Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!henry From: henry@utzoo.UUCP (Henry Spencer) Newsgroups: net.micro.68k,net.micro.16k Subject: Re: Re: PDP11s vs the micros Message-ID: <5900@utzoo.UUCP> Date: Thu, 22-Aug-85 13:08:55 EDT Article-I.D.: utzoo.5900 Posted: Thu Aug 22 13:08:55 1985 Date-Received: Thu, 22-Aug-85 13:08:55 EDT References: <1617@hao.UUCP> <847@mako.UUCP> <2422@sun.uucp>, <223@uthub.UUCP> Organization: U of Toronto Zoology Lines: 18 > [discussion about saving floating-point-unit state only when needed] > 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. It should also be possible to get a similar effect by using the SETCFG instruction to tell the cpu "no floating point", which will produce a trap when the user tries to use floating point. Save the state and then turn floating point on again. When I asked the local National man about this, he said it would work. Beware that I have *not* tried it on real hardware yet. -- Henry Spencer @ U of Toronto Zoology {allegra,ihnp4,linus,decvax}!utzoo!henry