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000433_news@newsmaster….columbia.edu _Mon Sep 29 10:35:25 1997.msg
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From: fdc@watsun.cc.columbia.edu (Frank da Cruz)
Newsgroups: comp.protocols.kermit.misc
Subject: Re: How, exactly, should Kermit encode data?
Date: 29 Sep 1997 14:35:19 GMT
Organization: Columbia University
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In article <60ko7e$pts@nr1.calgary.istar.net>,
Russell Magee <bigruss@cheetah.spots.ab.ca> wrote:
: 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!
:
I don't know what Kermit protocol spec you found on what ftp site, but no
reverse engineering was necessary; the Kermit protocol is specified in the
book "Kermit, A File Transfer Protocol":
http://www.columbia.edu/kermit/manuals.html
- Frank