[sane-devel] reverse engineering / usbsnoop

[Henning Meier-Geinitz]

Hi,

On Sat, Sep 11, 2004 at 07:07:01PM -0400, Mbosowo I Sampson wrote:

No. 1:

> SetupPacket:
> 0000: 80 06 00 01 00 00 12 00
> bmRequestType: 80
>   DIR: Device-To-Host

So this URB is the answer to a request from the host.

>   TYPE: Standard

No vendor-specific command.

>   RECIPIENT: Device

The request was sent to the device as a whole (not a specific
interface or endpoint).

> bRequest: 06
>   GET_DESCRIPTOR

That's a standard request.

> Descriptor Type: 0x0001
>   DEVICE

We want to get the device descriptor (wValue = 1).

No. 2:

> 0000: 80 06 00 02 00 00 09 00
> bmRequestType: 80
>   DIR: Device-To-Host
>   TYPE: Standard
>   RECIPIENT: Device
> bRequest: 06
>   GET_DESCRIPTOR
> Descriptor Type: 0x0002
>   CONFIGURATION

Same as above but this time we want to get the configuration
descriptor (wValue = 2). Also we limit the transfer size to 9 bytes
(wLength = 9). That's the minimum size of a descriptor.

> TransferBuffer: 0x00000009 (9) length
> 0000: 09 02 27 00 01 01 00 e0 01
>     bLength            : 0x09 (9)
>     bDescriptorType    : 0x02 (2)
>     wTotalLength       : 0x0027 (39)

But really the descriptor has 0x27 bytes. So we get it again with 0x27
bytes:

No. 3:
> 0000: 80 06 00 02 00 00 27 00

And we got all 0x27 bytes. So these three requests are actually
different.

> 4	??? down	n/a	0.093	SELECT_CONFIGURATION
> URB Header (length: 100)

That's a new request. Now that we have all descriptors, we can set the
configuration (config 0 usually).

Bye,
  Henning