On Mon, 6 Aug 2007, Gabriel Maganis wrote:

quoted text
> Hello,
>     How could one communicate with usb devices on the packet level
> i.e. chapter 8 of the usb spec instead of the device requests in
> chapter 9? I'd like to be able to send SETUP packets or DATA0 packets
> and get the ACK coming from the devices versus a GET_DESCRIPTOR
> request over the control pipe thru usb_control_msg.

It depends on what you mean.  Individual packets in USB don't form a
complete communication; not much below the level of a transaction is
meaningful.  If that's good enough for you (a Setup transaction
followed by an IN or OUT transaction for instance), you can do it by
hacking the host controller drivers.

If you really want control at the level of single packets, you will 
have to build your own hardware.  Normal host controllers don't provide 
that capability.

But why would you want to do this?  What's wrong with the existing 
facilities?  I don't see any point in, say, just sending a SETUP 
packet.  You won't know whether the device has processed it without 
going through the remainder of the control transfer (data stage and 
status stage).  And if you're going to go through all that anyway, then 
why not let the existing drivers take care of the details for you?

Alan Stern


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