[Linux] read / write serial port

這幾天在CentOS 6.2裡練習寫 USB轉serial port功能記錄一下以免以後忘記


#include <stdio.h>   /* Standard input/output definitions */
#include <string.h>  /* String function definitions */
#include <unistd.h>  /* UNIX standard function definitions */
#include <fcntl.h>   /* File control definitions */
#include <errno.h>   /* Error number definitions */
#include <termios.h> /* POSIX terminal control definitions */

int fd;
#define DEVICE "/dev/ttyUSB0"

int writeport(int fd, unsigned char *chars, int numBytes)
{
//show array contents
//printf("write array contents:\n");
int counter = 0;
printf("write array = ");
while(counter < numBytes)
{
printf("%x,", chars[counter]);
counter++;
}
printf("\n");

int n = write(fd, chars, numBytes);
if (n < 0) {
fputs("write failed!\n", stderr);
return 0;
}
//all good
return 1;
}

int readport(int fd, unsigned char *result)
{
int iIn = read(fd, result, 254); //13); //254);

//show result array
int counter = 0;
printf("read array = ");
while(counter < iIn)
{
printf("%x,",result[counter]);
counter++;
}
printf("\n");

if (iIn < 0) {
if (errno == EAGAIN) {
printf("SERIAL EAGAIN ERROR\n");
return 0;
} else {
printf("SERIAL read error %d %s\n", errno, strerror(errno));
return 0;
}
}
return 1;
}

int getbaud(int fd)
{
struct termios termAttr;
int inputSpeed = -1;
speed_t baudRate;
tcgetattr(fd, &termAttr);
/* Get the input speed.                              */
baudRate = cfgetispeed(&termAttr);
switch (baudRate) {
case B0:      inputSpeed = 0; break;
case B50:     inputSpeed = 50; break;
case B110:    inputSpeed = 110; break;
case B134:    inputSpeed = 134; break;
case B150:    inputSpeed = 150; break;
case B200:    inputSpeed = 200; break;
case B300:    inputSpeed = 300; break;
case B600:    inputSpeed = 600; break;
case B1200:   inputSpeed = 1200; break;
case B1800:   inputSpeed = 1800; break;
case B2400:   inputSpeed = 2400; break;
case B4800:   inputSpeed = 4800; break;
case B9600:   inputSpeed = 9600; break;
case B19200:  inputSpeed = 19200; break;
case B38400:  inputSpeed = 38400; break;
case B115200:  inputSpeed = 115200; break;
}
return inputSpeed;
}

int initport(int fd)
{
struct termios options;
// Get the current options for the port...
tcgetattr(fd, &options);

// Set the baud rates to 115200...
cfsetispeed(&options, B115200);
cfsetospeed(&options, B115200);

// Enable the receiver and set local mode...
options.c_cflag |= (CLOCAL | CREAD);

//disable hardware flow control
options.c_cflag &= ~CRTSCTS;

//disable software flow control
options.c_iflag &= ~(IXON | IXOFF | IXANY);

//raw input
options.c_lflag &= ~(ICANON | ECHO | ECHOE | ISIG);

//raw output
options.c_oflag &= ~OPOST;

//No parity - 8N1
options.c_cflag &= ~PARENB;
options.c_cflag &= ~CSTOPB;
options.c_cflag &= ~CSIZE;
options.c_cflag |= CS8;

// Set the new options for the port...
tcsetattr(fd, TCSANOW, &options);

return 1;
}

int main(void)
{
unsigned char command[7];
unsigned char sResult[7];

printf("Start open port...\n");
fd = open(DEVICE, O_RDWR);
//fd = open(DEVICE, O_RDWR | O_NOCTTY | O_NDELAY);
if (fd == -1)
{
perror("open_port: Unable to open /dev/ttyS0 - ");
return 1;
}
else
{
fcntl(fd, F_SETFL, 0);
}

initport(fd);
printf("baud=%d\n", getbaud(fd));

command[0]=0xC0;
command[1]=0x73;
command[2]=0x07;
command[3]=0x0A;
command[4]=0x00;
command[5]=0x00;
command[6]=0xBE;

if (!writeport(fd, command, 7))
{
printf("write failed\n");
close(fd);
return 1;
}

sleep(2);

fcntl(fd, F_SETFL, 0);    

if (!readport(fd,sResult))
{
printf("read failed\n");
close(fd);
return 1;
}

close(fd);
return 0;
}

參考網站: http://forums.devx.com/showthread.php?t=170839