MIPS Studio

An interactive MIPS assembly interpreter in HTML5/JavaScript

Currently, it is capable of:

• Parsing .data sand .text segments into executable
• Parsing and running most common MIPS instructions/pseudoinstructions
• Single-step or bulk interpetation of instructions
• Providing useful errors and output

Try it out via the testbed (test.s is an excellant sample MIPS program)! To run the testbed:

• Run "npm install mongodb" from your MIPSStudio directory to install the necessary node module
• Start up MongoDB (see comments in server.js for an example command)
• Run "node server.js" to start the server
• Navigate to localhost:1337 in your browser.

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Compilation

To compile for use with require.js: run "python compile.py" to create mips.js.

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Usage

With require (assuming mips.js is in the same diretory as the calling script):

require(["mips"], function(MIPS) {
	var text = "mips code here";
	// 'text' is the MIPS we want to parse/run as a javascript string
	var parse_result = MIPS.Parser.parse(text);

	// check for errors
	if(!parse_result.error) {
		// Create the runtime
		var runtime = MIPS.Runtime.create(parse_result.data, parse_result.text);

		// Run to completion or error
		var state = runtime.run_to_end();
	}
});

Parser Results

MIPS.Parser.parse(text) will parse the 'text' string and returns an object with properties:

• error: Either boolean 'false' (indicating no error), or an exception object. If an exception is present, none of the following properties will be.
• constants: A hash table mapping constants to their values.
• data: The data segment object. See data.js for more information.
• text: The text segment object. See text.js for more information.

Runtime Usage

MIPS.Runtime.create(data_object, text_object) will create a runtime from the data and text objects returned from the parser. The runtime object has the following methods:

• run_n(int): Runs int cycles, or stops before if the program ends or there is an error. Returns the state after completion.
• run_to_end(): Runs the program until it terminates due to completion or error. Returns the state after completion.
• get_state(): Returns the current state of the runtime.
• reset(): Resets the runtime (and its memory) to its original state.
• toggle_breakpoint(line): Toggles a breakpoint at line

The runtime state object contains the following properties:

• registers: A hash table mapping register names (eg: "PC" or "$5") to their current values
• has_exited: Boolean that indicates whether or not the system has exited (either due to error or program completion)
• cycles: The current number of elapsed cycles.
• data: The current state of the data segment (as a hash table mapping addresses to bytes)
• stack: The current state of the stack segment (as a hash table mapping addresses to bytes)
• error: The current error, or null if none.
• output: A string indicating what the MIPS program has printed to the virtual 'temrinal'
• current_inst: The last executed instruction.
• breakpoints: The current list of breakpoints.
• breaked: True iff execution is stopped at a breakpoint.

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Future Plans

In the (distant) future, I hope to:

• Support .kdata, .ktext, and interrupts
• Support for basic extended addressing modes (eg: "lbu $a0 4+oldest($sp)")
• Support for more isntructions and pseudoinstructions, and more intelligent psuedoinstruction conversion.
• Support for lines with multiple labels
• Support for ".globl" and multiple-file programs/linking
• Protections aginst using $at, .setat, .setnoat

Unfortinately, due to limits in the capabilities of JavaScript, I don't think I'll ever (easily) be able to:

• Acheive 1-to-1 numerical behavior with a real MIPS machine
• Handle floating point numbers (single or double precion) in any fashion
• Handle the HI of a 'mul' instructions correctly.
• A total, complete, proper LR parse and subsequent assembly. Thus, many advanced expressions are not possible (eg: ".space NUM_FLAGS * 2 * 4").