AlexanderVasiljev commented on a change in pull request #3618:
URL: https://github.com/apache/incubator-nuttx/pull/3618#discussion_r622245636
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File path: arch/arm/src/stm32h7/stm32_serial.c
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@@ -3375,10 +3375,7 @@ static void up_dma_txavailable(struct uart_dev_s *dev)
/* Only send when the DMA is idle */
- if (resid != 0)
Review comment:
> I think this is the wrong approach. We have to wait if there is a
residual.
Why we should care about residuals?
Every **up_dma_txavailable** should be followed by one
**up_dma_txcallback**. After **up_dma_txcallback** residuals should be zero.
This all we need.
> Having an initial count of 1 means the first time, the DMA can be active
and we ignore it.
The DMA shouldn't be activated before any **up_dma_txavailable**. So the
first **up_dma_txavailable** takes the resource named DMA transmit instance.
**up_dma_txcallback** will free resource. Or is there any other who can trigger
the DMA transmit?
> I think the correct approach it the DMA completion should check the count
and only post if the semaphore is being waited on.
Manually checking a semaphore count has never been a good thing. You will
definitely fall into the race condition. You can check the count, but on the
next moment everything can turn upside down.
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