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Dave Baum <dbaum@spambgoneenteract.com> wrote:
> In article <FB0GKF.3s@lugnet.com>, "Mike Moran" <mm@ee.ed.ac.uk> wrote:
> > - In general, I was wondering what the low-level protocol details were,
> > apart from the frame/segment details that I have seen?
>
> Transmit whenever you feel like it and hope you didn't obliterate data
> coming from the other direction. Rudimentary, but still quite effective
> given the typical use pattern with is host driven command/response. With
> RCX to RCX communication you're just taking chances on missing stuff
> unless you implement a specific master/slave relationship on top of the
> basic messages.
Dave, did you catch the crosspost from lugnet.robotics.rcx.legos? I think
there were details discussed there that may or may not have amounted to a
fairly specific proposal for a protocol for LegOS. Anybody care to
summarize whatever was decided? I'd be interested in hearing also, I
skipped a lot of the discussion. Specifically, I would like to find out
what was decided about the underlying packet format, down to the 55ff00s of
the protocol.
Regarding Mike's questions and ideas, I thought I'd share some thoughts
I've had about serial protocols for the RCX.
- Since the RCX receives its own echo, you can detect collisions by
checking to see if the echo matches the transmission; the caveat is that
echos aren't reliable if the IR link has been inactive for a few seconds.
- You can avoid collisions to some extent by holding off transmission if
you are currently receiving data. You might be able to use larger
segment sizes than you would otherwise expect if you make use of this.
The right segment size can only be determined by experiment, I think.
A #define is in order.
- I would argue against using a "slotted" protocol unless you expect all
RCXs to be in IR proximity of one another and you expect them all to be
talking a lot of the time. I don't know how often this would be the
case.
Mike, regarding synchronization for a slotted protocol, what did you mean
by embedding that in "the wire-line signal"? Do you mean a physical wire,
or the IR protocol?
-Kekoa
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