thanks for the pointers.... it turned out that it is being queued
but for the wrong reason...

in the submit_urb.. (this is the SL811)... it checks the 
RH.DEVNUM (which is 1)... against the PIPEDEVICE which is 2...
so it does not send it out and queue it up... and i am now trying
to find out where the 2 comes from????  (all the communication
were working ... ie pipedevice(pipe) == 1 until /dev/ttyUSB0 is
opened and i guess pl2302 is involved... 

like an onion... just keep peeling!!!

David Brownell wrote:
> 
> thomas chen wrote:
> > ohci can handle two urb_submit by DELAYing one for the next frame?
> 
> No, it handles them by _queueing_ the second one so that it'll
> start after the first one finishes.  In the case of OHCI, the
> typical case is that the hardware automatically advances that
> queue ... no software attention is needed until later, unless
> there's some kind of fault seen with the first URB.  (And NAK
> isn't a fault.)
> 
> > i guess the question is that can two packets be sent in the same frame?
> 
> URB != packet.  At USB 1.1 speeds, multiple packets per frame
> will be typical.
> 
> - Dave
> 
> > if not.. then the driver is responsible for delaying one??? i guess that
> > is the problem... the driver i have does not seem to do that properly
> > and slave starts sending nack after that...
> >
> > thanks
> >


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