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MIPSEmulator.java
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MIPSEmulator.java
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import java.util.*;
import java.io.*;
/**
* Main class for holding all objects, I/O, and giving directions
*
*/
public class MIPSEmulator {
public Register reg;
public DataSegment data;
public TextSegment instr;
public StackSegment stack;
//Constructor - all executed during object instantiation
public MIPSEmulator(String s) {
reg = new Register();
data = new DataSegment();
instr = new TextSegment();
stack = new StackSegment();
clrscr();
try {
if(s.equals(""))
s = getUserInput("Name of your file: ");
loadFile(s);
} catch (IOException e) {
out("failed loading file");
return;
}
//Initialize register values
reg.pc = instr.getStart();
reg.set(29, 0x7FFFEFFC); //initialize $sp
reg.set(31, -1); // $ra so as to know when to end the program (on jr -1)
reg.set(28, 0x10011000); // set $gp
reg.set(30, 0x7FFFEFFC); // set $fp (not sure if right but never really used)
String opt = getUserInput("Single step (s) or run to complete (c): ");
if(opt.toLowerCase().charAt(0) == 's') {
singleStep();
} else {
runToCompletion();
}
}
public MIPSEmulator() {
this("");
}
/**
* Helper function to output to command line
* @param s Message to be output
* @param newLine Whether or not to use print or println
*/
public static void out(String s, boolean newLine) {
if(newLine) System.out.println(s);
else System.out.print(s);
}
/**
* Overloaded function for out, assumes that we want to print a new line
* @param s
*/
public static void out(String s) {
out(s, true);
}
/**
* Static function to output a message and wait for user input
* @param message message to output before user input
* @return the user inputed string
*/
public static String getUserInput(String message) {
System.out.print(message);
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
String ret = "";
try {
ret = br.readLine();
} catch (IOException ioe) {
System.out.println("IO ERROR");
return "";
}
return ret;
}
/**
* Run all commands loaded into MIPS until program is over
* Do not display commands as they are run
*/
private void runToCompletion() {
int callOut = 0;
// -1 means program is done
while (callOut != -1) {
callOut = instr.run(this, false);
}
}
/**
* Run MIPS Emulator in single step mode
* Display commands as they are run, among other features
* Type h (for help) in this mode to see details of commands
*/
public void singleStep() {
int callOut = 0;
boolean isDone = false;
boolean isValid = false;
int moveForward = 0;
char cmd;
while(!isDone) {
isDone = false;
callOut = 0;
moveForward = 0;
isValid = false;
String instruction = getUserInput("Please type your single step instruction: ").toLowerCase();
clrscr();
if(instruction.length() == 0) {
invalidCommand();
continue;
}
cmd = instruction.charAt(0);
if(cmd == 'p')
isValid = pInstruction(instruction);
else if (cmd == 'd')
isValid = dInstruction(instruction);
else if (cmd == 'q') {
isDone = true;
isValid = true;
} else if (cmd == 'h' || cmd == '?'){
outputHelp();
isValid = true;
} else if (cmd == 's') {
if(instruction.length() <= 2) {
moveForward = 0;
isValid = false;
} else {
String instructionNum = instruction.substring(2);
try{
moveForward = Integer.parseInt(instructionNum);
isValid = true;
} catch (NumberFormatException e) {
moveForward = 0;
isValid = false;
}
}
}
if(!isValid)
invalidCommand();
int i = 0;
while(i < moveForward && !isDone) {
i++;
callOut = instr.run(this, true);
if (callOut == -1)
isDone = true;
}
}
}
/**
* Command used to keep screen cleared except for current and last command.
*/
private void clrscr() {
for(int i = 0; i < 100; i++) {
out("\n");
}
}
/**
* Parse instruction input if it is command involving memory
* @param instruction input from user
* @return boolean for if there was an error in the command
*/
private boolean dInstruction(String instruction) {
if(instruction.length() <= 2) return false;
String[] parts = instruction.split("\\s+");
if(parts.length < 2) return false;
int location = 0;
String address = parts[parts.length-1];
boolean inputHex = false;
int output = 0; //0 is decimal, 1 is binary, 2 is hex;
for(int i = 1; i < parts.length-1; i++) {
if(parts[i].equals("-h"))
inputHex = true;
if(parts[i].equals("-oh"))
output = 2;
if(parts[i].equals("-ob"))
output = 1;
}
if(address.equals("stack")) {
this.stack.printAll();
return true;
}else if (address.equals("data")) {
this.data.printAll();
return true;
} else if(inputHex) {
try {
if(address.startsWith("0x"))
address = address.substring(2);
location = loadHex(address);
address = "0x"+address;
} catch (NumberFormatException e) {
return false;
}
} else {
try{
location = Integer.parseInt(address);
} catch (NumberFormatException e) {
return false;
}
}
String out = "";
if(output == 0)
out = getFromMemory(location, 0) + "";
else if (output == 1)
out = Integer.toBinaryString(getFromMemory(location, 0));
else if (output == 2)
out = "0x"+MIPSEmulator.formatHex(getFromMemory(location, 0));
System.out.println("MEM[ " + address + " ] = " + out);
return true;
}
/**
* Parse instruction input if it is command involving registers
* @param instruction input from user
* @return boolean for if there was an error in the command
*/
private boolean pInstruction(String instruction) {
if(instruction.length() <= 2) return false;
String spec = instruction.substring(2);
int loc = 0;
boolean isInt = true;
try{
loc = Integer.parseInt(spec);
} catch (NumberFormatException e) {
isInt = false;
}
if (spec.equals("all"))
reg.printAll();
else if( isInt || spec.equals("hi") || spec.equals("lo") || spec.equals("pc"))
if (isInt) reg.printReg(loc);
else reg.printReg(spec);
else
return false;
return true;
}
/**
* Display command help
*/
private void outputHelp() {
out("p [#/HI/LO/PC/all] - print registers either specific #, hi, lo, pc, or all registers");
out("d [#/data/stack] - print memory at specific location, default takes a decimal int\n\t-h : take in hex\n\t-oh : output hex\n\t-ob : output binary");
out("s # - execute next # instructions (# is decimal)");
out("q - quit");
}
/**
* Output message if error in user inputed command
*/
private void invalidCommand() {
out("Sorry you typed in an invalid command");
}
/**
* Load instructions and static data from file into data and instr objects
* @param filename file to read for hexadecimal formatted commands and data
* @throws IOException throws exception in case of error reading the file
*/
public void loadFile(String filename) throws IOException {
System.out.println("load file");
BufferedReader in = new BufferedReader(new FileReader(filename));
String line = "";
int i = 0;
boolean hasStartedStaticData = false;
while((line = in.readLine()) != null) {
if(line.equals("DATA SEGMENT")) {
hasStartedStaticData = true;
} else if(!line.startsWith("0x")) {
System.out.println("ERROR on line "+ i + ": " + line);
} else {
if(hasStartedStaticData) {
String[] nums = line.split(" ");
int loc = loadHex(nums[0].substring(2));
int val = loadHex(nums[1].substring(2));
this.setMemory(loc, 0, val);
} else {
line = line.substring(2);
int val = loadHex(line);
instr.add((Integer)val);
}
}
i++;
}
in.close();
}
/**
* Get a value from memory
* Chooses which block of memory to read from based on memory address
* @param start Location in memory from which to offset from
* @param offset Offset in memory
* @return 32 bit (4 bytes) integer read from memory
*/
public int getFromMemory(int start, int offset) {
if(start >= 0x10010000 && start <= 0x10010000 + 4*1024)
return data.get(start+offset);
if(start <= 0x7FFFEFFF && start >= 0x7FFFEFFF-2*1024)
return stack.get(start+offset);
if(start >= 0x00400000 && start <= 0x00400000 + 2*1024)
return instr.get(start+offset);
return 0;
}
/**
* Set one word, 4 bytes, in memory
* @param start Location in memory from which to offset from
* @param offset Offset in memory
* @param rt 32 bit (4 bytes) integer to set in memory
*/
public void setMemory(int start,int offset, int rt) {
if(start >= 0x10010000 && start <= 0x10010000 + 4*1024)
this.data.set(start+offset, rt);
if(start <= 0x7FFFEFFF && start >= 0x7FFFEFFF-2*1024)
this.stack.set(start+offset, rt);
if(start >= 0x00400000 && start <= 0x00400000 + 2*1024)
this.instr.set(start+offset, rt);
}
/**
* Set a byte of memory to given value
* @param start Location in memory to set
* @param offset Offset from the start location
* @param val 8 bit value to be saved
*/
public void setMemoryByte(int start, int offset, int val) {
val = Memory.getBitsFromVal(val, 0, 7, false);
int word = getFromMemory(start+offset, 0);
int byteOffset= (start+offset) % 4;
word = (Memory.getBitsFromVal(word, 31-8*byteOffset, 31, false) << (31-8*byteOffset)) | (Memory.getBitsFromVal(word, 0, 7*(3-byteOffset), false));
//word = Memory.getBitsFromVal(word, 8, 31, false) << 8;
int newVal = word | (val<<(8*(3-byteOffset)));
this.setMemory(start+offset, 0, newVal);
}
/**
* Read 8 bits from memory
* @param start Memory location
* @param offset Optional offset from memory location
* @param signed Take the byte as a signed or unsigned value
* @return the value at the given location byte is returned as an int
*/
public int getMemoryByte(int start, int offset, boolean signed) {
int word = getFromMemory(start, offset);
int byteOffset = (start+offset) % 4;
int val = Memory.getBitsFromVal(word,24-8*byteOffset,31-8*byteOffset, signed);
return val;
}
/**
* Read a hexidecimal string
* Can't use parseInt because it fails for 8 character values
* @param s String to be parsed
* @return int value from inputed hexadecimal string
* @throws NumberFormatException throws exception if not a true hex string
*/
public static int loadHex(String s) throws NumberFormatException {
int full = 0;
for(int i = 0; i < s.length(); i++) {
int t = Integer.parseInt(s.charAt(i) + "", 16);
full = full << 4;
full = full | t;
}
return full;
}
/**
* Format an int to be output as hexidecimal
* similar to Integer.toHexString() but always 8 characters long
* @param n 32 bit integer to be output as hex
* @return a string of 8 uppercase hexadecimal characters
*/
public static String formatHex(int n) {
String s = Integer.toHexString(n).toUpperCase();
while(s.length() < 8) {
s = "0"+s;
}
return s;
}
/**
* If running from command prompt, can run by:
* java MIPSEmulator a.in
* Otherwise will ask for a filename
* @param args optional first argument can be the filename to bread
*/
public static void main(String[] args) {
String s = "";
if(args.length > 0)
s = args[0];
MIPSEmulator m = new MIPSEmulator(s);
}
}