On Thu, 7 Jun 2007, Curran, Dominic wrote: > > In Documentation/usb/error-codes.txt it says: > > -ENOENT URB was synchronously unlinked by usb_unlink_urb
This line is mistaken; it should say "unlinked by usb_kill_urb". > -ECONNRESET URB was asynchronously unlinked by > usb_unlink_urb > > What is the difference between a synchronously and an asynchronously > unlink ? With usb_unlink_urb, the subroutine call returns almost immediately but the URB isn't fully unlinked until some time later, when its completion handler runs. With usb_kill_urb, you are guaranteed that the URB will be fully unlinked and the completion handler will have run before the subroutine call returns. > My understanding from the answer to a previous question is that if you > have the situation where 2 URBS are sent to the HCD: > 1) URB 4K URB_SHORT_NOT_OK > 2) URB 8K URB_SHORT_NOT_OK > > If then only 1K of data is sent back from the Device (short packet) then > the HCD would complete the 4K URB with: > actual_length=1024 > status = -EREMOTEIO > > The client driver should then call usb_unlink_urb() for the 8K URB which > would then complete this URB with: > status = -ECONNRESET > > So I assume that would be an example of an asynchronously > unlink...although I'm not entirely sure I understand whats > 'asynchronous' about it. It's asynchronous in the sense that the subroutine call doesn't wait for the unlink to finish. It _can't_ wait, because the caller (the completion handler) runs in an interrupt context. The timing of the subroutine call and the timing of the unlink aren't synchronized -- hence they are "asynchronous". > I don't think I understand what 'synchronous ' & 'asynchronous' mean in > this context. In general, "synchronous" means roughly "at the same time" or "synchronized with". A call is synchronous if all its actions have finished by the time the call returns. "Asynchronous" is the opposite -- some of the actions may not have finished when the call returns. Alan Stern ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/ _______________________________________________ linux-usb-devel@lists.sourceforge.net To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
