CANBUS 發送與接收使用Socket CAN

參考文件 https://www.kernel.org/doc/Documentation/networking/can.txt
中文參考 http://blog.csdn.net/yuanlulu/article/details/7220060

控制器區域網路 (Controller Area Network, 簡稱 CAN 或 CANbus)

一種通訊協定，主要應用在汽車、工控領域。

目前版本CAN 2.0A與CAN 2.0B ,B是A的擴充。2.0B 的ID長度占29bit， 2.0A 的ID長度占11bit

節點架構


CAN Controller 通常內建於MCU內(也有獨立的ex: SJA1000)，會在外接Transceiver(ex:ISO1050)轉成類比訊號。

CAN封包格式


寫基本的CAN，只需要注意仲裁欄位、控制欄位、資料欄位

Field name	Length (bits)	Purpose
Start-of-frame	1	Denotes the start of frame transmission
Identifier (green)	11	A (unique) identifier which also represents the message priority
Remote transmission request (RTR)	1	Must be dominant (0) for data frames and recessive (1) for remote request frames (see Remote Frame, below)
Identifier extension bit (IDE)	1	Must be dominant (0) for base frame format with 11-bit identifiers
Reserved bit (r0)	1	Reserved bit. Must be dominant (0), but accepted as either dominant or recessive.
Data length code (DLC) (yellow)	4	Number of bytes of data (0–8 bytes)[a]
Data field (red)	0–64 (0-8 bytes)	Data to be transmitted (length in bytes dictated by DLC field)
CRC	15	Cyclic redundancy check
CRC delimiter	1	Must be recessive (1)
ACK slot	1	Transmitter sends recessive (1) and any receiver can assert a dominant (0)
ACK delimiter	1	Must be recessive (1)
End-of-frame (EOF)	7	Must be recessive (1)

CAN BUS的操作可以如同使用SOCKET。

參考Linux下範例 candsend.c   candump.c

看完除了會can 的發送與接收，也可以學到命令列參數使用方法 (function: getopt_long)

以下簡單範例：

Setting :

    struct can_frame frame;
    struct ifreq ifr;
    struct sockaddr_can addr;
    char *interface = "can0";
    int family = PF_CAN, type = SOCK_RAW, proto = CAN_RAW;

    s = socket(family, type, proto)
    strncpy(ifr.ifr_name, interface, sizeof(ifr.ifr_name));
    if (ioctl(s, SIOCGIFINDEX, &ifr)) {
        perror("CAN ioctl");
        return 1;
    }
    addr.can_family = family;
    addr.can_ifindex = ifr.ifr_ifindex;

    if (bind(s, (struct sockaddr *)&addr, sizeof(addr)) < 0) {
        perror("CAN bind");
        return 1;
    }

Send :

//sendcanbus();
            frame.can_id = 0x0321;
            frame.can_dlc = 4;
            frame.data[0] = 0;
            frame.data[1] = 1;
            frame.data[2] = 2;
            frame.data[3] = 3;

            ret = send(s,&frame,sizeof(frame),0);

Read :

            //dropt the timeout packets
            while(nbytes = recvfrom(s,&frame,sizeof(struct can_frame),0,(struct sockaddr*)&addr,&len)>=0)
            {
                printf("\r\nrecvfrom nbytes %d",nbytes);
                memcpy(b,&frame,sizeof(frame));
                for (i=0 ; i < sizeof(struct can_frame) ; i++)
                {
                    printf(" 0x%x ",b[i]);
                }
                usleep(10000);//
            }