Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!wuarchive!waikato.ac.nz!canterbury!phys169
Newsgroups: comp.protocols.tcp-ip.ibmpc
Subject: Re: SLIP failing at high baud rates?
Message-ID: <1991Apr29.100822.518@csc.canterbury.ac.nz>
From: phys169@csc.canterbury.ac.nz
Date: 29 Apr 91 10:08:22 +1200
References: <9104191316.AA14684@ftp.com> <1991Apr22.151501.18590@tc.fluke.COM>
Organization: University of Canterbury, Christchurch, New Zealand
Lines: 25

In article <1991Apr22.151501.18590@tc.fluke.COM>, dag@tc.fluke.COM (David Gunderson) writes:
> 
> All this points out that the PC's implemenation of RS-232 isn't too 
> robust and shouldn't be trusted in critical situations.
> 
Well, it is at least better than many mini computers where even things like the
system clock spoil fast real time responses. The answer is either to install an
interface that has a bigger buffer (perhaps with its own CPU - there are a few 
around) or to write the software to take bursts of data, responding to the
first header byte perhaps via an interrupt but then disabling interrupts and
polling. You can get 115Kbaud quite easily then. Unfortunately, this latter
method is the exact same problem (turning off interrupts for a relatively long
period of time) that in other software was causing our problem in the first
place! Moral of story: if you want a fast response, you want a dedicated
processor. The advantage/disadvantage with the PC is that is is relatively easy
to make the main CPU dedicated to what ever job you are interested in, at the
expense of others. People should be asking for better bufferring in the IO
cards instead, but have developed the cheap-n-nasty habit of grabbing the main
processor for the job, a trick that is fine if you're the only one that wants
it. Even then, when it comes to some networking jobs, e.g. X-windows, you can't
really beat a dedicated processor for value for money. Getting the main CPU to
respond to trivial jobs quickly is like training an elephant to tap-dance!

Just my thoughts,
Mark Aitchison, Dept. of Physics, University of Canterbury, New Zealand.