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From: Theodore Tso <>
To: "Grzegorz Jaśkiewicz" <>
Cc: Willy Tarreau <>, Johannes Stezenbach <>,
	Joe Barr <>,
	Linux Kernel mailing List <>
Subject: Re: Serial port blues
Date: Sun, 21 Jan 2007 13:52:18 -0500	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Sun, Jan 21, 2007 at 04:10:58PM +0100, Grzegorz Jaśkiewicz wrote:
> you're right, I used wrong term to describe.
> But the problem still exists. Nowadays it should be possible to run many
> serial ports fully accurate "at the same time". It is also true that the
> same problem exists in windows, and bsd worlds. So it is not only Linux
> problem.

It's not so much a "problem", but rather, most people aren't
particularly interested in using the millions and millions of
transisters of a modern CPU to generate a square wave.  So OS's aren't
optimized to do that.  Linux has no problems running many serial
ports; but in their normal designed function, which is to send and
receive characters, using the UART's FIFO's and interrupts to do so.  

The question of manually toggling DTR/CTS RS-232 lines to generate a
tone is something that you *can* do, but you won't be doing anything
else --- and that's simply because fundamentally that's a very silly
thing to do.  Most people will use a tiny amount of dedicated hardware
--- like the sound care that is built into every single modern PC ---
rather than manually waggling the RS-232 lines in order to generate a

> Like I said previously, 30$ board (usb+avr+max232) would do it accurately +
> over 300$ PC to control it :D funny...

You *can* do it, and we've described how to do it.  It won't be
efficient (you won't be doing much else), but that's because a PC and
Linux is optimized for different set of tasks.  Sometimes dedicated
hardware is the far superior option to a general purpose OS and a
general-purpose hardware.  This should not at all be surprising.

						- Ted

  parent reply	other threads:[~2007-01-21 18:58 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-01-19 21:37 Joe Barr
2007-01-20 17:36 ` Willy Tarreau
2007-01-21  5:54   ` Theodore Tso
2007-01-21  7:05     ` Willy Tarreau
2007-01-21 14:04       ` Johannes Stezenbach
     [not found]         ` <>
2007-01-21 14:58           ` Willy Tarreau
     [not found]             ` <>
2007-01-21 18:52               ` Theodore Tso [this message]
     [not found]                 ` <>
2007-01-21 19:30                   ` Theodore Tso
2007-01-21 18:55       ` Theodore Tso
2007-01-21  5:09 ` Stuart MacDonald
2007-01-21  7:07 ` H. Peter Anvin
2007-01-21  7:08 ` H. Peter Anvin
2007-01-21 20:44   ` H. Peter Anvin
2007-01-22 11:37 ` Alan

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