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.
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.
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.
The following is a feature comparison of CPUlator with some popular simulators used for teaching.
|CPUlator||MARS 4.5||QtSPIM 9.1.20||ARMSim# 1.91||ARMSim# 2.1|
|No installation required|
|Platform||Web browser||Java JRE||Windows, OSX, Linux||.NET 3.0||.NET 3.0|
|C or other languages|
|Step over function|
|Step out of function|
|Modify registers||(except pc)|
|Show call stack|
|Runtime calling convention checks|
|Instruction sets||MIPS32 r5|
|Memory model||4 GB flat||5 segments||5 segments||1 segment||1 segment|
|Maximum usable memory||2042 MB||4+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
|Simulation speed (Minst/second)||13||3||10||2||3|