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Diffstat (limited to 'Documentation/networking/can.txt')
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1 files changed, 290 insertions, 64 deletions
diff --git a/Documentation/networking/can.txt b/Documentation/networking/can.txt index 820f55344ed..2236d6dcb7d 100644 --- a/Documentation/networking/can.txt +++ b/Documentation/networking/can.txt @@ -2,21 +2,20 @@ can.txt -Readme file for the Controller Area Network Protocol Family (aka Socket CAN) +Readme file for the Controller Area Network Protocol Family (aka SocketCAN) This file contains - 1 Overview / What is Socket CAN + 1 Overview / What is SocketCAN 2 Motivation / Why using the socket API - 3 Socket CAN concept + 3 SocketCAN concept 3.1 receive lists 3.2 local loopback of sent frames - 3.3 network security issues (capabilities) - 3.4 network problem notifications + 3.3 network problem notifications - 4 How to use Socket CAN + 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 @@ -25,10 +24,16 @@ This file contains 4.1.5 RAW socket option CAN_RAW_FD_FRAMES 4.1.6 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 Socket CAN core module + 5 SocketCAN core module 5.1 can.ko module params 5.2 procfs content 5.3 writing own CAN protocol modules @@ -45,20 +50,20 @@ This file contains 6.6 CAN FD (flexible data rate) driver support 6.7 supported CAN hardware - 7 Socket CAN resources + 7 SocketCAN resources 8 Credits ============================================================================ -1. Overview / What is Socket CAN +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, Socket CAN uses the Berkeley +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, @@ -68,7 +73,7 @@ sockets. 2. Motivation / Why using the socket API ---------------------------------------- -There have been CAN implementations for Linux before Socket CAN so the +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 @@ -83,10 +88,10 @@ 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. -Socket CAN was designed to overcome all of these limitations. A new +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, so to use all of the provided queueing functionality. A device +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 @@ -140,15 +145,15 @@ solution for a couple of reasons: 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 - Socket CAN does. + 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. Socket CAN concept +3. SocketCAN concept --------------------- - As described in chapter 2 it is the main goal of Socket CAN to + 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(!) @@ -162,11 +167,11 @@ solution for a couple of reasons: 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 Socket CAN core + 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 Socket CAN core that are + 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 @@ -211,21 +216,7 @@ solution for a couple of reasons: * = you really like to have this when you're running analyser tools like 'candump' or 'cansniffer' on the (same) node. - 3.3 network security issues (capabilities) - - The Controller Area Network is a local field bus transmitting only - broadcast messages without any routing and security concepts. - In the majority of cases the user application has to deal with - raw CAN frames. Therefore it might be reasonable NOT to restrict - the CAN access only to the user root, as known from other networks. - Since the currently implemented CAN_RAW and CAN_BCM sockets can only - send and receive frames to/from CAN interfaces it does not affect - security of others networks to allow all users to access the CAN. - To enable non-root users to access CAN_RAW and CAN_BCM protocol - sockets the Kconfig options CAN_RAW_USER and/or CAN_BCM_USER may be - selected at kernel compile time. - - 3.4 network problem notifications + 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 @@ -245,11 +236,11 @@ solution for a couple of reasons: by default. The format of the CAN error message frame is briefly described in the Linux header file "include/linux/can/error.h". -4. How to use Socket CAN +4. How to use SocketCAN ------------------------ Like TCP/IP, you first need to open a socket for communicating over a - CAN network. Since Socket CAN implements a new protocol family, you + 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, @@ -280,8 +271,8 @@ solution for a couple of reasons: }; The alignment of the (linear) payload data[] to a 64bit boundary - allows the user to define own structs and unions to easily access the - CAN payload. There is no given byteorder on the CAN bus by + 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. @@ -473,11 +464,46 @@ solution for a couple of reasons: setsockopt(s, SOL_CAN_RAW, CAN_RAW_FILTER, NULL, 0); - To set the filters to zero filters is quite obsolete as not read + 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 @@ -563,12 +589,6 @@ solution for a couple of reasons: not specified in the struct can_frame and therefore it is only valid in CANFD_MTU sized CAN FD frames. - As long as the payload length is <=8 the received CAN frames from CAN FD - capable CAN devices can be received and read by legacy sockets too. When - user-generated CAN FD frames have a payload length <=8 these can be send - by legacy CAN network interfaces too. Sending CAN FD frames with payload - length > 8 to a legacy CAN network interface returns an -EMSGSIZE error. - Implementation hint for new CAN applications: To build a CAN FD aware application use struct canfd_frame as basic CAN @@ -593,21 +613,232 @@ solution for a couple of reasons: 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. Socket CAN core module +5. SocketCAN core module ------------------------- - The Socket CAN core module implements the protocol family + 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 Socket CAN core statistics + - 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. @@ -616,7 +847,7 @@ solution for a couple of reasons: 5.2 procfs content - As described in chapter 3.1 the Socket CAN core uses several filter + 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 @@ -643,15 +874,15 @@ solution for a couple of reasons: Additional procfs files in /proc/net/can - stats - Socket CAN core statistics (rx/tx frames, match ratios, ...) + stats - SocketCAN core statistics (rx/tx frames, match ratios, ...) reset_stats - manual statistic reset - version - prints the Socket CAN core version and the ABI version + 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 Socket CAN core can be + 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 @@ -821,7 +1052,7 @@ solution for a couple of reasons: 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" + "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 @@ -888,7 +1119,7 @@ solution for a couple of reasons: $ ip link set canX up type can bitrate 125000 - A device may enter the "bus-off" state if too much errors occurred on + 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.: @@ -908,7 +1139,7 @@ solution for a couple of reasons: 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 bittiming has to be specified in order to enable the CAN FD bitrate. + 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 @@ -933,21 +1164,16 @@ solution for a couple of reasons: 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 Socket CAN project website + 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. Socket CAN resources +7. SocketCAN resources ----------------------- - You can find further resources for Socket CAN like user space tools, - support for old kernel versions, more drivers, mailing lists, etc. - at the BerliOS OSS project website for Socket CAN: - - http://developer.berlios.de/projects/socketcan - - If you have questions, bug fixes, etc., don't hesitate to post them to - the Socketcan-Users mailing list. But please search the archives first. + 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 ---------- |