前言
本文主要介绍socketCan中的发送函数cansend的源码解析.
代码
/*
* 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 = ;
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 ;
} /* open socket */
if ((s = socket(PF_CAN, SOCK_RAW, CAN_RAW)) < ) {
perror("socket");
return ;
} 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 ;
} memset(&addr, , 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, ); if (bind(s, (struct sockaddr *)&addr, sizeof(addr)) < ) {
perror("bind");
return ;
} /* 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 ;
} close(s); return ;
}
解析
1.message的格式；
char* input = "008#abcd1234cdef567830";
其中‘008表示can_id，必须是三位十六进制数据，可以表示标准帧或者扩展帧；符号#“是can_id和can数据的分界符，最后的数据是报文的数据，标准帧一次最多只能发送8bits的数据，多余的数据自动丢弃；
2.parse_canframe函数，具体内容可参考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.创建socket；
s = socket(PF_CAN, SOCK_RAW, CAN_RAW)
创建socket套接字
PF_CAN 为域位，同网络编程中的AF_INET，即ipv4协议；
SOCK_RAW使用的协议类型，SOCK_RAW表示原始套接字，报文头由自己创建；
CAN_RAW为使用的具体协议，为can总线协议；
4. 指定can口名称；
const char* ifrname = "can1";
5.发送数据则禁止过滤；
setsockopt(s, SOL_CAN_RAW, CAN_RAW_FILTER, NULL, ); //Disable filter.
6.绑定socketCan；
bind(s, (struct sockaddr *)&addr, sizeof(addr)
bind函数用于绑定套接字，即将套接字和canbus外设进行绑定；
7.发送数据；
/* send frame */
if (write(s, &frame, required_mtu) != required_mtu) { //发送数据！
perror("write");
return ;
}
8.数据格式的定义；
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()));
};
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()));
};
#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；
参考
完