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Differences between report descriptors for digitizer HID devices RRS feed

  • Question

  • Hi all,

    I develop drivers for I2C based input devices on non-Windows operating systems. I am interested in knowing what exactly the indicators are for one to be able to tell the difference between parallel and hybrid packet reporting in Windows Digitizer Class input devices (as laid out, for example, here: https://docs.microsoft.com/en-us/windows-hardware/design/component-guidelines/touchpad-buttons-report-level-usages)

    As far as I can tell, the only difference between the report descriptors is the number of collections representing contacts. A single-finger hybrid device would have 1 finger collection, a 5 finger parallel device would have 5 finger collections.

    This does not seem to me enough to determine, a priori, what kind of reporting the device uses. For example, we could consider a touchscreen whose report descriptor has 4 finger collections. It is not immediately clear what kind of packet reporting this device supports: it could be 4 fingers parallel or 8 fingers by a 2-finger hybrid configuration.

    Is there something I am missing here? Is it not possible to tell, a priori, what packet reporting type the device implements before interrupts start coming in?

    Friday, December 29, 2017 9:56 AM

All replies

  • Well, you could look up the descriptors in the HUT, or you could do it empirically by extracting the descriptors from a working device, using something like TDD

     -Brian


    Azius Developer Training www.azius.com Windows device driver, internals, security, & forensics training and consulting. Blog at www.azius.com/blog

    Sunday, December 31, 2017 10:12 PM
    Moderator