Subject:
|
Re: CM-RCX comm
|
Newsgroups:
|
lugnet.robotics
|
Date:
|
Wed, 31 Jan 2001 12:59:54 GMT
|
Original-From:
|
Steve Baker <sjbaker1@!StopSpammers!airmail.net>
|
Reply-To:
|
sjbaker1@airmail[avoidspam].net
|
Viewed:
|
1151 times
|
| |
|
|
"Marco C." wrote:
>
> At 22:30 30-01-2001 -0600, Steve Baker wrote:
> > "Marco C." wrote:
> > >
> > > 2) My first tests with the two pBricks (CyberMaster and RCX) prove that
> > > it's possible to communicate using a (ten times) slower version of VLL
> > > protocol (I call it SlowVLL for short). *It works*, and it transmits data
> > > very accuratly (I'd thought it would suffer some variations in timmings but
> > > no, the Wait() value on the OUTPUT pBrick is exactly the measured Timer()
> > > value on the INPUT pBrick.
> >
> > Wooaahhh! That can't be true. Both machines are running some kind of
> > (hopefully) crystal oscillator to generate the clock that drives the
> > Timer() and Wait() commands. No two cystal oscillators generate the
> > *exact* same timing - so your two clock could easily differ by one
> > part per million or so. Hence, once in a while, you'll find that
> > you either miss a bit or drop a bit. That may be quite rarely or
> > quite frequently depending on the quality of the oscillators that
> > Lego used for the RCX.
>
> That's exactly what my common sense made me believe.
> But various tests I did, using a dump of a Datalog with the timmings
> measured by the RCX, proved me wrong.
>
> Every Wait(10) was correctly measured as a Timer(3)==1, and every Wait(50)
> as a Timer(3)==5 and so on...
Well, yes - but then crystal oscillators are quite accurate (but crucially,
not 100% accurate). You might have to run as long as one or two MILLION
attempts before you see an error - but you *will* see an error if you do
it for long enough.
If your code does one test per second (say) and the clocks differ by one
part per million (which I believe to be a reasonable figure) - then it
might take as long as 11 days for you to see a problem....or it might happen
on the very first try.
--
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
http://freeglut.sourceforge.net
|
|
Message is in Reply To:
 | | Re: CM-RCX comm
|
| (...) That's exactly what my common sense made me believe. But various tests I did, using a dump of a Datalog with the timmings measured by the RCX, proved me wrong. Every Wait(10) was correctly measured as a Timer(3)==1, and every Wait(50) as a (...) (24 years ago, 31-Jan-01, to lugnet.robotics)
|
20 Messages in This Thread:
 
 
- Entire Thread on One Page:
- Nested:
All | Brief | Compact | Dots
Linear:
All | Brief | Compact
|
|
|
|
