[Bluez-devel] Multiple headsets with one dongle

[Bluez-devel] Multiple headsets with one dongle

[Michael Puchol]

Hi everyone,

Firs, I'd like to introduce myself, having just joined the list. I'm the 
hardware engineer at Southwing, a Barcelona-based company that develops 
Bluetooth headsets and carkits. We do both software and hardware design 
in-house. We have a decent lab, and quite a nice range of phones, 
dongles and headsets for testing. Most of our designs are based on the 
BC3 AudioFlash, and now we're dwelling into the SiW3500 now, plus the 
BC4 External. As far as coding goes, I can understand C code, cannot 
really write it without following examples, and could modify code to do 
simple things.

I haven't studied the Bluetooth specs fully (not enough time!), but I 
have begun playing with Asterisk, a BT dongle and a couple of headsets.

Asterisk is configured OK, with a 2.6 kernel on a CentOS 4.2 distro, 
chan_bluetooth is working just fine, as is the BT stack. I have managed 
to have two headsets paired with the dongle, and thus visible to 
Asterisk, and either of them answer an incoming call, or dial a preset 
number, but what I haven't been able to get working is one headset 
calling the other. Well, actually, it *does* work, but the audio is 
totally unusable.

 From what I have been able to gather so far, the headsets are using 
RFCOMM channel 2 (sdptool search --bdaddr 0x111E), and so when both are 
communicating with the dongle at the same time, they most likely are 
interfering each other. My questions are:

1. Am I correct in thinking the RFCOMM channel is derived from the BT 
address/MAC? If so, I could change the MAC of one of the headsets so 
that it would use a different hop sequence.

2. If 1) is incorrect, *where* is this RFCOMM channel configured in the 
CSR pskeys?

3. The dongle, configured as master, *should* support up to three slaves 
using the handsfree profile?

Best regards,

Mike


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Re: [Bluez-devel] Multiple headsets with one dongle

[Brad Midgley]

Michael

> number, but what I haven't been able to get working is one headset
> calling the other. Well, actually, it *does* work, but the audio is
> totally unusable.
> 
> From what I have been able to gather so far, the headsets are using
> RFCOMM channel 2 (sdptool search --bdaddr 0x111E), and so when both are
> communicating with the dongle at the same time, they most likely are
> interfering each other. My questions are:

The rfcomm channel communication is not where interference happens. It's
when both headsets try to build the sco connection at the same time.

> 3. The dongle, configured as master, *should* support up to three slaves
> using the handsfree profile?

I'm not totally sure how to do this anyway. Marcel has hinted at it and
apparently there's a boot-time parameter to set something to allow two
sco connections. I tried to capture everything in the btsco bug for
multiple headsets, but this is all I come up with there:

Marcel adds: "To get more than one SCO channel working the hci_usb
driver must be fixed to dynamicaly change the alternate settting."

I think he was working on the generic case but if you know how many
headsets you have paired with you could set the alternate setting once
and leave it alone I think.

Brad


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Re: [Bluez-devel] Multiple headsets with one dongle

[Southwing - Miquel Puchol]

Hi Brad,

Thanks for your reply!

 >> The rfcomm channel communication is not where interference
 >> happens. It's when both headsets try to build the sco
 >> connection at the same time.

OK, that gives me some point where to start looking.

 >> I'm not totally sure how to do this anyway. Marcel has hinted
 >> at it and apparently there's a boot-time parameter to set
 >> something to allow two sco connections. I tried to capture
 >> everything in the btsco bug for multiple headsets, but this
 >> is all I come up with there:

This would be boot-time for the dongle's boot, or the actual machine's boot?

 >> Marcel adds: "To get more than one SCO channel working the
 >> hci_usb driver must be fixed to dynamicaly change the
 >> alternate settting."

Also, fixed as in repaired, or as in set to something permanent? I'll 
take a look at the archives and bug log.

Best regards,

Mike




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