C AVR UART读取单个字节两次

我目前正在编写一个UART接收代码，使用AVR ATtiny87读取和解析来自另一台机器的命令。 其思想是检测起始字符并将其存储在缓冲区中，并一直存储UART字节，直到接收到0x0a（FL）。我不反对这样做，但出于某种原因，我的代码每个字节读取两次。下面是我的函数，它由我的内核循环调用

void vehicle_recv(void) {
uint8_t n = 0;
char byte;

byte = LINDAT; //Reads and stores the content of the UART data register. 

if(compass_packet.state == BUFFER_RX_IDLE) {
    if(byte == '*' || byte == '#') {
        compass_packet.buffer[0] = byte;
        compass_packet.index = 1;
        compass_packet.state = BUFFER_RX_IN_PROG;
    }
}
if(compass_packet.state == BUFFER_RX_IN_PROG) {
    compass_packet.buffer[compass_packet.index] = byte;
    (compass_packet.index)++;
    if(byte == 0x0a) {
        compass_packet.buffer[compass_packet.index] = byte;
        (compass_packet.index)++;
        compass_packet.size = compass_packet.index;
        compass_packet.state = BUFFER_RX_DONE;
    }
}
if(compass_packet.state == BUFFER_RX_DONE) {
    decode_vehicle_command(&compass_packet);
    compass_packet.state = BUFFER_RX_IDLE;
}
}


uint8_t decode_vehicle_command(struct compass_comm_packet *RX_buffer) {

debugChar(debug_str);
sendChar(RX_buffer->buffer[0]);
sendCRLF();
sendChar(RX_buffer->buffer[1]);
sendCRLF();
sendChar(RX_buffer->buffer[2]);
sendCRLF();
sendChar(RX_buffer->buffer[3]);
sendCRLF();
sendChar(RX_buffer->buffer[4]);
sendCRLF();
sendChar(RX_buffer->buffer[5]);
sendCRLF();
sendChar(RX_buffer->buffer[6]);
sendCRLF();
sendChar(RX_buffer->buffer[7]);
sendCRLF();

uint8_t return_value = 0;


if(RX_buffer->buffer[0] == '*') {
    switch(RX_buffer->buffer[1]) {

        case 'H':
            strcpy(debug_str, "Heading\r\n");
            debugChar(debug_str);
            break;
        case 'R':
            strcpy(debug_str, "Reset\r\n");
            debugChar(debug_str);
            break;
        case 'S':
            strcpy(debug_str, "Stop\r\n");
            debugChar(debug_str);
            break;
        case 'C':
            strcpy(debug_str, "Calibrate\r\n");
            debugChar(debug_str);
            break;
    }
}

---

当我发送*H（CR）（FL）时，我希望decode_vehicle_command（）函数会吐出*H（CR）（FL）。然而，我一直看到**HH（CR）（CR）（FL）（FL）。我可以通过使用RX_buffer->buffer[2]而不是RX_buffer->buffer[1]来解决这个问题，但我很好奇我到底做错了什么。

部分问题在于，您设置了一个状态，然后在同一过程中对其进行操作。处理特定字符后，将代码更改为退出例程，或将第二个和第三个

if

语句更改为

else if

用调试器一步一步地检查它，看看我的意思

将状态设置为idle，将接收的字符设置为“*”，您将得到以下序列：

if(compass_packet.state == BUFFER_RX_IDLE) {
    // TRUE
    if(byte == '*' || byte == '#') {
        // TRUE
        compass_packet.buffer[0] = byte;
        compass_packet.index = 1;
        compass_packet.state = BUFFER_RX_IN_PROG;
    }
}

此时，前导字符存储在缓冲区中，索引为1，您的状态为“正在接收”

换行符终止字符也有类似的问题

尝试：

---

顺便说一句，您的状态机中还有其他漏洞。如果在行尾标记之前有太多字符，会发生什么情况？

查看函数

vehicle\u recv（）

，您有：

if(compass_packet.state == BUFFER_RX_IDLE) {
    if(byte == '*' || byte == '#') {
        compass_packet.buffer[0] = byte;
        compass_packet.index = 1;
        compass_packet.state = BUFFER_RX_IN_PROG;
    }
}
if(compass_packet.state == BUFFER_RX_IN_PROG) {
    compass_packet.buffer[compass_packet.index] = byte;
    (compass_packet.index)++;
    if(byte == 0x0a) {
        compass_packet.buffer[compass_packet.index] = byte;
        (compass_packet.index)++;
        compass_packet.size = compass_packet.index;
        compass_packet.state = BUFFER_RX_DONE;
    }
}
if(compass_packet.state == BUFFER_RX_DONE) {
    decode_vehicle_command(&compass_packet);
    compass_packet.state = BUFFER_RX_IDLE;
}

在第一个条件中设置

compass\u packet.state=BUFFER\u RX\u（在_PROG

中）后，输入第二个条件，因为您刚刚设置了要这样做的状态。在第二个条件中，您再次将

字节
保存到缓冲区---每个字节都保存相同的字节

if(compass_packet.state == BUFFER_RX_IN_PROG) {
    compass_packet.buffer[compass_packet.index] = byte;
    ...

通常，我对这些条件使用
开关
（或
if…else
）；这可能也是您的需要：

switch(compass_packet.state) {
    case BUFFER_RX_IDLE: 
        if(byte == '*' || byte == '#') {
            compass_packet.buffer[0] = byte;
            compass_packet.index = 1;
            compass_packet.state = BUFFER_RX_IN_PROG;
        }
        break;
    case BUFFER_RX_IN_PROG:
        compass_packet.buffer[compass_packet.index] = byte;
        (compass_packet.index)++;
        if(byte == 0x0a) {
            compass_packet.buffer[compass_packet.index] = byte;
            (compass_packet.index)++;
            compass_packet.size = compass_packet.index;
            compass_packet.state = BUFFER_RX_DONE;
        }
        break;
    case BUFFER_RX_DONE:
        decode_vehicle_command(&compass_packet);
        compass_packet.state = BUFFER_RX_IDLE;
        break;
    default:
        /* WTF? */
}

如果不看你的代码，另一台设备可能会回显接收到的字符吗？我不这么认为。我给sendChar打了8次电话，我得到了8个字符。你应该添加
compass\u comm\u packet
结构的最小定义，以及
vehicle\u recv（）
的使用及其上下文。天哪，我觉得自己很笨。非常感谢你抓住了我的错误。非常感谢！是的，你是对的。我当然也应该处理好这种情况。
if(compass_packet.state == BUFFER_RX_IN_PROG) {
    compass_packet.buffer[compass_packet.index] = byte;
    ...

switch(compass_packet.state) {
    case BUFFER_RX_IDLE: 
        if(byte == '*' || byte == '#') {
            compass_packet.buffer[0] = byte;
            compass_packet.index = 1;
            compass_packet.state = BUFFER_RX_IN_PROG;
        }
        break;
    case BUFFER_RX_IN_PROG:
        compass_packet.buffer[compass_packet.index] = byte;
        (compass_packet.index)++;
        if(byte == 0x0a) {
            compass_packet.buffer[compass_packet.index] = byte;
            (compass_packet.index)++;
            compass_packet.size = compass_packet.index;
            compass_packet.state = BUFFER_RX_DONE;
        }
        break;
    case BUFFER_RX_DONE:
        decode_vehicle_command(&compass_packet);
        compass_packet.state = BUFFER_RX_IDLE;
        break;
    default:
        /* WTF? */
}