Simmerv

Simmerv is a RISC-V SoC emulator written in Rust and compilable to WebAssembly. It began as a fork of Takahiro's riscv-rust emulator, but has by now been extensively rewritten, making it far more complete and much faster. Ultimately, we expect it to become substantially faster, but this work is delayed until we are able to run standard benchmarks and off-the-shelf Linux distributions.

Online Demo

You can run Linux on the emulator in your browser: online demo is here

Screenshots (somewhat out of date)

Features

• Emulates RISC-V RV64GC_Zba_Zicond processor and peripheral devices (PLIC, CLINT, virtio block device and a UART)
• Targets native and WASM

Instructions/Features support status

• RV64IMAC
• RV64FD (PARTIALLY: flags/rounding modes not complete for all insns)
• RV64Zifencei
• RV64Zicsr
• Svnapot
• Zba (part of "B", RVA22)
• Zbb (part of "B", RVA22)
• Zbs (part of "B", RVA22)
• Zicond
• CSR (nearly complete)
• Sv39, Sv48, Sv57
• Privileged instructions
• [-] PMP (this is intensionally not implemented as it will negatively affect performance)

The emulator supports all instructions listed above but some (like many FP instructions) are not 100% to the spec.

• Boots Buildroot and Debian Trixie
• Linux OpenSBI and legacy BBL boot support

Current Issues Being Worked

• Newer Linux kernel have issues with VirtIO block devices (initramfs works)
• U-boot loads but hangs before hand-off; might be an issue with ELF loading

High Priority Work Post Issues

• Snapshot and resume

• Disk support without an in-memory copy (can WASM support this?)

• Improve the disassembler to recognize pseudo ops like li, mv, ret, etc. (This requires a structural change).

How to run Linux with VirtIO Block Device (/dev/vda)

VERY IMPORTANT: images are stored with git LFS. Install LFS (don't forget git lfs install also) and recheckout if needed. Otherwise the images will be small files with LFS pointers.

$ cargo r -r -- linux/fw_payload.elf -f linux/rootfs.img

or

$ cargo r -r -- -c linux/opensbi/fw_jump.elf,0x80000000 linux/vmlinux,0x80200000 -f linux/rootfs.img

How to run Linux with initramfs (/dev/ram)

Allocate 2 GiB, use a device tree with initramfs at 0xa0000000 and load the initrd2+gdb.cpio binary at that address.

$ (cd linux;cargo r -r -- -m 2048 -d with-initrd.dtb fw_payload.elf initrd2+gdb.cpio,0xa0000000)

How to run riscv-tests

$ ./run-riscv-tests.sh

How to import and use WebAssembly RISC-V emulator in a web browser

See wasm/web

How to install and use WebAssembly RISC-V emulator npm package

See wasm/npm

Links

Linux RISC-V port

Running 64-bit RISC-V Linux on QEMU

Specifications

• RISC-V ISA
• Virtio Device
• UART
• CLINT, PLIC (SiFive E31 Manual)
• SiFive Interrupt Cookbook