Lec08 - The Problem with Single-Cycle Processor...

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1 The Problem with Single-Cycle Processor Implementation: Performance Performance is limited by the slowest instruction Example: suppose we have the following delays Memory read/write 200ps ALU and adders 100ps Register File read/write 50ps What is the critical path for each instruction?
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2 What is the critical path for lw? lw: 200 + 50 + 100 + 200 + 50 600ps P C address Inst. R1 (rt) R2 (rs) -100 lw ReadRegister#1 ReadRegister#2 WriteRegister Data Port#1 Port#2 ALU REGISTERS ROM Instruction Memory Data Memory RAM DataIn Address DataOut 16 (Imm) SIGN-EXTEND 16 32 Memory read/write 200ps ALU and adders 100ps Register File read/write 50ps
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3 sw R1, -100(R2) P C address Inst. R1 R2 -100 sw ReadRegister#1 ReadRegister#2 WriteRegister Data Port#1 Port#2 ALU REGISTERS ROM Instruction Memory Data Memory RAM DataIn Address DataOut 16 SIGN-EXTEND 16 32 What is the critical path for sw? Memory read/write 200ps ALU and adders 100ps Register File read/write 50ps Sign-Extended 10ps
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4 sw R1, -100(R2) P C address Inst. R1 R2 -100 sw ReadRegister#1 ReadRegister#2 WriteRegister Data Port#1 Port#2 ALU REGISTERS ROM Instruction Memory Data Memory RAM DataIn Address DataOut 16 SIGN-EXTEND 16 32 Memory read/write 200ps ALU and adders 100ps Register File read/write 50ps sw: 200 + 50 + 100 + 200 550ps What is the critical path for sw?
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5 What is the critical path for each instruction? R-format 200 + 50 + 100 + 0 + 50 400ps Load word 200 + 50 + 100 + 200 + 50 600ps Store word 200 + 50 + 100 + 200 550ps Branch 200 + 50 + 100 350ps Jump 200 200ps What is the implication?
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6 Alternatives to Single-Cycle Multicycle Processor Implementation Shorter clock cycle Multiple clock cycles per instruction Some instructions take more cycles then others Less hardware required Pipelined Implementation Overlap execution of instructions Try to get short cycle times and low CPI More hardware required … but also more performance!
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This note was uploaded on 11/03/2009 for the course CS 20929 taught by Professor Taoxie during the Spring '09 term at San Diego State.

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Lec08 - The Problem with Single-Cycle Processor...

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