Path: utzoo!attcan!uunet!wuarchive!decwrl!purdue!bu-cs!dartvax!eleazar.dartmouth.edu!earleh
From: earleh@eleazar.dartmouth.edu (Earle R. Horton)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Need info on multitasking capabilities on the mac
Message-ID: <17247@dartvax.Dartmouth.EDU>
Date: 24 Nov 89 21:41:25 GMT
References: <6391@tank.uchicago.edu> <9072@hoptoad.uucp>
Sender: news@dartvax.Dartmouth.EDU
Reply-To: earleh@eleazar.dartmouth.edu (Earle R. Horton)
Organization: Thayer School of Engineering
Lines: 32

In article <9072@hoptoad.uucp> tim@hoptoad.UUCP (Tim Maroney) writes:
>In article <6391@tank.uchicago.edu> gft_robert@gsbacd.uchicago.edu writes:
>>Sounds like it's your comm program, not the Mac OS.  I've never had any
>>problems of that nature when downloading (using Versaterm).  I can choose
>>menus, play games, etc.  Pretty good multitasking, as far as I'm concerned.
>
>I wonder how they do that.  Can anyone provide any information?

>[Discussion of how MultiFinder context switching breaks attempts to 
>schedule file transfer protocol.]

I don't know, but won't an asynchronous read/write with an
ioCompletion routine installed work?  IO operation gets completed,
then ioCompletion routine gets called, and file transfer can be
restarted at that point.  Make sure you get the correct A5 before
storing your data!

The protocols used by VersaTerm use handshaking on each packet.  You
don't get a new packet, in other words, until you acknowledge the last
one.  With these protocols, you can actually pause a fairly long time
between times when you service the file transfer.  I suspect that
VersaTerm doesn't do anything special to make sure it gets time, but
that you just never see it time out because you never push it that
hard.

ZTerm, on the other hand, uses zmodem, a streaming protocol.  This
means that it MUST service the file transfer periodically, or serial
buffers will overflow, etc.  Apparently, the author hasn't figured out
this problem, because ZTerm will time out on you if you do too much
other processing while it is transfering a file.

Earle R. Horton