pySerial Windows write problem

[Bob Greschke]

We have some equipment that communicates at 57600 baud RS232.  The path from 
the PC is USB to a Phillips USB hub, then off of that a TUSB3410 USB/Serial 
converter.  The driver for the 3410 chip creates a "normal" comm port (like 
COM3).  There is a C++ program that has no problem talking to the equipment, 
but two Python programs have trouble.  One is a big, scary, controller 
program, and the other, since that is the one I'm having trouble with, is a 
while() loop.

The while loop program seems to be able to open and close the serial port 
all day.  It also seems to be able to open, send "blahblahblah", and close 
the port for the same length of time.  But writing anything to the port 
quickly (not always right away...like maybe 5-6 iterations through the 
loop?) causes the

    win32file.CloseHandle(self.hComPort)

statement in the 'def close(self)' function of the serialwin32.py file of 
the pySerial package to hang for a few seconds, then return.  The next 
open() attempt fails with the 'could not open port: (995, 'CreateFile', 'The 
I/O operation has been aborted because of either a thread exit or an 
application request.') exception.

The failure mode with the large program is it opens the port successfully 
completes a bunch of back and forth talking, then hangs for a few seconds 
when the port is closed, and then can't reopen the port.  It never seems to 
fail in the middle of a bunch of reads and writes, but only when/after the 
port is closed.  It can also run for the better part of an hour with no 
problems then all of a sudden...  Like I said, the C++ program never fails.

I've looked at the settings in the C++ program, and in the serialwin32.py 
file and tried to set them the same as best I can, but no luck.  Digging 
into the win32all stuff gets me lost quite quickly.  I see all of the 
settings, but have no idea what to try.  This is all on WinXP, Python 2.4.1, 
the latest pySerial and win32all.

Does this ring any bells with anyone?

Thanks!

Bob