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From: ForthNet@willett.pgh.pa.us (ForthNet articles from GEnie)
Newsgroups: comp.lang.forth
Subject: Memory Management/PIC
Message-ID: <2843.UUL1.3#5129@willett.pgh.pa.us>
Date: 2 Jun 91 14:09:39 GMT
Organization: (n.) to be organized.  But that's not important right now.
Lines: 38

Category 10,  Topic 36
Message 25        Sat Jun 01, 1991
R.BERKEY [Robert]            at 21:18 PDT
 
 
 Re: Address Alignment

S. Wheeler writes, 91-05-19,

 sw> Actually, though, ALIGN shouldn't have much effect on run-time
 sw> performance, since my understanding of it is that one would
 sw> normally use it at compile time.

In BASIS, ALIGNED must be used as a runtime operator, to match the compiled
ALIGNments.

 sw> In any case, 8086 processors take a performance hit (4
 sw> cycles/access) when making word accesses to odd addresses...
 sw> That may not make much difference, but I can just see a tight
 sw> timing loop changing because someone changed a name from WAIT to
 sw> DELAY :-).

Ho! is that a good point.  It's one the engineers here missed when they ported
the application from the 8085 to the 80186.  I've got an 80286 timing loop
whose time variation between an odd and an even alignment is 20%!  Here's a
note in my files for an F-PC running on an 80286 system:

 \ Alignment of code words, execution routines, and vocabulary tables
 \ costs about $C0 bytes, and on an 80286 increases compilation speed
 \ by 2%.

Robert

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