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From: daveh@cbmvax.UUCP (Dave Haynie)
Newsgroups: comp.sys.amiga.tech
Subject: Re: LUCAS FPU LOGIC ERROR
Message-ID: <8405@cbmvax.UUCP>
Date: 3 Nov 89 16:02:26 GMT
References: <174@intersil.uucp>
Organization: Commodore Technology, West Chester, PA
Lines: 26

in article <174@intersil.uucp>, hamilton@intersil.uucp (Fred Hamilton) says:

> So I finally got my LUCAS/FRANCES purring away last night [..] [run]
> SetCPU (V15, 1.5, or 0.15) and it says:

> "FPU Logic Error"

> What does this mean?  Is this anything I should worry about?

What this means is that the FPU address isn't fully decoded.  The 68020
accepts 8 coprocessors, each of which sits at a particular address in CPU
space.  If the coprocessor address isn't fully decoded in hardware, you'll
see that coprocessor aliased at one or more valid coprocessor addresses. 
In practice, most systems only use two coprocessors; the FPU and the MMU. 
What SetCPU is telling you here is that the FPU in your system is
responding to an MMU coprocessor address.  While this state can be detected
without causing any real problem if you're looking for this situation,
there's no guarantee that any future MMU client (like some future OS) will
check for incorrectly decoded FPUs when it's looking for the MMU.  So this
isn't a big deal today, but could be a problem in the future. 

> Fred Hamilton                  Any views, comments, or ideas expressed here
-- 
Dave Haynie Commodore-Amiga (Systems Engineering) "The Crew That Never Rests"
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