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Switching between Channels DMA and BUS relationship

Camila Nunes
Prodigy 135 points

Hi,

I can understand when the DMA controller has to change between channels,

I, also, know the causes that makes the DMA switch between channels.

But, I can't understand how the DMA do that for one specific case.

When the DMA is reading data from a synchronized device and the RSYNC bit is set, the DMA has to wait for the synchronization signal, and while doing that, it has to change to other channels and do others transfers. That is exactly the problem, how the DMA changes to other transfers, since it has already send an address to the bus, and after the synchronization signal comes, it changes back to the first transfer that is synchronized, since the bus is already making another transfer?

Can the bus make two transfers at the same time? or the bus has some kind of logic control to switch between transfers?

I can't understand how the bus will act in this case...

Have I made my doubt clear?

 

  • Prodigy 10 points

    owww, she didn´t specificated the DMA, we are working with the DMA controller speficated in SPRU577A.

    att,

    Angelo Brito

  • TI__Guru* 84110 points

    There are many questions which remain:

    Which DSP are you using?

    Which EVM/DSK or other platform are you using for the test cases or your development work?

    What are the source/destination addresses for your two synchronized transfers?

    The DSP has many internal busses, some can have reads and writes both in progress, but generally only one transfer would be taking place at a time. If the DMA controller is trying to service multiple transfer requests to the same bus, there will be arbitration logic used to select which transfer should occur first, but all transfers should still complete within a short amount of time.

    Understanding the details of the internal bus architecture may not be possible outside of the DSP design team, but if you will explain your requirements or what transfers you are trying to perform from some sources to some destinations, perhaps we can help.