From:	Shawn Hargreaves <Shawn AT talula DOT demon DOT co DOT uk>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: memcpy after djgpp nearptr enable//VESA 2.0 double buffer problem
Date:	Mon, 30 Jun 1997 21:17:56 +0100
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Distribution:	world
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References:	<33B7DA72 DOT DDF8E94E AT mwci DOT net>
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To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp

Larry Swanson writes:
>I'm kind of embarassed to admit this, but I'm having trouble getting a
>double buffer working.
...
>* In the above code "video" is  the address of the linear frame buffer
>obtained from VESA 2.0 plus *__djgpp_conventional_base.   

The address you get back from the VESA driver is a physical, hardware
memory location, while your djgpp code is using virtualised protected
mode addressing. The nearptr hack lets you access memory outside your
data segment, but you still need to map the physical address range into
your linear address space, with the __dpmi_physical_address_mapping()
function. There's some example code to do this on 
http://www.rt66.com/~brennan/djgpp, or you might want to look at the
vesa.c and dpmi.c files from Allegro...


--
Shawn Hargreaves - shawn AT talula DOT demon DOT co DOT uk - http://www.talula.demon.co.uk/
Beauty is a French phonetic corruption of a short cloth neck ornament.

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