DMA Controllers

[Kevin McGuire]

I was curious since there are a lot of people here in this forum, and I assume there are a number of you who have various knowledge of things that I can not foresee so I was wanting ask about DMA.

I understand that motherboards have a built-in DMA controller like Intel 8237 chip which provides four eight bit and four sixteen bit channels. However I have also seen what appears to be onboard DMA controllers for certain groups of cards like networking and hard disk controllers. Then the PCI bus can directly transfer memory between RAM and it's devices.

What is technology moving towards? The buses providing the direct memory access like PCI with a onboard controller in the device dubbed the DMA controller? Is there anything else that I am forgetting about?

[Kevin McGuire]

The Intel 82374 EISA System Component (ESC) was introduced in early 1996 and includes a DMA controller that provides a superset of 8237 functionality as well as other PC-compatible core peripheral components in a single package. This chip is targeted at both EISA and PCI platforms, and provides modern DMA features like scatter-gather, ring buffers as well as direct access by the system DMA to all 32 bits of address space.

I just found this interesting information. Is this potentially what is being used by some, a lot, or a few devices that I was talking about in the last post?

Anyone know of any devices that use this 82374's DMA functionality?

[~]

The only ones I know are the older ISA sound cards like SoundBlaster's and the floppy drives.

I'm not sure wheter ATA drives have ever been able to use that DMA controller instead of the one present in the motherboard's IDE controller.

Basically, any ISA device, that should be designed to access the first 16Mb of physical RAM.