[libhid-discuss] Using multiple HID devices with same vendor / product ID

[Sarah Mount]

Hi All,

I'm trying to communicate with a number of HID devices at once, using
the Python bindings for libhid(*). I know this has been covered in the
list before and I've looked over the discussion here:
http://lists.alioth.debian.org/pipermail/libhid-discuss/2008-January/000336.html

However, I'm still a bit confused over how libhid works. Turning on
debugging I notice that HIDInterfaceMatcher objects do indeed find all
HID devices on the USB bus, but I can't see any way to get to that
list from the SWIG interface. Obviously(?) asking the matcher to open
a device twice results in an error, not in two devices being opened,
as discussed in the other thread.

Is it actually possible to do what I'm trying to do from the Python
bindings? Presumably I need to subclass HIDInterfaceMatcher to
manipulate the internal list of matched devices, but will this have to
be done in the C library and if so where would be best to start
looking -- hid_opening.c or linux.c?

Many thanks,

Sarah


(*) Ubuntu Ibex GNU/Linux
python-hid 0.2.15+20060325-2.1
libhid0 0.2.15+20060325-2.1
libusb 1:0.1.5-1
Python2.5
--
Sarah Mount, Senior Lecturer, University of Wolverhampton
Web: http://www.wlv.ac.uk/~in0316/
Book: http://www.pythonforrookies.org/
Blog: http://varspool.blogspot.com/
Photos: http://flickr.com/photos/sarahmount/

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[Charles Lepple]

Post by Sarah Mount
Is it actually possible to do what I'm trying to do from the Python
bindings? Presumably I need to subclass HIDInterfaceMatcher

Subclassing is the Python way, but HIDInterfaceMatcher is a C struct
wrapped by SWIG, not a full-fledged Python class.

Post by Sarah Mount
to manipulate the internal list of matched devices, but will this
have to
be done in the C library and if so where would be best to start
looking -- hid_opening.c or linux.c?

Looks like it's there in the SVN version:

http://libhid.alioth.debian.org/doc/hid__opening_8c-source.html#l00109

I almost forgot - someone finally contributed code to do just that.

You might be breaking new ground with that, though - I don't know if
that code has been tested much in Python.

My advice would be to open all of the devices sequentially in an
initialization function, and not to spawn off any new threads until
after you have opened the devices. (I don't think thread safety was
considered there.)