Bluetooth headset routed over USB on Freerunner: why we need it and what problems i faced

Paul Fertser fercerpav at
Tue Feb 24 08:42:56 CET 2009

Andy Green <andy at> writes:
> WM8753 can't make a routing between it's two digital audio ports (one
> goes off to BT module and the other to the CPU).
> We can make paths between the analogue ports for the GSM module and
> either of the digital ports, so BT for phone calls works and recording
> audio works on CPU side.

Let me put it in a more clear way: we can either use BT for GSM calls
or record audio by routing ADC to SoC, but not both at the same time.

More generally, we can route almost any analogue signal available
inside WM8753 to ADC which can be connected to either DAI (but not
both simultaneously due to inability to sync digital interfaces). And
when the ADC is connected to SoC DAI, there's no way to get audio from
BT via PCM.

> But for the case we are being an MP3 player, we can't pipe the result
> frm the CPU on digital audio interface, to the BT module over its
> digital audio interface inside WM8753.

Hm, for the weird case of being an MP3 player who needs to output to a
BT headset via SCO (that will give very poor quality), we can make an
analogue loopback inside the codec, but i don't see how it makes

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