Bus bridge and arbitration method

Abstract

A bus bridge is connected to a first bus and a second bus. In the bus bridge, an arbiter grants ownership of the first bus to one of a plurality of devices connected to the first bus. A detecting unit detects a read cycle initiated by the device on the first bus to read data from a memory which is also accessible by another device connected to the second bus. A first signaling unit sends a first signal to the arbiter, when the data is not yet transferable to the device when the read cycle is detected. A second signaling unit sends a second signal to the arbiter, when the data becomes transferable to the device. The arbiter deprives the device of the ownership of the first bus upon receipt of the first signal, and withholds from granting the ownership to the device until receipt of the second signal.

1 .- 12 . (canceled) 
   
   
       13 . A data transfer apparatus that is connected to a first bus and a second bus, comprising:
 an arbiter operable to grant ownership of the first bus to one of a plurality of devices connected to the first bus;   a detecting unit operable to detect a read cycle initiated by a first device, of the plurality of devices, on the first bus, the read cycle being a cycle to read data stored in a second device, of the plurality of devices connected to the second bus or a local memory that is locally connected with the data transfer apparatus;   wherein the arbiter deprives the first device of the ownership of the first bus and withholds from granting the ownership of the first bus to the first device until the data becomes transferable to the first device, and the arbiter grants the ownership of the first bus to the first device when the data is transferable to the first device;   wherein the detecting unit is operable to judge whether the data to be read is stored in the second device or the local memory.   
   
   
       14 . An arbitration method for a data transfer apparatus that is connected to a first bus and a second bus, comprising the steps of:
 detecting a read cycle initiated by a first device on the first bus, the read cycle being a cycle to read data stored in one of a second device connected to the second bus and a local memory that is locally connected with the data transfer apparatus;   judging whether the data to be read is stored in the second device or the local memory;   withholding ownership of the first bus to the first device until the data becomes transferable to the first device; and   granting ownership of the first bus to the first device when the data is transferable from one of the second device and the local memory as determined by the judging step.