Difference between Demand Mode and Single Cycle DMA

Updated Feb 12, 2018

Reported In

Hardware

  • AT-GPIB/TNT

Issue Details

What is the difference between Demand Mode and Single Cycle DMA?

Solution

Demand Mode DMA allows PC hardware to transfer many bytes of data, via a DMA channel, with only a single programming of the DMA controller. Single Cycle DMA, on the other hand, can only transfer a word of data with each programming of the DMA controller. This could make Single Cycle DMA a slower process than Demand Mode DMA, since the potential exists for a different process to get control of the DMA controller during data transfer. 

Our GPIB drivers attempt to use Demand Mode DMA for DMA transfers, but some computers cannot handle Demand Mode. In this case, you can try Single Cycle DMA.

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