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Linux 序列埠程式設計

Aaron Liao 這裡我們探討 Linux 序列埠程式設計,你需要熟悉 C 語言和 Linux。 首先,用下列的程式來開啟序列埠。
int open_port(const char *pathname) {
/* open the pathname, ex. pathname="/dev/ttyACM0" */
int serial_fd = open(pathname, O_RDWR|O_NOCTTY|O_NDELAY);
/* fail to open the serial port */
if(serial_fd<0) {
if( debug ) {
printf("%s: fail to open [%s].\n", __func__, pathname);
}
return -1;
}
printf("%s: %s, serial_fd: %3d\n", __func__, pathname, serial_fd);
// enable the nonblocking mode for reading.
fcntl(serial_fd, F_SETFL, FNDELAY);
return serial_fd;
}
接著透過 file descriptor(檔案描述子)設定序列埠。
#include <termios.h> /* more baud rates could be found here */
#include <fcntl.h>
struct termios options;
speed_t baud = B38400;
tcgetattr(serial_fd, &options); /* Get the original setting */
/* Setting the baudrate */
cfsetispeed(&options, baud);
cfsetospeed(&options, baud);
/* enable the receiver and set local mode */
options.c_cflag |= (CLOCAL|CREAD);
/* setting the character size (8-bits) */
options.c_cflag &= ~CSIZE;
options.c_cflag |= CS8;
/* Setting Parity Checking: NONE (NO Parity) */
options.c_cflag &= ~PARENB;
options.c_cflag &= ~CSTOPB;
/* Disable Hardware flow control */
options.c_cflag &= ~CRTSCTS;
/* Disable Input Parity Checking */
options.c_iflag &= ~INPCK;
/* Disable software flow control */
options.c_iflag &= ~(IXON|IXOFF|IXANY);
options.c_iflag &= ~(IGNPAR|ICRNL);
/* output raw data */
options.c_oflag &= ~OPOST;
/* disablestd input */
options.c_lflag &= ~(ICANON|ECHO|ECHOE|ISIG);
/* clean the current setting */
tcflush(serial_fd, TCIFLUSH);
/* Enable the new setting right now */
tcsetattr(serial_fd, TCSANOW, &options);
之後的部分,如讀寫則與一般網路程式設計大同小異,可利用 descriptor 進行讀寫,以及透過 select() 函式之類的方式檢查 serial port 是否有資料可讀寫。 select() 的使用請參考 Beej's Guide to Network Programming 正體中文版的第七章。
參考文獻
[1] Michael Kerrisk, The Linux Programming Interface, 2010. [2] Michael R. Sweet, Serial Programming Guide for POSIX Operating Systems, 5th Edition.