Re: What are the various alternate uses for the PC's LSB ?

Message-ID	<4DCCA852.6010806@SPAM.comp-arch.net> (permalink)
Date	2011-05-12 20:41 -0700
From	"Andy \"Krazy\" Glew" <andy@SPAM.comp-arch.net>
Organization	comp-arch.net
Newsgroups	comp.arch
Subject	Re: What are the various alternate uses for the PC's LSB ?
References	(1 earlier) <597275762326654751.812921acolvin-efunct.com@news.eternal-september.org> <iq9bii$58v$1@speranza.aioe.org> <rZqdnVxkBug9DlXQnZ2dnUVZ_smdnZ2d@speakeasy.net> <4DCAFE51.5000806@SPAM.comp-arch.net> <iqfdc2$73n$1@speranza.aioe.org>

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On 5/11/2011 5:45 PM, whygee wrote:
> Hi Andy !
>
> Andy "Krazy" Glew wrote:
>> On 5/9/2011 6:23 PM, Rob Warnock wrote:
>>> whygee<yg@yg.yg> wrote:
>>> +---------------
>>> <snip>
>>> | IRQ masking is performed at the program level
>>> | by the CRIT instruction which "opens" a predetermined
>>> | lenght critical section of up to 16 consecutive instructions.
>>> |
>>> | http://yasep.org/ISM/CRIT.html
>>> |
>>> | Yes, i know, it adds a tiny 4-bit counter ...
>>> +---------------
>>>
>>> Heh, heh! Indeed, it *has* been done already!! See the DCA[1]
>>> "SmartMux/3xx" series terminal networking switches circa 1972(!),
>>> which included *precisely* this functionality as an add-on
>>> to the PDP-8/e instruction set!! Yes, with a 4-bit counter. ;-}
>>
>> Intel i860 did something similiar.
>
> I can't locate a PDF of this architecture.
> Unless it's behind a paywall :-/

It predates the web.

I started looking for a manual that had been scanned and put up,
and found this:

    http://pages.swcp.com/~mccurley/humor/i860.html
    Our favorite manual

    (Intel i860 Processor Reference Manual)

    Bullet holes courtesy of Stephen Wheat,
    one of the chief architects of SUNMOS.
    It should be noted that he now works for Intel!


Unfortunately, can't find the manual.  Maybe I can scan it in.  If Intel 
will permit it.



> However I found this :
> http://ibmmuseum.com/ohlandl/CPU/wizard.html
>
> "* Bus lock/unlock instructions for flexible indivisible
> read-modify-write sequences. Interrupts are disabled
> while the bus is locked. "If ... the processor does
> not encounter a load or store following an unlock
> instruction by the time it has executed 32 instructions,
> it triggers an instruction fault...".
> For example: locked test and set is:
> // r22 <- semaphore, semaphore <- r23
> lock // next cache miss load/store locks bus
> ld.b semaphore, r22
> unlock // next load/store unlocks bus
> st.b r23, semaphore
> "
>
> Is this what you are refering to ?

My MS thesis describes it briefly (part of my MS thesis was a survey of 
all synchronization techniques current in 1990).  Hmm...  I don't think 
my MS thesis is on the web, either.  I have it on tape somewhere...

IIRC, the i860 LOCK instruction made the processor uninterruptible and 
asserted a LOCK# pin on the bus for 32 cycles.  So, if you could do your 
atomic operation in 32 cycles or less...  It was actually more flexible 
than LL/SC in this regard, although a later rev rediced what you were 
allowed to do in the locked 32 cycles.


> It's funny because when i defined the "CRIT" instruction,
> it remembered me of the "load/store locked" instructions
> of MIPS (eventually Alpha ?) but i wanted to do something
> more generic/general. And safe. That's why I define how
> many instructions are critical, instead of defining a couple
> of instructions (like the lock/unlock above).
>
> What's interesting in the MIPS flavor is that (IIRC) there
> is a status bit that is updated so the SW knows if the
> sequence was interrupted so it can rerun it. Here, the
> "critical" sequence is not meant to be interrupted (unless
> it traps because of a fault, too bad) so no need to get
> the status.
>
> yg

Thread

What are the various alternate uses for the PC's LSB ? whygee <yg@yg.yg> - 2011-05-08 23:01 +0200
Re: What are the various alternate uses for the PC's LSB ? kym@kymhorsell.com - 2011-05-09 04:07 +0000
Re: What are the various alternate uses for the PC's LSB ? whygee <yg@yg.yg> - 2011-05-09 08:45 +0200
Re: What are the various alternate uses for the PC's LSB ? "robertwessel2@yahoo.com" <robertwessel2@yahoo.com> - 2011-05-08 23:58 -0700
Re: What are the various alternate uses for the PC's LSB ? whygee <yg@yg.yg> - 2011-05-09 09:02 +0200
Re: What are the various alternate uses for the PC's LSB ? Quadibloc <jsavard@ecn.ab.ca> - 2011-05-09 09:43 -0700
Re: What are the various alternate uses for the PC's LSB ? MitchAlsup <MitchAlsup@aol.com> - 2011-05-09 09:38 -0700
Re: What are the various alternate uses for the PC's LSB ? "robertwessel2@yahoo.com" <robertwessel2@yahoo.com> - 2011-05-09 11:14 -0700
Re: What are the various alternate uses for the PC's LSB ? Anne & Lynn Wheeler <lynn@garlic.com> - 2011-05-09 14:51 -0400
Re: What are the various alternate uses for the PC's LSB ? torbenm@diku.dk (Torben Ægidius Mogensen) - 2011-05-09 16:31 +0200
Re: What are the various alternate uses for the PC's LSB ? whygee <yg@yg.yg> - 2011-05-09 18:16 +0200
Re: What are the various alternate uses for the PC's LSB ? mac <acolvin@efunct.com> - 2011-05-09 17:27 +0000
Re: What are the various alternate uses for the PC's LSB ? whygee <yg@yg.yg> - 2011-05-09 19:38 +0200
Re: What are the various alternate uses for the PC's LSB ? rpw3@rpw3.org (Rob Warnock) - 2011-05-09 20:23 -0500
Re: What are the various alternate uses for the PC's LSB ? whygee <yg@yg.yg> - 2011-05-10 03:04 +0200
Re: What are the various alternate uses for the PC's LSB ? "Andy \"Krazy\" Glew" <andy@SPAM.comp-arch.net> - 2011-05-11 14:23 -0700
Re: What are the various alternate uses for the PC's LSB ? whygee <yg@yg.yg> - 2011-05-12 02:45 +0200
Re: What are the various alternate uses for the PC's LSB ? "Andy \"Krazy\" Glew" <andy@SPAM.comp-arch.net> - 2011-05-12 20:41 -0700
Re: What are the various alternate uses for the PC's LSB ? George Neuner <gneuner2@comcast.net> - 2011-05-14 23:24 -0400
Re: What are the various alternate uses for the PC's LSB ? "Andy \"Krazy\" Glew" <andy@SPAM.comp-arch.net> - 2011-05-15 09:18 -0700
Re: What are the various alternate uses for the PC's LSB ? Michael S <already5chosen@yahoo.com> - 2011-05-15 10:00 -0700
Re: What are the various alternate uses for the PC's LSB ? "Andy \"Krazy\" Glew" <andy@SPAM.comp-arch.net> - 2011-05-15 12:06 -0700
Re: What are the various alternate uses for the PC's LSB ? "Andy \"Krazy\" Glew" <andy@SPAM.comp-arch.net> - 2011-05-15 12:12 -0700
Re: What are the various alternate uses for the PC's LSB ? Michael S <already5chosen@yahoo.com> - 2011-05-15 16:16 -0700
Re: What are the various alternate uses for the PC's LSB ? nmm1@cam.ac.uk - 2011-05-15 20:58 +0100
Re: What are the various alternate uses for the PC's LSB ? Michael S <already5chosen@yahoo.com> - 2011-05-15 15:59 -0700
Re: What are the various alternate uses for the PC's LSB ? nmm1@cam.ac.uk - 2011-05-16 08:58 +0100
Re: What are the various alternate uses for the PC's LSB ? "Andy \"Krazy\" Glew" <andy@SPAM.comp-arch.net> - 2011-05-16 07:43 -0700
Re: What are the various alternate uses for the PC's LSB ? Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-05-16 22:46 +0200
Re: What are the various alternate uses for the PC's LSB ? timcaffrey@aol.com (Tim McCaffrey) - 2011-05-19 16:13 +0000
Re: What are the various alternate uses for the PC's LSB ? George Neuner <gneuner2@comcast.net> - 2011-05-15 20:33 -0400
Re: What are the various alternate uses for the PC's LSB ? whygee <yg@yg.yg> - 2011-05-11 05:53 +0200
Re: What are the various alternate uses for the PC's LSB ? whygee <yg@yg.yg> - 2011-05-11 07:10 +0200
Re: What are the various alternate uses for the PC's LSB ? Quadibloc <jsavard@ecn.ab.ca> - 2011-07-04 09:39 -0700
Re: What are the various alternate uses for the PC's LSB ? Quadibloc <jsavard@ecn.ab.ca> - 2011-07-04 10:23 -0700

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