[Libusb-win32-devel] setConfiguration

[Dan E. <Dan...@ne...>]

I've spotted what to me seems a pretty major difference between libusb
and libusb-win32. In the call to set_configuration, libusb takes the
actual configuration value, i.e. the value specified in the
configuration descriptor, whereas libusb-win32 takes the index value +
1.

This means that if you have a quirky device which has one configuration
called configuration 2, then with libusb you would use
set_configuration(2) to set it, whereas on libusb-win32 you would use
set_configuration(1). This is a bit troublesome.

We have been hit by this since a device we are using makes the same
error in reverse, it returns the config descriptor by value instead of
index, so when windows initially asks for the 0th config descriptor,
unless there is a bogus descriptor in the device called configuration 0
(which of course doesn't make sense since config 0 is the unconfigured
state), the device returns an error. A workaround is to provide 2 config
descriptors, one bogus one called 0 and the real one called 1. This is
fine on linux since you can select config 1 by calling
set_configuration(1), but on windows you have to call
set_configuration(2). If someone decided not to have incrementing
configuration values you'd be sunk with libusb-win32 at the moment.

Anyway, for the moment I'm just happy that I've worked out what's going
on and that I can select my configuration using 2.

Dan