Revision as of 00:25, 26 October 2008 (view source) osdev>Yuhong m (DMA moved to ISA DMA: This article only describe ISA DMA, it do not describe any other kind of DMA) ← Older edit		Revision as of 00:29, 26 October 2008 (view source) osdev>Yuhong No edit summary Newer edit →
Line 1: ISA DMA~~, or~~ (Direct Memory Access,) in today's PC architecture, like ISA itself, is in many ways like an appendix. It is used by the floppy disk controller, ISA sound cards, ISA network cards and parallel ports (if they support ECP mode). Whilst interrupt, keyboard and timer interface circuits have obvious and relevant uses, the ISA DMA controller and it's programming interface are still well and truly stuck in the 1970's where they were first designed. Modern PCI controllers typically have their own "bus mastering", which is far better. The idea behind DMA is that you can set up a 'channel' with an address pointing into memory and the length of the data to be transferred. Once set up, you can tell the peripheral owning the 'channel' to do whatever it is supposed to do (e.g. read a sector). Then the CPU can go onto something else. Periodically when the data bus isn't being used by the CPU the DMA chip takes over and transfers data between the peripheral and memory without involving the CPU. When the transfer is complete (e.g. an entire sector has been sent to the floppy drive) the DMA chip will than signal that it is finished. The DMA chip can even signal if it has run out of data, allowing the CPU to program some new information and another transaction to proceed.

ISA DMA: Difference between revisions

ISA DMA (view source)

Revision as of 00:29, 26 October 2008