STM32 用串口 2 发生错误！内有代码

只看该作者 · 2017-11-5 15:29

本帖最后由情场探花于 2017-11-5 15:39 编辑

先说说我的环境：
KEIL MDK4.6， STM32F103C8T6，ST LINK
我想用 USART2 （PA2 和 PA3 ）收发数据。目前调试阶段，把 PA2 和 PA3 短接。
症状：总是会多收一个  0x00，检查后发现接收缓冲区的指针 in，就是 g_RxBuf.in 总是多加。按道理我发一个字节，它应该加1，实际增加了2，就是说收到了 2 个字节。由于是在办公室里，而且 TX 和 RX 都是短接的，所以也不像是是干扰。推测是初始化设置没弄好，特此请大侠指点一下。函数 SendChar() 是发送一个字节，我每次只发一个字节 0x55，然后就是接收了。结果收到的是 0x55 0x00
函数 GetKey() 是接收一个字节，如果缓冲区空则返回 -1.

#define CLOCK 72/8 //时钟频率72M

struct buf_st {
  unsigned int in;                      /* Next In Index                   */
  unsigned int out;                      /* Next Out Index                */
  char buf [RBUF_SIZE];                /* Buffer                         */
};

static struct buf_st g_RxBuf = { 0, 0, };
#define SIO_RBUFLEN ((unsigned short)(g_RxBuf.in - g_RxBuf.out))

static struct buf_st g_TxBuf = { 0, 0, };
#define SIO_TBUFLEN ((unsigned short)(g_TxBuf.in - g_TxBuf.out))

static unsigned int g_bTxRestart = 1;    /* NZ if TX restart is required    */

void USART2_Init(void)
{
            int i;
            RCC->APB2ENR |=  ( 1UL <<  0);       /* enable clock Alternate Function  */
            AFIO->MAPR &= ~( 1UL <<  3);       /* clear USART2 remap             */
            RCC->APB2ENR |=  ( 1UL <<  2);       /* enable GPIOA clock             */
            GPIOA->CRL &= 0xffff00ff;
            GPIOA->CRL |= 0xb00;       //PA2: output push-pull, Max. 50M speed
            GPIOA->CRL |= 0x4000;       //PA3: input floating
            RCC->APB1ENR |= 0x020000;  //¼´ RCC_APB1PeriphClockCmd(RCC_APB1Periph_USART2, ENABLE);
            USART2->BRR = 0x1d4c;
               USART2->CR1 = (( 1UL <<  2) |    /* enable RX                      */
                                             ( 1UL <<  3) |    /* enable TX                      */
                                             ( 1UL <<  5) |    /* enable RXNE Interrupt          */
                                             ( 1UL <<  7) |    /* enable TXE Interrupt          */
                                             ( 0UL << 12) );    /* 1 start bit, 8 data bits       */
            USART2->CR2 = 0x0000;                /* 1 stop bit                      */
            USART2->CR3 = 0x0000;                /* no flow control                */
            for (i = 0; i < 0x1000; i++) __NOP(); /* avoid unwanted output          */

            NVIC_EnableIRQ(USART2_IRQn);
            USART2->CR1  |= 0x2000;    /* enable USART                   */
}

void USART2_IRQHandler (void) {
         volatile unsigned int IIR;
         struct buf_st *p;
         IIR = USART2->SR;
         if (IIR & USART_SR_RXNE) {          /* read interrupt                */
                        USART2->SR &= ~USART_SR_RXNE;             /* clear interrupt                */
                        p = &g_RxBuf;
                        if (((p->in - p->out) & ~(RBUF_SIZE-1)) == 0) {
                                    p->buf [p->in & (RBUF_SIZE-1)] = (USART2->DR & 0x1FF);
                                    p->in++;
                        }
         }

         if (IIR & USART_SR_TXE) {
                     USART2->SR &= ~USART_SR_TXE;             /* clear interrupt                   */
                     p = &g_TxBuf;
                     if (p->in != p->out) {
                                 USART2->DR = (p->buf [p->out & (TBUF_SIZE-1)] & 0x1FF);
                                 p->out++;
                                 g_bTxRestart = 0;
                     }
                     else {
                                 g_bTxRestart = 1;
                                 USART2->CR1 &= ~USART_SR_TXE;    /* disable TX IRQ if nothing to send  */
                     }
         }
}

void buffer_Init (void) {
         g_TxBuf.in = 0;                         /* Clear com buffer indexes          */
         g_TxBuf.out = 0;
         g_bTxRestart = 1;
         g_RxBuf.in = 0;
         g_RxBuf.out = 0;
}

int SendChar (int c) {
      int iii;
   struct buf_st *p = &g_TxBuf;
      if (SIO_TBUFLEN >= TBUF_SIZE)          /* If the buffer is full             */
                     return (-1);                         /* return an error value             */
      p->buf [p->in & (TBUF_SIZE - 1)] = c; /* Add data to the transmit buffer. */
      p->in++;
      if (g_bTxRestart) {                      /* If TX interrupt is disabled       */
                  g_bTxRestart = 0;                      /*    enable it                   */
                  USART2->CR1 |= USART_SR_TXE;       /* enable TX interrupt             */
      }
      return (0);
}

char GetKey (void)
{       int iii;
   struct buf_st *p = &g_RxBuf;

   if (SIO_RBUFLEN == 0)
               return (0xff);
   return (p->buf [(p->out++) & (RBUF_SIZE - 1)]);
}