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DMA for Ethernet Controller (Announce)

posted by bretjohn(R) Homepage E-mail, Rio Rancho, NM, 21.04.2016, 20:18

I don't know specifically about the E3800, but I've been told by others that the 32-bit (linear) address provided by all known DPMI servers when you allocate memory is the same as the physical address. The physical address is all you need to know for DMA purposes. I don't use DPMI myself, so can't guarantee anything about it, though.

In PCI, it's not really DMA (in the same sense as a traditional DMA controller), but is called Bus Mastering. The PCI Bus temporarily grabs control of the address bus and to do its memory and I/O transfers, and then lets the other bus(ses) have control back again. There's a device called an Arbiter that makes sure only one thing has control of the address bus at a time. The only memory I know of that's not DMA/Bus-Mastering compatible is Shadow RAM, but sometimes even some Shadow RAM is compatible with DMA. AFAIK, Shadow RAM is almost always in the first MB of memory.

That's my understanding of how it all works. Someone please correct me if I'm wrong.


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