Path: utzoo!utgpu!jarvis.csri.toronto.edu!clyde.concordia.ca!uunet!mcsun!ukc!edcastle!aiajms
From: aiajms@castle.ed.ac.uk (-=Andy=-)
Newsgroups: comp.sys.amiga
Subject: Amiga Exception Vectors
Message-ID: <2780@castle.ed.ac.uk>
Date: 12 Mar 90 16:27:02 GMT
Reply-To: aiajms@castle.ed.ac.uk (-=Andy=-)
Organization: Edinburgh University Computing Service
Lines: 31


I am currently designing a mini operating system round the 68000 here at
Uni. I thought I might have a look at the Amiga Exception vectors and
found to my suprise that the system stack pointer seemed to be directed
to location 0, ie on top of itself. The PC pointed to an area of memory
in my fast ram which seemed fair enough but several of the other vectors
seemed to be pointing to the area between the Amiga ROM and the top of
the 68000 memory map, which according to the fabby (ahem) Amiga Manual
does not exist! It does however mention that the exception table has
some sort of overlay and I notice from the Gary chip that it has some
sort of Overlay input, presumably for some weird sort of decoding.

I am not really a hardware person, and I am a bit more than confused. It
just seems rather odd to have the SSP at location 0000 unless perhaps
the stack actually exists in this weird piece of memory between ROM and 
the top of memory which is in turn overlayed on another piece of
memory!!!

Anyone help me out???
Thanks


-=Andy=-

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Name  : Andy Mcsherry
Degree: Computer Science & Artificial Intelligence		   //
Univ  : University Of Edinburgh, Scotland.		       \\ //
Mail  : aiajms%uk.ac.ed.castle@nsfnet-relay			\X/
Motd  : Don't be STingy, buy a decent computer         -->     AMIGA 
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