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From: KRW1@Lehigh
Newsgroups: comp.lang.pascal
Subject: RE: I/O Port weirdness
Message-ID: <02109023:21:38KRW1@lehigh.bitnet>
Date: 3 Oct 90 04:21:38 GMT
Lines: 12
To: lusysnz@VAX1.CC.LEHIGH.EDU
X-Envelope-to: lusysnz

Use the following inline function instead of the Pascal port array
for reading:

    function inport(x: integer): byte;
      inline($5a/$eb/$00/$ec);

Then instead of p := port[x], use p := inport(x).

The problem is that on fast processors, the input may not be returned
before the result is used.  The inline function includes a short jump
which flushes the prefetch queue on 286's and higher, slowing down
the processor for the next (in) instruction.  -- Kevin