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#1 2007-07-04 23:59:57

Misterke
New member
Registered: 2007-07-04
Last visit: 2007-07-09
Posts: 2

UART OK for Bootloader, NOT for Linux

Hi all,

I've got a strange problem. I have a br6104k and attached a cable to the UART pins with the other end inserted into a special box that acts as 3.3V to RS232 converter. The box is used for similar purposes for the devices my employer makes.

This thing is working fine for the boot-loader. Is see the prompt, can press space three times and upload with XModem new firmware. All goes fine, the firmware is flashed and the router starts up with this new firmware and works fine, proving again that all went well.

BUT ... once the boot-loader gives control to "Linux", the UART output becomes rubish, as if it would be sent with the wrong rate. I've tried about every possible combination of bps, stop-bits, etc. that I could think of, but nothing helps. Is the Linux kernel using other settings than the boot-loader? If so, what should I change? Any clue what could be wrong here? Since the firmware upload and the firmware menu go well, I would assume the 3.3V UART to RS232 conversion is ok. What else can it then be?

Thanks in advance for any tips ...
K

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#2 2007-07-07 22:29:45

sergioag
Developer
Peru
From: Lima
Registered: 2006-02-16
Last visit: 2011-08-15
Posts: 166
Website

Re: UART OK for Bootloader, NOT for Linux

Hi

The correct baudrate combination is 115200 baud, 8 data bits, 1 stop bit, no parity. If those settings don't work, you should check your interface for problems. I would recommend using a MAX3233, which doesn't require capacitors and works with a 3.3v power supply (which the serial port header has).

Regards,

Sergio

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#3 2007-07-08 08:49:31

Misterke
New member
Registered: 2007-07-04
Last visit: 2007-07-09
Posts: 2

Re: UART OK for Bootloader, NOT for Linux

Hi there Sergio,

Those are the settings I'm using and they work fine for the boot-loader, so I have no real reason to suspect the conversion box (which by the way does a lot more than 3.3v UART to RS232 conversion and is connected through USB, which is a big plus if you don't have an RS232 to connect a MAX3233 to on your notebook).

The question therefor remains: is the Linux kernel doing something different than the boot-loader when using the UART of the BR6104K?  I'm pretty sure bit-rate, stop bits and so will be ok, but maybe flow control or such?  Does the kernel use XON/XOFF? Does the boot-loader?

Thanks,
Kurt

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#4 2007-07-09 09:42:34

sergioag
Developer
Peru
From: Lima
Registered: 2006-02-16
Last visit: 2011-08-15
Posts: 166
Website

Re: UART OK for Bootloader, NOT for Linux

Hi

You should not use a flow control. I've had problems using either one.

Regards,

Sergio

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#5 2007-07-31 11:22:50

Sunspot
Member
United Kingdom
From: New Forest
Registered: 2006-03-23
Last visit: 2008-04-25
Posts: 12
Website

Re: UART OK for Bootloader, NOT for Linux

What firmware are you loading? For example my Midge "distro" changes the rate to 9600baud on ttyS0 and ttyS1 - others versions are set to other speeds . So after the default boot up you need to change (quickly!) to 9600 to see the boot messages.

See http://www.sunspot.co.uk/Projects/sweexproject.htm menu item 5

You have to change serial.c before compile and you can't change at runtime - I wish you could....

No flow control

Newbies rule, OK?  cool

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