Message-ID:	<3E29CC98.DFE512DC@worldnet.att.net>
From:	Paul Cousoulis <paulcsouls AT worldnet DOT att DOT net>
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Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: DMA and DJGPP
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Date:	Sat, 18 Jan 2003 21:55:33 GMT
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Thanks Antti, that helps alot I'll go back through the PCI config data
and the PLX datasheet with this in mind.

Paul

Antti Koskipää wrote:
> 
> Paul Cousoulis wrote:
> > I'm building a data aquisition board that uses a PLX PCI chip to
> > communicate with the PCI bus. I need to set it up to use DMA to transfer
> > the data. I how to do I find the address and set up the memory in DJGPP
> > to get at the data?
> 
> PCI DMA is also called bus mastering. It's way different from the old
> ISA DMA, which is based on the 8237 chip, and a lot more complex. The
> 8237 cannot be used with the PCI bus. I don't know the details, but you
> should get your motherboard's northbridge manuals and look there. When a
> PC is booted up, the BIOS assigns the card some address near the end of
> the address space. DJGPP FAQ has more information on how to map this
> area for your program. If I remember correctly, the function was
> __dpmi_physical_address_mapping(). You can then access this area using
> movedata(), or simply using a pointer to it with the "Fat DS Hack" (read
> the FAQ). Bus mastering means that the card is given a command to feed
> its data straight to the main memory, bypassing CPU, so no movedata() or
> pointer usage is necessary. To find out the card's physical address,
> just use those PCI BIOS functions to access the PCI configuration space.
> Remember to zero out the lowest 4 bits from the address you get.
> 
> Hope this helps.
> 
> --
> - Antti
> 
> Address is munged.

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