TEAM FRONT END    ECEN 4243  

     Digital Computer Design

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What is MIPS?

• MIPS : Microprocessor without Interlocked Pipelined Stages developed in 1981

• Reduced Instruction Set Computing (RISC)

• Can be single cycle or pipelined– We will be developing a 5 pipeline version

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5 Stage Pipeline

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Pipelined Datapath

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Who is the Front End?Team Member Role

Rashmi Wadhwa Team Leader

Alex Whiteway Lead Engineer

Carolina Arbona Wiki Specialist

Rory Little Intra Team Relations 

Phillip Walker Researcher

Ran Liao  Production Line Principal

Ameen Alsharan Report Compiler

Tuan Phan Minutes of meeting(s)

What is the Front End?

• The Front End is the first section that an instruction traverses on its way through the pipeline

• Made up of two pipeline stages– Instruction Fetch– Instruction Decode

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Front End Stages: IF/ID

Fetch7

Instruction Fetch

• Pulls an instruction from memory• Updates the PC based on the PCSrc control line

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Front End Stages: ID

Decode9

Instruction Decode

• What’s in a MIPS Decode stage?– Definitely no decoding like x86

• Register File • Sign Extend• Register Destination Mux

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Read Ports

• Input:– Two Addresses: RR1 & RR2

• Each 5 bit bus determines what register will show on its respective read port

• Asynchronous Reading

• Output:– Two data outputs: RD1 & RD2

• 32 bit register contents sent to execution• Data is chosen from multiplexers using RS

and RT as the respective control lines

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Write Port• Input

– Write Address• 5 bit address input from WB Stage goes into

a 5 to 32 decoder

– Write Data• 32 bit word from WB Stage

– Write Enable• ANDed with decoder output so only 1

register is written• Tells register that Write Address specifies to

write the data on the negative edge12

Summary• Write Address (WA) is the input to the 5 to 32

decoder• Write Enable (WE) ANDed with the output of the

decoder and is the clock for the register• Write Data (WD) is the data input to the registers• Read Data 1 (RD1) is the 32 bit output of the mux

controlled by RR1• Read Data 2 (RD2) is the 32 bit output of the mux

controlled by RR2• The inputs for the muxes are all of the registers (32

32 bit registers, 1024 total in the register file)• Asynchronous reads and synchronous writes

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What is in a Register File?

Note: Register 0 will be hard wired to always have the value 014

Other Components

• 16 to 32 bit sign extender– Copies bit 15 to bits 16 through 31– Immediate values need to be 32 bits for ALU

• Reg Write Mux– Different types of instructions need to store to

registers in different parts of the instruction– R-Type writes to $rd– I-Type writes to $rt– J-Type writes to $ra

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Questions?

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