A new serial baud rate

Discussion:

henrique

2002-07-25 18:22:49 UTC

Hello !!!

I want to use the 14400 baud rate on a serial port (I have a lot of modems
configured to this baud rate) but the define B14400 doesn't exist. What
should I do. Is it a matter of simply insert the new define into termbits.h ?

thanks in advance
---
Henrique Gobbi

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Mike Dresser

2002-07-25 18:46:00 UTC

Permalink

Set your rate to 57600 then. Except for 2400's that didn't do
compression, generally, you set the rate to the highest the modem will
support. In this case, either 57600 or 115200, more likely the former.
If that doesn't work, then use 38400.

Post by henrique
Hello !!!
I want to use the 14400 baud rate on a serial port (I have a lot of modems
configured to this baud rate) but the define B14400 doesn't exist. What
should I do. Is it a matter of simply insert the new define into termbits.h ?
thanks in advance
---
Henrique Gobbi
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henrique

2002-07-25 19:14:08 UTC

Permalink

Hello Gary !!!

Thanks for your answer. Please see comments no the text.

14400 relates to the baud rate between the modems, not between the PC
and the modem (the serial port rate). The "B" defines control the serial
port rate.
If you want to use 14400, set a higher port rate (ie., 19200 or higher)
and enable flow control.
Obviously, you'll have to set the modem properly as well.

That's the problem. I can't change the modem configuration cause this modem
are provided by the Telco. I have to use this baud rate. And I wanna use it
with Linux.

I just wanna know what is the procedure to insert this new baud rate in the
linux kernel

regards
Henrique

-- Gary
-----Original Message-----
Sent: Thursday, July 25, 2002 12:23 PM
Subject: A new serial baud rate
Hello !!!
I want to use the 14400 baud rate on a serial port (I have a lot of
modems
configured to this baud rate) but the define B14400 doesn't exist. What
should I do. Is it a matter of simply insert the new define into
termbits.h ?
thanks in advance
---
Henrique Gobbi
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Neil Everton

2002-07-25 19:40:22 UTC

Permalink

Hi,
I may be wrong here, but 14400 isn't a 'serial' baud rate it's a 'modem'
baud rate.

I'm not aware that serial ports can port at 14400, they usually run at 9600
or 19200.

Most modems (unless they are fixed baud) you can talk at speeds other than
the connect speed.

Also I believe that 14400 is only 9600 with compression !!!

Regards
Neil

-----Original Message-----
From: linux-serial-***@vger.kernel.org
[mailto:linux-serial-***@vger.kernel.org]On Behalf Of henrique
Sent: 25 July 2002 20:14
To: Gary Frerking
Cc: linux-***@vger.kernel.org
Subject: Re: A new serial baud rate

Hello Gary !!!

Thanks for your answer. Please see comments no the text.

-- Gary
-----Original Message-----
Sent: Thursday, July 25, 2002 12:23 PM
Subject: A new serial baud rate
Hello !!!
I want to use the 14400 baud rate on a serial port (I have a lot of
modems
configured to this baud rate) but the define B14400 doesn't exist. What
should I do. Is it a matter of simply insert the new define into
termbits.h ?
thanks in advance
---
Henrique Gobbi
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Matti Aarnio

2002-07-25 19:45:07 UTC

Permalink

Post by henrique
Hello Gary !!!
Thanks for your answer. Please see comments no the text.

...

Post by henrique
That's the problem. I can't change the modem configuration cause this modem
are provided by the Telco. I have to use this baud rate. And I wanna use it
with Linux.

If the interface is asynchronous, the device will adapt to well-known
asynchronous baud-rates. If the interface is SYNCHRONOUS, your hardware
will be quite special, and it will receive the serial clock from the
modem -> DTE (computer) does not define the speed at all.

You are not giving details with the modem, and what you have tried
previously -- e.g. using it with 19200 baud speed, and observing it
to react on async serial port.

Post by henrique
I just wanna know what is the procedure to insert this new baud rate in
the linux kernel

A discussion at this forum, and getting maintainers (Ted Ts'o)
attention.

Post by henrique
regards
Henrique

/Matti Aarnio
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Matti Aarnio

2002-07-25 19:35:38 UTC

Permalink

There seem to exist two different approaches to the speed
parameter. The classical is to have Bnnnnn constant in
the <termios.h> POSIX tc{get|set}attr().

Another is to supply the speed, or at least the divisor explicitely.
This is done via TIO[GS]SERIAL ioctl. See setserial(8) for more
pointers.

Entirely separate issue is that modem speed of 14400 bauds is
roughly 18000 bauds of async speed, without considering any of
possible modem link compression effects. Modems do adapt to
your computer serial port speed, and to get full modem speed
bandwidth into use, your modem-computer link speed needs to
more capacitous, than what the modem can feed into it.

Post by henrique
thanks in advance
---
Henrique Gobbi

Ed Vance

2002-07-25 21:35:50 UTC

Permalink

Post by henrique
I just wanna know what is the procedure to insert this new baud rate
in the linux kernel.

Hi Henrique,

If you have a 2.4.x kernel, and your serial ports have "simple" UARTs like a
16550A, then use the setserial command to directly set the UART's divisor.
See the man page on setserial, which also has words about how to put the
setserial commands into a script that runs automatically when you boot the
system.

You will have to know the "baud base" rate of your UARTs. This is the baud
rate that you get if you set the divisor to 1 (probably 115200 bps).

The new divisor is baud_base / 14400 (which is probably 8).

Good luck with it!
Ed

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Macrolink, Inc. 1500 N. Kellogg Dr Anaheim, CA 92807
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henrique

2002-07-26 13:14:45 UTC

Permalink

Hello !!!

After the last e-mails about this issue I've checked the equipment. I am not
actually dealing with a modem, I'm dealing with a mux/demux which is
connected to a modem. The demux has 20 ports and 5 of these ports have the
mentioned speed. I have a multi-serial board that uses the UART 16550A.

I plan to make this implementation, firstly using a ioctl as suggested by
Matti Aarnio, and afterwards changing the termios.h, task that I believe to
be harder than the first one.

Ed, unfortunately my equipment uses the 2.2.14 kernel. Does your suggestion
work in such kernel ? It would be the easiest way to solve this.

regards
Henrique

Post by Ed Vance
Henrique,

Post by henrique
That's the problem. I can't change the modem configuration cause this

modem are provided by the Telco. I have to use this baud rate. And I
wanna use it with Linux. <<
I've never run across a modem that requires a 14400 baud rate on the
serial line. I *have* run across many, many people *thinking* they need
14400 on the serial line because it's a 14400 modem (is this for faxing?
14400 often comes up in relation to faxing).
We obviously have no way of knowing more about what you're dealing with
than what you're able/willing to tell us -- but based on past
experience, I'm skeptical about the fact that you need 14400 on the
serial line.
Can you provide more details about the modem itself? Do you have a model
number? What are you using it for?
-- Gary

--
---
Henrique Gobbi
Software Engineer
+55 11 50333339
Cyclades Corporation - The Leader in Linux Connectivity
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Ed Vance

2002-07-26 16:00:05 UTC

Permalink

Post by henrique

Post by Ed Vance

Post by henrique
I just wanna know what is the procedure to insert this new baud
rate (14400) in the linux kernel.

If you have a 2.4.x kernel, and your serial ports have "simple"
UARTs like a 16550A, then use the setserial command to directly
set the UART's divisor. See the man page on setserial, which also
has words about how to put the setserial commands into a script
that runs automatically when you boot the system.
You will have to know the "baud base" rate of your UARTs. This is
the baud rate that you get if you set the divisor to 1 (probably
115200 bps).
The new divisor is baud_base / 14400 (which is probably 8).

Ed, unfortunately my equipment uses the 2.2.14 kernel.
Does your suggestion work in such kernel ? It would be
the easiest way to solve this.

Hi Henrique,

I know of no specific reason why it would not work under 2.2. I just
have no direct experience with the 2.2 kernel and the corresponding
version of the serial driver. If the setserial functionality that I
described is in your setserial man page from 2.2, then I think the
method should work well.

Best regards,
Ed

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Macrolink, Inc. 1500 N. Kellogg Dr Anaheim, CA 92807
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henrique

2002-07-31 12:37:39 UTC

Permalink

Hello !!!

FYI, I have done the changes on the kernel to include 14400 bps support. The
modifications are:

- include/asm-ppc/termbits.h
- create the define B14400 after B9600 and shift all defines after this.
- drivers/char/tty_io.c
- add 14400 to baud_table

As you can see, I've done it for a PowerPC. I don't know if it is also quite
simple for another arch's.

thanks for your feedback
regards
Henrique

Post by Ed Vance

Post by henrique

Post by Ed Vance

Post by henrique
I just wanna know what is the procedure to insert this new baud
rate (14400) in the linux kernel.

Ed, unfortunately my equipment uses the 2.2.14 kernel.
Does your suggestion work in such kernel ? It would be
the easiest way to solve this.

Hi Henrique,
I know of no specific reason why it would not work under 2.2. I just
have no direct experience with the 2.2 kernel and the corresponding
version of the serial driver. If the setserial functionality that I
described is in your setserial man page from 2.2, then I think the
method should work well.
Best regards,
Ed
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Macrolink, Inc. 1500 N. Kellogg Dr Anaheim, CA 92807
----------------------------------------------------------------

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