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| -rw-r--r-- | Documentation/networking/can.txt | 217 |
1 files changed, 217 insertions, 0 deletions
diff --git a/Documentation/networking/can.txt b/Documentation/networking/can.txt index 820f55344edc..4c072414eadb 100644 --- a/Documentation/networking/can.txt +++ b/Documentation/networking/can.txt @@ -25,6 +25,12 @@ 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) @@ -593,6 +599,217 @@ 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 occured, 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) |