Re: Hi all, I'm newbe, so apologize for my stupid questions.

On Sat, 22 Sep 2007, Fabio Giovagnini wrote:

> Thanks i advance.
> 
> Found the problem, but not the solution.
> I'm using suse linux 10.2 with kernel 2.6.16.8-05-default;
> I added a printk line into:
> drivers/usb/host/uhci-q.c
> into the finction:
> uhci_result_common
> at line 943
> refers below for chunck of code.
> I got:
> len=8;explen=64
> in such condition is proper the HCD behaviour;
> But why I have 64 expected and 8 actual?

Because the kernel doesn't know the maxpacket size for endpoint 0,
since it hasn't yet seen the Device Descriptor.  It guesses 64, but on
your device the size is 8.  So the driver thinks your device has sent a
short packet and it ends the data stage of the transfer.  It goes
directly to the status stage without trying to read the other 10 bytes.  

Your device must be able to handle this.

> Is expected len a property the uhci set by the kernel, or something
> read form the device?

It is the packet size the driver expects to receive.

> len is the actual len received by the endpoint, or the field
> bMaxPacketSize0 of Standard Device Descriptor (USB Spec Rev 2.0; pag.
> 263; Table 9.8 cont.), or it is the max packet length set when you
> configure the endpoint?

It is the actual length received from the device.

Alan Stern


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