Set a perticular Baud rate

What UART, what crystal frequency, what baud rate generator (if separate) ?

When using non-standard bit rates, the first thing is to check if it is at all possible to load suitable divisor values into the baud rate generators to achieve the desired bit rate.

After that you may have to modify the device driver to load those divisor values.

Paul

Most UARTs have one or more registers used to set the baud rate divisor. You need to write the divisor value(s) corresponsing to 33.6K baud to the appropriate register(s).

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Correct, but since this is comp.os.LINUX.embedded, try

man termios [cfsetispeed(), cfsetospeed(), etc.]

Roberto Waltman

[ Please reply to the group, return address is invalid ]

That API does not support the desired baud rate.

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On Thu, 01 Mar 2007 17:42:32 -0000 Grant Edwards wrote: | On 2007-03-01, Roberto Waltman wrote: |> Grant Edwards wrote: |>>> I want to know how to read through serial port with a particular baud |>>> rate of 33.6 Kbaud. |>>

|>>Most UARTs have one or more registers used to set the baud rate |>>divisor. You need to write the divisor value(s) corresponsing |>>to 33.6K baud to the appropriate register(s). |>

|> Correct, but since this is comp.os.LINUX.embedded, try |>

|> man termios [cfsetispeed(), cfsetospeed(), etc.] | | That API does not support the desired baud rate.

Maybe it would be sufficient for the OP to add his own new ioctl() to set the divisor. But if there is no way to inquire the clock frequency, then it makes the caller more device dependent (less of an issue in embeeded than in hosted).

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After thinking about it some more, the API used by setserial to talk to tty devices supports setting an arbitrary baud rate divisior. I don't know if the low-level driver for the OP's device supports that API or not.

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On Thu, 01 Mar 2007 18:11:04 -0000 Grant Edwards wrote: | On 2007-03-01, snipped-for-privacy@ipal.net wrote: | |>|>>> I want to know how to read through serial port with a particular baud |>|>>> rate of 33.6 Kbaud. |>|>>

|>|>>Most UARTs have one or more registers used to set the baud rate |>|>>divisor. You need to write the divisor value(s) corresponsing |>|>>to 33.6K baud to the appropriate register(s). |>|>

|>|> Correct, but since this is comp.os.LINUX.embedded, try |>|>

|>|> man termios [cfsetispeed(), cfsetospeed(), etc.] |>| |>| That API does not support the desired baud rate. |>

|> Maybe it would be sufficient for the OP to add his own new ioctl() to set |> the divisor. But if there is no way to inquire the clock frequency, then |> it makes the caller more device dependent (less of an issue in embeeded |> than in hosted). | | After thinking about it some more, the API used by setserial to | talk to tty devices supports setting an arbitrary baud rate | divisior. I don't know if the low-level driver for the OP's | device supports that API or not.

Then he doesn't need a new ioctl(). He may need a new driver (or tweak the one he has). If it can set a standard baud rate and inquire what the divisor is, then other rates should be easy.

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|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org)  /  Do not send to the address below |
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Probably not.

He may need a new xtal or oscillator.

Not necessarily. For the standard PC UART setup, the baud rate is 115.2K divided by the baud rate divisor. That means you can't get to 33.6K w/o plugging in the soldering iron and swapping something.

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Hi Grant, For 33.6 there is no divisor value as if i use the value 4 then i get

28.8 baud rate , and if i use 3 then i get 38400 these both are the standard baud rate that are available. I want to have 33.6 baud which is can be achieved if i use 3.4 as divisor , but divisor should be an integer... i am still stucked in same problem. please help me out. thanks a lot, meenal

There is no problem. It isn't possible to do the baud rate you require using standard PC hardware.

Peter

It's already been explained to you several times.

You can not do 33.6K with a standard PC serial port.

You're going to have to buy a serial board that either can do

33.6K or can be modified by you by replacing a crystal or oscillator.

Somebody has even suggested a serial board that they knew would do 33.6K.

I'm tired of repeating myself.

I'm done with this thread.

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