NetNews Usenet Archive 1992 #16/NN_1992_16.iso/spool/comp/lang/c/11455

Internet Message Format | 1992-07-22 | 1.9 KB

Path: sparky!uunet!zaphod.mps.ohio-state.edu!cs.utexas.edu!torn!utzoo!dciem!jyan
From: [e-mail] (Joseph Yan)
Newsgroups: comp.lang.c
Subject: timing problem
Keywords: C++ Video Seminar Satellite
Message-ID: <[e-mail]>
Date: 22 Jul 92 18:04:10 GMT
References: <[e-mail]>
Organization: Defence and Civil Institute of Environmental Medicine
Lines: 29

Hi folks!  I'd like to solicit any help I can about this timing problem:

I'm working on some data acquisition from a "black box" that outputs
reports of a device's position and orientation.  Unfortunately, this
box will output a report at a frequency between 20 reports/sec to 50
reports/sec and the time interval between reports varies depending on
the time taken to process info within the "black box" and whether or not
there are any invalid reports in between.  My problem is that I want to
be able to analyze this data for velocities and accelerations so if the
time interval between reports varies, I'd like to store the time of the
report along with the report itself.  The time should be accurate to at
least 10 ms but the clock() function in C and the other time functions
I've looked at are only accurate to 55 ms (because it's updated 18.2
ticks/sec).  I tried some assembler code using function call 2Ch which
is supposed to report the time to hundredths of a second but I found
that it also was only updated at 18.2 ticks/sec.  In one technical
reference I flipped through, I read that the MC146818A Real Time Clock
generates a timer tick 1024 times/sec and this would be great but I
haven't figured out how to access it.

I'm using a 386 and accessing the "black box" through the RS-232 port
but that's probably not important.

Is there any kind soul out there, who can help this poor soul by telling
me how, or if it's even possible, to access a timer which is accurate to
10 ms?  Please reply directly to [e-mail] if you have
the answer.

Joe