serial port problem

Hi all,
I am working a device attached to the host PC through the serial
port. I have two threads in a process, one for sending data to the
serial device and the other to read the data obtained from the device.
The ‘write’ function call is succeeding ( It does not return any error
value, but returns the correct number of bytes sent out ).
But the other thread blocking on a select (no timeout set) for the
serial port ‘fd’ is not getting awakened. The same serial device works
fine with Linux. So the expected data is not received when trying to
make the application work on QNX Rtp.
What could be the problem ?

How can I make sure that the data sent out by ‘write’ function is
sent successfully to the device ? If I assume that it is sent
successfully, why is it that I am not able to read the data back from
the device ?

I have tried with ‘blocking read’ instead of ‘select’. It blocks on
the read.

Thanks in advance,