Python, USB and cygwin
Thu Dec 16 04:42:00 GMT 2004

I have a couple of USB devices which are based upon FTDI chips.  I am using
the FTDI virtual serial port drivers.

The devices appear to work properly except when attempting to communicate
with them via cygwin python.  Scripts which work o.k. with Windows python
will not work properly with cygwin python.  The point of failure depends
upon the Windows version.

Under Windows 98, the scripts fail to complete the opening of the virtual
serial port,.  The failure occurs in tcgetattr and an error '22, Invalid
argument' is returned.  I haven't followed this further into the bowels of
python to work out what this means but tcgetattr() in cygwin 'C' does not

Under Windows 2000, the same python scripts go further but fail further
down the track, early during the attempted transfer of data.

The same python scripts have worked well in the past under cygwin when I
use a real serial port.

Are there known problems with cygwin python and USB virtual serial ports?
If so, are there any solutions or work-arounds?

I have tried updating (which didn't work well) and then deleting and
re-installing cygwin (with the latest version as of a couple of days ago)
on the Windows 98 machine.  I also updated to the 2.1 version of the python
serial module.  The example which comes with the serial module
works o.k. on Windows 2000 but not on Windows 98 (because of the way in
which cygwin python fails in tcgetattr).
(See attached file: cygcheck-win2000.out)(See attached file:
Bill Metzenthen
Cochlear Limited
Level 1, 174 Victoria Parade
East Melbourne  Vic  3002
PH:  +61 3 9662 1202
FAX: +61 3 9663 8652



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