Berkeley COMPSCI 61C - Lecture Notes (41 pages)

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Lecture Notes



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Lecture Notes

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Lecture Notes


Pages:
41
School:
University of California, Berkeley
Course:
Compsci 61c - Machine Structures
Machine Structures Documents

Unformatted text preview:

inst eecs berkeley edu cs61c su05 CS61C Machine Structures Lecture 19 Pipelining II 2005 07 21 Andy Carle CS 61C L19 Pipelining II 1 A Carle Summer 2005 UCB 4 1 Instruction Fetch rs rt ALU Data memory rd registers PC instruction memory Review Datapath for MIPS imm 5 Write 2 Decode 3 Execute 4 Memory Back Register Read Use datapath figure to represent pipeline IFtch Dcd Exec Mem WB CS 61C L19 Pipelining II 2 Reg ALU I D Reg A Carle Summer 2005 UCB Review Problems for Computers Limits to pipelining Hazards prevent next instruction from executing during its designated clock cycle Structural hazards HW cannot support this combination of instructions single person to fold and put clothes away Control hazards Pipelining of branches other instructions stall the pipeline until the hazard bubbles in the pipeline Data hazards Instruction depends on result of prior instruction still in the pipeline missing sock CS 61C L19 Pipelining II 3 A Carle Summer 2005 UCB Review C f Branch Delay vs Load Delay Load Delay occurs only if necessary dependent instructions Branch Delay always happens part of the ISA Why not have Branch Delay interlocked Answer Interlocks only work if you can detect hazard ahead of time By the time we detect a branch we already need its value hence no interlock is possible CS 61C L19 Pipelining II 4 A Carle Summer 2005 UCB FYI Historical Trivia First MIPS design did not interlock and stall on load use data hazard Real reason for name behind MIPS Microprocessor without Interlocked Pipeline Stages Word Play on acronym for Millions of Instructions Per Second also called MIPS Load Use Wrong Answer CS 61C L19 Pipelining II 5 A Carle Summer 2005 UCB Outline Pipeline Control Forwarding Control Hazard Control CS 61C L19 Pipelining II 6 A Carle Summer 2005 UCB Piped Proc So Far CS 61C L19 Pipelining II 7 A Carle Summer 2005 UCB New Representation Regs more explicit ME WB S S Data Mem B Reg File A EX ME Exec DE EX Reg File IR Inst Mem PC Next PC IF DE M D IF DE Ir



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