Path: utzoo!dptcdc!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!rutgers!apple!oliveb!amiga!cbmvax!andy
From: andy@cbmvax.UUCP (Andy Finkel)
Newsgroups: comp.sys.amiga.tech
Subject: Re: Official Warnings...
Message-ID: <6621@cbmvax.UUCP>
Date: 18 Apr 89 20:09:20 GMT
References: <3082@haven.umd.edu>
Reply-To: andy@cbmvax.UUCP (Andy Finkel)
Organization: Commodore Technology, West Chester, PA
Lines: 23

In article <3082@haven.umd.edu> brett@sylvester-tr.UMD.EDU (Brett S Bourbin) writes:
>
>	In the Jan/Feb 1989 issue of Amiga-Mail, under the "Official Warnings
>to ROM-Jumpers, Structure-Hackers, and Others", it states that you should
>NOT use the TAS assembly instruction.  What is the reason for this?

The 68000 makes a couple assumptions about instructions like  TAS
(those of the read-modify-write type).  One is that the 68000 controls
the memory bus.  The other is that the read-modify-write cycle is atomic.

On the Amiga neither is necessarily true; the custom chips control
the memory bus, and read-modify-write may be interrupted.

So switch to the MOVEQ.  You'll be happier.  We'll be happier :-)
-- 
andy finkel		{uunet|rutgers|amiga}!cbmvax!andy
Commodore-Amiga, Inc.

  "There is no programming problem that cannot be solved by proper
  "application of the Delete command."

Any expressed opinions are mine; but feel free to share.
I disclaim all responsibilities, all shapes, all sizes, all colors.