linux-kernel - RE: Serial custom speed deprecated?

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Message-ID: <Pine.LNX.4.61.0608251148490.18661@chaos.analogic.com>
Date:	Fri, 25 Aug 2006 11:52:34 -0400
From:	"linux-os \(Dick Johnson\)" <linux-os@...logic.com>
To:	"Stuart MacDonald" <stuartm@...necttech.com>
Cc:	"Krzysztof Halasa" <khc@...waw.pl>,
	"Alan Cox" <alan@...rguk.ukuu.org.uk>,
	"David Woodhouse" <dwmw2@...radead.org>,
	<linux-serial@...r.kernel.org>,
	"LKML" <linux-kernel@...r.kernel.org>
Subject: RE: Serial custom speed deprecated?

On Fri, 25 Aug 2006, Stuart MacDonald wrote:

> From: On Behalf Of linux-os (Dick Johnson)
>> But the baud-rates have always been some approximation that starts
>> at 75 and increases by powers-of-two. This is because the hardware
>> always had fixed clocks with dividers that divided by powers-of-two.
>> What is the claim for the requirement of strange baud-rates set
>> as an integer of dimension "baud?" Where does this requirement
>> come from and what devices use these?
>
> Perhaps you'd like to check out our products
> http://www.connecttech.com/
>
> We build a lot of custom boards that have odd clocks to generate very
> odd baud rates for random serial devices. The Bxxx style has been a
> thorn in my side since 1999.
>
> Also, Oxford's 16PCI95x family has three different points of altering
> the clock; the clock prescaler, the actual sample rate (which is the
> classic /16 that most are used to), and the actual divisor. That can
> produce pretty much any baud rate, albeit with some error.
>
> ..Stu
>

Well when you change things, remember that you need not only something
that translates B9600 to your new 9600 (trivial it's a #define, but
ALSO (very important!) B0 needs to hang up the modem! This means
that some value (perhaps 0), as a divisor, needs to perform this
same function.

Cheers,
Dick Johnson
Penguin : Linux version 2.6.16.24 on an i686 machine (5592.62 BogoMips).
New book: http://www.AbominableFirebug.com/
_
..

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