DMA: get data count of descriptor in dmaengine
Elen.Song at atmel.com
Fri Sep 7 05:59:17 EDT 2012
When I am developing using dma for uart receive, I found a problem.
I use a cyclic dma transfer and set descriptor transfer size to lk,
only receive 1k bytes(descriptor transfer done) that will call an interrupt.
If I receive 1 byte, there will happened nothing except my peripherals have timeout function.
Fortunately, I got timeout function in uart peripheral, in timeout handler, I can receive data from uart.
But I do not know how many data I have receive, so there should be a count register in dma.
I found the count register but I do not found correlative api in dmaengine, I think we should add one.
Even during a single or multi buffer transfer, knowing how many data has been transfer in current descriptor is necessary.
Through that, we will not lose a data.
So there should be an api to get current descriptor receive data count.
Or we could get current descriptor status , the status with count value?
I submit an patch to retrieve descriptor data transfer size.
We use this to get data count .
We use Atmel dma, but it could be a common demand.
FYI & Best Regards
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