对C语言编程不熟悉,所以请容忍我。我写了一个程序来向串行端口写入/读取数据。除了我试图读取端口上已接收的可用字节数外,其他一切似乎都在工作。这是我的代码(请参阅read_port函数):
#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 */
#include <sys/ioctl.h> /* Serial Port IO Controls */
int fd; /* File descriptor for the port */
struct termios options_original; /* Original Serial Port Options */
int main()
{
fd = open_port();
flush_port();
write_port();
printf("FIONBIO value %d\n", FIONBIO);
usleep(2);
printf("FIONREAD value %d\n", FIONREAD);
read_port();
close_port();
}
/*
* open_port() - Open serial port 1.
*
* Returns the file descriptor on success or -1 on error
*/
int open_port(void)
{
struct termios options;
fd = open("/dev/ttyUSB0", O_RDWR | O_NOCTTY | O_NDELAY | O_NONBLOCK);
if (fd != -1)
{
printf("Serial Port Open\n");
fcntl(fd, F_SETFL, 0);
tcgetattr(fd, &options_original);
tcgetattr(fd, &options);
cfsetispeed(&options, B115200);
cfsetospeed(&options, B115200);
options.c_cflag |= (CLOCAL | CREAD); /* Enable the receiver and set local mode */
options.c_lflag &= ~(ICANON | ECHO | ECHOE | ISIG); /* Raw Input Mode */
tcsetattr(fd, TCSANOW, &options); /* Set the new options for the port */
}
else
{
/* Could not open the port */
perror("open_port: Unable to open /dev/ttyUSB0 - ");
}
return (fd);
}
int close_port(void)
{
tcsetattr(fd, TCSANOW, &options_original);
printf("Serial Port Closed\n");
close(fd);
}
int flush_port(void)
{
usleep(2); // required to make flush work, for some reason
printf("Flushing IO Buffers\n");
tcflush(fd, TCIOFLUSH);
}
int write_port(void)
{
int n = write(fd, "DSC", 3);
if (n < 0)
fputs("write() of 1 byte failed!\n", stderr);
else
printf("Wrote %0d bytes to serial port\n", n);
}
int read_port(void)
{
int chars_read = 3;
int bytes;
char read_buffer[3] = {0};
int i;
fcntl(fd, F_SETFL, 0);
ioctl(fd, FIONBIO, &bytes);
printf("Number of bytes = %d\n", bytes);
int n = read(fd, read_buffer, chars_read);
printf("Character at Port: %s\n", read_buffer);
printf("Number of chars read = %0d\n", n);
}
输出如下:
Serial Port Open
Flushing IO Buffers
Wrote 3 bytes to serial port
FIONBIO value 21537
FIONREAD value 21531
Number of bytes = 0
Character at Port: DSC
Number of chars read = 3
Serial Port Closed
出于某种原因,“字节数”始终等于0。我不知道为什么。这样做有什么不对吗?
int bytes;
ioctl(fd, FIONBIO, &bytes);
printf("Number of bytes = %d\n", bytes);
从这个网站上几乎一字不差:
http://www.cmrr.umn.edu/~strupp/serial.html#config
我是不是错过了什么?
顺便说一下,我只是在做一个简单的环回测试。
最佳答案
ioctl(fd, FIONBIO, ...)
将文件描述符(例如套接字)设置为阻塞或
非阻塞模式。你的意思可能是
ioctl(fd, FIONREAD, &bytes);
获取输入缓冲区中可用的字节数(即字节数
无需阻塞即可读取。)
关于c - 串行端口输入缓冲区的字节数,我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/23332908/