Re: Other types of usb audio devices.

[Takashi Iwai <tiwai@suse.de>]

At Mon, 7 Jul 2003 12:39:38 +0200 (CEST),
Jaroslav wrote:
> 
> On Sat, 5 Jul 2003, James Courtier-Dutton wrote:
> 
> > Jaroslav Kysela wrote:
> > > On Sat, 5 Jul 2003, James Courtier-Dutton wrote:
> > > 
> > > 
> > >>Hi,
> > >>
> > >>The current snd-usb-audio driver assumes that the audio device is 
> > >>attached to this computer, so it only talks to this endpoint.
> > >>If I have an audio usb device with USB_CLASS = 0xe0, it will be a 
> > >>wireless device. I.E. A bluetooth headset.
> > >>It uses isoc's just like the current snd-usb-audio driver but adds some 
> > >>extra requirements, in order to open a connection, one needs to also 
> > >>know the bd address of the destination device  (Like a MAC address for 
> > >>ethernet) and keep tabs of connection number.
> > >>The current bluetooth stack I am using is bluez, from the current 2.4.20 
> > >>  kernel, and it uses network sockets for the audio. I would prefer to 
> > >>use alsa for sending and receiving audio to/from the headset, with all 
> > >>other control of the device going via the bluetooth stack.
> > >>So the question is: -
> > >>How do I get the bdaddr to alsa so that an application can use 
> > >>snd_pcm_open with the bluetooth headset, just as if it was a local audio 
> > >>card.
> > > 
> > > 
> > > I think that there must be a way to determine new devices with the 
> > > bluetooth stack, so use the same mechanism as usb or pcmcia:
> > > 
> > > Register all found audio devices and create appropriate new cards in the 
> > > ALSA driver. The application does not know, if it communicates with usb, 
> > > bluetooth, PCI or ISA devices so passing some native information for the 
> > > transport layer is not our goal.
> > > 
> > > 						Jaroslav
> > 
> > Another approach would be to use some other tool outside alsa to enter 
> > the bdaddr, and just present a Playback and Capture PCM to alsa lib.
> > I was thinking that the "card" would be the bluetooth usb dongle, and 
> > the pcm's would dynamically appear and disappear as the user attaches 
> > different bluetooth devices (e.g. headset).
> > 
> > Does alsa allow for PCMs to appear and disappear?
> > E.g. Card appears but no pcms listed in /proc/asound/card0
> > User runs a tool (attach-bluetooth-pcm) what sorts out a pairing of 
> > bluetooth devices and then creates a PCM device in /proc/asound/card0
> > User changes devices, and has to re-run attach-bluetooth-pcm to remove 
> > the old PCM, and create a new one of the new device.
> > OR: -
> > Would a new "card" have to be created for each bluetooth headset?
> > Is alsa happy with dynamically adding and removing cards ?
> 
> I prefer the allocation of new card for each physical boxes, because it is
> common behaviour and the bluetooth devices might have more PCM devices and 
> / or MIDI devices. It would be difficult to enumerate all devices which
> belongs to one physical box. It was one of the major reason, why I
> introduced the card/device model rather than device only model used in
> OSS.
 
agreed.

in the case of usb audio/midi devices, a card instance is created for
each different usb device id (more exactly, the usb_device pointer).
this makes clear difference if you connect two different devices with
multi-pcm streams.

> And, yes, you can add/remove PCM or ALSA cards on the fly (if you handle 
> locking properly, of course).

yep.  for example, snd-usb-audio manages the creation/deleteion of
card instances on the fly.  also, ALSA pcmcia drivers create PCM/mixer
devices dynamically after the firmware is loaded by a user-space
tool.


i see the following scenario:

if the hotplug (or whatever a manager) can know the connection state
of bluetooth devices, it can invoke a script to notify the connection
/ disconnection to the ALSA driver.  then the driver wil create/delete
a corresponding card instance.

the question is how to tell the bd addr to the driver.
i think the bd addr can be given via hwdep device or via the control
API with a certain control.  the detailed implemention can be hidden
inside the alsa-lib like emu10k1's pcm set-up.


Takashi


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