Table of Contents
Decode/Rename/Reordering/Issue/Dispatch Example
Key Elements - Register File, Shelving Buffers
Key Elements - Reorder Buffer (ROB), ROB Map
Fetch
Decode/Reorder/Rename
Decode/Reorder/Rename (cont)
Instruction A: ROB allocate, Op fetch, Rename, Issue (add r8, r0, #25)
Instruction A: ROB allocate, Op fetch, Rename, Issue (add r8, r0, #25)
Operand Fetch
Instruction A: ROB allocate, Op fetch, Rename, Issue (add r8, r0, #25)
Instruction B: ROB allocate, Op fetch, Rename, Issue add r8, r8, #30
Instruction B: ROB allocate, Op fetch, Rename, Issue add r8, r8, #30
Instruction B: ROB allocate, Op fetch, Rename, Issue add r8, r8, #30
Operands are determined before RENAMING!
Instruction C: ROB shown after allocate, Op fetch, Rename, Issue after add r9, r8, #50
Instruction D: ROB shown after allocate, Op fetch, Rename, Issue of add r10, r9, r8
Comments
Instruction Dispatch by CRS (clock 3)
After Instruction Dispatch by CRS (Clock 3)
Clock 4: Execution of Instruction A
Clock 4: Execution of instruction A (Update of Reorder buffer)
Clock 4: Dispatch
Reality Check
Clock 5: Execution of instruction B
Clock 5: Execution of instruction B (Update of Reorder buffer)
Clock 5: Execution of instruction B (After retirement of instruction A)
Clock 5: Dispatch
ROB Status Changes
Clock 6: Execution of instruction C
Clock 6: Execution of instruction C (Update of Reorder buffer)
Clock 6: Execution of instruction C (Retire Instruction B)
Clock 6: Dispatch
Clock 7: Execution of instruction D
Clock 7: Execution of instruction D (retire instruction c)
Clock 8: Execution of instruction ??? (retire instruction D)
Comments
Controlling Stalls - the CRS
Controlling Stalls -- the DRR
Re-fetching Operands of Rejected Instructions
Re-Fetching operands (cont).
How is operand re-fetching different?
Controlling Stalls - the Execution Units
Determining if ROB is full
Load/Store Shelves versus Mult/Integer shelves
Dispatch Load/Store versus Dispatch of Mult/Int
Instruction Retirement
Register R0
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Author: Bob Reese
Email: reese@erc.msstate.edu
Home Page: http://www.erc.msstate.edu/~reese
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