DMA
PrintDirect Memory Access. A technique for data transfer from a hardware unit to memory, without involving the CPU. DMA is often controlled by a hardware device, thus freeing up the CPU to perform other tasks at the same time.
Options for DMA modes are single, demand, and block-mode transfers. In single-mode transfers, one data value is transferred for each DMA request asserted, which is the slowest method of transfer because the DMA controller must arbitrate for the system bus with each transfer. Block and demand transfer modes increase system throughput because the DMA controller performs several DMA transfers once the DMA controller has gained bus access. For block-mode transfers, the DMA controller performs the entire DMA sequence as specified by the transfer count register at the fastest possible rate in response to a single DMA request from the DAQ board. For demand-mode transfers, the DMA controller performs DMA transfers at the fastest possible rate as long as the DAQ board asserts its DMA request. When the DAQ board unasserts this DMA request, transfers are held off.
Reader Comments | Submit a comment »
how ?
How does the program know the data
has been transfered? How are the
destination buffers controled?
- John Phillips, teletek. john.phillips0@gmail.com - Oct 31, 2007
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