jMIPS: A Beginner’s Guide to Installation and First StepsjMIPS is a Java-based simulator and teaching tool for the MIPS assembly language. It provides a GUI environment where learners can write, assemble, run, and debug MIPS programs without needing physical hardware. This guide walks you through installing jMIPS, understanding its interface, writing your first programs, and using basic debugging and educational features.
What is jMIPS and who should use it
jMIPS emulates the MIPS instruction set architecture (ISA) and provides tools tailored for students learning assembly language and computer architecture. It’s useful for:
- Computer science students learning low-level programming and processor concepts.
- Instructors preparing lab exercises and demonstrations.
- Hobbyists exploring ISA design and assembly coding.
Key benefits: simplicity of setup, cross-platform availability (because it runs on Java), visualization tools for registers and memory, and an integrated assembler and debugger.
System requirements
jMIPS is written in Java, so you need a compatible Java Runtime Environment (JRE) or Java Development Kit (JDK).
- Java 8 or later (JRE/JDK) installed.
- At least 200 MB of free disk space for the tool and sample files.
- A modern OS: Windows, macOS, or Linux.
Check your Java version with:
java -version If Java isn’t installed, download and install OpenJDK or Oracle JDK appropriate for your OS.
Downloading jMIPS
- Locate the official jMIPS distribution or repository. Many academic projects host jMIPS on university websites or open-source platforms.
- Download the latest stable release (usually a ZIP or JAR file). If you find a source repository, you may need to build from source using Maven or Gradle—follow repository instructions.
Note: If you can’t find a maintained binary, building from source is common—Java projects typically include README instructions for compiling.
Installation steps
For a typical binary JAR distribution:
- Place the downloaded jMIPS JAR file in a folder you’ll remember (e.g., ~/apps/jmips).
- Make sure Java is installed (see System requirements).
- Run jMIPS with:
java -jar jmips.jarOn Windows you can double-click the JAR if .jar files are associated with Java.
For building from source:
- Clone the repository:
git clone <repository-url> cd jmips - Build with the provided build tool (example using Maven):
mvn package java -jar target/jmips.jar
First launch and project setup
On first launch you’ll see the main jMIPS window with several panels: source editor, registers view, memory view, console/output, and controls for assembling and running.
- Create a new file (File → New) and save it with a .asm or .s extension.
- Set your project or working directory for sample programs and I/O files.
Familiarize yourself with the toolbar: Assemble, Step, Run, Reset, Breakpoints, and Memory/Registers refresh.
Writing your first MIPS program
Start with a simple “Hello, World!” equivalent that writes to the console using syscalls.
Example program (write to console):
.data msg: .asciiz "Hello, jMIPS! " .text .globl main main: la $a0, msg # load address of msg into $a0 li $v0, 4 # syscall 4 = print_string syscall li $v0, 10 # syscall 10 = exit syscall - Paste this into the editor, save, and click Assemble.
- If assembly succeeds, click Run to execute. The console/output pane should display the message.
Assembling and running
- Assemble: translates your assembly code into machine code; errors appear in a message pane.
- Run: executes the program continuously until completion or until a breakpoint.
- Step/Step Over/Step Into: use these to execute instructions one at a time—helpful for learning how the CPU state changes.
- Reset: clears registers/memory and program counter so you can re-run from a clean state.
Understanding the interface panels
- Registers panel: shows general-purpose registers (\(t0–\)t9, \(s0–\)s7, \(a0–\)a3, \(v0–\)v1, $pc, hi, lo). Values update as instructions execute.
- Memory panel: lets you inspect memory segments (text, data, stack). You can edit memory directly in many versions—use carefully.
- Console/output: displays program output and syscall interactions.
- Breakpoints: set breakpoints by clicking the gutter next to a line number; execution will pause when the PC reaches that address.
Common beginner exercises
- Simple arithmetic: add, subtract, multiply two numbers and print results.
- Branching: implement conditional logic using beq, bne, slt and test different inputs.
- Loops: create loop constructs with labels and branch instructions to sum arrays.
- Function calls: write simple functions using jal and jr with stack-based saving of $ra and callee-saved registers.
Example: loop to sum array
.data arr: .word 5,10,15,20 n: .word 4 sum: .word 0 .text .globl main main: la $t0, arr # pointer to array lw $t1, n # n li $t2, 0 # index li $t3, 0 # sum loop: beq $t2, $t1, done lw $t4, 0($t0) add $t3, $t3, $t4 addi $t0, $t0, 4 addi $t2, $t2, 1 j loop done: # store sum into memory or print via syscall move $a0, $t3 li $v0, 1 syscall li $v0, 10 syscall Debugging tips
- Use breakpoints to inspect register and memory state at key moments.
- Step through suspicious sections to see exact changes.
- Watch the stack pointer (\(sp) and return address (\)ra) when calling functions.
- Keep console/logging messages with syscalls to trace runtime behavior.
Customizing jMIPS
- Preferences: change font size, assembler options, or default directories.
- Plugins/extensions: some distributions support additional visualization tools or assignment loaders—check documentation.
- Keybindings: learn shortcuts for Assemble, Run, Step to speed workflow.
Troubleshooting common issues
- “Java not found” — install or add Java to PATH.
- Assembly errors — read the error message, check line numbers and syntax (labels, directives like .data/.text).
- Program prints nothing — ensure syscalls use correct codes and registers (e.g., $v0 for syscall number).
- Incorrect values — check endianness assumptions, data directives (.word/.byte), and addressing.
Next steps and learning resources
- Work through example exercises: arithmetic, loops, recursion, and simple OS syscalls.
- Read a MIPS reference or textbook chapter to understand calling conventions and pipeline behavior.
- Compare behavior with other simulators like SPIM or MARS to see differences.
jMIPS is a lightweight, approachable environment for learning MIPS assembly. With the steps above you should be able to install, run, and start exploring assembly programs.
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