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Rust RISC-V Simulator (rrs)

A RISC-V ISS implemented in Rust. Supports the RV32IM instruction set (no exceptions or CSRs yet).

RRS is split into two parts, rrs-lib and rrs-cli


To build an example hello word program and run it on rrs-cli (requires a riscv toolchain):

> make -C ./riscv-sw/examples/hello_world all
> cd rrs-cli
> cargo run -- --binary ../riscv-sw/examples/hello_world/hello_world.bin -l run.log

After execution run.log will contain a trace of ISS execution.


This crate implements the components required for the ISS. Documentation can be generated via rustdoc

> cd rrs-lib
> cargo doc

Once generated it can be found in target/doc/rrs-lib


rrs-lib implements a small number of tests, these can be run with cargo as usual.

> cd rrs-lib
> cargo test


This crate implements a CLI for the ISS, build and run rrs-cli with a --help argument to get full usage instructions.

> cd rrs-cli
> cargo run -- --help

E.g. to execute a binary prog.bin in a 1 MB memory starting at 0x20000000

> cargo run -- --load_addr 20000000 --mem_size 100000 --binary prog.bin

rrs-cli has two special memory locations for output and controlling the simulation.

  • 0x80000000 - Write a character here to output it to stdout
  • 0x80000004 - Write a non zero value here to terminate the simulation

RISC-V software

A RISC-V makefile based build flow with can be found in riscv-sw/build-flow. A RISC-V toolchain will be required, such as the ones available from lowRISC:

The makefile assumes GCC with the prefix riscv32-unknown-elf (which the lowRISC RV32IMC toolchain gives you). Adjust the relevant variables in riscv-sw/Makefile.include if you have something different.

To build the hello_world example in the repository root run:

> make -C ./riscv-sw/examples/hello_world all

This will build a .elf, .bin and .dis file. The .bin is suitable for running on rrs-cli and the .dis is a disassembly.

Using the build flow

To build a new program create a subdirectory under sw/ and create a Makfile with the following contents:

PROG_NAME = [program name here]

include ../Makefile.include # Adjust as required depending on sub-directory

Set PROG_NAME to whatever you want to call the binary. By default all .c and .s files in the directory will be built and linked together. The startup code is in riscv-sw/build-flow/crt0.s and calls the function main. See riscv-sw/Makefile.include for other variables that can be set to alter the build.

RISC-V Architectural Tests

rrs passes the M and I suites in the RISC-V architectural tests. To run the suites:

> cd rrs-cli
> cargo build
> cd ..
> make -C ./vendor/riscv-arch-test/ TARGETDIR=`pwd`/riscv-sw/tests/riscv-arch-test-target RISCV_TARGET=rrs RISCV_DEVICE=M
> make -C ./vendor/riscv-arch-test/ TARGETDIR=`pwd`/riscv-sw/tests/riscv-arch-test-target RISCV_TARGET=rrs RISCV_DEVICE=I


I've written about rrs on my blog, see:


Rust RISC-V Simulator




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