ng_ubt(4) (/sys/netgraph/bluetooth/drivers/ubt) driver (Bluetooth USB devices) makes use of two interfaces.
From a look into the driver these interfaces serve different protocols.
not sure what do you mean by protocol here. interface 0 has control, interrupt, bulk-in and bulk-out endpoints. interface 1 has isoc-in and isoc-out endpoints. also interface 1 has 5 different configurations (w/different packet sizes) allowing isoc. bandwidth scaling.
I asume they are unrelated from a logical standpoint, but I don't know bluetooth technology.
they are. interface 0 is used to control device (control/interrupt transfers) and to transfer data (via bulk-in/out transfers). interface 1 is used to transfer voice (via isoc. transfers).
We have a similar situation with ulpt, where we usually have up to three interfaces with different capabilities. ulpt currently pics one of them, but we could also have three different ulpt instances taking each one of them.
it is not exactly the same here. the device can only perform
1) data transfers 2) data transfers + voice transfers
Well the AC88172 PDF is very clear about having 2 interfaces. The document also speaks about 4 endpoints, which I expect to be on interface 0 as they also have listed endpoint number 0 - they don't tell in the document. What I currently don't know is why there are 2 interfaces. The document also mentions some homenet capabilities on RJ11 - whatever it means. Maybe it's an hardware optional interface, which is disabled in this special device.
in Bluetooth case they decided to put isoc. endpoints on the another interface so you can scale isoc. bandwidth (via max. packet size) without affecting the other transfers.
thanks, max
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