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From:	Andrew Cottrell <andnews AT ihug DOT com DOT oz DOT au>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: strange problem with dos DPMI
Date:	Fri, 18 Jan 2002 18:18:55 +1100
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Is the probelm that your program appears to  stop and start?

>The program installs protected mode driver for serial port, tries to
>sends some bytes over it, but wve it also writes/reads from disk during
>it, the program frees for several seconds (cca 30 secs) and then runs
>agains.
When saving to disk the BIOS will hog the CPU and as such you may lose
incoming charaters. I have use PMCOM and other DJGPP comms libraries
and I found that saving about 1024 chars at a time seems to be the
optimal length.  This does depend on the incoming rate, CPU and hard
drive access time.

The shorter the buffer to save the more times the more overhead there
will be on saveing charaters as an overall percentage. The larger the
block saved the longer the BIOS will hog the CPU and therefore you may
(will) miss characters.

>The same program runs under win95 without any problems and the same
>variation
>of this program build by borland runs without any problems.
Windows usually caches writes to the hard drive.

>I am looking for some tips as I have tried several test without success.
>I even created a small version of this program, but it works without any
>problems
>also in DOS.
Does it use the same comms library and save algorithm? Are you using
an interrupt driven comms library? Which one are you using?

Andrew

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