Re: Bluetooth headset driver

[James Courtier-Dutton <James@superbug.demon.co.uk>]

Christian Ege wrote:
> Hi anyone working on something simalar to this?
>    http://www.dcs.gla.ac.uk/~jp/snd-bt-sco/
> 
> The author of this driver won't continue his work because he switched to MAC OS
> ;-(
> 
> I think the way he tried to integrate this driver into alsa isn't the best way.
> 
> I am not that kind of Kernel guru but if there are some other people arround
> here interested in that stuff it shouldn't be too much work to integrate this
> driver in alsa.
> 
> Or isn't there any interest in bluetooth communication ;-)
> 
> 
> cu
> chege
> 

I have been working on a bluetooth alsa driver, but it turns out to be a 
lot more complicated that one would at first think.
1) The bluetooth headset profile is a "profile" and therefore deemed to 
be a user space and not a kernel space program.
2) The current bluez bluetooth stack in the kernel does not provide any 
"playback" position feedback, so we would not be able to implement 
snd_pcm_delay() and therefore it would be extremely difficult to make a 
low latency app using it. The first use of a headset profile is for full 
duplex speach, which requires low latency, so that is a problem.
3) audio data path would therefore go from alsa-lib(userspace) -> 
alsa-driver(kernel-space) -> headset profile (userspace) -> bluez stack 
(kernel space). Extremely messy in my view!
(What http://www.dcs.gla.ac.uk/~jp/snd-bt-sco/ currently does in fact)

Summary: -
Until the bluez stack provides a mechanism for us to do 
"snd_pcm_delay()", there is very little point advancing with the alsa 
side for bluetooth.

Who will want to use a headset that has large uncontrollable latencies?

Cheers
James



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