CareerCup 16.3

Describe direct memory access (DMA). Can a user level buffer / pointer be used by kernel or drivers?

why DMA?because some time, we just need move data around, don't need to go through CPU to put data in memory.

HOW?
DMA controller. send DMA request
CPU grants access by asserting DMA acknowledge signal
DMA reads/writes
DMA asserting bus release signal to notify CPU