Subject:
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Re: Message transmission speeds.
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Newsgroups:
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lugnet.robotics
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Date:
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Mon, 1 Jan 2001 09:37:10 GMT
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Original-From:
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Steve Baker <sjbaker1@airmailSAYNOTOSPAM.net>
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Reply-To:
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SJBAKER1@AIRMAIL.avoidspamNET
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Viewed:
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855 times
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Brian wrote:
> > That seems VERY long. I was under the impression that the IR link ran at
> > 4800 baud - which ought to be 480 bytes/sec - which is about 2ms to send a
> > message and another 2ms to get the reply back - plus the time to read the
> > three sensors on the Scout and a little software overhead.
> >
> > It doesn't seem reasonable that this should take more than about 10msec - not
> > 100ms!
> The data rate is 2400bps, and each packet of N bytes of data has 5 + N
> bytes of overhead. So the more realistic time to send a 1 byte message
> is 24ms.
That sounds believable. I send 6 one-byte messages in each comms cycle.
That's gotta be a good 150ms - which is probably about what I'm seeing.
How depressing. :-(
> Here is an excerpt from the Communication section of
> http://www.crynwr.com/lego-robotics
> (i.e. Did you check the web site first?:
> http://www.crynwr.com/lego-robotics)
Ack! Sorry. I read it months ago - but didn't recollect seeing that part.
So, the first major speedup would be to send a 3-byte message containing
the commands to the three scouts all bundled together. Then I could probably
even scrunch it down to 2-bytes. That'll save ~50ms. Only trouble is that then
the scouts don't know when it's safe for them to reply without them all talking
at once - I could probably fix that with some careful timing or something - but
still, it's more than 100ms which is WAY too slow for the things I had in mind.
The annoying part is that the four computers are all within a few inches
and facing each other - and could even be enclosed in a 'black' box to avoid
external interference. However, I'm stuck with this 'bullet-proof'
protocol that's evidently designed to work over long distances with imperfect
transmitter/receiver alignment and such.
I guess I could fix that in the RCX by doing all of this at a lower level
in LegOS/C - but since three out of the four machines are Scout's, that's
not possible either.
<sigh>
Oh well - back to the drawing board. :-(
--
Steve Baker HomeEmail: <sjbaker1@airmail.net>
WorkEmail: <sjbaker@link.com>
HomePage : http://web2.airmail.net/sjbaker1
Projects : http://plib.sourceforge.net
http://tuxaqfh.sourceforge.net
http://tuxkart.sourceforge.net
http://prettypoly.sourceforge.net
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Message is in Reply To:
 | | Re: Message transmission speeds.
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| (...) (snip) (...) The data rate is 2400bps, and each packet of N bytes of data has 5 + N bytes of overhead. So the more realistic time to send a 1 byte message is 24ms. Here is an excerpt from the Communication section of (URL) Did you check the (...) (24 years ago, 31-Dec-00, to lugnet.robotics)
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