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imxrt:Serial overcome race where DMA has not fetched TCD again"

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With TCD set to loop, there is a window where the
   DMA has raised Done, but not reloaded the TCD, resetting
   count and clearing Done.

   In this window  imxrt_dmach_getcount could then return 0.
   Resulting in imxrt_dma_nextrx returning RXDMA_BUFFER_SIZE.
   Which is not a valid index in the FIFO.

   Since the count will be set to RXDMA_BUFFER_SIZE. When the DMA
   engine completes the TCD reload. The imxrt_dma_nextrx would
   return 0. Therefore:

    (RXDMA_BUFFER_SIZE - dmaresidual) % RXDMA_BUFFER_SIZE

   accomplishes this.
This commit is contained in:
David Sidrane 2023-10-27 03:15:10 -07:00 committed by Xiang Xiao
parent 18819b6b24
commit 892fe45900
1 changed files with 1 additions and 1 deletions
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2
arch/arm/src/imxrt/imxrt_serial.c
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@ -1375,7 +1375,7 @@ static int imxrt_dma_nextrx(struct imxrt_uart_s *priv)
int dmaresidual = imxrt_dmach_getcount(priv->rxdma);
DEBUGASSERT(dmaresidual <= RXDMA_BUFFER_SIZE);
return RXDMA_BUFFER_SIZE - dmaresidual;
return (RXDMA_BUFFER_SIZE - dmaresidual) % RXDMA_BUFFER_SIZE;
}
#endif