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Subject: Re: Bluetooth LE battery reporting?
From: Bastien Nocera <hadess@hadess.net>
To: Marcel Holtmann <marcel@holtmann.org>, Luiz Augusto von Dentz
	 <luiz.dentz@gmail.com>
Cc: Szymon Janc <szymon.janc@codecoup.pl>, Bluez mailing list
	 <linux-bluetooth@vger.kernel.org>
Date: Thu, 07 Sep 2017 16:03:36 +0200
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On Thu, 2017-09-07 at 01:16 +0200, Bastien Nocera wrote:
> On Wed, 2017-09-06 at 16:37 +0200, Bastien Nocera wrote:
> > On Wed, 2017-09-06 at 10:40 +0200, Marcel Holtmann wrote:
> > > 
> > 
> > <snip>
> > > I assumed that it is forbidden to include HID battery reporting
> > > events via the GATT HID descriptors. I think the standard clearly
> > > says these have to come via battery service and not via HID.
> > 
> > So we're back to implementing battery reporting as a separate
> > profile.
> > What would be a good example/skeleton to use to implement this?
> 
> This is what I managed to do so far:
> https://github.com/hadess/bluez/commits/ble-battery
> 
> A first (gentle) pass at a review would be nice, especially if
> there's
> a better way to get notifications on both the attributes in one go.

Obviously, the reworked code I wrote at 1 AM didn't work correctly.
I've fixed the copy/paste bugs and pushed it.

> The second question is how I would export this.
> 
> I'm currently thinking that exporting a new interface on the device
> itself might be the best idea, and I'll monitor devices directly in
> UPower to export them to desktops. Would that be a good way?

Still unsure about this, comments welcome.

> And as UPower will be the likely consumer of this data, I think I'll
> try mapping this set of flags:
> https://www.bluetooth.com/specifications/gatt/viewer?attributeXmlFile
> =org.bluetooth.characteristic.battery_power_state.xml
> to UPower properties rather than trying to export it as-is.

I've written parsing code for this. Does anyone know of a device which
would use the Battery Power State characteristic so I could try it out?

Finally, I've realised that my code replicates a lot of the code in
bas.[ch], which is only used by the hog profile plugin. Seeing as this
does nothing (the Battery Level is at the same level as the HoG
characteristics, not a child of it), I've removed it.

Cheers