二进制串口读取c中丢失的字节

Question

我正在将二进制数据从 arduino 发送到运行此代码的串行端口。在十六进制模式下使用cutecom可以清楚地读取我对该串行端口的期望。如下所示。

00000000: 24 04 85 ab 47 43 04 04   24 04 85 ab 47 43 04 04 
00000010: 24 04 85 ab 47 43 04 04   24 04 85 ab 47 43 04 04 

到这里没有问题。我不认为我需要提供 arduino 代码。

我正在尝试用 c 读同样的东西。然而下面的代码只打印这个：

24 85 ab 47 43 24 85 ab 47 43 24 85 ab 47 43

由于某些原因，它跳过了 04。有什么想法吗？

#include <stdio.h>
#include <fcntl.h>   /* File Control Definitions           */
#include <termios.h> /* POSIX Terminal Control Definitions */
#include <unistd.h>  /* UNIX Standard Definitions      */ 
#include <errno.h>   /* ERROR Number Definitions           */
#include <signal.h>
#include <string.h>
#include <stdint.h>

int open_serial(char *port, int baud);

void main(void)
{
    int tty = open_serial("/dev/ttyUSB0", B115200);
    uint8_t buff[256];   /* Buffer to store the data received              */
    int  n;    /* Number of bytes read by the read() system call */

    while (1) {
        n = read(tty, &buff, sizeof buff); 
        if (n > 0){
            //printf("-%d-\n ", n);
            for(int i=0;i<n;i++){   
                printf("%02x ", buff[i]);
            }
            fflush(stdout); 
        }
    }
}

int open_serial(char *port, int baud)
{

    int fd = open( port, O_RDWR | O_NOCTTY);    

    if(fd == -1)                        /* Error Checking */
        printf("\n  Error! in Opening tty  ");

    struct termios SerialPortSettings;  /* Create the structure                          */

    tcgetattr(fd, &SerialPortSettings); /* Get the current attributes of the Serial port */

    /* Setting the Baud rate */
    cfsetispeed(&SerialPortSettings,B115200); /* Set Read  Speed as 115200                       */
    cfsetospeed(&SerialPortSettings,B115200); /* Set Write Speed as 115200                       */

    /* 8N1 Mode */
    SerialPortSettings.c_cflag &= ~PARENB;   /* Disables the Parity Enable bit(PARENB),So No Parity   */
    SerialPortSettings.c_cflag &= ~CSTOPB;   /* CSTOPB = 2 Stop bits,here it is cleared so 1 Stop bit */
    SerialPortSettings.c_cflag &= ~CSIZE;    /* Clears the mask for setting the data size             */
    SerialPortSettings.c_cflag |=  CS8;      /* Set the data bits = 8                                 */

    SerialPortSettings.c_cflag &= ~CRTSCTS;       /* No Hardware flow Control                         */
    SerialPortSettings.c_cflag |= CREAD | CLOCAL; /* Enable receiver,Ignore Modem Control lines       */ 


    SerialPortSettings.c_iflag &= ~(IXON | IXOFF | IXANY);          /* Disable XON/XOFF flow control both i/p and o/p */
    SerialPortSettings.c_iflag &= ~(ICANON | ECHO | ECHOE | ISIG);  /* Non Cannonical mode                            */

    SerialPortSettings.c_oflag &= ~OPOST;/*No Output Processing*/

    /* Setting Time outs */
    SerialPortSettings.c_cc[VMIN] = 10; /* Read at least 10 characters */
    SerialPortSettings.c_cc[VTIME] = 0; /* Wait indefinetly   */


    if((tcsetattr(fd,TCSANOW,&SerialPortSettings)) != 0) /* Set the attributes to the termios structure*/
        printf("\n  ERROR ! in Setting attributes");
    else
        printf("\n  BaudRate = 115200 StopBits = 1 Parity   = none\n");

    /*------------------------------- Read data from serial port -----------------------------*/

    tcflush(fd, TCIFLUSH);   /* Discards old data in the rx buffer            */
    return fd;
}

Answer 1

I am sending binary data from an arduino to a serial port where this code is running.

Transmission of binary data necessitates that the POSIX serial terminal be configured for non-canonical (aka raw) mode.

For some reasons it is skipping the 04. Any ideas?

数值在 ASCII 控制字符范围内（即 0x00 到 0x1F）的数据持续丢失几乎总是表明 termios 配置不正确。
由于数据丢失似乎发生在接收端，因此首先要验证的是非规范输入模式的正确规范。
你的代码有

SerialPortSettings.c_iflag &= ~(ICANON | ECHO | ECHOE | ISIG);  /* Non Cannonical mode                            */

赋值语句右侧的属性都属于c_lflagtermios 结构的属性，而不是c_iflag编码的属性。
因此，推测串行终端的默认模式是规范模式，并且由于此拼写错误，您的程序无法重新配置为非规范输入模式。

使用cfmakeraw()调用增强代码的解决方法并不理想。
使用cfmakeraw()可以很方便地避免像您遇到的错误。但是应该纠正有错误的语句，或者更好的是可以删除因cfmakeraw()
调用而变得多余的操作。

cfmakeraw() sets the terminal to something like the "raw" mode of the old 
Version 7 terminal driver: input is available character by character, echoing is 
disabled, and all special processing of terminal input and output characters is 
disabled. The terminal attributes are set as follows:

termios_p->c_iflag &= ~(IGNBRK | BRKINT | PARMRK | ISTRIP
                | INLCR | IGNCR | ICRNL | IXON);
termios_p->c_oflag &= ~OPOST;
termios_p->c_lflag &= ~(ECHO | ECHONL | ICANON | ISIG | IEXTEN);
termios_p->c_cflag &= ~(CSIZE | PARENB);
termios_p->c_cflag |= CS8;

顺便说一句，您的代码确实使用了调用tcgetattr()的推荐/首选方法，然后使用布尔运算设置/修改终端属性。使用“干净的结构”的建议不被认为是可移植的。

附录

这个c_iflag和ICANON错误的起源似乎是来自 xanthium.in 的串行端口教程。作者早在 2016 年就收到了有关该错误的通知，但并未修复它。