Message-ID: <446CDD43.3050604@free.fr>
From: Fabien Chevalier <fabchevalier@free.fr>
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To: bluez-devel@lists.sourceforge.net
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Subject: [Bluez-devel] New bluez headset implementation
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Date: Thu, 18 May 2006 22:46:59 +0200


Hello all, i've been spending most of my spare time in the past
month writing an alternative implementation to btsco for headsets support.
The starting point was me being frustrated not to be able to use my
laptop for VoIP because of crappy microphones the manufacturers usually
put in. So my goal now is to go wireless with bluetooth. :-)
So here i am. The software i wrote is now mature enough to be shared
with others.

What i'm looking for now is peer review from experienced bluez
developpers about it. But that's enough about me, let's talk about the
software :-)

So What's In ?

What is implemented is the AG side of the headset profile. Both Headset
initiated connections and access gateway initiated connections are
supported. It does not support A2DP, as it is another profile, and
moreover people here are already working on the subject :-)

The spirit that governed the design was the following:
   - be able to handle voice over IP applications well (this means
keeping buffering at a minimum for a reduced latency)
   - make it easy to use for open source VoIp apps developpers (the idea
is that it should be very easy for the apps to provide some basic
support for bluetooth headsets with no change to the application itself)
   - support 100% of bluetooth headset profile (device
connect/disconnect, headset button push)

The architecture is the following:
   - 1 daemon, responsible for doing SDP, handling RFCOMM and SCO
channels, parsing AT commands, sending DBUS signals when things happen.
The daemon handles application requests (referred to as AG initiated
connection in HSP spec) or headset connection requests (referred to as
HS initiated connection in HSP spec)
The daemon also handles session caching between PCM open/close.
   - 2 ALSA user space IO plugins (1 control, 1 PCM). Both of them
communicate with the daemon using unix sockets. The PCM also has an
instance of the SCO socket, so that it can reads/write data directly to it.

Compared to btsco, it differs in the following way:
   - it is 100% userspace. No more kernel module.
   - all parameters are supplied by the application to the alsa pcm
plugin, that will eventually forward them to the daemon. This will make
implementation of user friendly MMI much easier (in particular, there
is no need to lauch the daemon separately with a predefined BD address.
The gui will thus be able to provide bd address).
   - it handles only one active headset at a time
   - it supports HS initiated connections as well
   - codebase cleaner. It should be possible with minimal pain to
     support handsfree profile.

Still to be done :
   1) more testing
   2) DBUS signalling to tell the world about connected /
disconnected / button pushed events.
   3) some kind of switching from headset to an alternate sound device
in case the headset is unavailable.
   4) interoperability testing against a variety of devices.
   5) document the design
   6) debug kernel sco support (more on that on a separate e-mail)

I'm likely to do 3), 5), however 1 and 2 might be better handled
by somebody else, and 4 is just everybody's work :-)

Where to get the software:
   Simple! On my hard disk!!   No i'm kidding... but in fact not
completely. ;-)
   I don't wanna start a whole open source project for such a small
thing. So for now i will send it by private e-mail to developers
interested in giving it a try. Just reply to this e-mail if you are
interested.

How to play with the software:
   - use standard aplay/arecord tools (not very funny)
   - use xmms (a litte more funny :-) )
   - use ekiga 2.0.1 (top fun!- however you will need to patch it and
rebuild it)


Fabien


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