从C中的帧中提取错误的数据? [英] Extract wrong data from a frame in C?

问题描述

我正在编写一个程序，该程序从Linux上的串行端口读取数据.数据是由另一台设备以以下帧格式发送的:

I am writing a program that reads the data from the serial port on Linux. The data are sent by another device with the following frame format:

|start | Command | Data               | CRC  | End |
|0x02  | 0x41    | (0-127 octets)     |      | 0x03|
----------------------------------------------------

数据字段包含127个八位位组，如图所示，八位位组1,2包含一种类型的数据；字节3,4包含另一个数据.我需要获取这些数据.

The Data field contains 127 octets as shown and octet 1,2 contains one type of data; octet 3,4 contains another data. I need to get these data.

因为在 C 中，一个字节只能容纳一个字符，并且在帧的开始字段中，它是0x02，表示STX是3个字符.

Because in C, one byte can only holds one character and in the start field of the frame, it is 0x02 which means STX which is 3 characters.

所以，为了测试我的程序，

So, in order to test my program,

在发送方，我按照上面的格式构造一个数组，如下所示:

On the sender side, I construct an array as the frame formatted above like:

char frame[254];
frame[0] = 0x02; // starting field
frame[1] = 0x41; // command field which is character 'A'
..so on..

然后，在接收器端，我取出像这样的字段:

And, then On the receiver side, I take out the fields like:

char result[254];
// read data
read(result);
printf("command = %c", result[1]); // get the command field of the frame

// get other field's values

命令字段值(结果[1])不是字符'A'.

the command field value (result[1]) is not character 'A'.

我认为，这是因为帧的第一个字段值为0x02(STX)，在数组帧中占据3个首位，并导致接收器端出现错误的结果.

I think, this because the first field value of the frame is 0x02 (STX) occupying 3 first places in the array frame and leading to the wrong results on the receiver side.

我该如何解决此问题，或者我在发件人一方做错了什么?

How can I correct the issue or am I doing something wrong at the sender side?

相关问题:
在C语言中解析和读取数据帧?
在Linux中使用C语言清除串行端口上的数据吗?

related questions:
Parse and read data frame in C?
Clear data at serial port in Linux in C?

推荐答案

如果您的程序实际上包含

If your program actually contains

read(result);

然后您需要添加

#include <unistd.h>

在顶部，以获取read的函数原型.然后，您需要open串行端口，并将生成的文件描述符与缓冲区一起传递给read，以便它知道要读取的内容.参见man 2 read和man 2 open.

at the top, to get the function prototype for read. Then you need to open the serial port and pass the resulting file descriptor to read along with your buffer, so it knows what to read. See man 2 read and man 2 open.

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