Re: Atmel AT43USB326-based device: too many ports

[Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>]

On Tue, 27 Mar 2007, Casey Ballentine wrote:

> On 3/27/07, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote:
> > That doesn't mean it's working right.  But you didn't collect a trace log
> > so we can't see what actually happened.
> 
> Sorry.  See attached bus analyzer output when connected to a WinXP
> machine.  I didn't send the whole trace because it's pretty long and I
> didn't want to risk this message getting bounced.  Let me know if I
> got the right information.

The interesting part is here.  This is Windows apparently asking for the 
hub descriptor:

> [232]  0:02.817.471.812 / SETUP
> Duration = 2812 ns
> Length = 3 bytes
> 
> 0000: 2D 01 E8
> 
> 
> [233]  0:02.817.474.979 / DATA0
> Duration = 8145 ns
> Length = 11 bytes
> 
> 0000: C3 A0 06 00 00 00 00 47
> 0008: 00 E0 7C

The wValue word (bytes 3 & 4) in that setup request is equal to 0x0000.  
However according to the USB spec, it must be equal to 0x2900.  (The
high-order byte is the descriptor type and 0x29 represents a hub
descriptor.)  Compare this to entry [225] in the Linux log.

In other words, Windows has sent an invalid request and the device
accepted it.  If you look a little farther down at the start of the
device's reply:

> [237]  0:02.818.474.687 / DATA1
> Duration = 8166 ns
> Length = 11 bytes
> 
> 0000: 4B 09 29 03 0D 00 16 64
> 0008: 02 A0 6B

you'll see that the descriptor type in the reply (byte 2) is indeed equal
to 0x29.  So the device did send a hub descriptor even though Windows had
asked for an invalid descriptor.

Perhaps that indicates where the bug is.  The firmware is set up to accept 
an incorrect request, so maybe it can't handle correct requests.  How 
ironic.


> Apparently our hardware engineers don't trust the usbmon output.  They
> insisted, I acquiesced.

Well, just tell them they should should trust it more than they should 
trust the firmware they are testing.

Alan Stern


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