Aborting a DMA transfer

Altera_Forum · ‎03-15-2006

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

Altera_Forum · ‎03-15-2006

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