Evensgn_RISC-V-CPU/README.md

# RISC-V CPU

Zhou Fan (范舟)

This project is a RISC-V CPU with 5-stage pipeline implemented in Verilog HDL, which is a course project of Computer Architecture, ACM Class @ SJTU.

## Documents

* My [**Project Report**](doc/project-report.pdf)
* My [blog post](http://blog.evensgn.com/riscv-gnu-toolchain/) for installation and usage of RISV-V GNU toolchain (In Chinese) ([on GitHub](doc/riscv-toolchain-installation-usage.md))
* [RISC-V 32I subset](doc/inst-supported.md) supported in this CPU project

## Design
 Feature | RISC-V CPU
--- | ---
ISA | RISC-V ([RV32I subset](doc/inst-supported.md))
Pipelining | 5 stages
Data forwarding | √
Cache | N-way set associate I-cache and D-cache [1]
UART module | passed simulation [2]
Security | perfect proof against Meltdown and Spectre attack [3]

- [1] The cache is based on [Zhekai Zhang's code](https://github.com/sxtyzhangzk/mips-cpu/blob/master/src/cpu/cache.v)
- [2] UART module has not passed test on FPGA yet for the limited time. I re-designed part of CPU code to avoid hidden danger on FPGA, and it may need some more debugging.
- [3] Just kidding ;-) That's because the CPU is not with branch prediction or out-of-order execution.

This CPU project has a five stage pipeline with data forwarding.
In the picture below, red paths show stall control flow, while orange ones show data forwarding path.
![cpu-pipeline-graph](doc/cpu-pipeline-graph.png)

For program test on FPGA without capable memory, this CPU uses UART protocol to communicate with PC, where runs a memory simulator.
![uart-simulate-memory](doc/uart-simulate-memory.png)

## Simulation
This CPU is simulated with UART communication module in Xilinx vivado.
![test-bench-wave](doc/test-bench-wave.png)

## Implementation
Implementation on Basys3 FPGA, using Xilinx vivado.
![implementation-graph](doc/implementation-graph.png)
Scematic Overview
![implementation-circuit-overview](doc/implementation-circuit-overview-captioned.png)
CPU Module Scematic
![implementation-circuit-cpu](doc/implementation-circuit-cpu.png)

## References

* 雷思磊. 自己动手写 CPU. 电子工业出版社, 2014.
* John L. Hennessy, David A. Patterson, et al. Computer Architecture: A Quantitative
Approach, Fifth Edition, 2012.
* David A. Patterson. PPT of CS252 Graduate Computer Architecture, 2001.
* [Zhekai Zhang's CPU project](https://github.com/sxtyzhangzk/mips-cpu)
* [Verilog: always @ Blocks by Chris Fletcher](doc/Always@.pdf)