https://blog.csdn.net/jinhongdu/article/details/43413071
对于非标准的任意波特率需要用ioctl(fd, TIOCGSERIAL, p)和ioctl(fd, TIOCSSERIAL, p)的配合，ioctl的最后一个参数是struct serial_struct *类型，在linux/serial.h中定义。
其中baud_base是基准晶振频率/16，通常是115200，你需要设的是custom_divisor这个值，最终的波特率为baud_base/custom_divisor，比如你需要28800，因为115200/4=28800，所以要设置custom_divisor=4，。
具体过程为，先设置波特率设为38400(tcsetattr)，然后用TIOCGSERIAL得到当前的设置，将flags设置ASYNC_SPD_CUST位，设置custom_divisor，最后用TIOCSSERIAL设置。
使用setserial其实就是利用上述方法,来设置baud_base, custom_divisor等, 其内部实现就是使用ioctl来进行设置。
网上的东西真的是参差不齐，希望能呈现完善的正确的Blog给大家。
由于是测试代码，只是保证可以运行。另外推荐一个串口调试助手AccessPort，可以提供28800的串口比特率作为测试。
#include <termios.h>
#include <sys/ioctl.h>
#include <stdio.h> /*标准输入输出定义*/
#include <stdlib.h> /*标准函数库定义*/
#include <unistd.h> /*Unix标准函数定义*/
#include <sys/types.h> /**/
#include <sys/stat.h> /**/
#include <fcntl.h> /*文件控制定义*/
#include <termios.h> /*PPSIX终端控制定义*/
#include <errno.h> /*错误号定义*/
#include <linux/serial.h>
#define TRUE 1
#define FALSE 0
/*
*功能：用于测试非标准波特率串口。
*此代码仅限于运行在X86架构的环境下，其他架构并未测试。在arm下未测试
*请在root下编译此代码
*如有问题，联系我：靳小都 hellojinhongdu#126.com
*/
struct serial_t {
int fd;
char *device;/*/dev/ttyS0,...*/
int baud;
int databit;/*5,6,7,8*/
char parity;/*O,E,N*/
int stopbit;/*1,2*/
int startbit;/*1*/
struct termios options;
};
int speed_arr[] = { B38400, B19200, B9600, B4800, B2400, B1200, B300,
B38400, B19200, B9600, B4800, B2400, B1200, B300, };
int name_arr[] = {38400, 19200, 9600, 4800, 2400, 1200, 300,
38400, 19200, 9600, 4800, 2400, 1200, 300, };
void set_speed(int fd, int speed)
{
int i;
int status;
struct termios Opt;
tcgetattr(fd, &Opt);
for ( i= 0; i < sizeof(speed_arr) / sizeof(int); i++)
{
if (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);
}
}
//设置为特诉波特率，比如28800
int serial_set_speci_baud(struct serial_t *tty,int baud)
{
struct serial_struct ss,ss_set;
tcgetattr(tty->fd,&tty->options);
cfsetispeed(&tty->options,B38400);
cfsetospeed(&tty->options,B38400);
tcflush(tty->fd,TCIFLUSH);/*handle unrecevie char*/
tcsetattr(tty->fd,TCSANOW,&tty->options);
if((ioctl(tty->fd,TIOCGSERIAL,&ss))<0){
printf("BAUD: error to get the serial_struct info:%s ",strerror(errno));
return -1;
}
ss.flags = ASYNC_SPD_CUST;
ss.custom_divisor = ss.baud_base / baud;
printf("ss.custom_divisor = %d ",ss.custom_divisor);
if((ioctl(tty->fd,TIOCSSERIAL,&ss))<0){
printf("BAUD: error to set serial_struct:%s ",strerror(errno));
//return -2;
}
ioctl(tty->fd,TIOCGSERIAL,&ss_set);
printf("BAUD: success set baud to %d,custom_divisor=%d,baud_base=%d ",
baud,ss_set.custom_divisor,ss_set.baud_base);
return 0;
}
/*get serial's current attribute*/
static int serial_get_attr(struct serial_t *tty)
{
if(tcgetattr(tty->fd,&tty->options) != 0){
printf("SERIAL: can't get serial's attribute ");
return -1;
}
return 0;
}
/*update serial's attrbute*/
static int serial_attr_update(struct serial_t *tty)
{
tcflush(tty->fd,TCIFLUSH);/*handle unrecevie char*/
if((tcsetattr(tty->fd,TCSANOW,&tty->options)) < 0){
return -1;
}
return 0;
}
static int serial_init_databit(struct serial_t *tty)
{
if(serial_get_attr(tty)<0)
return -1;
tty->options.c_cflag &= ~CSIZE;
switch(tty->databit){
case 5: tty->options.c_cflag |= CS5;break;
case 6: tty->options.c_cflag |= CS6;break;
case 7: tty->options.c_cflag |= CS7;break;
case 8: tty->options.c_cflag |= CS8;break;
default:
printf("SERIAL: unsupported databit %d ",tty->databit);
return -2;
}
if(serial_attr_update(tty) < 0)
return -3;
printf("SERIAL: set databit to %d ",tty->databit);
return 0;
}
static int serial_init_parity(struct serial_t *tty)
{
if(serial_get_attr(tty)<0)
return -1;
/*ignore framing and parity error*/
tty->options.c_iflag = IGNPAR;
switch (tty->parity){
case 'n':
case 'N':
/* Clear parity enable */
tty->options.c_cflag &= ~PARENB;
/* Enable parity checking */
tty->options.c_iflag &= ~INPCK;
break;
case 'o':
case 'O':
/* 设置为奇校检*/
tty->options.c_cflag |= (PARODD|PARENB);
/* Disnable parity checking */
tty->options.c_iflag |= (INPCK|ISTRIP);
break;
case 'e':
case 'E':
/* Enable parity */
tty->options.c_cflag |= PARENB;
/* 转换为偶效验*/
tty->options.c_cflag &= ~PARODD;
/* Disnable parity checking */
tty->options.c_iflag |= (INPCK|ISTRIP);
break;
default:
printf("SERIAL: unsupported parity %c ",tty->parity);
return -2;
}
if(serial_attr_update(tty) < 0)
return -3;
printf("SERIAL: set parity to %c ",tty->parity);
return 0;
}
static int serial_init_stopbit(struct serial_t *tty)
{
if(serial_get_attr(tty)<0)
return -1;
switch(tty->stopbit){
case 1:
tty->options.c_cflag &= ~CSTOPB;break;
case 2:
tty->options.c_cflag |= CSTOPB;break;
default:
printf("SERIAL: unsupported stopbit %d ",tty->stopbit);
return -2;
}
if(serial_attr_update(tty) < 0)
return -3;
printf("SERIAL: set stopbit to %d ",tty->stopbit);
return 0;
}
/**
*@brief 设置串口数据位，停止位和效验位
*@param fd 类型 int 打开的串口文件句柄*
*@param databits 类型 int 数据位 取值 为 7 或者8*
*@param stopbits 类型 int 停止位 取值为 1 或者2*
*@param parity 类型 int 效验类型 取值为N,E,O,,S
*/
int set_Parity(int fd,int databits,int stopbits,int parity)
{
struct termios options;
if ( tcgetattr( fd,&options) != 0)
{
perror("SetupSerial 1");
return(FALSE);
}
options.c_cflag &= ~CSIZE;
switch (databits) /*设置数据位数*/
{
case 7:
options.c_cflag |= CS7;
break;
case 8:
options.c_cflag |= CS8;
break;
default:
fprintf(stderr,"Unsupported data size ");
return (FALSE);
}
switch (parity)
{
case 'n':
case 'N':
options.c_cflag &= ~PARENB; /* Clear parity enable */
options.c_iflag &= ~INPCK; /* Enable parity checking */
break;
case 'o':
case 'O':
options.c_cflag |= (PARODD | PARENB); /* 设置为奇效验*/
options.c_iflag |= INPCK; /* Disnable parity checking */
break;
case 'e':
case 'E':
options.c_cflag |= PARENB; /* Enable parity */
options.c_cflag &= ~PARODD; /* 转换为偶效验*/
options.c_iflag |= INPCK; /* Disnable parity checking */
break;
case 'S':
case 's': /*as no parity*/
options.c_cflag &= ~PARENB;
options.c_cflag &= ~CSTOPB;
break;
default:
fprintf(stderr,"Unsupported parity ");
return (FALSE);
}
/* 设置停止位*/
switch (stopbits)
{
case 1:
options.c_cflag &= ~CSTOPB;
break;
case 2:
options.c_cflag |= CSTOPB;
break;
default:
fprintf(stderr,"Unsupported stop bits ");
return (FALSE);
}
/* Set input parity option */
if (parity != 'n')
options.c_iflag |= INPCK;
options.c_cc[VTIME] = 150; // 15 seconds
options.c_cc[VMIN] = 0;
tcflush(fd,TCIFLUSH); /* Update the options and do it NOW */
if (tcsetattr(fd,TCSANOW,&options) != 0)
{
perror("SetupSerial 3");
return (FALSE);
}
return (TRUE);
}
//用法：只要指定serial_t的baud就可以了
static struct serial_t __seri_conf[] = {
[0] = {//connect with b board, ttyS0
.device = "/dev/ttyS1",
.baud = 28800,
.databit = 8,
.parity = 'N',
.stopbit = 1,
},
};
/**
*@breif main()
*/
int main(int argc, char **argv) {
int fd;
int nread;
char buff[512];
fd = open(__seri_conf->device, O_RDWR | O_NOCTTY | O_NONBLOCK);
__seri_conf->fd = fd;
serial_set_speci_baud(__seri_conf, __seri_conf->baud);
/*
if (set_Parity(__seri_conf->fd, 8, 1, 'N') == FALSE)
{
printf("Set Parity Error ");
}
*/
if(serial_init_databit(__seri_conf)<0)
printf("serial_init_databit error ");
if(serial_init_parity(__seri_conf)<0)
printf("serial_init_parity error ");
if(serial_init_stopbit(__seri_conf)<0)
printf("serial_init_stopbit error ");
//struct termios opt;
tcgetattr(__seri_conf->fd,&__seri_conf->options);
__seri_conf->options.c_iflag &=~(BRKINT|ICRNL|INPCK|ISTRIP|IXON);
__seri_conf->options.c_lflag &=~(ICANON|ECHO|ECHOE|ECHONL|ISIG|IEXTEN);
__seri_conf->options.c_oflag &=~(OPOST);
if(tcsetattr(__seri_conf->fd,TCSANOW,&__seri_conf->options)!=0)
printf("error");
while (1) {
char ct[10] = "hello";
write(__seri_conf->fd, ct, 10);
puts("hello world 28800 test 8888! ");
sleep(1);
nread = read(__seri_conf->fd,buff,256);
if(nread>0)
{
printf("recv :%d ***%s ",nread,buff);
}
}
close(fd);
}