Fuxi

Fuxi (伏羲) is a 32-bit pipelined RISC-V processor written in Chisel.

Implemented ISAs

• RV32I 2.1
• Zifencei extension 2.0
• Zicsr extension 2.0
• M extension 2.0
• A extension 2.0
• Machine-level ISA 1.11
• Supervisor-level ISA 1.11

Unimplemented Details

Fuxi processor is designed for running GeeOS, or other simple operating systems or bare-metal software. Considering the complexity, the following functions has not yet been implemented:

• Memory privilege in mstatus register: MPRV bit and MXR bit are hardwired to 0.
• Virtualization support in mstatus register: TVM bit, TW bit and TSR bit are hardwired to 0.
• Physical Memory Protection: all PMP registers are hardwired to 0.

Performance

With default configuration:

• Dhrystone 2.1: 0.60 DMIPS/MHz.
• CoreMark: 2.15 CoreMark/MHz.

Getting Started

Fuxi currently targets Chisel 7.13.0 and Scala 2.13.18. JDK 17 and sbt are recommended for building it; running the unit tests also requires Verilator.

By issuing the following command lines, you can get generated verilog file in directory verilog/build:

$ git clone https://github.com/MaxXSoft/Fuxi
$ cd Fuxi
$ make

Running Tests

Running Unit Tests

All unit tests are available in directory src/test/scala. For example, unit test for decode stage is available in core/DecoderTest.scala, you can run this test by executing the following command lines:

$ sbt
> Test / runMain core.DecoderTest

Running CoreTest

CoreTest is a special unit test provided in this repository, it can run simple RISC-V programs using the Fuxi core. We also provided some programs in directory src/test/resources. For example, you can run one of it:

$ sbt
> Test / runMain core.CoreTest -if src/test/resources/fib.txt

Trace information during running program fib.txt will be printed to the console.

CoreTest supports the following command line arguments:

Option	Abbreviation	Argument	Description
--init-file	-if	path to program file	Specify the initialization file of ROM.
--trace-file	-tf	path to trace file	Specify the trace file, default to empty.
--gen-trace	-gt	0 or other values	Set to 0 for trace comparison, otherwise use Fuxi core to generate trace file. Default to 0.

So you can test the core using a trace file generated by other processor or emulator:

> Test / runMain core.CoreTest -if src/test/resources/fib.txt -tf src/test/resources/fib_trace.txt

For other details, please read the source file of CoreTest.scala.

All provided programs:

Name	Description
fib.txt	Generate the first 10 terms of the Fibonacci sequence.
mdu.txt	Perform some multiplications and divisions.
mecall.txt	Test machine mode environment call.
secall.txt	Test supervisor mode environment call.

Copyright and License

Copyright (C) 2020-2026 MaxXing. License GPLv3.

Special thanks to @Yukiteru Lee.