无法读取串行端口 (UART)

Question

下面的代码正在打开第二个串行端口，我正在尝试读取和写入它。现在我正在使用第一个端口上的控制台功能（ Tera 术语控制台 ）查看那里的日志（printf 或 dmesg）。

但我无法从端口阅读。控制台挂起。

    int fd; /* File descriptor for the port */
    #define BUFF_SIZE 1024
    struct termios options;
    char to_write[1024];
    char to_read[1024];
    int bytes_written;
    int init_uart()
    {
        tcgetattr(fd, &options);
         /* Set Baud Rate */
        cfsetispeed( &options, B115200 );
        cfsetospeed( &options, B115200 );
        // Set the Charactor size
        options.c_cflag &= ~CSIZE; /* Mask the character size bits */
        options.c_cflag |= CS8;    /* Select 8 data bits */
        // Set parity - No Parity (8N1)
        options.c_cflag &= ~PARENB;/*no parity bit*/
        options.c_cflag &= ~CSTOPB;/* One bit stop bit*/
        options.c_cflag &= ~CSIZE;
        options.c_cflag |= CS8;/* 8 Bits Character length*/
        // Disable Hardware flowcontrol
        options.c_cflag &= ~CRTSCTS;
        // Enable Raw Input
        options.c_lflag &= ~(ICANON | ECHO | ECHOE | ISIG);
        // Disable Software Flow control
        options.c_iflag &= ~(IXON | IXOFF | IXANY);
        // Chose raw (not processed) output
        options.c_oflag &= ~OPOST;
        if ( tcsetattr( fd, TCSANOW, &options ) == -1 ){
            printf ("Error with tcsetattr = %sn", strerror ( errno ) );
            return -1;
        }
        return 0;
    }
    int write_uart()
    {
        int i=0;
        while (i < BUFF_SIZE-2){
            to_write[i]='a';
            i++;
        }
        to_write[i]='n';
        to_write[i+1]='r';
        // Write to the port
        bytes_written = write(fd, to_write, BUFF_SIZE);
        if(bytes_written < BUFF_SIZE){
            fputs("write() of 1024 bytes failed!n", stderr);   
            return -1;
        }
        return 0;
    }
    int
    read_port(void)
    {
        int n = read(fd, to_read, sizeof(BUFF_SIZE));
        if (n < 1024){
            fputs("read failed!n", stderr);
            return -1;
        }
        return 0;
    }
    int main()
    {
        int i=0;
        fd = open("/dev/ttyS1",O_RDWR | O_NOCTTY);
        if(fd == -1)
            perror("open_port: Unable to open /dev/ttyS1n");
        else
            printf("ttyS0 Opened successfullyn");
        if(init_uart())
            perror("open_port: Unable to initialize /dev/ttyS0 Portn");
        else
            printf("Port Initialization is done successfulyn");
        if(write_uart())
            perror("write_port: Unable to write to /dev/ttyS0 Portn");
        else
            printf("Write to the port happened successfullyn");
        if(read_port())
            perror("read_port: Unable to read from /dev/ttyS0 Portn");
        else
            printf("Read to the port happened successfullyn");
        close(fd);
    return 0;
    }

Answer 1

@randomization，我认为您必须配置控制字符，即c_cc[VTIME]和c_cc[VMIN]。投放时间：调用读取时启动计时器。当至少有一个字节的数据可用时，或者当计时器过期时，读取将返回。如果计时器过期而没有任何输入可用，则读取返回 0。VMIN：读取块，直到最小字节数或请求的字节数中较小的可用，并返回这两个值中的较小者。尝试配置 VMIN 和 VTIME 并测试您的应用程序。您可以配置其中任何一个。将在手册页中找到有关这些内容的良好描述，即 #man termios。