*BSD News Article 79001


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From: "Arlie Davis" <arlie@thepoint.net>
Subject: Re: Simutaneous mono and vga under FreeBSD...
Message-ID: <01bbaa1e$83d5fa80$070906c6@roanoke>
Date: Tue, 24 Sep 1996 14:44:46 GMT
References: <32388517.BA4@wsg.net> <3238632A.6516@www.play-hookey.com> <51eoiu$6ck@diemos.isdfa.sei-it.com> <323C1975.4FA7@www.play-hookey.com>
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Ken Bigelow <kbigelow@www.play-hookey.com> wrote in article
<323C1975.4FA7@www.play-hookey.com>...

> Now, if you want the Hercules card to run in text mode (which was the
> original stated requirement) it will occupy at least 32K at segment B000
> (in half mode; 64K in full mode). You can't change this, and any VGA
> graphics mode can't be allowed to use this memory space. This
> tremendously limits the graphics modes and amount of memory they can
> access directly.

I agree with everything you've written about simultaneously using multiple
video adapters, except this.  Many video cards can map their frame buffers
into a linear region of the processor's physical address space, far beyond
the realistic end of physical memory.  For example, the Diamond Viper VLB
does this (I think); it can map it's frame buffer to any of these physical
addresses: 40000000H, 80000000H, or A0000000H.  (I may be wrong on the
details, but the concept is right.)

-- arlie