前言

本文主要介紹socketCan中的發送函數cansend的源碼解析.

代碼

/** cansend.c - simple command line tool to send CAN-frames via CAN_RAW sockets** Copyright (c) 2002-2007 Volkswagen Group Electronic Research* All rights reserved.** Redistribution and use in source and binary forms, with or without* modification, are permitted provided that the following conditions* are met:* 1. Redistributions of source code must retain the above copyright* notice, this list of conditions and the following disclaimer.* 2. Redistributions in binary form must reproduce the above copyright* notice, this list of conditions and the following disclaimer in the* documentation and/or other materials provided with the distribution.* 3. Neither the name of Volkswagen nor the names of its contributors* may be used to endorse or promote products derived from this software* without specific prior written permission.** Alternatively, provided that this notice is retained in full, this* software may be distributed under the terms of the GNU General* Public License ("GPL") version 2, in which case the provisions of the* GPL apply INSTEAD OF those given above.** The provided data structures and external interfaces from this code* are not restricted to be used by modules with a GPL compatible license.** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH* DAMAGE.** Send feedback to <linux-can@vger.kernel.org>**/#include <stdio.h> #include <stdlib.h> #include <string.h> #include <unistd.h>#include <net/if.h> #include <sys/ioctl.h> #include <sys/socket.h>#include <linux/can.h> #include <linux/can/raw.h>#include "lib.h"int main( ) {int s; /* can raw socket */ int required_mtu;int mtu;int enable_canfd = 1;struct sockaddr_can addr;struct canfd_frame frame;struct ifreq ifr;char* input = "008#abcd1234cdef567830";/* parse CAN frame */required_mtu = parse_canframe(input, &frame);printf("required_mtu is %d\n", required_mtu);printf("CAN_MTU is %d\n", (long unsigned int)CAN_MTU);//printf("CANID_DELIM is %d\n", CANID_DELIM);//#-35-0x23.printf("IFNAMSIZ is %d\n", IFNAMSIZ);if (!required_mtu){fprintf(stderr, "\nWrong CAN-frame format! Try:\n\n");fprintf(stderr, " <can_id>#{R|data} for CAN 2.0 frames\n");fprintf(stderr, " <can_id>##<flags>{data} for CAN FD frames\n\n");fprintf(stderr, "<can_id> can have 3 (SFF) or 8 (EFF) hex chars\n");fprintf(stderr, "{data} has 0..8 (0..64 CAN FD) ASCII hex-values (optionally");fprintf(stderr, " separated by '.')\n");fprintf(stderr, "<flags> a single ASCII Hex value (0 .. F) which defines");fprintf(stderr, " canfd_frame.flags\n\n");fprintf(stderr, "e.g. 5A1#11.2233.44556677.88 / 123#DEADBEEF / 5AA# / ");fprintf(stderr, "123##1 / 213##311\n 1F334455#1122334455667788 / 123#R ");fprintf(stderr, "for remote transmission request.\n\n");return 1;}/* open socket */if ((s = socket(PF_CAN, SOCK_RAW, CAN_RAW)) < 0) {perror("socket");return 1;}const char* ifrname = "can1";strcpy(ifr.ifr_name, ifrname);ifr.ifr_ifindex = if_nametoindex(ifr.ifr_name);if (!ifr.ifr_ifindex) {perror("if_nametoindex");return 1;}memset(&addr, 0, sizeof(addr));addr.can_family = AF_CAN;addr.can_ifindex = ifr.ifr_ifindex; /*if (required_mtu > CAN_MTU) {//* check if the frame fits into the CAN netdevice if (ioctl(s, SIOCGIFMTU, &ifr) < 0) {perror("SIOCGIFMTU");return 1;}mtu = ifr.ifr_mtu;if (mtu != CANFD_MTU) {printf("CAN interface is not CAN FD capable - sorry.\n");return 1;}//* interface is ok - try to switch the socket into CAN FD mode if (setsockopt(s, SOL_CAN_RAW, CAN_RAW_FD_FRAMES,&enable_canfd, sizeof(enable_canfd))){printf("error when enabling CAN FD support\n");return 1;}//* ensure discrete CAN FD length values 0..8, 12, 16, 20, 24, 32, 64 frame.len = can_dlc2len(can_len2dlc(frame.len));} *//* disable default receive filter on this RAW socket *//* This is obsolete as we do not read from the socket at all, but for *//* this reason we can remove the receive list in the Kernel to save a *//* little (really a very little!) CPU usage. */setsockopt(s, SOL_CAN_RAW, CAN_RAW_FILTER, NULL, 0);if (bind(s, (struct sockaddr *)&addr, sizeof(addr)) < 0) {perror("bind");return 1;}/* send frame */printf("frame.len is %d\n", frame.len);printf("frame.can_id is %x\n", frame.can_id);if (write(s, &frame, required_mtu) != required_mtu) {perror("write");return 1;}close(s);return 0; } View Code

解析

1.message的格式；

char* input = "008#abcd1234cdef567830";

其中‘008表示can_id，必須是三位十六進制數據，可以表示標準幀或者擴展幀；符號#“是can_id和can數據的分界符，最后的數據是報文的數據，標準幀一次最多只能發送8bits的數據，多余的數據自動丟棄；

2.parse_canframe函數，具體內容可參考lib.h和lib.c文件；

int parse_canframe(char *cs, struct canfd_frame *cf);
?/* parse CAN frame */
?required_mtu = parse_canframe(input, &frame);

function --?Transfers a valid ASCII string decribing a CAN frame into struct canfd_frame.

3.創建socket；

s = socket(PF_CAN, SOCK_RAW, CAN_RAW)

創建socket套接字

PF_CAN?為域位，同網絡編程中的AF_INET，即ipv4協議；?

SOCK_RAW使用的協議類型，SOCK_RAW表示原始套接字，報文頭由自己創建；?

CAN_RAW為使用的具體協議，為can總線協議；

4. 指定can口名稱；

const char* ifrname = "can1";

5.發送數據則禁止過濾；

setsockopt(s, SOL_CAN_RAW, CAN_RAW_FILTER, NULL, 0); //Disable filter.

6.綁定socketCan；

bind(s, (struct sockaddr *)&addr, sizeof(addr)

bind函數用于綁定套接字，即將套接字和canbus外設進行綁定；

7.發送數據；

/* send frame */ if (write(s, &frame, required_mtu) != required_mtu) { //發送數據！ perror("write"); return 1; }

8.數據格式的定義；

struct can_frame {canid_t can_id; /* 32 bit CAN_ID + EFF/RTR/ERR flags */__u8 can_dlc; /* frame payload length in byte (0 .. CAN_MAX_DLEN) */__u8 __pad; /* padding */__u8 __res0; /* reserved / padding */__u8 __res1; /* reserved / padding */__u8 data[CAN_MAX_DLEN] __attribute__((aligned(8))); }; struct canfd_frame {canid_t can_id; /* 32 bit CAN_ID + EFF/RTR/ERR flags */__u8 len; /* frame payload length in byte */__u8 flags; /* additional flags for CAN FD */__u8 __res0; /* reserved / padding */__u8 __res1; /* reserved / padding */__u8 data[CANFD_MAX_DLEN] __attribute__((aligned(8))); };#define CAN_MTU (sizeof(struct can_frame)) #define CANFD_MTU (sizeof(struct canfd_frame))

struct can_frame - basic CAN frame structure；

struct canfd_frame - CAN flexible data rate frame structure；

參考

1.linux平臺can總線編程模型；

2.can-utils-git；

完

轉載于:https://www.cnblogs.com/happyamyhope/p/8882568.html

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