Re: USB devices changing UIDs
Re: USB devices changing UIDs
- Subject: Re: USB devices changing UIDs
- From: Matt Local Mora <email@hidden>
- Date: Wed, 12 Dec 2001 12:41:11 -0800
On Wednesday, December 12, 2001, at 12:03 PM, Jeff Moore wrote:
on 12/12/01 12:40 AM, Sven Duwenhorst <email@hidden> wrote:
the Roland UA-30 changes its uniqued ID string, when switching thr
sampling
frequency from 44.1 to 48. This is a strange behaviour, because unique
IDs
of devices shouldn't change at all, especially when changing a
property of
the device.
The unique ID string should NEVER contain any setup information of the
device as sampling frequency, number of channels, bit depth, clock
source,
input ...
Agreed! Please write a bug report about this.
That said, the UID for a device can change since it is derived in part
from
its position in the USB network topology, assuming the device doesn't
have
it's own UID as described in the USB spec.
In the Roland UA-30 case this might be correct behavior. When you switch
the sampling rate switch on the UA-30 device it actually disconnects
from the bus and re-enumerates as a new device running at a different
sample rate. The USB audio driver would see the device go away and a new
device come back in the same port but running at a new rate. If the
UA-30 had a unique id then the driver should be able to tell that the
same device was plugged in. I think one of the things the USB audio
driver does to check to see if a hot-plugged device is the same is to
see if a) it is plugged into the same port and b) if it had the same
properties.
Matt