Subject:
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RE: Checksum download of text to RCX
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Newsgroups:
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lugnet.robotics.rcx.pbforth
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Date:
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Sun, 2 Apr 2000 20:38:13 GMT
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Viewed:
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2383 times
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> I wrote a simple addition to pbforth that allows it to receive text with a
> checksum across every line. Every line is ACK/NAK-ed and if necessary
> resent. Timeouts are not implemented.
This is a neat idea, Ernst. I think it would be a good addition to the pbForth
system if we can allow the user to use it for text uploads and then switch
to normal mode for interactive use.
> Now, the main word looks like this:
>
> : PBX-RECEIVE ( -- )
> BEGIN pbx.buf DUP size-of-pad pbx.ACCEPT EVALUATE AGAIN ;
> 1) This is an endless loop. The protocol terminates by throwing a user
> interrupt when it receives an ETX (^C). This is easy to implement and has
> the advantage that the interpreter returns to a known state when the
> transmission is cancelled by the user. OTOH, this is abusing the exception
> mechanism a bit. Any thoughts on the necessity of using a different
> termination mechanism?
I'll have to think about this a bit..
> 2) PBX (=PBforth Xfer) uses its own buffer, pbx.buf. I would like to use the
> TIB instead to conserve memory. This feels allowable because both ACCEPT and
> pbx.ACCEPT use the same communication channel; just a different protocol.
> Any thoughts?
Using the TIB is fine, since only one channel can be active at a time. It would
be best if PBX-RECEIVE could filter lines with/without sums. Maybe a special
leadin char to indicate the line needs a checksum?
> As a marginal note: Using PBX, I uploaded quite large files without a single
> line needing retransmission, whereas ascii-xfer uploads failed miserably
> 10 out of 10 times. The most important difference between the two (apart
> from the checksum) seems to be that when using PBX, the RCX doesn't talk
> back ('ok', 'redefine ...', etc.). Does anybody know for sure whether a more
> silent RCX results in a better transmission?
Again, I'm not sure if shutting the RX up helps much. I'm going to release a
new version in the next two weeks, and I really like the idea of PBX. Maybe
we can integrate it into the kernel if we have the leadin/checksum mode
option...
Thanks for sharing this with us, Ernst.
Cheers,
Ralph Hempel - P.Eng
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Check out pbFORTH for LEGO Mindstorms at:
<http://www.hempeldesigngroup.com/lego/pbFORTH>
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Reply to: rhempel at bmts dot com
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Message has 1 Reply:
 | | Re: Checksum download of text to RCX
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| (...) would (...) Can do... Currently a line is transmitted as <text>NL<checksum>, so a checksummed line can already be distinguished from a non-checksummed, CR-terminated line. Adding a line header (any objections against STX?) is more failsafe, of (...) (25 years ago, 3-Apr-00, to lugnet.robotics.rcx.pbforth)
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Message is in Reply To:
| | Checksum download of text to RCX
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| I wrote a simple addition to pbforth that allows it to receive text with a checksum across every line. Every line is ACK/NAK-ed and if necessary resent. Timeouts are not implemented. Now, the main word looks like this: : PBX-RECEIVE ( -- ) BEGIN (...) (25 years ago, 2-Apr-00, to lugnet.robotics.rcx.pbforth)
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