[libhid-discuss] usage path help

[Charles Lepple]

On May 1, 2009, at 9:47 AM, Andreas Starlinger wrote:

> I'm new to libhid and I have the following situation: I have a Wacom
> tablet (it's recognized as a HID device in Windows) and I'm trying to
> access the device on my linux system by using the libhid library
> (package version 0.2.15, libusb version 1.0).

libusb 1.0 or 0.1? libhid was only written with libusb 0.1 in mind.

> It looks to me that it's
> recognized by the linux kernel (see lsusb_output below).
> I compiled the test_libhid.c and the simple open and close looks good
> to me (see test_libhid_output below) but I can't find the HID usage
> paths for the device, none of the 0x80 paths (0x90 is not available at
> all) from the hid_dump_tree (see hid_dump_tree_output below)

The problem is that the HIDParser code in libhid is not parsing (or  
properly displaying) the 0xFF00 usage page. This may have something to  
do with how they are using Physical Collections.

> or via
> the suggested calculation method in the sourcecode can be used for
> e.g. hid_set_output_report, it always leads to a warning that the
> object can't be found and a timeout.
> Is there any other possibility to find the correct usage paths for
> this device or is the only way contacting the vendor for this
> information?

The term "usage path" is something specific to libhid, since other HID  
libraries use different ways of representing nested collections. You  
might want to consider one of the other HID APIs for Linux, such as  
hidraw.