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.