Path: utzoo!utgpu!watserv1!watmath!att!att!bu.edu!rpi!crdgw1!ge-dab.ge.com!tarpit!bilver!jwt!john
From: john@jwt.UUCP (John Temples)
Newsgroups: comp.dcom.modems
Subject: Re: UARTS for speed...
Message-ID: <1990Nov25.163916.536@jwt.UUCP>
Date: 25 Nov 90 16:39:16 GMT
References: <5073.274CAD27@zswamp.fidonet.org>
Organization: Private System -- Orlando, FL
Lines: 23

In article <5073.274CAD27@zswamp.fidonet.org> root@zswamp.fidonet.org (Geoffrey Welsh) writes:
>*IF* the software is configured to do it, installing a 16550 
>*can* reduce CPU overhead slightly.
>   However, you won't feel the difference.

Depending on the environment, I would say the reduction is more than
"slight."  At one time, I had both a 16450 and a 16550 on my dumb
Digiboard.  I was switching my 38.4 kbps terminal between the two
ports to see what difference it made.  CPU utilization (as measured
by u386mon) went from over 40% on the 16450 to under 10% on the
16550.  This was measured on a 386/33 running UNIX, with serial
drivers that took advantage of the 16550.  I imagine the difference
would be even more noticeable on a slower machine.

>   Here's a quick DOS Turbo Pascal program I hacked together to enable the 
>FIFOs on a 16550 and set the trigger level to 1 byte

It should probably be mentioned that enabling FIFO mode can make some
software quit working.  I've seen the extra bits that are set in the
IIR when FIFOs are enabled mess up some interrupt handlers that
weren't expecting them.
-- 
John W. Temples -- john@jwt.UUCP (uunet!jwt!john)