Path: utzoo!attcan!uunet!cbmvax!ditto
From: ditto@cbmvax.UUCP (Michael "Ford" Ditto)
Newsgroups: comp.sys.amiga
Subject: Re: Atalk III 1.0e
Summary: Xmodem is almost non-bogus
Keywords: CP/M Xmodem
Message-ID: <5742@cbmvax.UUCP>
Date: 20 Jan 89 03:12:20 GMT
References: <5707@cbmvax.UUCP> <6842@killer.DALLAS.TX.US>
Reply-To: ditto@cbmvax.UUCP (Michael "Ford" Ditto)
Organization: Commodore Technology, West Chester, PA
Lines: 36

In article <6842@killer.DALLAS.TX.US> elg@killer.DALLAS.TX.US (Eric Green) writes:
>History: Ward Christenson needed to transfer binary files from one
>CP/M system to another. CP/M binary files are all a multiple of 128
>bytes long. So all files he transferred were a multiple of 128 bytes
>long -- with no padding, and with no padding block.

This is not quite true.  Ward Christensen's spec says that when
transferring files which are not a multiple of 128 bytes (such as
text files, terminated by ^Z on CP/M) the last sector should be
padded with control-Z's, and the receiving system should remove any
control-Z's from the end of the last sector if it supports arbitrary
sized files.  This system will correctly transfer any file as long
as the last data byte is not a control-Z.  That is the fundamental
flaw in Xmodem protocol: that it can not properly transfer a file
which ends in ^Z.

>If I called your system (which creates the extra padding blocks) with
>my CP/M system (a Commodore 128 running MEX), and uploaded a binary
>file, then downloaded it back to myself, what I got back would be
>incorrect.

It shouldn't be incorrect if both sides use the spec'd "chopping"
method.

>CP/M is the ultimate test of whether an Xmodem protocol is "right" or
>not. If it don't work under CP/M, it ain't Real Xmodem.

Fine, but that doesn't mean that all files must become padded to
a 128-byte boundary in the transfer.
-- 
					-=] Ford [=-

"The number of Unix installations	(In Real Life:  Mike Ditto)
has grown to 10, with more expected."	ford@kenobi.cts.com
- The Unix Programmer's Manual,		...!sdcsvax!crash!elgar!ford
  2nd Edition, June, 1972.		ditto@cbmvax.commodore.com