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

From	whygee <yg@yg.yg>
Newsgroups	comp.arch
Subject	Re: What are the various alternate uses for the PC's LSB ?
Date	2011-05-12 02:45 +0200
Organization	Aioe.org NNTP Server
Message-ID	<iqfdc2$73n$1@speranza.aioe.org> (permalink)
References	<iq96pc$n6e$1@speranza.aioe.org> <597275762326654751.812921acolvin-efunct.com@news.eternal-september.org> <iq9bii$58v$1@speranza.aioe.org> <rZqdnVxkBug9DlXQnZ2dnUVZ_smdnZ2d@speakeasy.net> <4DCAFE51.5000806@SPAM.comp-arch.net>

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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 :-/

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 ?

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
-- 
http://ygdes.com / http://yasep.org

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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