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Matt Goldman

CS 505

Final Project Description

Compile with $ make Run with cpu.test.run +img=

Note: This project was written on a Mac, so the Makefile may need to be modified to function on Linux (or Windows, I guess). Specifically, on line 19, you may need to change gsed'' to just sed'' (Mac sed isn't strictly gnu compatible).

##Intro

Here is a very basic implementation of a 5-stage pipeline. The x86 instruction subset implemented here is very small. I spent a majority of my time working out kinks in the inter-stage communication process, eventually settling on a quite hacky method in which the sending stage must wait a couple cycles for the receiving stage to obtain the data.

Memory

I use the provided memory cell system to store the instructions.

TODO:

  • implement writing to memory

Fetch

Implemented instructions:

  • 0x00-0x5F

My fetch stage is heavily based on my combined fetch/decode from warm-up 2. (you can see the leftover infrastructure commented out.) As the process of implementing more instructions stretched on, I elected to implement fewer instructions so that I could move on to other pipeline stages. I have a writeback pathway implemented for branch instructions, althought since I cannot fetch or decode branch instructions, this remains untested.

TODO:

  • fetch the rest of the instruction set
  • test the PC input

Decode

Implemented instructions:

  • 0x00-0x5F

Again, this is heavily based on my warm-up 2 submission.

TODO:

  • decode the rest of the instruction set

Memory

My memory stage contains the register file within it for reading the operand values. It also determines which register is the destination register for the instruction and marks that register as dirty. If one of the source registers is marked as dirty, this stage stalls until it is marked as clean again by the writeback stage

TODO:

  • implement communication with the memory module for LOAD instructions

Execute

Implemented instructions:

  • XOR

My execute stage contains the alu from warm-up 1, for the intended purpose of executing aritmetic instructions. However, I chose to forgo hooking up the alu module so that I could spend more time working on other modules. I only implemented the XOR instruction as it is the first instruction in all my test files (the classic xor %ebp, %ebp to zero it out).

TODO:

  • implement more than just XOR

Writeback

My writeback module is just about the bare minimum needed to be called a ``writeback'' module. The only implemented feature is to writeback the PC from a branch instruction, although I did not implement branch instructions so this is untested.

TODO:

  • implement memory writeback
  • implement regfile writeback

Conclusion

This project was extremely interesting to me. I only wish that I had devoted the time it deserved to it. I'm definitely considering finishing up this project over the summer for my own edification.

Global TODO:

  • implement pipeline flush mechanism
  • implement stack for POP/PUSH instructions
  • implement I-cache and D-cache