Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10 beta 3/9/83; site uthub.UUCP
Path: utzoo!utcsri!utai!uthub!thomson
From: thomson@uthub.UUCP (Brian Thomson)
Newsgroups: net.micro.68k,net.micro.16k
Subject: Re: Re: PDP11s vs the micros
Message-ID: <223@uthub.UUCP>
Date: Wed, 21-Aug-85 10:33:50 EDT
Article-I.D.: uthub.223
Posted: Wed Aug 21 10:33:50 1985
Date-Received: Wed, 21-Aug-85 23:30:52 EDT
References: <1617@hao.UUCP> <847@mako.UUCP> <2422@sun.uucp>
Organization: CSRG, University of Toronto
Lines: 17
Xref: utai net.micro.68k:771 net.micro.16k:259

Dave Trissel (davet@oakhill.UUCP) brags about the Motorola FPU:

>Concerning floating-point state saves we gave a lot of thought to minimizing
>latency times.  What we did was give an indication to the OS of whether any
>of the FP registers had been used.  If not, the OS could skip the context
>save and restore completely.

Careful reading of the specs for the National FPU, plus a little experimenting,
shows that they also provided this capability, though their implementation
has the look of being a fortuitous accident (hint: check the behaviour of the
Trap Type field of the Floating Status Register).
Unfortunately, whoever wrote the documentation made no mention of this
use, which suggests that they don't realize what they have and are in danger
of making it not work in future releases of the hardware.
-- 
		    Brian Thomson,	    CSRI Univ. of Toronto
		    {linus,ihnp4,uw-beaver,floyd,utzoo}!utcsrgv!uthub!thomson