Question

我正在使用Arduino Due，在速度至关重要的项目中尝试使用DMA函数。我发现以下功能可以通过串行接收：

uint8_t DmaSerial::get(uint8_t* bytes, uint8_t length) { 

// Disable receive PDC
uart->UART_PTCR = UART_PTCR_RXTDIS;

// Wait for PDC disable to take effect
while (uart->UART_PTSR & UART_PTSR_RXTEN);

// Modulus needed if RNCR is zero and RPR counts to end of buffer
rx_tail = (uart->UART_RPR - (uint32_t)rx_buffer) % DMA_SERIAL_RX_BUFFER_LENGTH;

// Make sure RPR follows (actually only needed if RRP is counted to the end of buffer and RNCR is zero)
uart->UART_RPR = (uint32_t)rx_buffer + rx_tail;

// Update fill counter
rx_count = DMA_SERIAL_RX_BUFFER_LENGTH - uart->UART_RCR - uart->UART_RNCR;

// No bytes in buffer to retrieve
if (rx_count == 0) { uart->UART_PTCR = UART_PTCR_RXTEN; return 0; } 

uint8_t i = 0;

while (length--) {

    bytes[i++] = rx_buffer[rx_head];

    // If buffer is wrapped, increment RNCR, else just increment the RCR
    if (rx_tail > rx_head) { uart->UART_RNCR++; } else { uart->UART_RCR++; }    

    // Increment head and account for wrap around
    rx_head = (rx_head + 1) % DMA_SERIAL_RX_BUFFER_LENGTH;

    // Decrement counter keeping track of amount data in buffer
    rx_count--;

    // Buffer is empty
    if (rx_count == 0) { break; }
}

// Turn on receiver
uart->UART_PTCR = UART_PTCR_RXTEN;

return i; 
}

据我所知，此函数将指针接收的内容写入变量 bytes ，只要不超过 length 。所以我这样称呼它：

 dma_serial1.get(data, 8);

，不将其返回值分配给变量。我认为接收到的值存储在uint8_t* data中，但是我可能错了。

最后，我想做的是检查接收到的数据是否是某个字符以做出决定，例如：

if (data == "t"){
//do something//}

我该如何做？

Answer 1

要比较if (data == "t")想要的字符串，您需要一个字符串比较函数，例如strcmp。为此，必须确保参数实际上是（0终止）C字符串：

uint8_t data[9];
uint8_t size = dma_serial1.get(data, 8);
data[size]='\0';
if (strcmp(data,"t")==0) {
   ...
}

如果您环境中的默认字符类型为signed char，要将data直接传递给字符串函数，则需要从无符号到有符号的转换：

if (strcmp(reinterpret_cast<const char*>(data),"t")==0) {
   ...
}

因此完整的MVCE可能如下所示：

int get(uint8_t *data, int size) {
    data[0] = 't';
    return 1;
}

int main()
{
    uint8_t data[9];
    uint8_t size = get(data, 8);
    data[size]='\0';
    if (strcmp(reinterpret_cast<const char*>(data),"t")==0) {
        cout << "found 't'" << endl;
    }
}

输出：

found 't'

将usart接收到的uint8_t *数据与常量字符串进行比较

1 个答案: