linux – 从串口读取失败

我有以下C程序：

#include <fcntl.h>
#include <termios.h>
#include <stdio.h>

int main()
{
    int fd = open("/dev/ttyS0",O_RDWR | O_NOCTTY | O_NONBLOCK);
    if(fd < 0)
    {
        perror("Could not open device");
    }
    printf("Device opened\n");

    struct termios options;
    tcgetattr(fd,&options);
    cfmakeraw(&options);
    cfsetispeed(&options,B19200);
    cfsetospeed(&options,B19200);
    tcsetattr(fd,TCSANow,&options);

    char txpacket[] = {0x23,0x06,0x00,0xdd,0xf9};
    ssize_t written = write(fd,txpacket,sizeof(txpacket));
    printf("Written %d bytes\n",written);

    printf("Starting to wait for target to respond\n");
    while(1)
    {
        fd_set readset;
        FD_ZERO(&readset);
        FD_SET(fd,&readset);
        int nCount = select(fd + 1,&readset,NULL,NULL);
        if(nCount > 0)
        {
            if(FD_ISSET(fd,&readset))
            {
                int i;
                char buffer[128];
                ssize_t bytesread = read(fd,buffer,sizeof(buffer));
                printf("Received %d bytes\n",bytesread);
                for(i = 0; i < bytesread; i++)
                {
                    printf("  %02x",buffer[i]);
                }
            }
        }
    }
}

该程序打开串行设备/ dev / ttyS0,向其写入一系列数据并开始监听响应.我得到以下输出：

Device opened
Written 6 bytes
Starting to wait for target to respond
Received 0 bytes
Received 0 bytes
Received 0 bytes
Received 0 bytes
Received 0 bytes
Received 0 bytes
...

并且该应用程序消耗100％的cpu.即使目标硬件实际传输它,我也无法接收任何数据.

怎么了？

解决方法

read()返回0表示文件结束条件.如果发生这种情况,你应该检查它并突破循环.

至于导致什么 – 串口上的文件结尾表明它已检测到挂断,这意味着DCD线路已被丢弃.

如果您的设备没有正确设置它们,您可以在options.c_cflag中设置CLOCAL标志以忽略调制解调器控制线.