Serial port programming in Unix/Linux

最近有機會接觸了serial port programming(另外還有Video for Linux API,socket programming等等), 由於平台是Linux,所以有機會比較深入地去接觸kernel,發覺Linux真是個很漂亮的系統(當然不是指各套件預裝User Interface :P ),在欣賞這個精湛的設計時,也期許未來能夠參許這樣的藝術工作.

以下整理了一些serial programming常用的功能:

1.標頭檔,是在寫serial port programming時常用的,為了簡化版面,我就不細說每個標頭檔是那些函式會到了

#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 */

2.開啟/關閉serial port

int fd = open("/dev/ttyS0", O_RDWR | O_NOCTTY | O_NDELAY);

if (fd == -1)
{

//Could not open the port.

}
else

fcntl(fd, F_SETFL, 0);

close(fd) ;

3.設定control options

struct termios options;
//Get the current options for the port...

tcgetattr(fd, &options);

//Set the baud rates to 19200...
cfsetispeed(&options, B19200);
cfsetospeed(&options, B19200);

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

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

4.常用的組合

• No parity (8N1):

options.c_cflag &= ~PARENB ;
options.c_cflag &= ~CSTOPB ;
options.c_cflag &= ~CSIZE ;
options.c_cflag |= CS8 ;

• Even parity (7E1):

options.c_cflag |= PARENB ;
options.c_cflag &= ~PARODD ;
options.c_cflag &= ~CSTOP ;
options.c_cflag &= ~CSIZE;
options.c_cflag |= CS7;

• Odd parity (7O1):

options.c_cflag |= PARENB ;
options.c_cflag |= PARODD ;
options.c_cflag &= ~CSTOPB ;
options.c_cflag &= ~CSIZE ;
options.c_cflag |= CS7;

• Space parity is setup the same as no parity (7S1):

options.c_cflag &= ~PARENB ;
options.c_cflag &= ~CSTOPB ;
options.c_cflag &= ~CSIZE;
options.c_cflag |= CS8;

5.設定hardware flow control

options.c_cflag |= CNEW_RTSCTS; /* Also called CRTSCTS */
或是 options.c_cflag &= ~CNEW_RTSCTS;

6.讀寫

直接用 read() , write()就好了