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.