HiKelChip: A RV64I Implementation in Chisel

Author: Artyom Liu artyomliu@foxmail.com

Introduction

指揮官、わたしがいれば十分ですよ。 --That's the way to comfort the machine spirit *laugh*.

Let's be serious. HikelChip is a project for YSYX project, which is a project aiming to training young chip designers. In the project, each participant is asked to implement his/her own chip design, in ISA of RISC-V. The minimun goal is to support RISC-V I-extension and support simple interrupts like timer interrupt.

And HikelChip is my piece of work participanting in this project. It implements a full implementation of I-extension, and with Zicsr extension too. The chip uses a 5-stage classical implementation, with Fetch, Decode, Issue, Execute and Commit. The chip also implements an interface of standard AXI4 bus protocol, for connecting to peripherals outside the chip itself.

Thanks to the previous work of all YSYX project and Xiangshan project, a mechanic called "Difftest" is introduced in the debugging. With this certain mechanic, we can now connect our implementation to a standard software implementation of RISC-V. By comparing the commit stage of each instruction, bugs in chip design can be found more effeciently.

Prerequirements

To run the programs, with difftest, requires two more repos: NEMU and DRAMsim3. The previous one is meant to be standard implementation for Difftest, while the later one provides an software implementation of DRAM that can be accessed by AXI4 bus. Both these two repos can be cloned from github.

Once the repos are cloned onto local machine, you need to set two environment variables to help the building Makefile script to find the repos: DRAMSIM3_HOME and NEMU_HOME. Both pointing to the root path of relevant repo.

For simulation, we use verilator as the very tool. This is a tool that transfer the given HDL codes into a C++ class, and final build it into an executable file with the help of some user-implement C++ codes. In this sense, to "simulate" the design is to run the executable.

Diagram