Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!bbn!gatech!hubcap!rchampe
From: rchampe@hubcap.clemson.edu (Richard Champeaux)
Newsgroups: comp.sys.amiga.tech
Subject: Re: Official Warnings...
Message-ID: <5352@hubcap.clemson.edu>
Date: 1 May 89 17:11:07 GMT
References: <3082@haven.umd.edu> <11394@well.UUCP> <3773@sugar.hackercorp.com>
Organization: Clemson University, Clemson, SC
Lines: 26

In article <3773@sugar.hackercorp.com>, karl@sugar.hackercorp.com (Karl Lehenbauer) writes:
> In article <11394@well.UUCP>, ewhac@well.UUCP (Leo 'Bols Ewhac' Schwab) writes:
> > 	TAS uses an indivisible memory cycle to do its work.  It's supposed
> > to be used in multi-processor systems, where many CPU's share the same
> > memory.  
> 
> 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?
> 
> -- 
> -- uunet!sugar!karl  | "Nobody hipped me to that, dude." -- Pee Wee
> -- Usenet BBS (713) 438-5018

    As I and other people mentioned before, BSET will perform the same
function as TAS and will work on the Amiga.  TAS won't let anything else
take the bus durring the instruction, therefore it works great for 
semaphores on multiprocessor computers, but it won't work on the Amiga.
BSET, how ever, also tests the bit before setting it, allows another
device to grab the bus durring the instruction, and lets you set any bit
as well.  You don't have to turn off interrupts before using it, because
the 68000 doesn't service interrupts until the current instruction is
completed.

Rich Champeaux
Clemson University