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Altera_Forum
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21 years ago

How to increase DMA fifo depth?

I need to increase the depth of the fifo in an Avalon dma. I thought I remembered reading about it, but I can't seem to find anything that jumps out at me in the .ptf. (dma v3.1, Nios v3.2) ...
Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
20 years ago

Hi Kero,

Boy were you great to help out with that problem! Thanks again! http://forum.niosforum.com/work2/style_emoticons/<#EMO_DIR#>/smile.gif

If you search I did post the changes that made it work. I don&#39;t remember any more. It involved editting the .ptf. - maybe a latency setting.

Sorry I can&#39;t be of more help. Ultimately we had to abandon DMA for the streaming data, because although dma emptied the fifo into sdram lickety split, reaccessing the data to operate on it was dismally slow. (12-13 clocks per access!!!!)

We wound up having a Custom Instruction written that would pop a 32 bit fifo word into a register in 2 clocks. Then we could operate on it quickly.

I think with the new features in the latest Nios this would all be much easier. Namely the tightly-coupled memory interface. I&#39;m pretty sure our dilema was a motivation for its creation. (thanks James, Jesse, Kero !!!)

Ken