Re: Switching between SBC and MPEG audio on headsets

[Brian Gix <bgix@codeaurora.org>]

Hi Arun,

On 3/15/2011 12:51 PM, Arun Raghavan wrote:
> Hey Brian,
>

[...]

>
> I'm quite unfamiliar with how this works, so please excuse any wild
> inaccuracies in terminology. I believe that I am doing it this way
> already (mostly discovered by trial and error). When I want to
> reconfigure, I do the following:
>
> - Send a BT_STOP_STREAM request, get the expected response
> - Send a BT_CLOSE request, get the expected response
> - Send a BT_OPEN request with the new seid, get the expected response
> - Send a BT_SET_CONFIGURATION request with the new caps, get the
> expected response
> - Send a BT_START_STREAM, wait for the response
> - Start streaming

Well, with full knowledge that I *haven't* examined this part of BlueZ, 
I can say that from a protocol perspective, the AVDTP_SET_CONFIG must go 
over the air/be acknowledged  before the AVDTP_OPEN can be 
sent/acknowledged.  I haven't checked to see if those step are 
obfuscated at all by the BT_OPEN/BT_SET_CONFIGURATION naming convention, 
or if it is a simple mapping.

On a compliant device, an Open directly following a Close should return 
a NOT_CONFIGURED error. But it may be that a less strict SNK device 
might assume the last configuration and overlook the protocol error.

>
> This actually does work here after I apply my patch, although switching
> sample rates doesn't seem to actually happen (probably just something
> broken in my code).
>
> So if I understand this correctly, it should be sufficient to modify my
> patch so we only search for a new remote endpoint if the local endpoint
> changed (or a more specific change limited to if the codec type
> changed)?
>
> Cheers,
> Arun
>
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-- 
Brian Gix
bgix@codeaurora.org
Employee of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum