CPUlator Computer System Simulator

CPUlator is a Nios II, ARMv7, and MIPS simulator of a computer system (processor and I/O devices) and debugger that runs in a modern web browser. It is designed as a tool for learning assembly-language programming and computer organization.

To start using CPUlator now, choose a computer system to simulate, then follow the link.

To learn more, try a sample program in the simulator (Help → Sample programs), or see the documentation.

New! Added MIPS32 release 5 ISA (2018/11/23) — MIPS32 release 6 (2014) made major changes to the instruction set and broke compatibility with all earlier MIPS ISA versions, but courses still use (much) older MIPS versions. Conversely, MIPS32 release 5 is (almost) a superset of earlier MIPS versions. The newly-added MIPS32r5 simulation model should make CPUlator more compatible with SPIM, MARS, and the MIPS dialects being taught in courses.

Choose a system to simulate

Architecture

System

Features

Nios II, ARMv7, and MIPS Simulator?

It turns out that writing a CPU simulator (or four) is relatively easy. The difficult part is creating a full-featured debugger with a usable and efficient user interface. Thus, CPUlator supports several instruction sets, while reusing the same debugging and UI infrastructure.

The simulator was first written for Nios II in January 2016, for use at the University of Toronto. Support for ARMv7 was added fall 2016, and MIPS32r6 was added in January 2018. MIPS32 release 5 was added November 2018 because it turns out release 6 is incompatible with all earlier MIPS instruction sets, and nobody teaches with r6 yet.

Comparison Chart

The following is a feature comparison of CPUlator with some popular simulators used for teaching.

CPUlatorMARS 4.5QtSPIM 9.1.20ARMSim# 1.91ARMSim# 2.1
No installation required
PlatformWeb browserJava JREWindows, OSX, Linux.NET 3.0.NET 3.0
Free
Open-source
Editor
Code completionn/an/an/a
AssemblerGNUcustomcustomcustomGNU
C or other languages
Debugger
Breakpoints
Single-step
Reverse step
Step over function
Step out of function
Modify registers(except pc)
Modify memory
Show call stack
Runtime calling convention checks
Data watchpoints
Instruction setsMIPS32 r5
MIPS32 r6
ARMv7
Nios II
MIPS32MIPS32ARMv5ARMv5
Self-modifying codemaybemaybe
MMU
FPU
Memory model4 GB flat5 segments5 segments1 segment1 segment
Maximum usable memory2042 MB4+4+4 MB data
4+4 MB code
4+1+0.5 MB data
256+64 KB code
64 KB data
512 MB code
96 KB data
512 MB code
I/O devices
Terminal
File I/O
Other devices
Simulation speed (Minst/second)1331023

Looking for the previous version?

CPUlator v1 is here.