1. A method of operating a data processing apparatus in connection with an I/O device, the method comprising: receiving by a bus controller of the data processing apparatus a descriptor sent to said bus controller by a processor core of the data processing apparatus; transferring by the bus controller, operating according to said descriptor, data from a shared processor cache coupled to said bus controller to said I/O device writing the descriptor to the shared processor cache by the processor core; and forwarding the descriptor to the bus controller by the shared processor cache.