Lecture_16 - ECE 445 Computer Organization Pipelining...

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ECE 445 – Computer Organization Pipelining (Lecture #16)
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ECE 445 - Computer Organization 2 Hazards and Forwarding
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ECE 445 - Computer Organization 3 Data Hazards in ALU Instructions Consider this sequence: sub  $2 , $1,$3 and $12, $2 ,$5 or  $13,$6, $2 add $14, $2 , $2 sw  $15,100( $2 ) We can resolve hazards with forwarding - How do we detect when to forward?
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ECE 445 - Computer Organization 4 Dependencies & Forwarding
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ECE 445 - Computer Organization 5 Detecting the Need to Forward Pass register numbers along pipeline - e.g., ID/EX.RegisterRs = register number for Rs sitting in ID/EX pipeline register ALU operand register numbers in EX stage are given by - ID/EX.RegisterRs, ID/EX.RegisterRt Data hazards when 1a. EX/MEM.RegisterRd = ID/EX.RegisterRs 1b. EX/MEM.RegisterRd = ID/EX.RegisterRt 2a. MEM/WB.RegisterRd = ID/EX.RegisterRs 2b. MEM/WB.RegisterRd = ID/EX.RegisterRt Fwd from EX/MEM pipeline reg Fwd from MEM/WB pipeline reg
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ECE 445 - Computer Organization 6 Detecting the Need to Forward
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Lecture_16 - ECE 445 Computer Organization Pipelining...

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