Hi, all,

I am not sure whether this is the right place for my question. If there is a better place, please let me know.

I am playing with an arm9 embedded Linux device. When I open the serial port, it sends out 1 byte 0 to the RS232 bus. When I close it, it sends out 0xFF. Is this behavior normal? Is there a way to disable it?

Thanks,
Derek

Sending data at driver open/close is certainly not the behaviour expected. There is a number of possibilities:
* your're observing non-data pin (unlikely, as I understand that except those extra 0x0 and 0xff it works fine)
* parity problem - check parity settings on both the device and your PC
* driver problem/peripherial problem - check documentation of your processor (esp. errata)
* opening in some unexpected manner - please include the code you use to open/close your port (plus the configuration you pass)

Which processor is it (it's peripherial issue, so arm9 is not enough)?

Thanks, Mara. With a scope, I can see a short pulse on the serial port when I open the serial port and a little bigger pulse when I close the serial port. The real term mistakes them as 0x00 and 0xFF. If this is not normal, it must be something wrong in the serial port driver or the processor configuration.

This is an Cirrus Logic EP9302 processor. And I am playing with the second serial port of the processor. We are using the linux 2.6.19.1 kernel with embedded file system, busy box, redboot...