所有示例均源自miniterm.c. 预输入缓冲区限制为 255 个字符，就像规范输入处理的最大字符串长度一样 (<linux/limits.h>或<posix1_lim.h>).
请参阅代码中的注释，了解不同输入模式的用法说明。 我希望代码是易于理解的。 规范输入的示例注释最为详尽，其他示例仅在与规范输入示例不同的地方进行注释，以突出差异。
描述并不完整，但鼓励您尝试这些示例，以便为您的应用程序找到最佳解决方案。
别忘了给予相应的串口正确的权限 (例如chmod a+rw /dev/ttyS1)!
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <termios.h>
#include <stdio.h>
/* baudrate settings are defined in <asm/termbits.h>, which is
included by <termios.h> */
#define BAUDRATE B38400
/* change this definition for the correct port */
#define MODEMDEVICE "/dev/ttyS1"
#define _POSIX_SOURCE 1 /* POSIX compliant source */
#define FALSE 0
#define TRUE 1
volatile int STOP=FALSE;
main()
{
int fd,c, res;
struct termios oldtio,newtio;
char buf[255];
/*
Open modem device for reading and writing and not as controlling tty
because we don't want to get killed if linenoise sends CTRL-C.
*/
fd = open(MODEMDEVICE, O_RDWR | O_NOCTTY );
if (fd <0) {perror(MODEMDEVICE); exit(-1); }
tcgetattr(fd,&oldtio); /* save current serial port settings */
bzero(&newtio, sizeof(newtio)); /* clear struct for new port settings */
/*
BAUDRATE: Set bps rate. You could also use cfsetispeed and cfsetospeed.
CRTSCTS : output hardware flow control (only used if the cable has
all necessary lines. See sect. 7 of Serial-HOWTO)
CS8 : 8n1 (8bit,no parity,1 stopbit)
CLOCAL : local connection, no modem contol
CREAD : enable receiving characters
*/
newtio.c_cflag = BAUDRATE | CRTSCTS | CS8 | CLOCAL | CREAD;
/*
IGNPAR : ignore bytes with parity errors
ICRNL : map CR to NL (otherwise a CR input on the other computer
will not terminate input)
otherwise make device raw (no other input processing)
*/
newtio.c_iflag = IGNPAR | ICRNL;
/*
Raw output.
*/
newtio.c_oflag = 0;
/*
ICANON : enable canonical input
disable all echo functionality, and don't send signals to calling program
*/
newtio.c_lflag = ICANON;
/*
initialize all control characters
default values can be found in /usr/include/termios.h, and are given
in the comments, but we don't need them here
*/
newtio.c_cc[VINTR] = 0; /* Ctrl-c */
newtio.c_cc[VQUIT] = 0; /* Ctrl-\ */
newtio.c_cc[VERASE] = 0; /* del */
newtio.c_cc[VKILL] = 0; /* @ */
newtio.c_cc[VEOF] = 4; /* Ctrl-d */
newtio.c_cc[VTIME] = 0; /* inter-character timer unused */
newtio.c_cc[VMIN] = 1; /* blocking read until 1 character arrives */
newtio.c_cc[VSWTC] = 0; /* '\0' */
newtio.c_cc[VSTART] = 0; /* Ctrl-q */
newtio.c_cc[VSTOP] = 0; /* Ctrl-s */
newtio.c_cc[VSUSP] = 0; /* Ctrl-z */
newtio.c_cc[VEOL] = 0; /* '\0' */
newtio.c_cc[VREPRINT] = 0; /* Ctrl-r */
newtio.c_cc[VDISCARD] = 0; /* Ctrl-u */
newtio.c_cc[VWERASE] = 0; /* Ctrl-w */
newtio.c_cc[VLNEXT] = 0; /* Ctrl-v */
newtio.c_cc[VEOL2] = 0; /* '\0' */
/*
now clean the modem line and activate the settings for the port
*/
tcflush(fd, TCIFLUSH);
tcsetattr(fd,TCSANOW,&newtio);
/*
terminal settings done, now handle input
In this example, inputting a 'z' at the beginning of a line will
exit the program.
*/
while (STOP==FALSE) { /* loop until we have a terminating condition */
/* read blocks program execution until a line terminating character is
input, even if more than 255 chars are input. If the number
of characters read is smaller than the number of chars available,
subsequent reads will return the remaining chars. res will be set
to the actual number of characters actually read */
res = read(fd,buf,255);
buf[res]=0; /* set end of string, so we can printf */
printf(":%s:%d\n", buf, res);
if (buf[0]=='z') STOP=TRUE;
}
/* restore the old port settings */
tcsetattr(fd,TCSANOW,&oldtio);
}
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在非规范输入处理模式下，输入不会被组装成行，并且不会发生输入处理（擦除、终止、删除等）。 两个参数控制此模式的行为c_cc[VTIME]设置字符定时器，以及c_cc[VMIN]设置在满足读取之前要接收的最少字符数。
如果 MIN > 0 且 TIME = 0，则 MIN 设置在满足读取之前要接收的字符数。 由于 TIME 为零，因此不使用定时器。
如果 MIN = 0 且 TIME > 0，则 TIME 用作超时值。 如果读取到单个字符或超过 TIME (t = TIME * 0.1 s)，则读取将被满足。 如果超过 TIME，则不会返回任何字符。
如果 MIN > 0 且 TIME > 0，则 TIME 用作字符间定时器。 如果接收到 MIN 个字符，或者两个字符之间的时间超过 TIME，则读取将被满足。 每次接收到字符时，定时器都会重新启动，并且仅在接收到第一个字符后才变为活动状态。
如果 MIN = 0 且 TIME = 0，则读取将立即满足。 将返回当前可用的字符数或请求的字符数。 根据 Antonino（参见贡献），您可以发出fcntl(fd, F_SETFL, FNDELAY);在读取之前以获得相同的结果。
通过修改newtio.c_cc[VTIME]和newtio.c_cc[VMIN]可以测试上述所有模式。
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <termios.h>
#include <stdio.h>
#define BAUDRATE B38400
#define MODEMDEVICE "/dev/ttyS1"
#define _POSIX_SOURCE 1 /* POSIX compliant source */
#define FALSE 0
#define TRUE 1
volatile int STOP=FALSE;
main()
{
int fd,c, res;
struct termios oldtio,newtio;
char buf[255];
fd = open(MODEMDEVICE, O_RDWR | O_NOCTTY );
if (fd <0) {perror(MODEMDEVICE); exit(-1); }
tcgetattr(fd,&oldtio); /* save current port settings */
bzero(&newtio, sizeof(newtio));
newtio.c_cflag = BAUDRATE | CRTSCTS | CS8 | CLOCAL | CREAD;
newtio.c_iflag = IGNPAR;
newtio.c_oflag = 0;
/* set input mode (non-canonical, no echo,...) */
newtio.c_lflag = 0;
newtio.c_cc[VTIME] = 0; /* inter-character timer unused */
newtio.c_cc[VMIN] = 5; /* blocking read until 5 chars received */
tcflush(fd, TCIFLUSH);
tcsetattr(fd,TCSANOW,&newtio);
while (STOP==FALSE) { /* loop for input */
res = read(fd,buf,255); /* returns after 5 chars have been input */
buf[res]=0; /* so we can printf... */
printf(":%s:%d\n", buf, res);
if (buf[0]=='z') STOP=TRUE;
}
tcsetattr(fd,TCSANOW,&oldtio);
}
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#include <termios.h>
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/signal.h>
#include <sys/types.h>
#define BAUDRATE B38400
#define MODEMDEVICE "/dev/ttyS1"
#define _POSIX_SOURCE 1 /* POSIX compliant source */
#define FALSE 0
#define TRUE 1
volatile int STOP=FALSE;
void signal_handler_IO (int status); /* definition of signal handler */
int wait_flag=TRUE; /* TRUE while no signal received */
main()
{
int fd,c, res;
struct termios oldtio,newtio;
struct sigaction saio; /* definition of signal action */
char buf[255];
/* open the device to be non-blocking (read will return immediatly) */
fd = open(MODEMDEVICE, O_RDWR | O_NOCTTY | O_NONBLOCK);
if (fd <0) {perror(MODEMDEVICE); exit(-1); }
/* install the signal handler before making the device asynchronous */
saio.sa_handler = signal_handler_IO;
saio.sa_mask = 0;
saio.sa_flags = 0;
saio.sa_restorer = NULL;
sigaction(SIGIO,&saio,NULL);
/* allow the process to receive SIGIO */
fcntl(fd, F_SETOWN, getpid());
/* Make the file descriptor asynchronous (the manual page says only
O_APPEND and O_NONBLOCK, will work with F_SETFL...) */
fcntl(fd, F_SETFL, FASYNC);
tcgetattr(fd,&oldtio); /* save current port settings */
/* set new port settings for canonical input processing */
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 */
while (STOP==FALSE) {
printf(".\n");usleep(100000);
/* after receiving SIGIO, wait_flag = FALSE, input is available
and can be read */
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 */
}
}
/* restore old port settings */
tcsetattr(fd,TCSANOW,&oldtio);
}
/***************************************************************************
* signal handler. sets wait_flag to FALSE, to indicate above loop that *
* characters have been received. *
***************************************************************************/
void signal_handler_IO (int status)
{
printf("received SIGIO signal.\n");
wait_flag = FALSE;
}
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本节内容尽量保持简洁。 它仅旨在作为提示，因此示例代码保持简短。 这不仅适用于串口，而且适用于任何文件描述符集。
select 调用和随附的宏使用一个fd_set. 这是一个位数组，它为每个有效的文件描述符编号都有一个位条目。select将接受一个fd_set其中为相关文件描述符设置了位，并返回一个fd_set，其中在发生输入、输出或异常时，为文件描述符设置了位。 所有处理fd_set都是使用提供的宏完成的。 另请参阅手册页select(2).
#include <sys/time.h>
#include <sys/types.h>
#include <unistd.h>
main()
{
int fd1, fd2; /* input sources 1 and 2 */
fd_set readfs; /* file descriptor set */
int maxfd; /* maximum file desciptor used */
int loop=1; /* loop while TRUE */
/* open_input_source opens a device, sets the port correctly, and
returns a file descriptor */
fd1 = open_input_source("/dev/ttyS1"); /* COM2 */
if (fd1<0) exit(0);
fd2 = open_input_source("/dev/ttyS2"); /* COM3 */
if (fd2<0) exit(0);
maxfd = MAX (fd1, fd2)+1; /* maximum bit entry (fd) to test */
/* loop for input */
while (loop) {
FD_SET(fd1, &readfs); /* set testing for source 1 */
FD_SET(fd2, &readfs); /* set testing for source 2 */
/* block until input becomes available */
select(maxfd, &readfs, NULL, NULL, NULL);
if (FD_ISSET(fd1)) /* input from source 1 available */
handle_input_from_source1();
if (FD_ISSET(fd2)) /* input from source 2 available */
handle_input_from_source2();
}
}
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给定的示例无限期阻塞，直到来自其中一个源的输入变为可用。 如果您需要在输入时超时，只需将 select 调用替换为
int res;
struct timeval Timeout;
/* set timeout value within input loop */
Timeout.tv_usec = 0; /* milliseconds */
Timeout.tv_sec = 1; /* seconds */
res = select(maxfd, &readfs, NULL, NULL, &Timeout);
if (res==0)
/* number of file descriptors with input = 0, timeout occurred. */
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此示例将在 1 秒后超时。 如果发生超时，select 将返回 0，但请注意Timeout会被实际等待输入的时间递减select. 如果超时值为零，select 将立即返回。