Hi Peter, On Sun, Oct 11, 2020 at 1:04 PM Peter Mullen <omaolaip@xxxxxx> wrote: > > Hi all, > > I've been working on a plugin that adds support for battery level > reporting and Active Noise Cancelling (ANC) control for the Bose QC 35 > headphones. The patch is nearly ready to go, but because of the > non-standard way it's implemented I figured it might be necessary to get > some preliminary feedback on it prior to submission (or to see if it's > worth submitting). > > As a brief overview of device control, the QC35 has a set of additional > controls operating over rfcomm channel 8 where messages are passed back > and forth between devices. The messages consist of a 3-byte opcode, a > 1-byte payload length, and N-bytes of payload. There's some more > information on the specifics here: > https://blog.davidventura.com.ar/reverse-engineering-the-bose-qc35-bluetooth-protocol.html > > As this is a non-standard "profile", there's no profile UUID assigned to > it which makes adding a profile somewhat more complicated. My solution > here was to add a profile under the iPod Accessory Protocol (iAP) > profile UUID which the QC35 lists, and to then filter out devices in the > profile probe callback based on manufacturer ID, device class, and > product ID. This isn't ideal as the probe will be called for any device > listing the iAP UUID, so suggestions for alternative approaches (if > necessary) are appreciated. We could in possibly add pid/vid to btd_profile that way it can be probed by pid/vid in addition to UUID, that way one can make a driver that is specific to a vendor or a product. > For session state control, I've hooked into the AVDTP state-change > callback. Again, possibly non-standard but this seemed to be the best > way to trigger the initiatiation/tearing down of the rfcomm connection. I would recommend hooking to the btd_service state, like for example the policy plugin is doing. > For battery level integration, I've basically just wrapped the dbus > interface from the standard GATT battery profile. This has been working > fine with my DE; the battery level shows immediately after connection > and updates as the level drops. We had some discussion on weather we should continue using a custom D-Bus interface or just emulate the battery reports over UHID given that is probably better integrated with the system. > For ANC integration, I've added a new dbus interface under > "org.bluez.Anc1". The interface contains a read-only "Range" property, > which indicates the number of discrete values the ANC can be set to, and > a read-write property "Level" which gets/sets the level. This interface > layout was chosen to be device agnostic, so that ANC support could > potentially be added for more devices in future. I'd probably add Bose to the name of the interface if it is bose specific. > Let me know if there are any thoughts on this; I can get the patch ready > and submitted if desired. > > Kind regards, > Peter > -- Luiz Augusto von Dentz
