Re: [Bluez-users] SCO question

[Marcel Holtmann <marcel@holtmann.org>]

Hi Thor,

> When opening an SCO connection between two clients using Bluez, there is
> a continous
> stream of incoming data on both ends, even without issuing any sends on
> either side.
> The stream ends when the SCO connection is terminated.
> 
> I have done some tests, and this happens in both of the following cases:
> 
> 1. With scotest, by blocking for some time right before the send(...)
> call in scotest.c:send_mode.
>    By using hcidump, it is clear that both devices receive streams of
> data without sending anything.
> 
> 2. I wrote an application that used hci_sock w/ hci_usb (raw data and
> hci_raw bit set) to manually
>    setup an acl and then sco connection. Same result.
> 
> This was tested on machines running Linux 2.4.25 (usb-uhci), with Belkin
> USB (CSR) devices. The SCO connection
> in case 2 was setup to use HV2 packets.
> 
> I have tested this with different voice settings, but pretty much with
> the same results (although the data changes). 
> Most of the data is SCO packets of length 0x30 and the data contents are
> either garbage or 0x00.
> 
> Is this generated by the BT-devices to maintain a ~ 64kb/s synchronous
> stream of data, is it generated 
> by the Bluez modules, or is there something wrong in the hci_usb driver
> isoc. interface rx implementation that makes it 
> deliver garbage to the socket?

it is all fine. You get the audio stream from the other side, even if
you don't input anything.

Regards

Marcel




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