Mail Archives: djgpp/1997/01/13/14:26:41
Hi Shawn Betts:
> In protected mode, to make a DMA buffer, one must allocate memory under
> 1M, correct?
Yes.
>This memory cannot cross page breaks right?
Yes.
>So in protected mode, where there are no page breaks,
No, wrong, the page breaks as you said are in FISICAL memory so is the same in
PM that RM.
>does it matter where the DMA buffer is as long as it under 1M?
Yes it matter, you must make the same as RM.
>If it does matter, how do you find if it crosses a page break?
The pages of DMA are 64Kb so:
1) Calculate the linear address of your buffer.
2) Chack that the page (linear/64Kb) of the start of your buffer is the same as
the page of the end of your buffer.
That's because the 8237 can address only 64K of elements (64Kb in 8-bits DMA or
128Kb in 16-bit DMA).
Ever talking about ISA DMA!
SET
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Salvador Eduardo Tropea (SET).
Address: Curapaligue 2124, Caseros, 3 de Febrero
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