Ex parte KAHLE et al. - Page 2




              Appeal No. 96-1426                                                                                                                             
              Application 08/001,863                                                                                                                         

                                                         DECISION ON APPEAL                                                                                  
                        This is a decision on appeal under 35 U.S.C.  134 from the rejection of claims 1, 3, 6, and                                         
              7, which constitute all the claims pending in the application.  Claims 2, 4, and 5 have been                                                   
              cancelled.                                                                                                                                     
                        The invention is directed to a method and system for eliminating data dependency hazards                                             
              in a superscalar computer which includes instructions having a greater number of source operands                                               
              than may be interlocked utilizing a data dependency interlock circuit.  Data dependency hazards                                                
              occur, for example, when a first instruction must write its result (to a destination operand) before                                           
              the second instruction can read and subsequently use the result (as a source operand).  To allow                                               
              this write before read, execution of the read must be blocked until the write has occurred; that is,                                           
              there is an "interlock" between the write and read instructions, specifically between the destination                                          
              operand and the source operand.  Modern superscalar machines use "data dependency interlock                                                    
              circuits" which "contain logic which operates in concert with instruction dispatch circuitry to                                                
              ensure that an instruction is not dispatched until such time as a result from a preceding instruction                                          
              which is necessary for correct execution of that instruction has been obtained" (specification,                                                
              page 3).  It is common in existing superscalar machines to use a source-to-destination interlock                                               
              circuit "which is capable of interlocking two source operands with two destination operands, to                                                
              ensure that data dependency hazards for such operands clear prior to permitting dispatch of an                                                 
              instruction containing these operands" (specification, page 9).  To use an instruction with three                                              
              operands would require a proportional increase in the logic required to implement a data                                                       

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