Message-Id:	<m0vjlms-000S1oC@natacha.inti.edu.ar>
Comments:	Authenticated sender is <salvador AT natacha DOT inti DOT edu DOT ar>
From:	"Salvador Eduardo Tropea (SET)" <salvador AT natacha DOT inti DOT edu DOT ar>
Organization:	INTI
To:	hotpulp AT netidea DOT com, djgpp AT delorie DOT com
Date:	Mon, 13 Jan 1997 15:56:44 +0000
MIME-Version:	1.0
Subject:	Re: DMA buffer in protected mode

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 
--------------- 0 --------------------------------
Salvador Eduardo Tropea (SET).
Address: Curapaligue 2124, Caseros, 3 de Febrero
Buenos Aires, (1678), ARGENTINA
TE: +(541) 759 0013

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