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Subject: Re: How can i configure bluez to transmit Voice over PCM
From: Marcel Holtmann <marcel@holtmann.org>
To: "Matuschka, Sebastian" <Sebastian.Matuschka@gcd-solutions.de>
Cc: linux-bluetooth@vger.kernel.org
In-Reply-To: <49ED01FC03EE524BB7BB258E8F93BFF32F3DB5@bfl-exchange-1.BFL.local>
References: <49ED01FC03EE524BB7BB258E8F93BFF32F3DB5@bfl-exchange-1.BFL.local>
Content-Type: text/plain
Date: Sun, 01 Feb 2009 17:52:05 +0100
Message-Id: <1233507125.4809.2.camel@californication>
Mime-Version: 1.0
Sender: linux-bluetooth-owner@vger.kernel.org
List-ID: <linux-bluetooth.vger.kernel.org>

Hi Sebastian,

> i'm using bluez 3.36 on an embedded system with a CSR Chip connected.
> Communication via HCI over UART works well. I need to receive and send
> voice from/to a headset and therefore I want to send/get the voice as
> PCM to the CSR chip. The PCM pins of the CSR Chip are connected to the
> SSC pins of an avr32 microcontroller. The CSR chip is configured to use
> PCM as soon as the Host produces Clock, otherwise it tries to transmit
> voice per HCI which is too slow (only 115200 baudrate for a 8kHz PCM
> stream).
> In etc/bluetooth/audio.conf I have set SCORouting=PCM
> In etc/Bluetooth/asound.conf I have written the following:
> #####################
> pcm.headset {
> 	type bluetooth
> }
> ctl.headset {
> 	type bluetooth
> }
> #####################
> But bluez is still sending voice over HCI, which is ok because: How
> should it know where to transmit the PCM stream. I need a device but I
> am not sure what exactly is needed.
> Do I have to write a dummy soundcard driver which only sends and
> receives pcm over the ssc pins? I guess a pseudo UART device for SSC
> isn't enough because bluez needs an alsa device, correct?
> 
> For a quick and dirty solution: Is it possible to let bluez reduce the
> soundquality so it works over HCI any way?
> 
> Are my settings correct or have I missed something?

I would really advise you to start using 4.27 instead of a previous
major version that is not developed.

Also when using PCM for SCO then you need to use the D-Bus API for
headsets and not the ALSA plugin.

Regards

Marcel