A single-cycle datapath

contents: 0-1. CA Intro

Single-cyle datapath

A single-cycle datapath executes instructions in one clock cycle with a clocking methodology.

We will study how this works according to instructions

R-format

• don't need to access memory

    - MemRead = 0

    - MemtoReg = 0

    - MemWrite = 0

• have to update value of rd register

    - RegDst = 1

    - RegWrite = 1

• PC just have to be updated +4

    - branch = 0

• ALU control determines the arithmetic type according to ALUOp and func code of instruction

Load

• need to access memory and read data

    - MemRead = 1

    - MemtoReg = 1

    - MemWrite = 0

• have to get value from memory to rs field (destination)

    - RegDst = 0 (rs to destination)

    - RegWrite = 1

• PC just have to be updated +4

    - branch = 0

• ALU control determines the arithmetic type according to ALUOp

• offset is extended from 16-bit to 32-bit by Sign-extend unit and added with Read data 1 (base addr)

Branch-on-equal

• don't need to access memory

    - MemRead = 0

    - MemtoReg = 0

    - MemWrite = 0

• Calculate target address

    - extend the offset to 32 bit and shift left twice (multiply 4)

    - add with PC + 4

• RegDst doesn't matter

More about: jump

• Calculate target address

    - offset is extended to 28-bit

    - concatenate with 0000

• Jump signal = 1