Outline of MIPS Simulator project Write a simulator

Outline of MIPS Simulator project § Write a simulator for the MIPS five-stage pipeline that does the following: • Implements a subset of the instruction set (ADD, SUBI, OR, LW, SW, BEQ, BNE, J, SLT) • Reads from a file an assembly language program • Simulates, cycle by cycle, the activity in all registers associated with that program • Displays the values of registers (0 -15) and the PC • Displays memory locations 0 -15 • Displays contents of each pipeline stage • Displays on a per cycle basis 2014 simulator. 1

Sample GUI – timing diagram – registers – memory – pipe stages 2014 simulator. 2

Type of Simulator: Architecture Simulator § Time-Driven Simulator: Has a central clock and moves from one clock cycle to the next, simulating all the activity of interest in that clock cycle. 2014 simulator. 3

Five-Stage Pipeline § IF Stage: Fetches instructions • If a conditional branch is encountered, use the predict not taken scheme explained in class • The IF stage places fetched instructions in an instruction queue, to be consumed by the ID stage. • Assume the PC has its own dedicated adder to increment the byte address by 4 (or word address by 1). § ID Stage: Decodes the instructions in the instruction queue, one by one. • Immediate operands are sign-extended to 32 bits • Makes operands available to the EX stage • Generates control signals 2014 simulator. 4

register forwarding, we need the new value for instruction 0 within the ALU phase of instruction 1. 2014 simulator. 5

Five-Stage Pipeline (contd. ) § EX Stage: • Executes arithmetic/logical instructions • BEQ instructions are resolved in this stage • Check data dependencies and implement forwarding § MEM Stage: • Carries out access to the data memory § WB Stage: • Writes back into the register file (if necessary) 2014 simulator. 6

Parsing Instructions § The assembly language program must be read by the simulator • You can use a case statement associated with each possible instruction, which tells the simulator what to do with that instruction. § When an instruction reaches the ID stage, controls governing the rest of its activity will be generated. 2014 simulator. 7

A Straightforward Approach § Mimic within the simulator what happens in the MIPS pipeline • Generate the control signals associated with each instruction in the ID stage • Pass these signals along, stage by stage, along with the instruction. • check for data hazards § Every clock, mimic what is supposed to happen in each of the five stages and collect statistics on which stages are doing anything useful 2014 simulator. 8

Maintain Data Memory State § § 2014 Keep track of the contents of the data memory Assume the data memory size is 16 words Assume the instruction memory size is 16 words Data and instruction address spaces are separate simulator. 9

Instruction Memory & Register File § The program starts at location 0 of the instruction memory § The PC will point to this location at the beginning of the simulation § Each memory access takes 1 cycle § You can limit implementation to use registers 015 2014 simulator. 10

Simplifications § To make it easier for you to read in the assembly language program: • The assembly language use commas to separate operands; • No register names will be used: register numbers only. • Example: add 3 2 1 means add register 1 contents to those of register 2 and put the result in register 3. § Don’t use labels in your program: instead the beq instruction will identify its target by an offset. • Example: beq 4 5 -2 means that if the contents of registers 4 and 5 are identical, we branch to the instruction immediately preceding beq. 2014 simulator. 11

Reading the Assembly Language Program § C provides a number of ways in which to read input. For example, fscanf(fp, “%s %d %d %d”, opcode, &field 2, &field 3, &field 4); where fp is a file pointer, opcode is a character array, and field 2, field 3, and field 4 are integers 2014 simulator. 12

Parsing the Assembly Language Program § Some useful library functions (remember to #include <string. h>): • strcpy: Copies one string into another • strcmp: Compares two strings. Note that this will give you an output of 0 if the two strings match. 2014 simulator. 13

Simulator Output § The simulator must operate in single-step mode § Output consists of • Contents of each of the first 16 registers $1 to $15 and that of the PC (in decimal) • Output of data memory (0 -15) • The number of clock cycles that have elapsed • Contents of each stage IF, ID, EX, MEM, WB. 2014 simulator. 14