Re: [Bluez-devel] experimental ALSA/A2DP plugin patch

[Fabien Chevalier <fabchevalier@free.fr>]

Hi Kai,


> Hi,
> 
> On 23 Oct 2007,  Fabien Chevalier wrote:
>> Except for the timing part, i'm not really sure the receiver 
>> is that clever. I guess at least some of them will expect to 
>> receive data with at their local clock speed...
> 
> hmm, based on further reading of the spec, I think the receivers
> must be that clever. And this makes sense, as it's basicly RTP, 
> so an off-the-shelf RTP receiver implementation would work
> for the headsets.

There is a major difference between Internet RTP and Bluetooth RTP.
AFAIK the senders and the receivers' clocks are not syncrhonized on the 
Internet, while using bluetooth technology all slaves devices have an 
estimate of the master clock.

As for off the shelf implementations, i guess everybody just rewrites an 
  RTP implementation for it's own device, as we have done for the Bluez 
project :-)

> 
> And that assumption leads to an experimental patch (patch plus
> patched pcm_bluetooth.c for convenience):
> 
> http://sofia-sip.org/~vehmanek/bluez-patches/patch-pcm_bluetooth-kv-2007
> 1025-works.txt
> http://sofia-sip.org/~vehmanek/bluez-patches/pcm_bluetooth.c
> 
>  - send errors are now ignored (packets dropped), seems
>    to have no bad side effects on the headsets I've tested
>    with
>      -> the positive impact is that we can more easily keep
> 	  up the correct timing even with bigger period sizes
>  - a2dp_write() now loops'n'sends until all data submitted by
>    the app is  encoded (needed to work with MMAP using clients)
>  - allowed period sizes defined as set of values (vs range), 
>    this works with for example pcm.c (seems to be an alsa-lib bug,
>    but didn't have time to track it down)
>  - period count fixed to 3 (seems to work best and still 
>    doesn't confuse ALSA apps)
> 


I'm gonna have a look to that :-)

Fabien

-------------------------------------------------------------------------
This SF.net email is sponsored by: Splunk Inc.
Still grepping through log files to find problems?  Stop.
Now Search log events and configuration files using AJAX and a browser.
Download your FREE copy of Splunk now >> http://get.splunk.com/
_______________________________________________
Bluez-devel mailing list
Bluez-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/bluez-devel