Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!cs.utexas.edu!uunet!portal!cup.portal.com!Sullivan
From: Sullivan@cup.portal.com (sullivan - segall)
Newsgroups: comp.sys.amiga.tech
Subject: Re: Official Warnings...
Message-ID: <17869@cup.portal.com>
Date: 3 May 89 02:21:40 GMT
References: <3082@haven.umd.edu> <11394@well.UUCP> <3773@sugar.hackercorp.com> <10819@mcdphx.phx.mcd.mot.com> <8904302141.AA21035@explorer.dgp.toronto.edu>
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Organization: The Portal System (TM)
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>In article <10819@mcdphx.phx.mcd.mot.com> dbk@teroach.UUCP (Dave Kinzer) writes:
>>In article <3773@sugar.hackercorp.com> karl@sugar.hackercorp.com (Karl Lehenbauer) writes:
>>>
>>>Isn't TAS useful on a single CPU system, though, for providing fast,
>>>uninterruptable test and set for use as a semaphore, without having 
>>>to turn off interrupts?
>>
>>   Semaphore to who?  Another task?   That's what the operating system is
>>in there for.  It takes care of all the system dependent stuff.  
>>
>
>Occasionally one may wish to have a lightweight method of accessing
>shared memory without the burden of an OS call. Seems as if Motorola
>would have provided the TAS in the 68000 series for that purpose.
>
Thinkee before speakee.  All single instructions are indivisible on a one
processor system.  If you want to make your own semaphores you can do so
without risk using any instruction which both reads/sets flags, and writes.
The 680x0's don't save enough machine state info to resume an interrupt from
the middle of an instruction.  

 
                           -Sullivan Segall
_____________________________________________________________
 
/V\  Sully set the example: to fly without moving.  We shall
 '   learn to soar on wings of thought. And the student will
     surpass the teacher.
To Quote the immortal Socrates: "I drank what?" -Sullivan
_____________________________________________________________
 
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