Question

我有两个应用程序通过串口通信。目标有一个导航的状态机。它将接收并丢弃数据，直到它获得消息字节（0xE3）的开始，然后处理数据直到消息字节（0x3E）结束。我对某些数据有疑问。我认为这是一个处理问题，而不是沟通问题。我也知道这很简单，但很难找到问题。

主机正在向目标发送数据。 bfr数据为：FlowLayoutPanel

{0xAA, 0xFF, 0x05, 'H', 'e', 'l', 'l', 'o'};

目标是使用select（）和read（）来接收数据。

byte = MSG_START_BYTE; // 0xE3
if (write(fd, &byte, 1) < 0)
    return -1;

if (write(fd, bfr, bfr_len) < 0)
    return -1;

if (write(fd, &crc, sizeof(crc)) < 0)
    return -1;

byte = MSG_END_BYTE;  // 0x3E
if (write(fd, &byte, 1) < 0)
    return -1;

目标控制台输出为：

char rx_bfr[128];
uint8_t max_bytes_to_read = 1;

memset(rx_bfr, 0, strlen(rx_bfr));
...
printf("\tactivity...");
bytes_read = read(fd, rx_bfr, max_bytes_to_read);
if (bytes_read < 0)
    return -1;
else if (bytes_read == 0)
    return -1;

printf(" %d bytes to process...\n", bytes_read);
for (i = 0; i < bytes_read; i++)
{
    printf("byte[%d] = 0x%x\n", i, rx_bfr[i]);
    switch (state)
    {
        case SOM:
            if (rx_bfr[i] == 0xE3)
 ...

所以在我的状态机中，if条件是寻找Waiting for message... activity... 1 bytes to process... byte[0] = 0xffffffe3 activity... 1 bytes to process... byte[0] = 0xffffffaa activity... 1 bytes to process... byte[0] = 0xffffffff activity... 1 bytes to process... byte[0] = 0x5 activity... 1 bytes to process... byte[0] = 0x48 activity... 1 bytes to process... byte[0] = 0x65 activity... 1 bytes to process... byte[0] = 0x6c activity... 1 bytes to process... byte[0] = 0x6c activity... 1 bytes to process... byte[0] = 0x6f activity... 1 bytes to process... byte[0] = 0xffffffd4 activity... 1 bytes to process... byte[0] = 0xffffff81 activity... 1 bytes to process... byte[0] = 0x1a activity... 1 bytes to process... byte[0] = 0x3c activity... 1 bytes to process... byte[0] = 0x3b activity... 1 bytes to process... byte[0] = 0x3e作为SOM，但第一个＆＃34;字节＆＃34;从printf看到的缓冲区是0xE3。

Answer 1

char rx_bfr[128];

在您的平台上char已签名。值为0xE3的带符号的char为负，但值为0xE3的整数为正，因此它们不会相等。请改用unsigned char。

Linux串行读取（）无关数据

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