This repository represents the RISCV Processor Project for the TDT-4255 course at NTNU. This project covers using Chisel to design a simple 32bit RISCV processor using RISCV32I integer instruction set. Please read the entire README before beginning work on this project as it will clarify many details of how the project work is to be carried out.
The project itself is broken into four seperate milestones where each one adds additional functionality to the CPU. Functionality for each milestone is progressive, so it is necessary to complete earlier milestones before proceeded to subsequent ones.
The goal of the first milestone is to establish basic CPU functionality and correctness for simple programs. To facilite this four NOP instructions will be inserted in between each regular instruction so that the CPU does not have to deal with any kind of hazards or forwarding. To get full credit on milestone 1 all “basic” tests must run with NOPs inserted.
Milestone 2 is a simple evolution of milestone 1. To get full credit on milestone 2 all of the RISCV32I instructions should be added to the design, and the full battery of tests in “basic” and “programs” should successfully execute when NOPs are turned on.
For the 3rd milestone NOPs between every instruction are disabled, and the support for pipelining is added so as to increase CPU performance. Getting this working requires adding support to handle RAW Hazards, Control Hazards, and delay after load. To get full credit for milestone 3 NOPs must be turned off, and all tests in “basic” and “programs” must run successfully.
The forth and final milstone represents the culmination of all previous work into a single deisgn while aiming to further increase performance. For the final part of this project students are required to add additional hardware of their own choosing to the CPU to try and make it even faster than what was done in milestone 3. Student have the freedom to choose their own component to work on, though we have several optional suggestions as well. To get full credit on milestone 4 a simple version of at least one of the following hardware upgrades must be implemented, this will need to be explained verbally to a TA during a lab session. Additionally all tests in “basic” and “programs” must run successfully. Finally, your code must be uploaded to the course website where it will be evaluated.
- Branch Prediction
- Fast Branch Handling
- Value Prediction
- Data Cache (Quite Advanced)
To complete this project it is necessary to do the following tasks. They will guide you through setting up the project files, and explain how to start writing th HDL to complete the CPU.
To get started designing your 5-stage RISC-V pipeline first read the introduction section.
When designing your CPU, reference the instructions file. This contains a list of all of the RISCV instructions and their bit layouts that you will evenetually need to add to your deisgn. It is not necessary to read through the whole thing, but it is useful as a reference.
Milestones 1 and 2 are started by reading exercise file. To pass milestone 1 it is necessary to pass the 7 tests located in ./src/test/resources/tests/basic/. For milestone 2 it is necessary to pass all of the tests in “basic” and “programs”.
Milestones 3 and 4 are started by looking at exercise2 file.
Each time you are finished with a milestone and wish to get points is it necessary to come to a lab session. Once there show a TA that all of the necessary tests run successfully. You will likely also be asked a few questions about your code.
In addition to showing the code during lab sessions, it is necessary at the end of the course to upload your final milestone to the course website as a compressed archive such as a zip. Details for this will come at a later date.
Since much of the tooling for HW design is rather difficult to work with this skeleton comes with a lot of reinvented wheels which should make inspecting what is really going on a little clearer.
The FiveStage suite works in the following way:
The Parser parses an assembly test found in the test resource directory. The resulting program can then be loaded on to a VM, or assembled into machine code.
Next the parsed assembly code is run on a virtual machine. Relevant information is then compiled in an execution trace log which shows which instruction was performed at a given step and what the resulting state was.
Next up the chisel design is synthesized into a circuit emulator. The (relatively seamless) test harness provided for your circuit is then used in order to preload the instruction memory with the assembled machinecode, as well as test defined initial memory and register configurations.
As with the VM, your circuit will leave an extensive log which is parsed and used to verify the correctness of your design
If your processor performed the same updates to registers and memory, and terminated at the same address the test is successful.
When a test fails, (or if you have enabled verbose logging) a side by side execution log is shown, allowing you to pinpoint exactly how your processor went wrong.