Subject:
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Re: Lego Network Protocol questions
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Newsgroups:
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lugnet.robotics
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Date:
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Thu, 6 May 1999 17:30:02 GMT
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Original-From:
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Ben Laurie <ben@!StopSpammers!algroup.co.uk>
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Viewed:
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912 times
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Kekoa Proudfoot wrote:
>
> Ben Laurie <ben@algroup.co.uk> wrote:
> > > I think something like this is possible on the H8. You might be able to
> > > use the rhythm established by the reception of bytes from other RCXs to
> > > keep clocks in sync, although the timings would be somewhat coarse grained
> > > and you'd have to leave space for whatever the margin of error ended up
> > > being.
> >
> > I'm not sure why you think the timing would be coarse? It only has to be
> > fine enough to get you down to the bit level (meaning you waste around
> > 10% of the available bandwidth in avoiding overlap), and most UARTs
> > sample 16 times per bit, so that should be easy...
>
> Even though the UARTs may sample 16 times per bit, and even though the UART
> knows when each bit has arrived, the RCX does not let you get at this
> information. So as far as I know you are stuck reading a timer only after
> having received each individual byte, not bit. Also, since you have to do
> the measurement in an ISR, the timings are not entirely reliable.
Sure, but you should be able to get the edge of the stop bit(s) to
within 1/16th bit+interrupt latency (which I'd guess is tiny in
comparison to the bit timing) which gives you the position of any other
bit just as accurately (give or take clock drift - but that should be
tiny). So, allowing a whole bit for slop is generous, IMO. This should
make a slotted protocol quite achievable and efficient. Some fun in
getting started, but after that, no problem.
Cheers,
Ben.
--
http://www.apache-ssl.org/ben.html
"My grandfather once told me that there are two kinds of people: those
who work and those who take the credit. He told me to try to be in the
first group; there was less competition there."
- Indira Gandhi
--
Did you check the web site first?: http://www.crynwr.com/lego-robotics
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Message has 1 Reply:
 | | Re: Lego Network Protocol questions
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| (...) I was under the impression you wanted to sync a clock to the rhythm of bit arrivals. You cannot do this. You can definitely sync a clock to the rhythm of byte arrivals. I was trying to point out this distinction to you. You must have been (...) (25 years ago, 6-May-99, to lugnet.robotics)
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Message is in Reply To:
| | Re: Lego Network Protocol questions
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| (...) This is a possibility I hadn't considered, and it sounds reasonable to expect to see that effect at some point. I never tested how a second source affects echo reception, but it seems easy enough to test. If I get around to testing this I'll (...) (25 years ago, 6-May-99, to lugnet.robotics)
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