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From: black@par1.cs.umass.edu (David K. Black)
Newsgroups: comp.sys.m88k
Subject: Exception handling in the 88's
Message-ID: <28961@dime.cs.umass.edu>
Date: 8 Apr 91 16:32:05 GMT
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Reply-To: black@par1.cs.umass.edu.CS.UMASS.EDU (David K. Black)
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Organization: University of Massachusetts, Amherst
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In the MC88100 User's manual on pages 6-8 and 6-9 (Section 6.4.2)
there apears a discussion of two methods for exception processing
in the 88's.  To summarize:

Method 1: Disable interrupts etc and don't save any context to memory.
Use the rte instruction to restore control registers.  Shadowing remains
disabled and a non-trap exception will crash the machine.

Method 2: The exception handler saves control register context to memory
and shadowing is re-enabled, allowing for nested exceptions.  

My question is: Under what cicumstances is the first method acceptable?
Are there any OS code writers within "the sound of my voice" who have 
actually confronted this problem?

In general, would anyone  care to comment on exception processing in 
the 88's in general?  Any caveats to be known? etc.

If all this is of little interest (imagine that!) personal replies will
be greatly appreciated.

David Black