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From:   Emil Lenngren <emil.lenngren@gmail.com>
Date:   Tue, 13 Nov 2018 11:47:49 +0100
Message-ID: <CAO1O6sdawagz6nfL0J=4EZ7YbLGUd2YmMbiJZVqd-BtyqLN0GA@mail.gmail.com>
Subject: Re: Operating central and peripheral roles concurrently
To:     mtownsend1973@gmail.com
Cc:     Luiz Augusto von Dentz <luiz.dentz@gmail.com>,
        Bluez mailing list <linux-bluetooth@vger.kernel.org>
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Hi,

Den m=C3=A5n 12 nov. 2018 kl 17:19 skrev Martin Townsend <mtownsend1973@gma=
il.com>:
> I've just been reading the 4.1 spec on GAP and on page 224 it states:
>
>
> "In LE, GAP defines four specific roles: Broadcaster, Observer, Periphera=
l, and
> Central. A device may support multiple LE GAP roles provided that the und=
erly-
> ing Controller supports those roles or role combinations. However, only o=
ne LE
> GAP role may be supported at a given time. Each role specifies the requir=
e-
> ments for the underlying Controller. This allows for Controllers to be op=
timized
> for specific use cases."
>
> Now to me that says a device can support being a central and
> peripheral but doesn't have to support them concurrently so I'm
> guessing if the device is in the peripheral role and then wanted to
> connect to another device you would have to stop being a peripheral
> (ie drop this connection) and then become a central, make the
> connection and when finished disconnect and become a peripheral again
> and wait for the other devices to reconnect to you.  Or am I
> mis-reading this?

This restriction is lifted in newer versions of the spec. The same
section in version 4.2 says this:
"In LE, GAP defines four specific roles: Broadcaster, Observer, Peripheral,=
 and
Central. A device may support multiple LE GAP roles provided that the
underlying Controller supports those roles or role combinations. Each role
specifies the requirements for the underlying Controller. This allows for
Controllers to be optimized for specific use cases."

If you use the btmon tool you can easily see what combination of
supported states the controller supports. If you have btmon running
while you initiate bluetoothd you will see the packet LE Read
Supported States Command, which contains this info.