Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!ames!apple!sun-barr!newstop!sun!coherent!dplatt
From: dplatt@coherent.com (Dave Platt)
Newsgroups: comp.sys.mac
Subject: Re: zterm emulation problems
Keywords: vt100
Message-ID: <27951@coherent.com>
Date: 13 Jul 89 17:37:27 GMT
References: <23@bernoulli.stanford.edu>
Reply-To: dplatt@coherent.com (Dave Platt)
Distribution: na
Organization: Coherent Thought Inc., Palo Alto CA
Lines: 73

In article <23@bernoulli.stanford.edu> dudevoir@bernoulli.stanford.edu (Glen P. Dudevoir) writes:
> I have tried out both versions 0.75 and 0.8 of Zterm and have found
> some problems in the vt100 emulation. Neither version will handle
> editing in vi or gnuemacs.  0.75 scrolls the entire screen after 
> a cr in the command line (bottom line of terminal) and then fails
> to redraw the screen so the cursor positioning is not correct.
> In version 0.8 moving the cursor to the left in the editors causes the
> characters that it is passing over to be erased from the screen, but
> not from the file being edited.
>
> Has anyone else had problems of this nature or am I doing something 
> wrong?  I am using the standard vt100 termcap entry on our sun unix
> systems.

I had the same problems with 0.7 and 0.75, and kept my copy of MacKermit
handy for doing GNUmacs editing on our Sun.  These scrolling-problems
were eliminated in 0.8.

The problem with "destructive backspace" in 0.8 is a little glitch that
David Alverson inadvertently introduced when cleaning up the VT100
emulation code.  It was called to his attention very shortly after 0.8
was shipped out.  He didn't want to do an 0.81 release so soon after
0.8, and so he posted (on MacCincy, at least) a procedure for patching
the 0.8 application to eliminate the destructive backspace.

With this patch in place, ZTerm 0.8 works very nicely under GNU Emacs
with the standard VT100 termcap entry.  I now use ZTerm 0.8 as my
standard term'ulator, both for BBS access and for logging into my Sun
server and workstation at work.

I don't have the patch-information available here at work;  I'll post it
tomorrow if I can remember to dig it off of my Mac at home.  If you want
to call MacCincy you can probably find it in the ZTerm message area.

> One other note: I have had some problems transferring files using the
> zmodem protocol at 19200.  I consistently get errors of the type 
> ZRPOS 0 . At 9600 everything goes well.

Hmmm.  My experiments with a USR Courier HST modem seem to indicate that
19200-bps connections between the modem and my Sun 3/60 are not
reliable.  The Sun appears to drop characters on the floor if they
arrive at high speeds from the modem.  I suspect that the Sun's serial
port isn't fast enough to keep up with sustained input bursts at 19200.
This sort of occasional character-loss would raise merry hell with
ZMODEM handshaking.

I have my Mac II talking to an HST modem at 19200.  ZTerm 0.8 seems to
have no problem receiving data from the modem at a burst rate of 19200
bits/sec; the sustained data rate is limited by the Sun->HST link, which
is running at 9600 bps.  The Sun 3/60 has no problem accepting ZMODEM
handshakes or uploads at 9600 bits/sec.

You might try downloads at 19200 with the undocumented "-w 2000" option
of "sz".  This specifies a "receiver window" of 2000 characters.  sz
will send 500-byte packets, will ask for an acknowledgement after each
packet, and will use a sliding window of 3 packets.  This _might_
eliminate data-overrun problems.  It may also slow down the transfer
more than you like.  I find that a straight 9600-bps streaming download
is very reliable indeed, and fast enough for my purposes.

> Disclaimer:  I think this is a very nice product. The inclusion of 
> the zmodem protocol is a big step forward in shareware. I hope 
> these minor problems can be corrected.  If so I'll be convinced 
> to send in my registration.

The former problem can be patched.  I suspect that the latter problem is
not ZTerm's fault.

-- 
Dave Platt    FIDONET:  Dave Platt on 1:204/444        VOICE: (415) 493-8805
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