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Subject: Re: Beta Test:  CWSDPMI r7 - 4GB support
From: Georg Potthast <dosusb AT googlemail DOT com>
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The memory mapped registers usually "hang out" at the end of the 4GB memory area. 

I think there should be enough memory within the 4 GB area to allocate a DMA buffer there. But to allocate the buffer anywhere starting above the 4 GB area you will have to be able to write a 64bit linear address into the HW register. So far I have only seen 32bit HW registers.

If you manage to write a 64bit linear address into the HW register, CWSDPMI 
would need to provide a DPMI function like "Int 31H Function 0800H" for the area above 4 GB to allow you to access that with 32bit addresses. I doubt that this was on the agenda yet.