YNC);
tcgetattr(fd,&oldtio); /* save current port settings */
/* set new port settings for canonical input processing */
// 设置新的串口为标准输入模式
newtio.c_cflag = BAUDRATE | CRTSCTS | CS8 | CLOCAL | CREAD;
newtio.c_iflag = IGNPAR | ICRNL;
newtio.c_oflag = 0;
newtio.c_lflag = ICANON;
newtio.c_cc[VMIN]=1;
newtio.c_cc[VTIME]=0;
tcflush(fd, TCIFLUSH);
tcsetattr(fd,TCSANOW,&newtio);
/* loop while waiting for input. normally we would do something
useful here 循环等待输入，通常我们会在这里做些其它的事情 */
while (STOP==FALSE) {
printf(".\n");usleep(100000);
/* after receiving SIGIO, wait_flag = FALSE, input is availableand can be read */
// 在收到 SIGIO 信号后，wait_flag = FALSE, 表示有输入进来，可以读取了
if (wait_flag==FALSE) {
res = read(fd,buf,255);
buf[res]=0;
printf(":%s:%d\n", buf, res);
if (res==1) STOP=TRUE; /* stop loop if only a CR was input */
wait_flag = TRUE; /* wait for new input 等待新的输入*/
}
}
/* restore old port settings */
tcsetattr(fd,TCSANOW,&oldtio);
}
/***************************************************************************
* signal handler. sets wait_flag to FALSE, to indicate above loop that *
* characters have been received. *
***************************************************************************/
// 信号处理函数，设置 wait_flag 为 FALSE, 以告知上面的循环函数串口收到字符了
void signal_handler_IO (int status) {
printf("received SIGIO signal.\n");
wait_flag = FALSE;
}
3.4. Waiting for Input from Multiple Sources 等待来自多个源的输入
This section is kept to a minimum. It is just intended to be a hint, and therefore the example code is kept short. This will not only work with serial ports, but with any set of file descriptors.
The select call and accompanying macros use a fd_set. This is a bit array, which has a bit entry for every valid file descriptor number. select will accept a fd_set with the bits set for the relevant file descriptors and returns a fd_set, in which the bits for the file descriptors are set where input, output, or an exception occurred. All handling of fd_set is done with the provided macros. See also the manual page select(2).
这一部分的内容很少，只是作为一个提示，因此这段代码也很简短。而且这部分内容不仅适用于串口编程，而且适用于任意的一组文件描述符。
select 调用及其相应的宏，使用 fd_set. 这是一个比特数组，其中每一个比特代表了一个有效的文件描述符号。 select 调用接收一个有效的文件描述符结构，并返回 fd_set 比特数组，如果此比特数组中有某一个位设为1，就表示对应的文件描述符发生了输入，输出或者有例外事件。所有 fg_set 的处理都由宏提供了，具体参考 man select 2 。
Other Sources of Information 其它资源信息
· The Linux Serial-HOWTO describes how to set up serial ports and contains hardware information.
Linux Serial HOWTO 介绍了如何安装串口，并包括了硬件信息。
· Serial Programming Guide for POSIX Compliant Operating Systems, by Michael Sweet.
POSIX 兼容的操作系统上的串口编程
· The manual page termios(3) describes all flags for the termios structure.
man termios 3 介绍了所有 termios 结构里的设置。
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