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000426_news@newsmaster….columbia.edu _Sun Sep 28 01:00:08 1997.msg
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From: Russell Magee <bigruss@cheetah.spots.ab.ca>
Newsgroups: comp.protocols.kermit.misc
Subject: How, exactly, should Kermit encode data?
Date: 28 Sep 1997 04:59:26 GMT
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Xref: news.columbia.edu comp.protocols.kermit.misc:7749
Hi all, my apologies for a (probably) stupid question.
At work we needed a quick and dirty solution for downloading boot images
into an embedded controller's Flash chips. Not wanting to re-invent the
wheel, I decided the best thing to do would be to use an existing protocol
for sending the boot image; so I found the Kermit protocol spec on an ftp
site and began coding a Kermit receive bootstrap.
I've got the transfer working properly now (I think), but it took a few
modifications to what I understood the Kermit encoding algorithm to be.
Here's the encoding scheme I have so far (for 8-bit transfers):
-All ASCII codes under 32 are prefixed with '#' (the control-quote escape),
and have bit 6 inverted (modulo 64);
-The '#' character is prefixed by itself ('#' => '##');
-ASCII DEL ($7f) is prefixed by '#' and has bit 6 inverted (modulo 64);
The same rules seem to be applied to all values over 127, as if they were
7-bit characters (e.g., '#'+128 (code $a3) is prefixed with '#' , resulting
in the code $23a3; $FF, which is DEL+128, is prefixed with $23 resulting in
$23BF).
The Kermit docs I have are quite detailed as to how to encode 8-bit data over
a 7-bit line, but they didn't mention these peculiarities about 8-bit encoding.
I determined these rules by examining the packets sent by the PD term program
'Telix' on the IBM PC. If anyone could clarify/correct these rules I would
appreciate it!
Thanks,
Russ Magee,
Systems Programmer, Steady State Automation Ltd.