Serial port issues

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I've got an PXA255 Intel ARM processor from 'arcom' (Viper board from It is running embedded linux slightly modified for
their viper board. specifically

uname -a
Linux bluebox 2.4.21-rmk1-pxa1-arcom1-2-viper #1 Tue Feb 10 15:33:52
GMT 2004 armv5tel unknown

I'm getting what appears to be serial port lockups with this and I'm
wondering if, after reading my symptoms below, anyone can give me some
pointers into solving this.

Basically I have a application that resembles a glorifed PLC/Telemetry
system. It uses seperate threads that act as "PORTS" which use serial
ports to connect to the outside world. Generally this includes engine
managment systems, FSK radio modems, GPS and Touch screen.

The touchscreen is an intelligent device in that you program it with
screens, it has memory etc. and it polls our program to find out what
screen it should be displaying etc.. This is via RS232.

In production our application runs on bootup and any configuration
changes you download into it force a restart of the application (Not
the hardware). So our application on starting opens up serial ports
uses them and then restarts, opening them up again.

After a few restarts of the application I noticed that, for example,
the touchscreen would stop communicating, I thought well maybe its
because we arent cleaning shutting down the serial ports, so I
implemented that. (Please note that this application was previosuly
running on a standard linux kernel on a PII celeron based system and
worked fine). This didnt seem to solve anything.Resetting the hardware
fixes the issues and the serial ports work fine again until you stop
and start the application a number of times.

So I looked deeper.

When the application is running /proc/interrupts showns the serial
ports interrupt numbers as normal and when the serial port is working
that interrupt value is increasing when commands come in from the
touchscreen. Once the serial ports lock up, that number stops

I then plugged an RS232 LED debugging device onto the cable going to
the touchscreen so I could confirm that the signal is in fact polling
the application. And it is. Once the serial ports lockup the
touchscreen can be seen to periodically poll the device. A digital CRO
also confirmed this.

Can anyone suggest anywhere to look in the kernel or something so I can
find out the cause of the problem?
Any suggests would be most welcome.



Re: Serial port issues
And further, I wrote a simple serial program that opens up the same
serial port as what the touchscreen connects to (ttyS1) which simply
sends out ATZ\n 20 times then attempts to read a few bytes from the
serial port.

When the serial port is in that locked up state I shut down our main
application and run this little test one. The lights on my RS232 tester
show that the TX is working and the touchscreen is still polling. But I
never return from my read() command in my test program.
I get no errors opening up the port or writing/reading.

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