Mail Archives: djgpp/2000/09/23/04:45:28

From: danspam2000 AT my-deja DOT com
Newsgroups: comp.os.msdos.djgpp
Subject: fast access to parallel port
Date: Sat, 23 Sep 2000 08:08:39 GMT
Organization: - Before you buy.
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To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp
Reply-To: djgpp AT delorie DOT com

I am working on a project that requires accessing
the parallel port as a means to generating a data
stream according to a pre defined standard. That
standard dictates that the length of any one bit
of data within the packet should be four micro
seconds long. This means that i have to write to
the parallel port and hold it high or low for
four microseconds at a time. This is not a
problem, as one cycle of the bus, running at 1.3
MHz gives me plenty of time. Also, the uclock
function in DJGPP is accurate to less than 1
microsecond, so i should be able to use that for
the timings. The problem is, that by the time
i've called uclock, written to the port and
called uclock again, even using register
variables takes about eighteen uclock ticks,
which is about three times longer than i can
allow. Does anyone know of a way around this?
Perhaps coding in assembler would speed the whole
process up enough to work? Any help or pointers
in the right direction would be appreciated.

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