Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!bellcore!texbell!wuarchive!kuhub.cc.ukans.edu!markv
From: markv@kuhub.cc.ukans.edu
Newsgroups: comp.sys.amiga.tech
Subject: Re: YANQ
Message-ID: <22100.25c6e8fe@kuhub.cc.ukans.edu>
Date: 31 Jan 90 19:32:46 GMT
References: <42700026@m.cs.uiuc.edu>
Organization: University of Kansas Academic Computing Services
Lines: 44

In article <42700026@m.cs.uiuc.edu>, schwager@m.cs.uiuc.edu writes:
> (Yet another novice question)
> 
> Just for yucks and to debug stuff from time to time, I try to print out the
> address of a 
> 	struct Screen *Screen;
> by doing this:
> 	printf ("Address of Screen: %08lx\n", Screen);
> I'm using Aztec C, 3.4 version, by the way (I'll upgrade this time).
Good idea...
> Anyway, I get a hellacious number like 00C194E0, which as we all know is
> about 12 Million.  This is especially strange considering I have a 1 Meg
> Amiga 500.  Any ideas why this  is so bizarre?  Most of my addresses turn
> out to be some various shade of weird, just like this example.  Thanks.

Actually not so wierd.  On Amiga 500s and 2000's the first 512K of memory is
addressed from 000000-07FFFF as one would expect.  The second 512K is 
addressed from C00000-C7FFFF.  This the is infamous "slow-fast" RAM.

In theory, with Obese Agnes, a jumper gets moved and this memory gets moved
into the memory range reserved for CHIP ram (000000-1FFFFF, FAST RAM starts
at 200000 and can go to 9FFFFF).  In practice, with Obese Agnes and at 
least the Rev 6.X motherboards this now real CHIP RAM is still getting 
addressed at C00000 for (unexplained) "technical reasons".

On the official memory map C00000-CFFFFF is designated as "CPU Ram" whatever
that was supposed to be.  Some older Amiga 1000 memory boards put their 
memory here, which is why Commodore briefly advertised the 1000 as capable
of a Max of 9.5 megs (Not that you would ever get a 1000's bus to be happy
talking to enough boards to do that.)

So your findings make since.  In a 512K CHIP ram machine if you were to look
at the bitmap pointers in the various rastports, they would indeed be in
the 000000-07FFFF range.
> -Mike
-- 
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