Re: usb function framework

On Tuesday 13 November 2007, Brian Swetland wrote:
> [David Brownell <[email protected]>]
> > 
> > The notion of "dynamic" pluggability is problematic in terms
> > of what the USB spec presents as the definition of a device,
> > with a given pair of vendor and product IDs ... it's expected
> > to be fixed function, where SET_CONFIGURATION is used to
> > change device capabilities.  (Or SET_INTERFACE.)
> 
> When I say "dynamic" here, I mean mostly "in response to user
> settings".  For example, perhaps you have an option to enable or
> disable usb mass storage, or enable or disable a debugging interface.
> 
> In standard configuration "from the factory", the feature is off and
> not present at all, but if the user turns it on, I'd expect the
> device to disconnect from USB, adjust its configuration (possibly
> changing VID/PID to work around win32 oddities with driver assignments,
> etc), and reconnect to USB with the new configuration.

I'd make that "certainly" changing VID/PID.  :)

There should be no particular issue making that work within
the framework I posted.  There'd be a toplevel driver which
combines the parts and registers the resulting gadget driver.

When that unregisters, it should be easy to register some
different gadget driver ... with different descriptors all
around, including VID/PID.

- Dave


> For mass storage, one can cheat a bit here and just have the mass
> storage device be removeable and have it "eject" when turned off.
> For other functions, one may want them to just not be there at all
> when not enabled -- debugging features that don't map to standard 
> class drivers and would potentially confuse users when something 
> like win32 starts popping up driver install dialogs at them.
> 
> Brian
> 



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