c - AVR UART 读取单个字节两次

Question

我目前正在编写一个 UART 接收代码，该代码使用 AVR ATtiny87 读取并解析来自另一台机器的命令。这个想法是检测起始字符并将其存储在缓冲区中，并继续存储 UART 字节，直到接收到 0x0a (FL)。我这样做没有问题，但由于某种原因，我的代码读取每个字节两次。以下是我的函数，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()函数输出*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。

Answer 1

查看函数 vehicle_recv()，您可以得到:

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_packet.state = BUFFER_RX_IN_PROG 后，您将进入第二个条件，因为您刚刚设置了状态。在第二个条件中，您再次将 byte 保存到缓冲区 - 每个相同的字节

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switch(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? */
}