsequent interval */ + canid_t can_id; /* unique can_id for task */ + __u32 nframes; /* number of can_frames following */ + struct can_frame frames[0]; + }; + + The aligned payload 'frames' uses the same basic CAN frame structure defined + at the beginning of section 4 and in the include/linux/can.h include. All + messages to the broadcast manager from user space have this structure. + + Note a CAN_BCM socket must be connected instead of bound after socket + creation (example without error checking): + + int s; + struct sockaddr_can addr; + struct ifreq ifr; + + s = socket(PF_CAN, SOCK_DGRAM, CAN_BCM); + + strcpy(ifr.ifr_name, "can0"); + ioctl(s, SIOCGIFINDEX, &ifr); + + addr.can_family = AF_CAN; + addr.can_ifindex = ifr.ifr_ifindex; + + connect(s, (struct sockaddr *)&addr, sizeof(addr)) + + (..) + + The broadcast manager socket is able to handle any number of in flight + transmissions or receive filters concurrently. The different RX/TX jobs are + distinguished by the unique can_id in each BCM message. However additional + CAN_BCM sockets are recommended to communicate on multiple CAN interfaces. + When the broadcast manager socket is bound to 'any' CAN interface (=> the + interface index is set to zero) the configured receive filters apply to any + CAN interface unless the sendto() syscall is used to overrule the 'any' CAN + interface index. When using recvfrom() instead of read() to retrieve BCM + socket messages the originating CAN interface is provided in can_ifindex. + + 4.2.1 Broadcast Manager operations + + The opcode defines the operation for the broadcast manager to carry out, + or details the broadcast managers response to several events, including + user requests. + + Transmit Operations (user space to broadcast manager): + + TX_SETUP: Create (cyclic) transmission task. + + TX_DELETE: Remove (cyclic) transmission task, requires only can_id. + + TX_READ: Read properties of (cyclic) transmission task for can_id. + + TX_SEND: Send one CAN frame. + + Transmit Responses (broadcast manager to user space): + + TX_STATUS: Reply to TX_READ request (transmission task configuration). + + TX_EXPIRED: Notification when counter finishes sending at initial interval + 'ival1'. Requires the TX_COUNTEVT flag to be set at TX_SETUP. + + Receive Operations (user space to broadcast manager): + + RX_SETUP: Create RX content filter subscription. + + RX_DELETE: Remove RX content filter subscription, requires only can_id. + + RX_READ: Read properties of RX content filter subscription for can_id. + + Receive Responses (broadcast manager to user space): + + RX_STATUS: Reply to RX_READ request (filter task configuration). + + RX_TIMEOUT: Cyclic message is detected to be absent (timer ival1 expired). + + RX_CHANGED: BCM message with updated CAN frame (detected content change). + Sent on first message received or on receipt of revised CAN messages. + + 4.2.2 Broadcast Manager message flags + + When sending a message to the broadcast manager the 'flags' element may + contain the following flag definitions which influence the behaviour: + + SETTIMER: Set the values of ival1, ival2 and count + + STARTTIMER: Start the timer with the actual values of ival1, ival2 + and count. Starting the timer leads simultaneously to emit a CAN frame. + + TX_COUNTEVT: Create the message TX_EXPIRED when count expires + + TX_ANNOUNCE: A change of data by the process is emitted immediately. + + TX_CP_CAN_ID: Copies the can_id from the message header to each + subsequent frame in frames. This is intended as usage simplification. For + TX tasks the unique can_id from the message header may differ from the + can_id(s) stored for transmission in the subsequent struct can_frame(s). + + RX_FILTER_ID: Filter by can_id alone, no frames required (nframes=0). + + RX_CHECK_DLC: A change of the DLC leads to an RX_CHANGED. + + RX_NO_AUTOTIMER: Prevent automatically starting the timeout monitor. + + RX_ANNOUNCE_RESUME: If passed at RX_SETUP and a receive timeout occurred, a + RX_CHANGED message will be generated when the (cyclic) receive restarts. + + TX_RESET_MULTI_IDX: Reset the index for the multiple frame transmission. + + RX_RTR_FRAME: Send reply for RTR-request (placed in op->frames[0]). + + 4.2.3 Broadcast Manager transmission timers + + Periodic transmission configurations may use up to two interval timers. + In this case the BCM sends a number of messages ('count') at an interval + 'ival1', then continuing to send at another given interval 'ival2'. When + only one timer is needed 'count' is set to zero and only 'ival2' is used. + When SET_TIMER and START_TIMER flag were set the timers are activated. + The timer values can be altered at runtime when only SET_TIMER is set. + + 4.2.4 Broadcast Manager message sequence transmission + + Up to 256 CAN frames can be transmitted in a sequence in the case of a cyclic + TX task configuration. The number of CAN frames is provided in the 'nframes' + element of the BCM message head. The defined number of CAN frames are added + as array to the TX_SETUP BCM configuration message. + + /* create a struct to set up a sequence of four CAN frames */ + struct { + struct bcm_msg_head msg_head; + struct can_frame frame[4]; + } mytxmsg; + + (..) + mytxmsg.nframes = 4; + (..) + + write(s, &mytxmsg, sizeof(mytxmsg)); + + With every transmission the index in the array of CAN frames is increased + and set to zero at index overflow. + + 4.2.5 Broadcast Manager receive filter timers + + The timer values ival1 or ival2 may be set to non-zero values at RX_SETUP. + When the SET_TIMER flag is set the timers are enabled: + + ival1: Send RX_TIMEOUT when a received message is not received again within + the given time. When START_TIMER is set at RX_SETUP the timeout detection + is activated directly - even without a former CAN frame reception. + + ival2: Throttle the received message rate down to the value of ival2. This + is useful to reduce messages for the application when the signal inside the + CAN frame is stateless as state changes within the ival2 periode may get + lost. + + 4.2.6 Broadcast Manager multiplex message receive filter + + To filter for content changes in multiplex message sequences an array of more + than one CAN frames can be passed in a RX_SETUP configuration message. The + data bytes of the first CAN frame contain the mask of relevant bits that + have to match in the subsequent CAN frames with the received CAN frame. + If one of the subsequent CAN frames is matching the bits in that frame data + mark the relevant content to be compared with the previous received content. + Up to 257 CAN frames (multiplex filter bit mask CAN frame plus 256 CAN + filters) can be added as array to the TX_SETUP BCM configuration message. + + /* usually used to clear CAN frame data[] - beware of endian problems! */ + #define U64_DATA(p) (*(unsigned long long*)(p)->data) + + struct { + struct bcm_msg_head msg_head; + struct can_frame frame[5]; + } msg; + + msg.msg_head.opcode = RX_SETUP; + msg.msg_head.can_id = 0x42; + msg.msg_head.flags = 0; + msg.msg_head.nframes = 5; + U64_DATA(&msg.frame[0]) = 0xFF00000000000000ULL; /* MUX mask */ + U64_DATA(&msg.frame[1]) = 0x01000000000000FFULL; /* data mask (MUX 0x01) */ + U64_DATA(&msg.frame[2]) = 0x0200FFFF000000FFULL; /* data mask (MUX 0x02) */ + U64_DATA(&msg.frame[3]) = 0x330000FFFFFF0003ULL; /* data mask (MUX 0x33) */ + U64_DATA(&msg.frame[4]) = 0x4F07FC0FF0000000ULL; /* data mask (MUX 0x4F) */ + + write(s, &msg, sizeof(msg)); + + 4.3 connected transport protocols (SOCK_SEQPACKET) + 4.4 unconnected transport protocols (SOCK_DGRAM) + + +5. SocketCAN core module +------------------------- + + The SocketCAN core module implements the protocol family + PF_CAN. CAN protocol modules are loaded by the core module at + runtime. The core module provides an interface for CAN protocol + modules to subscribe needed CAN IDs (see chapter 3.1). + + 5.1 can.ko module params + + - stats_timer: To calculate the SocketCAN core statistics + (e.g. current/maximum frames per second) this 1 second timer is + invoked at can.ko module start time by default. This timer can be + disabled by using stattimer=0 on the module commandline. + + - debug: (removed since SocketCAN SVN r546) + + 5.2 procfs content + + As described in chapter 3.1 the SocketCAN core uses several filter + lists to deliver received CAN frames to CAN protocol modules. These + receive lists, their filters and the count of filter matches can be + checked in the appropriate receive list. All entries contain the + device and a protocol module identifier: + + foo@bar:~$ cat /proc/net/can/rcvlist_all + + receive list 'rx_all': + (vcan3: no entry) + (vcan2: no entry) + (vcan1: no entry) + device can_id can_mask function userdata matches ident + vcan0 000 00000000 f88e6370 f6c6f400 0 raw + (any: no entry) + + In this example an application requests any CAN traffic from vcan0. + + rcvlist_all - list for unfiltered entries (no filter operations) + rcvlist_eff - list for single extended frame (EFF) entries + rcvlist_err - list for error message frames masks + rcvlist_fil - list for mask/value filters + rcvlist_inv - list for mask/value filters (inverse semantic) + rcvlist_sff - list for single standard frame (SFF) entries + + Additional procfs files in /proc/net/can + + stats - SocketCAN core statistics (rx/tx frames, match ratios, ...) + reset_stats - manual statistic reset + version - prints the SocketCAN core version and the ABI version + + 5.3 writing own CAN protocol modules + + To implement a new protocol in the protocol family PF_CAN a new + protocol has to be defined in include/linux/can.h . + The prototypes and definitions to use the SocketCAN core can be + accessed by including include/linux/can/core.h . + In addition to functions that register the CAN protocol and the + CAN device notifier chain there are functions to subscribe CAN + frames received by CAN interfaces and to send CAN frames: + + can_rx_register - subscribe CAN frames from a specific interface + can_rx_unregister - unsubscribe CAN frames from a specific interface + can_send - transmit a CAN frame (optional with local loopback) + + For details see the kerneldoc documentation in net/can/af_can.c or + the source code of net/can/raw.c or net/can/bcm.c . + +6. CAN network drivers +---------------------- + + Writing a CAN network device driver is much easier than writing a + CAN character device driver. Similar to other known network device + drivers you mainly have to deal with: + + - TX: Put the CAN frame from the socket buffer to the CAN controller. + - RX: Put the CAN frame from the CAN controller to the socket buffer. + + See e.g. at Documentation/networking/netdevices.txt . The differences + for writing CAN network device driver are described below: + + 6.1 general settings + + dev->type = ARPHRD_CAN; /* the netdevice hardware type */ + dev->flags = IFF_NOARP; /* CAN has no arp */ + + dev->mtu = CAN_MTU; /* sizeof(struct can_frame) -> legacy CAN interface */ + + or alternative, when the controller supports CAN with flexible data rate: + dev->mtu = CANFD_MTU; /* sizeof(struct canfd_frame) -> CAN FD interface */ + + The struct can_frame or struct canfd_frame is the payload of each socket + buffer (skbuff) in the protocol family PF_CAN. + + 6.2 local loopback of sent frames + + As described in chapter 3.2 the CAN network device driver should + support a local loopback functionality similar to the local echo + e.g. of tty devices. In this case the driver flag IFF_ECHO has to be + set to prevent the PF_CAN core from locally echoing sent frames + (aka loopback) as fallback solution: + + dev->flags = (IFF_NOARP | IFF_ECHO); + + 6.3 CAN controller hardware filters + + To reduce the interrupt load on deep embedded systems some CAN + controllers support the filtering of CAN IDs or ranges of CAN IDs. + These hardware filter capabilities vary from controller to + controller and have to be identified as not feasible in a multi-user + networking approach. The use of the very controller specific + hardware filters could make sense in a very dedicated use-case, as a + filter on driver level would affect all users in the multi-user + system. The high efficient filter sets inside the PF_CAN core allow + to set different multiple filters for each socket separately. + Therefore the use of hardware filters goes to the category 'handmade + tuning on deep embedded systems'. The author is running a MPC603e + @133MHz with four SJA1000 CAN controllers from 2002 under heavy bus + load without any problems ... + + 6.4 The virtual CAN driver (vcan) + + Similar to the network loopback devices, vcan offers a virtual local + CAN interface. A full qualified address on CAN consists of + + - a unique CAN Identifier (CAN ID) + - the CAN bus this CAN ID is transmitted on (e.g. can0) + + so in common use cases more than one virtual CAN interface is needed. + + The virtual CAN interfaces allow the transmission and reception of CAN + frames without real CAN controller hardware. Virtual CAN network + devices are usually named 'vcanX', like vcan0 vcan1 vcan2 ... + When compiled as a module the virtual CAN driver module is called vcan.ko + + Since Linux Kernel version 2.6.24 the vcan driver supports the Kernel + netlink interface to create vcan network devices. The creation and + removal of vcan network devices can be managed with the ip(8) tool: + + - Create a virtual CAN network interface: + $ ip link add type vcan + + - Create a virtual CAN network interface with a specific name 'vcan42': + $ ip link add dev vcan42 type vcan + + - Remove a (virtual CAN) network interface 'vcan42': + $ ip link del vcan42 + + 6.5 The CAN network device driver interface + + The CAN network device driver interface provides a generic interface + to setup, configure and monitor CAN network devices. The user can then + configure the CAN device, like setting the bit-timing parameters, via + the netlink interface using the program "ip" from the "IPROUTE2" + utility suite. The following chapter describes briefly how to use it. + Furthermore, the interface uses a common data structure and exports a + set of common functions, which all real CAN network device drivers + should use. Please have a look to the SJA1000 or MSCAN driver to + understand how to use them. The name of the module is can-dev.ko. + + 6.5.1 Netlink interface to set/get devices properties + + The CAN device must be configured via netlink interface. The supported + netlink message types are defined and briefly described in + "include/linux/can/netlink.h". CAN link support for the program "ip" + of the IPROUTE2 utility suite is available and it can be used as shown + below: + + - Setting CAN device properties: + + $ ip link set can0 type can help + Usage: ip link set DEVICE type can + [ bitrate BITRATE [ sample-point SAMPLE-POINT] ] | + [ tq TQ prop-seg PROP_SEG phase-seg1 PHASE-SEG1 + phase-seg2 PHASE-SEG2 [ sjw SJW ] ] + + [ loopback { on | off } ] + [ listen-only { on | off } ] + [ triple-sampling { on | off } ] + + [ restart-ms TIME-MS ] + [ restart ] + + Where: BITRATE := { 1..1000000 } + SAMPLE-POINT := { 0.000..0.999 } + TQ := { NUMBER } + PROP-SEG := { 1..8 } + PHASE-SEG1 := { 1..8 } + PHASE-SEG2 := { 1..8 } + SJW := { 1..4 } + RESTART-MS := { 0 | NUMBER } + + - Display CAN device details and statistics: + + $ ip -details -statistics link show can0 + 2: can0: <NOARP,UP,LOWER_UP,ECHO> mtu 16 qdisc pfifo_fast state UP qlen 10 + link/can + can <TRIPLE-SAMPLING> state ERROR-ACTIVE restart-ms 100 + bitrate 125000 sample_point 0.875 + tq 125 prop-seg 6 phase-seg1 7 phase-seg2 2 sjw 1 + sja1000: tseg1 1..16 tseg2 1..8 sjw 1..4 brp 1..64 brp-inc 1 + clock 8000000 + re-started bus-errors arbit-lost error-warn error-pass bus-off + 41 17457 0 41 42 41 + RX: bytes packets errors dropped overrun mcast + 140859 17608 17457 0 0 0 + TX: bytes packets errors dropped carrier collsns + 861 112 0 41 0 0 + + More info to the above output: + + "<TRIPLE-SAMPLING>" + Shows the list of selected CAN controller modes: LOOPBACK, + LISTEN-ONLY, or TRIPLE-SAMPLING. + + "state ERROR-ACTIVE" + The current state of the CAN controller: "ERROR-ACTIVE", + "ERROR-WARNING", "ERROR-PASSIVE", "BUS-OFF" or "STOPPED" + + "restart-ms 100" + Automatic restart delay time. If set to a non-zero value, a + restart of the CAN controller will be triggered automatically + in case of a bus-off condition after the specified delay time + in milliseconds. By default it's off. + + "bitrate 125000 sample-point 0.875" + Shows the real bit-rate in bits/sec and the sample-point in the + range 0.000..0.999. If the calculation of bit-timing parameters + is enabled in the kernel (CONFIG_CAN_CALC_BITTIMING=y), the + bit-timing can be defined by setting the "bitrate" argument. + Optionally the "sample-point" can be specified. By default it's + 0.000 assuming CIA-recommended sample-points. + + "tq 125 prop-seg 6 phase-seg1 7 phase-seg2 2 sjw 1" + Shows the time quanta in ns, propagation segment, phase buffer + segment 1 and 2 and the synchronisation jump width in units of + tq. They allow to define the CAN bit-timing in a hardware + independent format as proposed by the Bosch CAN 2.0 spec (see + chapter 8 of http://www.semiconductors.bosch.de/pdf/can2spec.pdf). + + "sja1000: tseg1 1..16 tseg2 1..8 sjw 1..4 brp 1..64 brp-inc 1 + clock 8000000" + Shows the bit-timing constants of the CAN controller, here the + "sja1000". The minimum and maximum values of the time segment 1 + and 2, the synchronisation jump width in units of tq, the + bitrate pre-scaler and the CAN system clock frequency in Hz. + These constants could be used for user-defined (non-standard) + bit-timing calculation algorithms in user-space. + + "re-started bus-errors arbit-lost error-warn error-pass bus-off" + Shows the number of restarts, bus and arbitration lost errors, + and the state changes to the error-warning, error-passive and + bus-off state. RX overrun errors are listed in the "overrun" + field of the standard network statistics. + + 6.5.2 Setting the CAN bit-timing + + The CAN bit-timing parameters can always be defined in a hardware + independent format as proposed in the Bosch CAN 2.0 specification + specifying the arguments "tq", "prop_seg", "phase_seg1", "phase_seg2" + and "sjw": + + $ ip link set canX type can tq 125 prop-seg 6 \ + phase-seg1 7 phase-seg2 2 sjw 1 + + If the kernel option CONFIG_CAN_CALC_BITTIMING is enabled, CIA + recommended CAN bit-timing parameters will be calculated if the bit- + rate is specified with the argument "bitrate": + + $ ip link set canX type can bitrate 125000 + + Note that this works fine for the most common CAN controllers with + standard bit-rates but may *fail* for exotic bit-rates or CAN system + clock frequencies. Disabling CONFIG_CAN_CALC_BITTIMING saves some + space and allows user-space tools to solely determine and set the + bit-timing parameters. The CAN controller specific bit-timing + constants can be used for that purpose. They are listed by the + following command: + + $ ip -details link show can0 + ... + sja1000: clock 8000000 tseg1 1..16 tseg2 1..8 sjw 1..4 brp 1..64 brp-inc 1 + + 6.5.3 Starting and stopping the CAN network device + + A CAN network device is started or stopped as usual with the command + "ifconfig canX up/down" or "ip link set canX up/down". Be aware that + you *must* define proper bit-timing parameters for real CAN devices + before you can start it to avoid error-prone default settings: + + $ ip link set canX up type can bitrate 125000 + + A device may enter the "bus-off" state if too many errors occurred on + the CAN bus. Then no more messages are received or sent. An automatic + bus-off recovery can be enabled by setting the "restart-ms" to a + non-zero value, e.g.: + + $ ip link set canX type can restart-ms 100 + + Alternatively, the application may realize the "bus-off" condition + by monitoring CAN error message frames and do a restart when + appropriate with the command: + + $ ip link set canX type can restart + + Note that a restart will also create a CAN error message frame (see + also chapter 3.4). + + 6.6 CAN FD (flexible data rate) driver support + + CAN FD capable CAN controllers support two different bitrates for the + arbitration phase and the payload phase of the CAN FD frame. Therefore a + second bit timing has to be specified in order to enable the CAN FD bitrate. + + Additionally CAN FD capable CAN controllers support up to 64 bytes of + payload. The representation of this length in can_frame.can_dlc and + canfd_frame.len for userspace applications and inside the Linux network + layer is a plain value from 0 .. 64 instead of the CAN 'data length code'. + The data length code was a 1:1 mapping to the payload length in the legacy + CAN frames anyway. The payload length to the bus-relevant DLC mapping is + only performed inside the CAN drivers, preferably with the helper + functions can_dlc2len() and can_len2dlc(). + + The CAN netdevice driver capabilities can be distinguished by the network + devices maximum transfer unit (MTU): + + MTU = 16 (CAN_MTU) => sizeof(struct can_frame) => 'legacy' CAN device + MTU = 72 (CANFD_MTU) => sizeof(struct canfd_frame) => CAN FD capable device + + The CAN device MTU can be retrieved e.g. with a SIOCGIFMTU ioctl() syscall. + N.B. CAN FD capable devices can also handle and send legacy CAN frames. + + FIXME: Add details about the CAN FD controller configuration when available. + + 6.7 Supported CAN hardware + + Please check the "Kconfig" file in "drivers/net/can" to get an actual + list of the support CAN hardware. On the SocketCAN project website + (see chapter 7) there might be further drivers available, also for + older kernel versions. + +7. SocketCAN resources +----------------------- + + The Linux CAN / SocketCAN project ressources (project site / mailing list) + are referenced in the MAINTAINERS file in the Linux source tree. + Search for CAN NETWORK [LAYERS|DRIVERS]. + +8. Credits +---------- + + Oliver Hartkopp (PF_CAN core, filters, drivers, bcm, SJA1000 driver) + Urs Thuermann (PF_CAN core, kernel integration, socket interfaces, raw, vcan) + Jan Kizka (RT-SocketCAN core, Socket-API reconciliation) + Wolfgang Grandegger (RT-SocketCAN core & drivers, Raw Socket-API reviews, + CAN device driver interface, MSCAN driver) + Robert Schwebel (design reviews, PTXdist integration) + Marc Kleine-Budde (design reviews, Kernel 2.6 cleanups, drivers) + Benedikt Spranger (reviews) + Thomas Gleixner (LKML reviews, coding style, posting hints) + Andrey Volkov (kernel subtree structure, ioctls, MSCAN driver) + Matthias Brukner (first SJA1000 CAN netdevice implementation Q2/2003) + Klaus Hitschler (PEAK driver integration) + Uwe Koppe (CAN netdevices with PF_PACKET approach) + Michael Schulze (driver layer loopback requirement, RT CAN drivers review) + Pavel Pisa (Bit-timing calculation) + Sascha Hauer (SJA1000 platform driver) + Sebastian Haas (SJA1000 EMS PCI driver) + Markus Plessing (SJA1000 EMS PCI driver) + Per Dalen (SJA1000 Kvaser PCI driver) + Sam Ravnborg (reviews, coding style, kbuild help) |