Subject:
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revised msleep() function for standard IC library
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Thu, 12 Oct 2000 17:56:28 GMT
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Viewed:
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983 times
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Based upon a student suggestion in our Autonomous Robotiics course
Subject: revised msleep() function for standard IC library
here at CWRU, I have written a new, multitasking-friendlier version of the
msleep() function. The old version was a CPU-intensive busy loop. The new
version does an immediate defer() if the sleep timer has not yet expired.
void msleep(long msec)
{
/* replaced 12 October 2000 by RFD, new in v.2.67 */
long end_time;
end_time = mseconds() + msec;
while (mseconds() < end_time)
defer(); /* this is the key change; */
/* no foreground busy-wait */
}
Benchmark tests in a 6-process system (1 main(), 4 operating motors with
0.5 second sleeps between each command, 1 incrementing a long counter)
showed 300% more throughput for the counter process, with 30% of the
over-sleep error time, compared to the old version. That is, over a fixed
operating time interval, non-sleeping processes were able to do 3x more
work, and the error in the times spent sleeping (always an overage, as the
sleep is a *minimum* time) was only 1/3 as great. For sensor-intensive
multitasking programs, this is a significant improvement. For single-tasking
programs, there does not appear to be significant additional overhead.
For Handy Board systems, replace the code in lib_hb.c (or equivalent).
For 6.270 systems, replace the code in lib_r22.c (or equivalent).
Comments and bug reports are welcome.
*Rich*
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