// Sets the registers with the alu's output according to
// the given instruction
// Throws ProgramException if destination contains M and A contains
// an illegal address.
protected void setDestination(short instruction) throws ProgramException {
boolean destA = (instruction & 0x0020) > 0;
boolean destD = (instruction & 0x0010) > 0;
boolean destM = (instruction & 0x0008) > 0;
if (destM) {
int address = A.get();
if ((address < 0) || (address >= M.getSize())) {
throw new ProgramException(
"At line "
+ PC.get()
+ ": Destination is M but A="
+ address
+ " is an illegal memory address.");
}
A.setUpdatePointer(true);
bus.send(alu, 2, M, address);
A.setUpdatePointer(false);
}
if (destA) {
bus.send(alu, 2, A, 0);
}
if (destD) {
bus.send(alu, 2, D, 0);
}
}
// sends a value from the appropriate stack (at sp-1) to the ram at the given index
// and increments sp.
private void popToRAM(int stackID, int index) throws ProgramException {
short newSP = (short) (getSP() - 1);
bus.send((stackID == MAIN_STACK ? stackSegment : workingStackSegment), newSP, ram, index);
checkSP(newSP);
setSP(newSP);
}
// Push a value from the calculator at the given index into the appropriate stack.
private void pushFromCalculator(int stackID, int index) throws ProgramException {
short sp = getSP();
bus.send(calculator, index, (stackID == MAIN_STACK ? stackSegment : workingStackSegment), sp);
checkSP((short) (sp + 1));
setSP((short) (sp + 1));
}
// sends a value from the appropriate stack (at sp-1) to the given segment at the given index
// and increments sp.
private void popToSegment(int stackID, short segmentCode, int index) throws ProgramException {
short newSP = (short) (getSP() - 1);
MemorySegment segment =
(segmentCode == HVMInstructionSet.STATIC_SEGMENT_CODE)
? staticSegment
: segments[segmentCode];
checkSegmentIndex(segment, segmentCode, index);
bus.send((stackID == MAIN_STACK ? stackSegment : workingStackSegment), newSP, segment, index);
checkSP(newSP);
setSP(newSP);
}
// sends a value from the given segment at the the given index to the appropriate stack (at sp)
// and increments sp.
private void pushFromSegment(int stackID, short segmentCode, int index) throws ProgramException {
short sp = getSP();
MemorySegment segment =
(segmentCode == HVMInstructionSet.STATIC_SEGMENT_CODE)
? staticSegment
: segments[segmentCode];
checkSegmentIndex(segment, segmentCode, index);
bus.send(segment, index, (stackID == MAIN_STACK ? stackSegment : workingStackSegment), sp);
checkSP((short) (sp + 1));
setSP((short) (sp + 1));
}
// computes the exp part of the given instruction.
// The result will be at the alu's output.
// Throws ProgramException if the calculation involves M and A contains
// an illegal address.
protected void computeExp(short instruction) throws ProgramException {
boolean indirect = (instruction & 0x1000) > 0;
boolean zd = (instruction & 0x0800) > 0;
boolean nd = (instruction & 0x0400) > 0;
boolean zm = (instruction & 0x0200) > 0;
boolean nm = (instruction & 0x0100) > 0;
boolean f = (instruction & 0x0080) > 0;
boolean no = (instruction & 0x0040) > 0;
try {
alu.setCommand(
assemblerTranslator.getExpByCode((short) (instruction & 0xffc0)), zd, nd, zm, nm, f, no);
} catch (AssemblerException ae) {
}
bus.send(D, 0, alu, 0); // sends D to input0 of the alu
// sends A or M[A] to input1 of the alu
if (indirect) {
int address = A.get();
if ((address < 0) || (address >= M.getSize())) {
throw new ProgramException(
"At line "
+ PC.get()
+ ": Expression involves M but A="
+ address
+ " is an illegal memory address.");
}
A.setUpdatePointer(true);
bus.send(M, address, alu, 1);
A.setUpdatePointer(false);
} else {
bus.send(A, 0, alu, 1);
}
alu.compute();
}
// Sets the program counter (if necessary) according to
// the given instruction and the alu's output.
// If the program counter was changed, returns true, otherwise false.
// Throws ProgramException if the program counter should be changed and A
// contains an illegal address.
protected boolean checkJump(short instruction) throws ProgramException {
boolean jumpNegative = (instruction & 0x0004) > 0;
boolean jumpEqual = (instruction & 0x0002) > 0;
boolean jumpPositive = (instruction & 0x0001) > 0;
boolean changed = false;
short exp = alu.getValueAt(2);
if (((exp < 0) && jumpNegative) || ((exp == 0) && jumpEqual) || ((exp > 0) && jumpPositive)) {
int newPC = A.get();
if ((newPC < 0) || (newPC >= Definitions.ROM_SIZE)) {
throw new ProgramException(
"At line "
+ PC.get()
+ ": Jump requested but A="
+ newPC
+ " is an illegal program address.");
}
bus.send(A, 0, PC, 0);
changed = true;
}
return changed;
}
/**
* Executes the current instruction (ROM at pc). Throws ProgramException if the current
* instruction is illegal or if it causes an illegal effect (read/write from M when A is an
* illegal address or jump when A is an illegal address).
*/
public void executeInstruction() throws ProgramException {
short instruction = rom.getValueAt(PC.get());
boolean pcChanged = false;
if ((instruction & 0x8000) == 0) {
bus.send(rom, PC.get(), A, 0);
} else if ((instruction & 0xe000) == 0xe000) {
computeExp(instruction);
setDestination(instruction);
pcChanged = checkJump(instruction);
} else if (instruction != HackAssemblerTranslator.NOP) {
throw new ProgramException("At line " + PC.get() + ": Illegal instruction");
}
if (!pcChanged) {
short newPC = (short) (PC.get() + 1);
if ((newPC < 0) || (newPC >= Definitions.ROM_SIZE)) {
throw new ProgramException("At line " + PC.get() + ": Can't continue past last line");
}
PC.setValueAt(0, newPC, true);
}
time++;
}
/** Returns the value of the function to the top of the stack. */
public void returnFromFunction() throws ProgramException {
// make sure that there's somewhere to return to (old local <> 0)
if (stackSegment.getValueAt(Definitions.LOCAL_POINTER_ADDRESS) == 0)
throw new ProgramException(
"Nowhere to return to in "
+ getCallStack().getTopFunction()
+ "."
+ getCurrentInstruction().getIndexInFunction());
// done in order to clear the method stack's contents
workingStackSegment.setStartAddress(getSP());
bus.send(ram, Definitions.LOCAL_POINTER_ADDRESS, ram, Definitions.R13_ADDRESS); // R13 = lcl
bus.send(
stackSegment,
stackSegment.getValueAt(Definitions.LOCAL_POINTER_ADDRESS) - 5,
ram,
Definitions.R14_ADDRESS); // R14 = return address
bus.send(
stackSegment,
getSP() - 1,
stackSegment,
ram.getValueAt(Definitions.ARG_POINTER_ADDRESS)); // *arg = return value
setSP((short) (ram.getValueAt(Definitions.ARG_POINTER_ADDRESS) + 1)); // SP = arg + 1
bus.send(
stackSegment,
ram.getValueAt(Definitions.R13_ADDRESS) - 1,
ram,
Definitions.THAT_POINTER_ADDRESS); // that = *(R13 - 1)
bus.send(
stackSegment,
ram.getValueAt(Definitions.R13_ADDRESS) - 2,
ram,
Definitions.THIS_POINTER_ADDRESS); // this = *(R13 - 2)
bus.send(
stackSegment,
ram.getValueAt(Definitions.R13_ADDRESS) - 3,
ram,
Definitions.ARG_POINTER_ADDRESS); // arg = *(R13 - 3)
bus.send(
stackSegment,
ram.getValueAt(Definitions.R13_ADDRESS) - 4,
ram,
Definitions.LOCAL_POINTER_ADDRESS); // lcl = *(R13 - 4)
// removes the top function from the call stack
callStack.popFunction();
// check whether there is a "calling frame"
if (stackFrames.size() > 0) {
// retrieve stack frame address of old function
int frameAddress = ((Integer) stackFrames.lastElement()).intValue();
stackFrames.removeElementAt(stackFrames.size() - 1);
workingStackSegment.setStartAddress(frameAddress);
// disable non relevant range of the local segment - enable only the locals
// of the function that we returned to.
localSegment.setEnabledRange(
Math.max(localSegment.getStartAddress(), Definitions.STACK_START_ADDRESS),
frameAddress - 1,
true);
// enable in the arg segment only the number of args that were sent to the function
// that we returned to.
argSegment.setEnabledRange(
argSegment.getStartAddress(), localSegment.getStartAddress() - 6, true);
// enable this, that according to their retrieved pointers
thisSegment.setEnabledRange(
Math.max(thisSegment.getStartAddress(), Definitions.HEAP_START_ADDRESS),
Definitions.HEAP_END_ADDRESS,
true);
thatSegment.setEnabledRange(
Math.max(thatSegment.getStartAddress(), Definitions.HEAP_START_ADDRESS),
Definitions.SCREEN_END_ADDRESS,
true);
} /* else {
error("Nowhere to return to");
} */
// Allow return if we previously had "function" even with no call -
// For the SimpleFunction test
short returnAddress = ram.getValueAt(Definitions.R14_ADDRESS);
if (returnAddress == VMProgram.BUILTIN_FUNCTION_ADDRESS) {
staticSegment.setEnabledRange(0, -1, true); // empty static segment
builtInFunctionsRunner.returnToBuiltInFunction(popValue(METHOD_STACK));
} else if (returnAddress >= 0 && returnAddress < program.getSize()) {
// sets the static segment range
if (stackFrames.size() > 0) {
setStaticRange(callStack.getTopFunction());
} else {
staticSegment.setStartAddress(Definitions.VAR_START_ADDRESS);
staticSegment.setEnabledRange(
Definitions.VAR_START_ADDRESS, Definitions.VAR_END_ADDRESS - 1, true);
}
program.setPC((short) (returnAddress - 1)); // set previousPC correctly
program.setPC(returnAddress); // pc = *sp
} else {
error("Illegal return address");
}
}