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精读OSAL --DMA方式串行通信(_hal_uart_dma.c)

跳过初始化的内容.

先讲接收操作:

DMA方式的具体操作可以查看DMA的相关内容.

这里有意思的是缓冲区算法的实现,和中断方式还是有些区别.

               |BAUD|DXBUF|

               |..........|............|

               |..........|............|

               |..........|............|

               |..........|............|

               |..........|............|

               |..........|............|

               |..........|............|

    Tail--> |..........|............|

               |..........|............|

               |..........|............|

               |..........|............|

               |..........|............|<--Head

               |..........|............|

 

读函数里只对Head操作,每读一字节就上移一字节,清BAUD,读到tail就停止了.

那么为啥要记录波特率呢?我想了好久也没明白.在DMA里会具体说.

代码不上了.

 

这里说Tail怎么变化,其实Tail指明的就是数据尾在哪里.

来自串口的数据通过DMA直接传到Tail所指的内容.不过因为

DMA所以Tail不能递增.那么Tail什么时候改呢?

是在每个OSAL的循环里:HalUARTPollDMA()里 ,调用HalUARTRxAvailDMA()里.

那么怎么知道数据写到哪呢?这就是为什么要存BAUD的原因.

算法里取反存起来作为没数据的标记,当DMA传输时,直接将BAUD和DxBUF一起

传过来存起来,于是BAUD就变成正常的BAUD值,而不是取反值.

然后POLL里就查找那个还是反的BAUD就是没数据.Tail就改到前一个..

都在HalUARTRxAvailDMA().

 

 

到这读操作完成了,下面是DMA的写..

里面有说写操作推荐 用 中断 方式,这和上篇没区别就不提了.

这里说DMA方式:

                     |SEL=0|SEL=1|

                     |IDX=n |IDX=m|

                     |...........|...........|

                     |...........|...........|

                     |...........|...........|

                     |...........|...........|

    (IDX=n)-->|...........|...........|

                     |...........|...........|

                     |...........|...........|<--(IDX=m)

                     |...........|...........|

                     |...........|...........|

                     |...........|...........|

                     |...........|...........|

                     |...........|...........|

                     |...........|...........|

                     |...........|...........|

算法理角了也很简单,IDX是记录侍发数据长度,发送完一列就清IDX,同时改SEL指向另一列..

不过看代码还是有点难..所以来注释:

static void HalUARTArmTxDMA(void)
{
  halDMADesc_t *ch = HAL_DMA_GET_DESC1234(HAL_DMA_CH_TX);
  HAL_DMA_SET_SOURCE(ch, dmaCfg.txBuf[dmaCfg.txSel]);
  HAL_DMA_SET_LEN(ch, dmaCfg.txIdx[dmaCfg.txSel]);

  dmaCfg.txSel ^= 1; //注意这里取反了txSEL.
  dmaCfg.txTrig = 1;
  HAL_DMA_ARM_CH(HAL_DMA_CH_TX);

  HalUARTPollTxTrigDMA();

  if (DMA_PM)
  {
    HAL_UART_DMA_SET_RDY_OUT();
  }
}

每次调用完,SEL都改成另一个.这是要注意.

static void HalUARTPollTxTrigDMA(void)  //这个也是在POLL里调用.

{
  if ((UxCSR & CSR_TX_BYTE) == 0)  // If no TXBUF to shift register transfer, then TXBUF may be MT.
  {
    if ((dmaCfg.txTick == 0) || ((uint8)(ST0 - dmaCfg.txTick) > HAL_UART_TX_TICK_MIN))
    {
      dmaCfg.txTick = 0;

      if (dmaCfg.txTrig && HAL_DMA_CH_ARMED(HAL_DMA_CH_TX)) //这里判断是否要人工触发DMA传输
      {
        HAL_DMA_MAN_TRIGGER(HAL_DMA_CH_TX);
      }
      dmaCfg.txTrig = 0;
    }
  }
  else
  {
    UxCSR = (CSR_MODE | CSR_RE);  // Clear the CSR_TX_BYTE flag.
    dmaCfg.txTick = ST0;

    if (dmaCfg.txTick == 0)  // Reserve zero to signify that the minimum delay has been met.
    {
      dmaCfg.txTick = 0xFF;
    }
  }
}


 

void HalUART_DMAIsrDMA(void)
{
  if (dmaCfg.txIdx[dmaCfg.txSel]) //这里判断是否还有数据要传输
{
    // If there is more Tx data ready to go, re-arm the DMA immediately on it.
    HalUARTArmTxDMA();

    // Indicate that the Tx buffer just finished is now free (re-arming did a ^= toggle of txSel).
    dmaCfg.txIdx[dmaCfg.txSel] = 0;//因为这前ARM的时候,SEL取反了,
                                   //刚刚完成DMA才进中断,在上面ARM中SEL又取反了,那么
 
 
				   //此列已发送所有数据,IDX清零.
 }
  else
  {
    dmaCfg.txIdx[(dmaCfg.txSel ^ 1)] = 0;  // Indicate that the Tx buffer just finished is now free.
// 当前没数据,因为没有再ARM,所以要取反清零.
// Clear the CSR_TX_BYTE flag & start the txTick to allow the possibility of an immediate
// manual trigger from the next Write(), if it occurs more than one character time later.
    HalUARTPollTxTrigDMA();
  }

  dmaCfg.txMT = TRUE;  // Notify CB that at least one Tx buffer is now free to use.
}


 

static uint16 HalUARTWriteDMA(uint8 *buf, uint16 len)
{
  txIdx_t txIdx;
  uint8 txSel;
  halIntState_t his;

  HAL_ENTER_CRITICAL_SECTION(his);
  txSel = dmaCfg.txSel;
  txIdx = dmaCfg.txIdx[txSel];
  HAL_EXIT_CRITICAL_SECTION(his);

  // Enforce all or none.
  if ((len + txIdx) > HAL_UART_DMA_TX_MAX)
  {
    return 0;
  }

  (void)memcpy(&(dmaCfg.txBuf[txSel][txIdx]), buf, len);

  HAL_ENTER_CRITICAL_SECTION(his);
  /* If an ongoing DMA Tx finished while this buffer was being *appended*, then another DMA Tx
   * will have already been started on this buffer, but it did not include the bytes just appended.
   * Therefore these bytes have to be re-copied to the start of the new working buffer.
   */
  if (txSel != dmaCfg.txSel)//这里是判断这个过程是否有中断发生,如果有SEL不同,要重要整理过数据.
   {
    HAL_EXIT_CRITICAL_SECTION(his);
    txSel ^= 1;

    (void)memcpy(&(dmaCfg.txBuf[txSel][0]), buf, len);
    HAL_ENTER_CRITICAL_SECTION(his);
    dmaCfg.txIdx[txSel] = len;
  }
  else
  {
    dmaCfg.txIdx[txSel] = txIdx + len;
  }

  // If there is no ongoing DMA Tx, then the channel must be armed here.
  if (dmaCfg.txIdx[(txSel ^ 1)] == 0)
  {
    HAL_EXIT_CRITICAL_SECTION(his);
    HalUARTArmTxDMA();
  }
  else
  {
    dmaCfg.txMT = FALSE;
    HAL_EXIT_CRITICAL_SECTION(his);
  }
  return len;
}


到此对DMA的UART就没什么疑问了.