InOrder

This page provides a general overview of the InOrderCPU model, its pipeline stages, and its resources.

Soumyaroop Roy has been kind enough to provide a "test-status-page" of the M5-Inorder model in the work he has been doing. (Note: The latest versions of the inorder model can be found in the m5-dev repository. Please check there for updates and additional information.)

The relevant sources files are in src/cpu/inorder.

Pipeline Stages

In it's most basic incarnation, the In-Order model models a 5-stage pipeline.

The 5-stage pipeline is based on the 5-stage MIPS pipeline and has the following stages:

• Instruction Fetch (IF)
• Instruction Decode (ID)
• Execute (EX)
• Memory Access (MEM)
• Register Write Back (WB)

Relevant source files:

• first_stage.[hh,cc]
• pipeline_stage.[hh,cc]

Pipeline Resources

The following pipeline resources are defined for InOrderCPU:

• Fetch Unit
• Instruction Cache (I-Cache)
• Branch Prediction Unit (BPred Unit)
• Register File Manager (RF Manager)
• Address Generation Unit (AGen Unit)
• Execution Unit (EXU)
• Integer Multiply and Divide Unit (Int MDU)
• Data Cache (D-Cache)
• Graduation Unit (Grad Unit)

Relevant source files:

• resources/*.[hh,cc]

Resource Pool

@TODO

Pipeline Definition

@TODO

Instruction Schedules

Instruction scheduling is divided into a front-end schedule (IF and ID), which is uniform for all the instructions, and a back-end schedule, which varies across the different instructions.

• Front-end Schedule
  • The front-end schedule comprises of the IF and ID stages
    • IF
      • NPC is updated by the Fetch unit
      • Instruction fetch from the I-Cache is initiated
    • ID
      • Instruction fetch is completed by I-Cache
      • Instruction decode is performed by the Decode unit
      • Branch prediction is performed by the BPred unit
      • Target PC is updated by the Fetch unit

• Back-end Schedule
  • The back-end schedule comprises of the ID, EX, MEM, and WB stages
    • ID
      • For non-store instructions, the source registers, if any, are read by the RF Manager
      • For load instructions, address generation is performed by the AGEN unit and data read from the D-Cache is initiated
      • The rest of the instructions are executed in the execution units
        • Single cycle operations are sent to the integer EXU
        • Execution is initiated for the multicycle/pipelined operations
    • EX
      • Execution is finished for the multicycle/pipelined operations
      • For load instructions, data read from the D-Cache is completed
      • For store instructions, the following tasks are performed
        • The source registers are read by the RF manager
        • Address generation is performed by the AGen unit
        • Data write into the D-Cache is initiated
    • MEM
      • For store instructions, data write into the D-Cache is completed
    • WB
      • Destination registers are written into by the RF manager
      • The instruction is graduated by the Grad unit

Relevant source files:

• pipeline_traits.[cc,hh]