linux-kernel - Re: Serial port blues

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Message-ID: <20070121145817.GE31780@1wt.eu>
Date:	Sun, 21 Jan 2007 15:58:17 +0100
From:	Willy Tarreau <w@....eu>
To:	Grzegorz Ja?kiewicz <gryzman@...il.com>
Cc:	Johannes Stezenbach <js@...uxtv.org>, Theodore Tso <tytso@....edu>,
	Joe Barr <joe@...rimer.com>,
	Linux Kernel mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Serial port blues

On Sun, Jan 21, 2007 at 03:50:32PM +0100, Grzegorz Ja?kiewicz wrote:
> funny, how even very fast box can be useless for such activities with modern
> kernels, such as linux. After all, serial ports don't require too much
> horsepower to be highly accurate.
> >From designer perspective, I would rather go for uC solution in his case.
> That is, design and build fairly simple board - based on atmega AVRs. 16mhz
> 8bit chip can do so much better compared to N gigs mhz box running "modern"
> operating system, these days....

It is true, but the point is not "modern" vs "ancient" OS, it's "multitasking"
vs "monotasking" kernel. If your program does the busy loop, you'll get a
very high accuracy at the expense of burning watts polling one bit one
billion times a second waiting for a change every millisecond.

18 years ago, I wrote a soft-only 8250 emulator to connect my second 8088
to the first one's serial port at 19200 bauds. At this time, waiting for
a change only took a few hundred cycles and the busy loop was the default
mode of the OS anyway. Things have changed since.

Willy

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