Re: USB disconnect/connect messages

[James Courtier-Dutton <James@superbug.demon.co.uk>]

Takashi Iwai wrote:
> At Mon, 21 Jul 2003 00:40:32 +0100,
> James Courtier-Dutton wrote:
> 
>>Hi,
>>
>>Is there any way to tell if a USB sound card has been disconnected or not?
> 
>  
> IIRC, this is not notified to the application.
> the app simply would get an error at the further access.
> it sounds not bad to notify the status change to the application by
> some way.
> perhaps we can add a new control element for this purpose.
> and after disconnection, only this element survives to communicate
> with the application...
> 
So, the app gets an error. Which error?
How do I test to see if the error is due to a non-existant device, or 
just underrun/overrun etc.
I would be happy if there was a reliable way to tell.
This would only give us the "disconnect" event.
How would one know if the device was connected again?
Maybe a tidy way to do this would be a new alsa events device.
So, we open the "events" device, and it can then inform us of hardware 
changes. I know that USB is the only form of device that 
connects/disconnects via a user action at the moment, but I am sure 
others will come along. E.g. Bluetooth etc.
For USB, usbaudio.c definitely gets informed about usb device 
removal/addition, how can we get that message passed up to the application?

Cheers
James






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