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Altera_Forum's avatar
Altera_Forum
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20 years ago

Aborting a DMA transfer

I'm looking for a way to abort a DMA transfer without using the flow control. I'm blown away that there's not a control bit in the DMA controller to abort a transfer!

We have a peripheral that can fail before transferring the entire data packet and need a way to be able to abort/reset the DMA controller. It currently does *not* use flow control and we'd rather not have to add it and the associated logic just to be able to abort a DMA.

Regards,

Mark

1 Reply

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    20 years ago

    I think all you have to do is clear the "GO" bit in the command register. I just realized that I was missing that functionality in my DMA routines (for a USB chip) so I added a function like this: 

    int AbortUSBTransfer()
{
  if ((IORD_ALTERA_AVALON_DMA_STATUS(DMA_0_BASE) & ALTERA_AVALON_DMA_STATUS_BUSY_MSK) == 0)
    return 1; // nothing to do
  // clear control register (mainly clear "GO" bit
  IOWR_ALTERA_AVALON_DMA_CONTROL(DMA_0_BASE, 0);
    
  if ((IORD_ALTERA_AVALON_DMA_STATUS(DMA_0_BASE) & ALTERA_AVALON_DMA_STATUS_BUSY_MSK) == 0)
    return 1; // abort worked
  else
    return -1; // abort failed
  
}

    I just tried it and it seems to work. I started a DMA transfer but didn't send any data from the PC. I then aborted the DMA transfer and the DMA engine went back to idle (busy and done bit cleared). After that I executed some more DMA transfers and they worked fine.

    Hope that helps,

    Andrew