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From: thad@cup.portal.com (Thad P Floryan)
Newsgroups: unix-pc.general,comp.sys.att
Subject: Re: Interesting Parts List
Message-ID: <25903@cup.portal.com>
Date: 14 Jan 90 01:03:12 GMT
References: <607@alfred.UUCP>
Organization: The Portal System (TM)
Lines: 50

elliot@alfred.UUCP (Elliot Dierksen) in <607@alfred.UUCP> writes:

	I was looking through the documentation today (Amazing what's in
	there :-)) and I stumbled on the service & parts ordering information.
	In there was listed: 105160253  Math Acc. Unit MC 68881

	Comments anybody??

A repost from the past:

>From: jbm@uncle.UUCP (John B. Milton)
>Newsgroups: unix-pc.general,comp.sys.att
>Subject: Could a 68881 Math co-processor go fast?; HwNote07
>Message-ID: <372@uncle.UUCP>
>Date: 23 Oct 88 19:12:19 GMT
>Date-Received: 25 Oct 88 06:18:41 GMT
>
>Parts of this article are copied from mail to David Wexelblat
>(dwex@mtgzz.att.com), who suggested a 68881 when I asked for hw ideas. The
>rest of you just don't seem to have any ideas :-!
>
>I was thinking about that one a while ago. AT&T actually made a 68881 board,
>they even have a part number, 105160253. I talked to some guy at AT&T, and
>he says the board was never release due to poor performance. Since the 68010
>does not have a coprocessor interface, the 68881 would have to operate as an
>I/O device, so it would work fine as an expansion card. David tells me that
>the software interface was implemented using an F-line exception handler. Whil
e
>this is clean from the compiler point of view (you just generate 68881
>instructions), it is expensive:
>1. Execute instruction
>2. Get F-line exception
>3. Stack everything away
>4. Start running the common kernel exception code
>5. Pull all the parameters from the user PC and talk to the 68881 through I/O
>6. Defer to another process while the instruction runs on the 68881
>7. Get an interrupt, get the status
>8. Call the kernel code to return from exception.
>
>Steps 6&7 could be replaced with
>6. Loop polling the 68881 for completion
>7. Get the status
>
>I don't know what they did about having an expanded process context for procs
>using the 68881.

...other material deleted...


Thad Floryan [ thad@cup.portal.com (OR) ..!sun!portal!cup.portal.com!thad ]