Path: utzoo!mnetor!uunet!husc6!think!ames!pasteur!ucbvax!CORY.BERKELEY.EDU!dillon
From: dillon@CORY.BERKELEY.EDU (Matt Dillon)
Newsgroups: comp.sys.amiga
Subject: Re: the Amiga Interrupt Cycle and Exec
Message-ID: <8802210745.AA20230@cory.Berkeley.EDU>
Date: 21 Feb 88 07:45:55 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Lines: 31

>	Could anybody please tell me what order Exec pushes what registers
>onto the stack right before it calls your interrupt service routine?  (It frees
>a1...?? to use as scratch.)  I need access to this data, and any help would
>be greatly appreciated.  The RKM's don't give the whole story.   I thank you in advance.
>

	Absolutely not!  DON'T!!! WRONG!  You can trace the ROM code if 
you want, but under no circumstances should you make assumptions as to what 
the interrupt tag code does!  When your interrupt service routine is entered,
the following is all you know:

	D0	-scratch
	D1	-scratch
	A0	-scratch
	A1	-server data segment pointer on call, scratch on return
	A5	-scratch
	A6	-EXEC library base pointer on call, scratch on return

	D2-D7/A2-A4	-must be preserved by your interrupt handler.

	Where the server data segment pointer is the one defined in
the Interrupt structure for that interrupt.  The interrupt service routine
should return with an RTS.  Obviously the tag code has saved D0/D1/A0/A1/
A5/A6, but what possible reason could you have for wanting the original
contents?  At the point your interrupt service routine is entered, the
previous state could have been *anything*.

	This is the Amiga.  Let us not get into the habit of using hardcoded
addresses and offsets that delve into the internals of the OS!

						-Matt