Subject:
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Re: Interactive communication with the RCX
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Newsgroups:
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lugnet.robotics.rcx
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Date:
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Wed, 24 Apr 2002 21:10:19 GMT
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Viewed:
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2983 times
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I don't think collision detection will be possible since the hardware/firmware
does a checksum (at least in lego firmware), and no message is provided to the
VM software (LASM), this prevents ACK/NAK protocols working. The Message()
function does not provide error indications to sending software, so local
error detection/retransmission is not possible either :(
I think a synchronous system would work best, with the PC providing a timing
message and the RCX only sending data after receiving a valid timing message.
Normally the PC would wait for an RCX message before sending the next timing
message out (collision avoidance), however it should also provide a re-sync
mechanism incase a message is lost somewhere, probably a simple timeout thing.
I've got a Scout (LASM/NQC only!) with a serial IR tower, so I might give
this a go myself...
Phil.
Giuseppe Menga wrote:
>
> I have recently discussed with Kekoa an interesting issue that apparently
> received scarce attention in the past.
>
> I'm trying to have interactive communication between the
> computer and the RCX through IR connected to an USB port:
> sendind commands from the computer to the RCX,
> while waiting for asynchronous event messages sent back from the RCX.
> I'm using the LEGO firmware with the LASM assembly, but the problem
> appears with any other substitute.
> Each one of the two functions separate operates properly: I can reach a rate of
> 1/50ms for messages from the RCX and 1/100ms for commands from the computer
> (send and receive the answer), however, when the two operations are
> intermixed sometime the messages are corrupted.
> Kekoa points out that the problem doesn't depend on the software but it is
> intrinsic with the IR communication media that in practice isn't full duplex.
> What is needed is to implement a kind of collision detection protocol
> if one want to use an asynchronous communication mode, or polling event from
> the computer (very bad solution), or continuous synchonization messages sent
> from te computer to marshall the communication.
>
> Someone can give me a suggestion? And particularly help me in implementing
> a kind of protocol at the very button level of the brick?
>
> Giuseppe Menga
> menga@polito.it
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Message is in Reply To:
 | | Interactive communication with the RCX
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| I have recently discussed with Kekoa an interesting issue that apparently received scarce attention in the past. I'm trying to have interactive communication between the computer and the RCX through IR connected to an USB port: sendind commands from (...) (22 years ago, 24-Apr-02, to lugnet.robotics.rcx)
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