[9fans] USB weirdness.

[9fans] USB weirdness.

[Dan Cross]

When scanning USB status files, I see a lot of ``Enabled 0x000000''.
Surely the vendor/class/device strings really *aren't* all zero's;
has anyone else seen this?

	- Dan C.

RE: [9fans] USB weirdness.

[Nigel Roles]

No, that's quite likely. If the device class of the device descriptor
is set to 0, so will be the subclass, and most likely the protocol. It
indicates that the real information is within the configuration.

As it says in Table 9-7 of USB 1,1:

	If this field is reset to zero, each interface
	within a configuration specifies its own
	class information and the various
	interfaces operate independently.

Configurations represent different operating modes of a device; this
is often used to have a device which has behaviour according to the
standard, and a proprietary mode as well. Quite a lot of proprietary
devices pass the buck to the configuration descriptor.

Unfortunately, the Plan 9 arrangements don't express alternate
configurations.

-----Original Message-----
From: 9fans-admin@cse.psu.edu [mailto:9fans-admin@cse.psu.edu]On Behalf
Of Dan Cross
Sent: 15 January 2003 21:11
To: 9fans@cse.psu.edu
Subject: [9fans] USB weirdness.


When scanning USB status files, I see a lot of ``Enabled 0x000000''.
Surely the vendor/class/device strings really *aren't* all zero's;
has anyone else seen this?

	- Dan C.

Re: [9fans] USB weirdness.

[Dan Cross]

> No, that's quite likely. If the device class of the device descriptor
> is set to 0, so will be the subclass, and most likely the protocol. It
> indicates that the real information is within the configuration.
> 
> As it says in Table 9-7 of USB 1,1:
> 
> 	If this field is reset to zero, each interface
> 	within a configuration specifies its own
> 	class information and the various
> 	interfaces operate independently.
> 
> Configurations represent different operating modes of a device; this
> is often used to have a device which has behaviour according to the
> standard, and a proprietary mode as well. Quite a lot of proprietary
> devices pass the buck to the configuration descriptor.

Okay, that makes sense, I guess.

> Unfortunately, the Plan 9 arrangements don't express alternate
> configurations.

Bummer.  So does this mean I'll have to open every device that's
``Enabled 0x000000'' and probe the configuration to find the device
I'm looking for?  Hmm....  Okay.

	- Dan C.