On Mon, 31 May 2004, Wolfgang M�es wrote:

> Hello Alan,
> 
> > It sounds like you are concerned about serializing interrupt messages
> > with control messages.
> 
> No. If I only send control messages from the INT IN completion handler, 
> all is fine.
> 
> The problem occurs if I send two control messages at the same time, one 
> from user context, one from interrupt context.

It may be that the device is unable to respond to a second control message 
coming so quickly after the first one, so it sends a protocol STALL.  
Just a guess...

> > In general, if usb_control_msg() returns -EPIPE it's because the
> > device responded to the control message with a STALL, not because of
> > any internal synchronization problem in the core or HCD.
> 
> So I will do a bus trace. This should be easy: the effect is 
> reproducable.

Good, that should give a clear picture.

Alan Stern



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