Ph.D. Comprehensive Exam

Ph.D. Qualifier Exams

Building a Datapath

The datapath (or encoded logic) defines the path instructions and data follow through the hardware. It consists of State Elements which maintain the state, and Combinational Elements which operate on data.

Instead of a single cycle datapath, we break the datapath into the following steps of the classic five stage pipeline:

Step name

Action for R-type Instructions

Action for memory-reference instructions

Action for branches

Action for jumps

Instruction fetch

IR=Memroy[PC], PC=PC+4

Instruction decode / register fetch

A=Reg[IR[25-21]]; B=Reg[IR[20-16]]; ALUOut=PC+(sign-extended(IR[15-0])<< 2)

Execution, address computer, Branch jump completion

ALUOut=A op B


if(A==B) then PC=ALUOut

PC=PC[31-28] | | (IR[25-0] << 2)

Memory access of R-type completion


Load: MDR =Memory[ALUOut] OR Store: Memory[ALUOut]=B

Memory read completion

Load: Reg[IR[20-16]]=MDR

Cheat Sheets:

Dissertation (last edited 2018-12-19 06:34:27 by scot)