JsSpim (link: https://shawnzhong.github.io/JsSpim/) is an online MIPS32 simulator based on Prof. James Larus’s Spim.

Spim is a self-contained simulator that runs MIPS32 programs. It reads and executes assembly language programs written for this processor. Spim also provides a simple debugger and minimal set of operating system services. Spim does not execute binary (compiled) programs.

Spim implements almost the entire MIPS32 assembler-extended instruction set. (It omits most floating point comparisons and rounding modes and the memory system page tables.) The MIPS architecture has several variants that differ in various ways (e.g., the MIPS64 architecture supports 64-bit integers and addresses), which means that Spim will not run programs for all MIPS processors.

The source code is published at GitHub



Screen Record


  • Click on an instruction to toggle breakpoint
  • Use the range slider to control the execution speed
  • Highlight on changed registers, data segment, and stack
  • Radix support for all values

Built With

  • Spim – The original simulator written in C++
  • Emscripten – Toolchain to compile C++ source code to WebAssembly using the LLVM IR.
  • Bootstrap – Using the CSS library to build the UI
  • highlight.js – For highlighting the source code

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