在网上搜了很多关于树莓派串口通讯的例子，但是都是用python写的，虽然python很有名，而且最近也在学习这门语言，
但是还是想用c语言实现一下，因为需要用到整套系统里，其他内容都是用c语言写的。但是网上没有找打现成的。
还好，之前做过天嵌2440开发板的串口程序（参照天嵌工程师提供的代码），发现串口程序其实是通用的，
驱动层屏蔽了硬件细节，个人猜测，几乎所有移植好的系统的串口，都可以用一样的代码来操作，至少2440和树莓派是通用的。
分享代码如下：
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <termios.h>
#include <errno.h>
#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <unistd.h>
#include"pthread.h"
#include "serial.h"
struct serial_config serialread;
static int serial_fd;
int speed_arr[] = {B230400, B115200, B57600, B38400, B19200, B9600, B4800, B2400, B1200, B300,
B38400, B19200, B9600, B4800, B2400, B1200, B300};
int name_arr[] = {230400, 115200, 57600, 38400, 19200, 9600, 4800, 2400, 1200, 300,
38400, 19200, 9600, 4800, 2400, 1200, 300};
//-----------------------------------------------
//打印配置文件serial.cfg的内容
//-----------------------------------------------
void print_serialread()
{
printf("serialread.dev is %s\n",serialread.serial_dev);
printf("serialread.speed is %d\n",serialread.serial_speed);
printf("serialread.databits is %d\n",serialread.databits);
printf("serialread.stopbits is %d\n",serialread.stopbits);
printf("serialread.parity is %c\n",serialread.parity);
}
//-----------------------------------------------
//读取serial.cfg文件并进行配置
//-----------------------------------------------
void readserialcfg()
{
FILE *serial_fp;
char j[10];
printf("readserailcfg\n");
serial_fp = fopen("./serial.cfg","r");
if(NULL == serial_fp)
{
printf("can't open serial.cfg");
}
else
{
fscanf(serial_fp, "DEV=%s\n", serialread.serial_dev);
fscanf(serial_fp, "SPEED=%s\n", j);
serialread.serial_speed = atoi(j);
fscanf(serial_fp, "DATABITS=%s\n", j);
serialread.databits = atoi(j);
fscanf(serial_fp, "STOPBITS=%s\n", j);
serialread.stopbits = atoi(j);
fscanf(serial_fp, "PARITY=%s\n", j);
serialread.parity = j[0];
}
fclose(serial_fp);
}
//-----------------------------------------------
//设置波特率
//-----------------------------------------------
void set_speed(int fd)
{
int i;
int status;
struct termios Opt;
struct termios oldOpt;
tcgetattr(fd, &oldOpt);
// printf("serialread.speed is %d\n",serialread.serial_speed);
for( i = 0; i < sizeof(speed_arr)/sizeof(int); i++)
{
if(serialread.serial_speed == name_arr[i])
{
tcflush(fd, TCIOFLUSH);
cfsetispeed(&Opt, speed_arr[i]);
cfsetospeed(&Opt, speed_arr[i]);
status = tcsetattr(fd, TCSANOW, &Opt);
if(status != 0)
{
perror("tcsetattr fd1");
return;
}
tcflush(fd, TCIOFLUSH);
}
}
}
//-----------------------------------------------
//设置其他参数
//-----------------------------------------------
int (int fd)
{
struct termios options;
struct termios oldoptions;
if(tcgetattr(fd, &oldoptions) != 0)
{
perror("SetupSerial 1");
return(FALSE);
}
options.c_cflag |= (CLOCAL|CREAD);
options.c_cflag &=~CSIZE;
// printf("serialread.databits is %d\n",serialread.databits);
switch(serialread.databits)
{
case 7:
options.c_cflag |= CS7;
break;
case 8:
options.c_cflag |= CS8;
break;
default:
options.c_cflag |= CS8;
fprintf(stderr, "Unsupported data size\n");
return(FALSE);
}
// printf("serialread.parity is %c\n",serialread.parity);
switch(serialread.parity)
{
case 'n':
case 'N':
options.c_cflag &= ~PARENB;
options.c_iflag &= ~INPCK;
break;
case 'o':
case 'O':
options.c_cflag |= (PARODD | PARENB);
options.c_iflag |= INPCK;
break;
case 'e':
case 'E':
options.c_cflag |= PARENB;
options.c_cflag &= ~PARODD;
options.c_iflag |= INPCK;
break;
default:
options.c_cflag &= ~PARENB;
options.c_iflag &= ~INPCK;
fprintf(stderr, "Unsupported parity\n");
return(FALSE);
}
// printf("serialread.stopbits is %d\n",serialread.stopbits);
switch(serialread.stopbits)
{
case 1:
options.c_cflag &= ~CSTOPB;
break;
case 2:
options.c_cflag |= CSTOPB;
break;
default:
options.c_cflag &= ~CSTOPB;
fprintf(stderr, "Unsupported stop bits\n");
return(FALSE);
}
if(serialread.parity != 'n')
options.c_iflag |= INPCK;
options.c_cc[VTIME] = 0; //150; //15 seconds
options.c_cc[VMIN] = 0;
#if 1
options.c_iflag |= IGNPAR|ICRNL;
options.c_oflag |= OPOST;
options.c_iflag &= ~(IXON|IXOFF|IXANY);
#endif
tcflush(fd, TCIFLUSH);
if(tcsetattr(fd, TCSANOW, &options) != 0)
{
perror("SetupSerial 3");
return(FALSE);
}
return(TRUE);
}
//-----------------------------------------------
//打开串口设备
//-----------------------------------------------
int OpenDev(char *Dev)
{
int fd = open(Dev, O_RDWR, 0);
if(-1 == fd)
{
perror("Can't Open Serial Port");
return -1;
}
else
return fd;
}
//--------------------------------------------------
//串口初始化
//--------------------------------------------------
void serial_init()
{
char *Dev;
int i;
readserialcfg();
//print_serialread();
printf("init serial\n");
Dev = serialread.serial_dev;
//打开串口设备
serial_fd = OpenDev(Dev);
if(serial_fd > 0)
set_speed(serial_fd); //设置波特率
else
{
printf("Can't Open Serial Port!\n");
exit(0);
}
//恢复串口未阻塞状态
if (fcntl(serial_fd, F_SETFL, O_NONBLOCK) < 0)
{
printf("fcntl failed!\n");
exit(0);
}
//检查是否是终端设备
#if 0 //如果屏蔽下面这段代码，在串口输入时不会有回显的情况，调用下面这段代码时会出现回显现象。
if(isatty(STDIN_FILENO)==0)
{
printf("standard input is not a terminal device\n");
}
else
printf("isatty success!\n");
#endif
//设置串口参数
if(set_Parity(serial_fd) == FALSE)
{
printf("Set parity Error\n");
exit(1);
}
}
int serial_write(char* cmd, int count)
{
printf("serial write for %d bytes\n",count);
return write(serial_fd,cmd,count);
}
void serial_close()
{
printf("close serial\n");
close(serial_fd);
}
/*
void serial_rw()
{
int i;
char buff[512];
int nread,nwrite;
char buff2[] = "hello!\n";
nwrite = write(serial_fd,buff2,sizeof(buff2));
printf("nwrite=%d\n",nwrite);
while(1)
{
if((nread = read(serial_fd,buff,512))>0)
{
buff[nread] = '\0';
#if 1 //调用这段代码可以实现回显，如果配合上面的回显，就会出现回显两次的情况。
write(serial_fd,buff,nread);
#endif
printf("recv:%d\n",nread);
#if 1
for(i=0;i<nread;i++)
{
printf("%c",buff[i]);
}
printf("\n");
#else
printf("%s",buff);
printf("\n");
#endif
}
}
}
*/
/*
int main(int argc, char **argv)
{
serial_init();
char cmd[]={0xfc,0x01,0x01,0x02,0x01,0x00,0x03,0x01,0xcf};
write(serial_fd,cmd,sizeof(cmd));
close(serial_fd);
return 0;
// close(serialread.serial_dev);
// serial_test(telnum, telmoney);
}
*/
当然，还需要对应的头文件：
#define FALSE 0
#define TRUE 1
#define WORDLEN 32
struct serial_config
{
unsigned char serial_dev[WORDLEN];
unsigned int serial_speed;
unsigned char databits;
unsigned char stopbits;
unsigned char parity;
};
void serial_init();
int serial_write(char* cmd, int count);
void serial_close();
以及分离出来的配置文件：
DEV=/dev/ttyAMA0
SPEED=9600
DATABITS=8
STOPBITS=1
PARITY=N
看到c文件可以发现，main函数被注释了，因为是编译的整个系统，这个文件只提供接口，所以没有main函数，如果需要，可以去掉注释。
内容很粗糙，有时间再修缮
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