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这是这个原始帖子的后续问题：

树莓派 RS-232 故障

我根据接受的答案对我的代码进行了更改，终端现在设置为阻止和规范输入。现在read()按预期工作，除了第一次读取（通常是一些额外的随机符号与一些好的数据混合）之外，我从激光测距仪得到单行数据，代表我期望看到的内容。

但是，我现在有一个问题，如果读取太多，激光测距仪会进入非工作状态，停止通信，只能通过重启电源来重置。设备上只有 4 次读取就发生了这种情况，而我无法进行超过 8 次读取。读取是一次全部还是跨越多个程序启动都没有关系。

int main(){
    int uart0_filestream = -1;
    int loop, i, sentBytes;
    int isError, rx_length;
    unsigned char rx_buffer[256];

    uart0_filestream = open("/dev/ttyAMA0", O_RDWR | O_NOCTTY | O_NDELAY);
    fcntl(uart0_filestream, F_SETFL, 0);

    if(uart0_filestream == -1){
        printf("ERROR: Unable to open UART\n");
        checkError(errno);
        exit(1);
    }

    struct termios options;

    isError = tcgetattr(uart0_filestream, &options);

    if(isError < 0){
        printf("ERROR: tcgetattr failed.\n");
        checkError(errno);
        exit(1);
    }

    //set c ontrol options and baud
    options.c_cflag |= (CLOCAL | CREAD);
    cfsetispeed(&options, B19200);
    cfsetospeed(&options, B19200);

    //set 8 data bits, 1 stop bit, no parity
    options.c_cflag &= ~PARENB;
    options.c_cflag &= ~CSTOPB;
    options.c_cflag &= ~CSIZE;
    options.c_cflag |= CS8;

    //set input options
    options.c_iflag |= (INPCK | ISTRIP);        //strip parity
    options.c_iflag &= ~(IXON | IXOFF | IXANY); //turn off software flow control

    //set canonical input processing
    options.c_lflag |= (ICANON | ECHO | ECHOE);

    tcflush(uart0_filestream, TCIFLUSH);
    isError = tcsetattr(uart0_filestream, TCSANOW, &options);

    if(isError < 0){
        printf("ERROR: tcsetattr failed.\n");
        checkError(errno);
        exit(1);
    }

    //read() successfully returns expected data, with the exception of the first 
    //read. Reading more than 6-8 times, regardless of same session or restarting
    //program puts LRF in non-working state which requires a power cycle to fix
    for(i=0; i<4;i++ ){
        rx_length = read(uart0_filestream, (void*)rx_buffer, 255);

        if(rx_length < 0){
            printf("ERROR: read() failed.\n");
            checkError(errno);
        }

        if(rx_length > 0){
            printf("rx_lentgh = %i:\t ", rx_length);
            for(loop=0; loop<rx_length; loop++){
                printf("%c", rx_buffer[loop]);
            }
            printf("\n");
        }
    }

    //writing once has no affect, sending command has no affect
    //looping the write, eventually 'something' gets to the LRF
    //but it puts it in the same state as when reading too many
    //times and have to power cycle
    for(i = 0; i<8; i++){
        sentBytes = write(uart0_filestream, "o\n", 2);

        if(sentBytes < 2){
            printf("ERROR: write() failed.\n");
            checkError(errno);
        }   
    }

    close(uart0_filestream);
}

我不相信它是测距仪，因为我可以运行 minicom，它会成功地连续显示输出。

正如我的代码注释中所述，我在向激光测距仪写入任何命令时也遇到了麻烦。每个命令由一个字符组成，后跟一个新行。一次写入没有影响，但循环多次会使设备处于与多次读取相同的状态。

我已阅读Posix Serial Programming Guide，并尝试了不同的标志组合，我认为这些组合可能会影响读取或写入，但没有成功。

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1 回答 1

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[Edit] This lead suggestion is my embarrassment - thought the string was "o/n".

The amount of data sent is short by 1.

// sentBytes = write(uart0_filestream, "o\n", 2);
// if(sentBytes < 2){
sentBytes = write(uart0_filestream, "o\n", 3);
if(sentBytes < 3){

Minor: Unclear why read buffer is reduced by 1 (sizeof rx_buffer is 256). read() is not going to append a \0 and neither does this code. Code nicely treats the incoming data as an array of bytes. Although in printf("%c"... something could be done if !isgraph(rx_buffer[loop])`.

// rx_length = read(uart0_filestream, (void*)rx_buffer, 255)
rx_length = read(uart0_filestream, (void*)rx_buffer, sizeof rx_buffer)
于 2013-10-04T18:18:31.390 回答