Message-Id: Comments: Authenticated sender is From: "Salvador Eduardo Tropea (SET)" 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 Content-type: text/plain; charset=US-ASCII Content-transfer-encoding: 7BIT 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