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f174f0312fe0c5ae33113ef23b7613221de27f2b
ksymon/src/main/java/com/loomcom/symon/Cpu.java
T
Seth Morabito f174f0312f * Correct implementation of Indirect Indexed and Indexed Indirect addressing modes. 
* Unit tests for Indirect Indexed and Indexed Indirect.
* Updated copyright dates.
* Started moving to JUnit 4.
2010-01-15 08:20:03 +00:00

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package com.loomcom.symon;
import com.loomcom.symon.InstructionTable;
import com.loomcom.symon.exceptions.MemoryAccessException;
/**
* Main 6502 CPU Simulation.
*/
public class Cpu implements InstructionTable {
public static final int DEFAULT_BASE_ADDRESS = 0x200;
/* Process status register mnemonics */
public static final int P_CARRY = 0x01;
public static final int P_ZERO = 0x02;
public static final int P_IRQ_DISABLE = 0x04;
public static final int P_DECIMAL = 0x08;
public static final int P_BREAK = 0x10;
// Bit 5 is always '1'
public static final int P_OVERFLOW = 0x40;
public static final int P_NEGATIVE = 0x80;
// NMI vector
public static final int IRQ_VECTOR_L = 0xfffa;
public static final int IRQ_VECTOR_H = 0xfffb;
// Reset vector
public static final int RST_VECTOR_L = 0xfffc;
public static final int RST_VECTOR_H = 0xfffd;
// IRQ vector
public static final int NMI_VECTOR_L = 0xfffe;
public static final int NMI_VECTOR_H = 0xffff;
/* The Bus */
private Bus bus;
/* User Registers */
private int a; // Accumulator
private int x; // X index register
private int y; // Y index register
/* Internal Registers */
private int pc; // Program Counter register
private int sp; // Stack Pointer register, offset into page 1
private int ir; // Instruction register
private int[] args = new int[3]; // Decoded instruction args
private int instSize; // # of operands for the instruction
/* Scratch space for addressing mode and effective address
* calculations */
private int irAddressMode; // Bits 3-5 of IR: [ | | |X|X|X| | ]
private int irOpMode; // Bits 6-7 of IR: [ | | | | | |X|X]
private int effectiveAddress;
private int effectiveData;
/* Internal scratch space */
private int lo = 0, hi = 0; // Used in address calculation
private int tmp; // Temporary storage
/* Unimplemented instruction flag */
private boolean opTrap = false;
private int addr; // The address the most recent instruction
// was fetched from
/* Status Flag Register bits */
private boolean carryFlag;
private boolean negativeFlag;
private boolean zeroFlag;
private boolean irqDisableFlag;
private boolean decimalModeFlag;
private boolean breakFlag;
private boolean overflowFlag;
/**
* Construct a new CPU.
*/
public Cpu() {}
/**
* Set the bus reference for this CPU.
*/
public void setBus(Bus bus) {
this.bus = bus;
}
/**
* Return the Bus that this CPU is associated with.
*/
public Bus getBus() {
return bus;
}
/**
* Reset the CPU to known initial values.
*/
public void reset() throws MemoryAccessException {
// Registers
sp = 0xff;
// Set the PC to the address stored in the reset vector
pc = address(bus.read(RST_VECTOR_L), bus.read(RST_VECTOR_H));
// Clear instruction register.
ir = 0;
// Clear status register bits.
carryFlag = false;
irqDisableFlag = false;
decimalModeFlag = false;
breakFlag = false;
overflowFlag = false;
// Clear illegal opcode trap.
opTrap = false;
}
public void step(int num) throws MemoryAccessException {
for (int i = 0; i < num; i++) {
step();
}
}
/**
* Performs an individual machine cycle.
*/
public void step() throws MemoryAccessException {
// Store the address from which the IR was read, for debugging
addr = pc;
// Fetch memory location for this instruction.
ir = bus.read(pc);
irAddressMode = (ir >> 2) & 0x07;
irOpMode = ir & 0x03;
// Increment PC
incrementPC();
// Clear the illegal opcode trap.
clearOpTrap();
// Decode the instruction and operands
instSize = Cpu.instructionSizes[ir];
for (int i = 0; i < instSize-1; i++) {
args[i] = bus.read(pc);
// Increment PC after reading
incrementPC();
}
// Get the data from the effective address (if any)
// TODO: Proper initialization.
// Using 0xfffffff is to help catch bugs by reading out of bounds.
effectiveAddress = 0xffffff;
effectiveData = -1;
switch(irOpMode) {
case 0:
case 2:
switch(irAddressMode) {
case 0: // #Immediate
effectiveAddress = -1;
effectiveData = args[0];
break;
case 1: // Zero Page
effectiveAddress = args[0];
effectiveData = bus.read(effectiveAddress);
break;
case 2: // Accumulator - ignored
break;
case 3: // Absolute
effectiveAddress = address(args[0], args[1]);
effectiveData = bus.read(effectiveAddress);
break;
case 5: // Zero Page,X / Zero Page,Y
if (ir == 0x96 || ir == 0xb6) {
effectiveAddress = zpyAddress(args[0]);
} else {
effectiveAddress = zpxAddress(args[0]);
}
effectiveData = bus.read(effectiveAddress);
break;
case 7: // Absolute,X / Absolute,Y
if (ir == 0xbe) {
effectiveAddress = yAddress(args[0], args[1]);
} else {
effectiveAddress = xAddress(args[0], args[1]);
}
effectiveData = bus.read(effectiveAddress);
break;
}
break;
case 1:
switch(irAddressMode) {
case 0: // (Zero Page,X)
tmp = args[0] + getXRegister();
effectiveAddress = address(bus.read(tmp), bus.read(tmp + 1));
effectiveData = bus.read(effectiveAddress);
break;
case 1: // Zero Page
effectiveAddress = args[0];
effectiveData = bus.read(effectiveAddress);
break;
case 2: // #Immediate
effectiveAddress = -1;
effectiveData = args[0];
break;
case 3: // Absolute
effectiveAddress = address(args[0], args[1]);
effectiveData = bus.read(effectiveAddress);
break;
case 4: // (Zero Page),Y
tmp = address(bus.read(args[0]),
bus.read((args[0]+1)&0xff));
effectiveAddress = (tmp + getYRegister())&0xffff;
effectiveData = bus.read(effectiveAddress);
break;
case 5: // Zero Page,X
effectiveAddress = zpxAddress(args[0]);
effectiveData = bus.read(effectiveAddress);
break;
case 6: // Absolute, Y
effectiveAddress = yAddress(args[0], args[1]);
effectiveData = bus.read(effectiveAddress);
break;
case 7: // Absolute, X
effectiveAddress = xAddress(args[0], args[1]);
effectiveData = bus.read(effectiveAddress);
break;
}
break;
}
// Execute
switch(ir) {
/** Single Byte Instructions; Implied and Relative **/
case 0x00: // BRK - Force Interrupt - Implied
if (!getIrqDisableFlag()) {
// Set the break flag before pushing.
setBreakFlag();
// Push program counter + 2 onto the stack
stackPush((pc+2 >> 8) & 0xff); // PC high byte
stackPush(pc+2 & 0xff); // PC low byte
stackPush(getProcessorStatus());
// Set the Interrupt Disabled flag. RTI will clear it.
setIrqDisableFlag();
// Load interrupt vector address into PC
pc = address(bus.read(IRQ_VECTOR_L), bus.read(IRQ_VECTOR_H));
}
break;
case 0x08: // PHP - Push Processor Status - Implied
stackPush(getProcessorStatus());
break;
case 0x10: // BPL - Branch if Positive - Relative
if (!getNegativeFlag()) {
pc = relAddress(args[0]);
}
break;
case 0x18: // CLC - Clear Carry Flag - Implied
clearCarryFlag();
break;
case 0x20: // JSR - Jump to Subroutine - Implied
stackPush((pc-1 >> 8) & 0xff); // PC high byte
stackPush(pc-1 & 0xff); // PC low byte
pc = address(args[0], args[1]);
break;
case 0x28: // PLP - Pull Processor Status - Implied
setProcessorStatus(stackPop());
break;
case 0x30: // BMI - Branch if Minus - Relative
if (getNegativeFlag()) {
pc = relAddress(args[0]);
}
break;
case 0x38: // SEC - Set Carry Flag - Implied
setCarryFlag();
break;
case 0x40: // RTI - Return from Interrupt - Implied
setProcessorStatus(stackPop());
lo = stackPop();
hi = stackPop();
setProgramCounter(address(lo, hi));
break;
case 0x48: // PHA - Push Accumulator - Implied
stackPush(a);
break;
case 0x50: // BVC - Branch if Overflow Clear - Relative
if (!getOverflowFlag()) {
pc = relAddress(args[0]);
}
break;
case 0x58: // CLI - Clear Interrupt Disable - Implied
clearIrqDisableFlag();
break;
case 0x60: // RTS - Return from Subroutine - Implied
lo = stackPop();
hi = stackPop();
setProgramCounter((address(lo, hi) + 1) & 0xffff);
break;
case 0x68: // PLA - Pull Accumulator - Implied
a = stackPop();
setArithmeticFlags(a);
break;
case 0x70: // BVS - Branch if Overflow Set - Relative
if (getOverflowFlag()) {
pc = relAddress(args[0]);
}
break;
case 0x78: // SEI - Set Interrupt Disable - Implied
setIrqDisableFlag();
break;
case 0x88: // DEY - Decrement Y Register - Implied
y = --y & 0xff;
setArithmeticFlags(y);
break;
case 0x8a: // TXA - Transfer X to Accumulator - Implied
a = x;
setArithmeticFlags(a);
break;
case 0x90: // BCC - Branch if Carry Clear - Relative
if (!getCarryFlag()) {
pc = relAddress(args[0]);
}
break;
case 0x98: // TYA - Transfer Y to Accumulator - Implied
a = y;
setArithmeticFlags(a);
break;
case 0x9a: // TXS - Transfer X to Stack Pointer - Implied
setStackPointer(x);
break;
case 0xa8: // TAY - Transfer Accumulator to Y - Implied
y = a;
setArithmeticFlags(y);
break;
case 0xaa: // TAX - Transfer Accumulator to X - Implied
x = a;
setArithmeticFlags(x);
break;
case 0xb0: // BCS - Branch if Carry Set - Relative
if (getCarryFlag()) {
pc = relAddress(args[0]);
}
break;
case 0xb8: // CLV - Clear Overflow Flag - Implied
clearOverflowFlag();
break;
case 0xba: // TSX - Transfer Stack Pointer to X - Implied
x = getStackPointer();
setArithmeticFlags(x);
break;
case 0xc8: // INY - Increment Y Register - Implied
y = ++y & 0xff;
setArithmeticFlags(y);
break;
case 0xca: // DEX - Decrement X Register - Implied
x = --x & 0xff;
setArithmeticFlags(x);
break;
case 0xd0: // BNE - Branch if Not Equal to Zero - Relative
if (!getZeroFlag()) {
pc = relAddress(args[0]);
}
break;
case 0xd8: // CLD - Clear Decimal Mode - Implied
clearDecimalModeFlag();
break;
case 0xe8: // INX - Increment X Register - Implied
x = ++x & 0xff;
setArithmeticFlags(x);
break;
case 0xea: // NOP
// Do nothing.
break;
case 0xf0: // BEQ - Branch if Equal to Zero - Relative
if (getZeroFlag()) {
pc = relAddress(args[0]);
}
break;
case 0xf8: // SED - Set Decimal Flag - Implied
setDecimalModeFlag();
break;
/** JMP *****************************************************************/
case 0x4c: // JMP - Absolute
pc = address(args[0], args[1]);
break;
case 0x6c: // JMP - Indirect
lo = address(args[0], args[1]); // Address of low byte
hi = lo+1; // Address of high byte
pc = address(bus.read(lo), bus.read(hi));
/* TODO: For accuracy, allow a flag to enable broken behavior
* of early 6502s:
*
* "An original 6502 has does not correctly fetch the target
* address if the indirect vector falls on a page boundary
* (e.g. $xxFF where xx is and value from $00 to $FF). In this
* case fetches the LSB from $xxFF as expected but takes the MSB
* from $xx00. This is fixed in some later chips like the 65SC02
* so for compatibility always ensure the indirect vector is not
* at the end of the page."
* (http://www.obelisk.demon.co.uk/6502/reference.html#JMP)
*/
break;
/** ORA - Logical Inclusive Or ******************************************/
case 0x01: // (Zero Page,X)
case 0x05: // Zero Page
case 0x09: // #Immediate
case 0x0d: // Absolute
case 0x11: // (Zero Page),Y
case 0x15: // Zero Page,X
case 0x19: // Absolute,Y
case 0x1d: // Absolute,X
a |= effectiveData;
setArithmeticFlags(a);
break;
/** ASL - Arithmetic Shift Left *****************************************/
case 0x0a: // Accumulator
a = asl(a);
setArithmeticFlags(a);
break;
case 0x06: // Zero Page
case 0x0e: // Absolute
case 0x16: // Zero Page,X
case 0x1e: // Absolute,X
tmp = asl(effectiveData);
bus.write(effectiveAddress, tmp);
setArithmeticFlags(tmp);
break;
/** BIT - Bit Test ******************************************************/
case 0x24: // Zero Page
case 0x2c: // Absolute
tmp = a & effectiveData;
setZeroFlag(tmp == 0);
setNegativeFlag((tmp & 0x80) != 0);
setOverflowFlag((tmp & 0x40) != 0);
break;
/** AND - Logical AND ***************************************************/
case 0x21: // (Zero Page,X)
case 0x25: // Zero Page
case 0x29: // #Immediate
case 0x2d: // Absolute
case 0x31: // (Zero Page),Y
case 0x35: // Zero Page,X
case 0x39: // Absolute,Y
case 0x3d: // Absolute,X
a &= effectiveData;
setArithmeticFlags(a);
break;
/** ROL - Rotate Left ***************************************************/
case 0x2a: // Accumulator
a = rol(a);
setArithmeticFlags(a);
break;
case 0x26: // Zero Page
case 0x2e: // Absolute
case 0x36: // Zero Page,X
case 0x3e: // Absolute,X
tmp = rol(effectiveData);
bus.write(effectiveAddress, tmp);
setArithmeticFlags(tmp);
break;
/** EOR - Exclusive OR **************************************************/
case 0x41: // (Zero Page,X)
case 0x45: // Zero Page
case 0x49: // Immediate
case 0x4d: // Absolute
case 0x51: // (Zero Page,Y)
case 0x55: // Zero Page,X
case 0x59: // Absolute,Y
case 0x5d: // Absolute,X
a ^= effectiveData;
setArithmeticFlags(a);
break;
/** LSR - Logical Shift Right *******************************************/
case 0x4a: // Accumulator
a = lsr(a);
setArithmeticFlags(a);
break;
case 0x46: // Zero Page
case 0x4e: // Absolute
case 0x56: // Zero Page,X
case 0x5e: // Absolute,X
tmp = lsr(effectiveData);
bus.write(effectiveAddress, tmp);
setArithmeticFlags(tmp);
break;
/** ADC - Add with Carry ************************************************/
case 0x61: // (Zero Page,X)
case 0x65: // Zero Page
case 0x69: // Immediate
case 0x6d: // Absolute
case 0x71: // (Zero Page),Y
case 0x75: // Zero Page,X
case 0x79: // Absolute,Y
case 0x7d: // Absolute,X
if (decimalModeFlag) {
a = adcDecimal(a, effectiveData);
} else {
a = adc(a, effectiveData);
}
break;
/** ROR - Rotate Right **************************************************/
case 0x6a: // Accumulator
a = ror(a);
setArithmeticFlags(a);
break;
case 0x66: // Zero Page
case 0x6e: // Absolute
case 0x76: // Zero Page,X
case 0x7e: // Absolute,X
tmp = ror(effectiveData);
bus.write(effectiveAddress, tmp);
setArithmeticFlags(tmp);
break;
/** STA - Store Accumulator *********************************************/
case 0x81: // (Zero Page,X)
case 0x85: // Zero Page
case 0x8d: // Absolute
case 0x91: // (Zero Page),Y
case 0x95: // Zero Page,X
case 0x99: // Absolute,Y
case 0x9d: // Absolute,X
bus.write(effectiveAddress, a);
setArithmeticFlags(a);
break;
/** STY - Store Y Register **********************************************/
case 0x84: // Zero Page
case 0x8c: // Absolute
case 0x94: // Zero Page,X
bus.write(effectiveAddress, y);
setArithmeticFlags(y);
break;
/** STX - Store X Register **********************************************/
case 0x86: // Zero Page
case 0x8e: // Absolute
case 0x96: // Zero Page,Y
bus.write(effectiveAddress, x);
setArithmeticFlags(x);
break;
/** LDY - Load Y Register ***********************************************/
case 0xa0: // Immediate
case 0xa4: // Zero Page
case 0xac: // Absolute
case 0xb4: // Zero Page,X
case 0xbc: // Absolute,X
y = effectiveData;
setArithmeticFlags(y);
break;
/** LDX - Load X Register ***********************************************/
case 0xa2: // Immediate
case 0xa6: // Zero Page
case 0xae: // Absolute
case 0xb6: // Zero Page,Y
case 0xbe: // Absolute,Y
x = effectiveData;
setArithmeticFlags(x);
break;
/** LDA - Load Accumulator **********************************************/
case 0xa1: // (Zero Page,X)
case 0xa5: // Zero Page
case 0xa9: // Immediate
case 0xad: // Absolute
case 0xb1: // (Zero Page),Y
case 0xb5: // Zero Page,X
case 0xb9: // Absolute,Y
case 0xbd: // Absolute,X
a = effectiveData;
setArithmeticFlags(a);
break;
/** CPY - Compare Y Register ********************************************/
case 0xc0: // Immediate
case 0xc4: // Zero Page
case 0xcc: // Absolute
cmp(y, effectiveData);
break;
/** CMP - Compare Accumulator *******************************************/
case 0xc1: // (Zero Page,X)
case 0xc5: // Zero Page
case 0xc9: // #Immediate
case 0xcd: // Absolute
case 0xd1: // (Zero Page),Y
case 0xd5: // Zero Page,X
case 0xd9: // Absolute,Y
case 0xdd: // Absolute,X
cmp(a, effectiveData);
break;
/** DEC - Decrement Memory **********************************************/
case 0xc6: // Zero Page
case 0xce: // Absolute
case 0xd6: // Zero Page,X
case 0xde: // Absolute,X
tmp = --effectiveData & 0xff;
bus.write(effectiveAddress, tmp);
setArithmeticFlags(tmp);
break;
/** CPX - Compare X Register ********************************************/
case 0xe0: // Immediate
case 0xe4: // Zero Page
case 0xec: // Absolute
cmp(x, effectiveData);
break;
/** SBC - Subtract with Carry (Borrow) **********************************/
case 0xe1: // (Zero Page,X)
case 0xe5: // Zero Page
case 0xe9: // Immediate
case 0xed: // Absolute
case 0xf1: // (Zero Page),Y
case 0xf5: // Zero Page,X
case 0xf9: // Absolute,Y
case 0xfd: // Absolute,X
if (decimalModeFlag) {
a = sbcDecimal(a, effectiveData);
} else {
a = sbc(a, effectiveData);
}
break;
/** INC - Increment Memory **********************************************/
case 0xe6: // Zero Page
case 0xee: // Absolute
case 0xf6: // Zero Page,X
case 0xfe: // Absolute,X
tmp = ++effectiveData & 0xff;
bus.write(effectiveAddress, tmp);
setArithmeticFlags(tmp);
break;
/** Unimplemented Instructions ****************************************/
default:
setOpTrap();
break;
}
}
/**
* Add with Carry, used by all addressing mode implementations of ADC.
* As a side effect, this will set the overflow and carry flags as
* needed.
*
* @param acc The current value of the accumulator
* @param operand The operand
* @return
*/
public int adc(int acc, int operand) {
int result = (operand & 0xff) + (acc & 0xff) + getCarryBit();
int carry6 = (operand & 0x7f) + (acc & 0x7f) + getCarryBit();
setCarryFlag((result & 0x100) != 0);
setOverflowFlag(carryFlag ^ ((carry6 & 0x80) != 0));
result &= 0xff;
setArithmeticFlags(result);
return result;
}
/**
* Add with Carry (BCD).
*/
public int adcDecimal(int acc, int operand) {
int l, h, result;
l = (acc & 0x0f) + (operand & 0x0f) + getCarryBit();
if ((l & 0xff) > 9) l += 6;
h = (acc >> 4) + (operand >> 4) + (l > 15 ? 1 : 0);
if ((h & 0xff) > 9) h += 6;
result = (l & 0x0f) | (h << 4);
result &= 0xff;
setCarryFlag(h > 15);
setZeroFlag(result == 0);
setNegativeFlag(false); // BCD is never negative
setOverflowFlag(false); // BCD never sets overflow flag
return result;
}
/**
* Common code for Subtract with Carry. Just calls ADC of the
* one's complement of the operand. This lets the N, V, C, and Z
* flags work out nicely without any additional logic.
*
* @param acc
* @param operand
* @return
*/
public int sbc(int acc, int operand) {
int result;
result = adc(acc, ~operand);
setArithmeticFlags(result);
return result;
}
/**
* Subtract with Carry, BCD mode.
*
* @param acc
* @param operand
* @return
*/
public int sbcDecimal(int acc, int operand) {
int l, h, result;
l = (acc & 0x0f) - (operand & 0x0f) - (carryFlag ? 0 : 1);
if ((l & 0x10) != 0) l -= 6;
h = (acc >> 4) - (operand >> 4) - ((l & 0x10) != 0 ? 1 : 0);
if ((h & 0x10) != 0) h -= 6;
result = (l & 0x0f) | (h << 4);
setCarryFlag((h & 0xff) < 15);
setZeroFlag(result == 0);
setNegativeFlag(false); // BCD is never negative
setOverflowFlag(false); // BCD never sets overflow flag
return (result & 0xff);
}
/**
* Compare two values, and set carry, zero, and negative flags
* appropriately.
*
* @param reg
* @param operand
*/
public void cmp(int reg, int operand) {
setCarryFlag(reg >= operand);
setZeroFlag(reg == operand);
setNegativeFlag((reg - operand) > 0);
}
/**
* Set the Negative and Zero flags based on the current value of the
* register operand.
*
* @param reg The register.
*/
public void setArithmeticFlags(int reg) {
zeroFlag = (reg == 0);
negativeFlag = (reg & 0x80) != 0;
}
/**
* Shifts the given value left by one bit, and sets the carry
* flag to the high bit of the initial value.
*
* @param m The value to shift left.
* @return the left shifted value (m * 2).
*/
private int asl(int m) {
setCarryFlag((m & 0x80) != 0);
return (m << 1) & 0xff;
}
/**
* Shifts the given value right by one bit, filling with zeros,
* and sets the carry flag to the low bit of the initial value.
*/
private int lsr(int m) {
setCarryFlag((m & 0x01) != 0);
return (m >>> 1) & 0xff;
}
/**
* Rotates the given value left by one bit, setting bit 0 to the value
* of the carry flag, and setting the carry flag to the original value
* of bit 7.
*/
private int rol(int m) {
int result = ((m << 1) | getCarryBit()) & 0xff;
setCarryFlag((m & 0x80) != 0);
return result;
}
/**
* Rotates the given value right by one bit, setting bit 7 to the value
* of the carry flag, and setting the carry flag to the original value
* of bit 1.
*/
private int ror(int m) {
int result = ((m >>> 1) | (getCarryBit() << 7)) & 0xff;
setCarryFlag((m & 0x01) != 0);
return result;
}
/**
* @return the negative flag
*/
public boolean getNegativeFlag() {
return negativeFlag;
}
/**
* @return 1 if the negative flag is set, 0 if it is clear.
*/
public int getNegativeBit() {
return (negativeFlag ? 1 : 0);
}
/**
* @param register the register value to test for negativity
*/
public void setNegativeFlag(int register) {
negativeFlag = (register < 0);
}
/**
* @param negativeFlag the negative flag to set
*/
public void setNegativeFlag(boolean negativeFlag) {
this.negativeFlag = negativeFlag;
}
public void setNegativeFlag() {
this.negativeFlag = true;
}
public void clearNegativeFlag() {
this.negativeFlag = false;
}
/**
* @return the carry flag
*/
public boolean getCarryFlag() {
return carryFlag;
}
/**
* @return 1 if the carry flag is set, 0 if it is clear.
*/
public int getCarryBit() {
return (carryFlag ? 1 : 0);
}
/**
* @param carryFlag the carry flag to set
*/
public void setCarryFlag(boolean carryFlag) {
this.carryFlag = carryFlag;
}
/**
* Sets the Carry Flag
*/
public void setCarryFlag() {
this.carryFlag = true;
}
/**
* Clears the Carry Flag
*/
public void clearCarryFlag() {
this.carryFlag = false;
}
/**
* @return the zero flag
*/
public boolean getZeroFlag() {
return zeroFlag;
}
/**
* @return 1 if the zero flag is set, 0 if it is clear.
*/
public int getZeroBit() {
return (zeroFlag ? 1 : 0);
}
/**
* @param zeroFlag the zero flag to set
*/
public void setZeroFlag(boolean zeroFlag) {
this.zeroFlag = zeroFlag;
}
/**
* Sets the Zero Flag
*/
public void setZeroFlag() {
this.zeroFlag = true;
}
/**
* Clears the Zero Flag
*/
public void clearZeroFlag() {
this.zeroFlag = false;
}
/**
* @return the irq disable flag
*/
public boolean getIrqDisableFlag() {
return irqDisableFlag;
}
/**
* @return 1 if the interrupt disable flag is set, 0 if it is clear.
*/
public int getIrqDisableBit() {
return (irqDisableFlag ? 1 : 0);
}
/**
* @param irqDisableFlag the irq disable flag to set
*/
public void setIrqDisableFlag(boolean irqDisableFlag) {
this.irqDisableFlag = irqDisableFlag;
}
public void setIrqDisableFlag() {
this.irqDisableFlag = true;
}
public void clearIrqDisableFlag() {
this.irqDisableFlag = false;
}
/**
* @return the decimal mode flag
*/
public boolean getDecimalModeFlag() {
return decimalModeFlag;
}
/**
* @return 1 if the decimal mode flag is set, 0 if it is clear.
*/
public int getDecimalModeBit() {
return (decimalModeFlag ? 1 : 0);
}
/**
* @param decimalModeFlag the decimal mode flag to set
*/
public void setDecimalModeFlag(boolean decimalModeFlag) {
this.decimalModeFlag = decimalModeFlag;
}
/**
* Sets the Decimal Mode Flag to true.
*/
public void setDecimalModeFlag() {
this.decimalModeFlag = true;
}
/**
* Clears the Decimal Mode Flag.
*/
public void clearDecimalModeFlag() {
this.decimalModeFlag = false;
}
/**
* @return the break flag
*/
public boolean getBreakFlag() {
return breakFlag;
}
/**
* @return 1 if the break flag is set, 0 if it is clear.
*/
public int getBreakBit() {
return (carryFlag ? 1 : 0);
}
/**
* @param breakFlag the break flag to set
*/
public void setBreakFlag(boolean breakFlag) {
this.breakFlag = breakFlag;
}
/**
* Sets the Break Flag
*/
public void setBreakFlag() {
this.breakFlag = true;
}
/**
* Clears the Break Flag
*/
public void clearBreakFlag() {
this.breakFlag = false;
}
/**
* @return the overflow flag
*/
public boolean getOverflowFlag() {
return overflowFlag;
}
/**
* @return 1 if the overflow flag is set, 0 if it is clear.
*/
public int getOverflowBit() {
return (overflowFlag ? 1 : 0);
}
/**
* @param overflowFlag the overflow flag to set
*/
public void setOverflowFlag(boolean overflowFlag) {
this.overflowFlag = overflowFlag;
}
/**
* Sets the Overflow Flag
*/
public void setOverflowFlag() {
this.overflowFlag = true;
}
/**
* Clears the Overflow Flag
*/
public void clearOverflowFlag() {
this.overflowFlag = false;
}
/**
* Set the illegal instruction trap.
*/
public void setOpTrap() {
this.opTrap = true;
}
/**
* Clear the illegal instruction trap.
*/
public void clearOpTrap() {
this.opTrap = false;
}
/**
* Get the status of the illegal instruction trap.
*/
public boolean getOpTrap() {
return this.opTrap;
}
public int getAccumulator() {
return a;
}
public void setAccumulator(int val) {
this.a = val;
}
public int getXRegister() {
return x;
}
public void setXRegister(int val) {
this.x = val;
}
public int getYRegister() {
return y;
}
public void setYRegister(int val) {
this.y = val;
}
public int getProgramCounter() {
return pc;
}
public void setProgramCounter(int addr) {
this.pc = addr;
}
public int getStackPointer() {
return sp;
}
public void setStackPointer(int offset) {
this.sp = offset;
}
/**
* @value The value of the Process Status Register bits to be set.
*/
public void setProcessorStatus(int value) {
if ((value&P_CARRY) != 0)
setCarryFlag();
else
clearCarryFlag();
if ((value&P_ZERO) != 0)
setZeroFlag();
else
clearZeroFlag();
if ((value&P_IRQ_DISABLE) != 0)
setIrqDisableFlag();
else
clearIrqDisableFlag();
if ((value&P_DECIMAL) != 0)
setDecimalModeFlag();
else
clearDecimalModeFlag();
if ((value&P_BREAK) != 0)
setBreakFlag();
else
clearBreakFlag();
if ((value&P_OVERFLOW) != 0)
setOverflowFlag();
else
clearOverflowFlag();
if ((value&P_NEGATIVE) != 0)
setNegativeFlag();
else
clearNegativeFlag();
}
/**
* @returns The value of the Process Status Register, as a byte.
*/
public int getProcessorStatus() {
int status = 0x20;
if (getCarryFlag()) { status |= P_CARRY; }
if (getZeroFlag()) { status |= P_ZERO; }
if (getIrqDisableFlag()) { status |= P_IRQ_DISABLE; }
if (getDecimalModeFlag()) { status |= P_DECIMAL; }
if (getBreakFlag()) { status |= P_BREAK; }
if (getOverflowFlag()) { status |= P_OVERFLOW; }
if (getNegativeFlag()) { status |= P_NEGATIVE; }
return status;
}
/**
* @return A string representing the current status register state.
*/
public String statusRegisterString() {
StringBuffer sb = new StringBuffer("[");
sb.append(getNegativeFlag() ? 'N' : '.'); // Bit 7
sb.append(getOverflowFlag() ? 'V' : '.'); // Bit 6
sb.append("-"); // Bit 5 (always 1)
sb.append(getBreakFlag() ? 'B' : '.'); // Bit 4
sb.append(getDecimalModeFlag() ? 'D' : '.'); // Bit 3
sb.append(getIrqDisableFlag() ? 'I' : '.'); // Bit 2
sb.append(getZeroFlag() ? 'Z' : '.'); // Bit 1
sb.append(getCarryFlag() ? 'C' : '.'); // Bit 0
sb.append("]");
return sb.toString();
}
/**
* Returns a string representing the CPU state.
*/
public String toString() {
String opcode = opcode(ir, args[0], args[1]);
StringBuffer sb = new StringBuffer(String.format("$%04X", addr) +
" ");
sb.append(String.format("%-14s", opcode));
sb.append("A=" + String.format("$%02X", a) + " ");
sb.append("X=" + String.format("$%02X", x) + " ");
sb.append("Y=" + String.format("$%02X", y) + " ");
sb.append("PC=" + String.format("$%04X", pc)+ " ");
sb.append("P=" + statusRegisterString());
return sb.toString();
}
/**
* Push an item onto the stack, and decrement the stack counter.
* Silently fails to push onto the stack if SP is
*/
void stackPush(int data) throws MemoryAccessException {
bus.write(0x100+sp, data);
if (sp == 0)
sp = 0xff;
else
--sp;
}
/**
* Pre-increment the stack pointer, and return the top of the stack.
*/
int stackPop() throws MemoryAccessException {
if (sp == 0xff)
sp = 0x00;
else
++sp;
int data = bus.read(0x100+sp);
return data;
}
/**
* Peek at the value currently at the top of the stack
*/
int stackPeek() throws MemoryAccessException {
return bus.read(0x100+sp+1);
}
/*
* Increment the PC, rolling over if necessary.
*/
void incrementPC() {
if (pc == 0xffff) {
pc = 0;
} else {
++pc;
}
}
/**
* Given two bytes, return an address.
*/
int address(int lowByte, int hiByte) {
return ((hiByte<<8)|lowByte) & 0xffff;
}
/**
* Given a hi byte and a low byte, return the Absolute,X
* offset address.
*/
int xAddress(int lowByte, int hiByte) {
return (address(lowByte, hiByte)+getXRegister()) & 0xffff;
}
/**
* Given a hi byte and a low byte, return the Absolute,Y
* offset address.
*/
int yAddress(int lowByte, int hiByte) {
return (address(lowByte, hiByte)+getYRegister()) & 0xffff;
}
/**
* Given a single byte, compute the Zero Page,X offset address.
*/
int zpxAddress(int zp) {
return (zp+getXRegister())&0xff;
}
/**
* Given a single byte, compute the offset address.
*/
int relAddress(int offset) {
// Cast the offset to a signed byte to handle negative offsets
return (pc + (byte)offset) & 0xffff;
}
/**
* Given a single byte, compute the Zero Page,Y offset address.
*/
int zpyAddress(int zp) {
return (zp+getYRegister())&0xff;
}
/**
* Given an opcode and its operands, return a formatted name.
*
* @param opcode
* @param operands
* @return
*/
String opcode(int opcode, int op1, int op2) {
String opcodeName = Cpu.opcodeNames[opcode];
if (opcodeName == null) { return "???"; }
StringBuffer sb = new StringBuffer(opcodeName);
switch (Cpu.instructionModes[opcode]) {
case ABS:
sb.append(String.format(" $%04X", address(op1, op2)));
break;
case ABX:
sb.append(String.format(" $%04X,X", address(op1, op2)));
break;
case ABY:
sb.append(String.format(" $%04X,Y", address(op1, op2)));
break;
case IMM:
sb.append(String.format(" #$%02X", op1));
break;
case IND:
sb.append(String.format(" ($%04X)", address(op1, op2)));
break;
case XIN:
sb.append(String.format(" ($%02X),X", op1));
break;
case INY:
sb.append(String.format(" ($%02X,Y)", op1));
break;
case REL:
case ZPG:
sb.append(String.format(" $%02X", op1));
break;
case ZPX:
sb.append(String.format(" $%02X,X", op1));
break;
case ZPY:
sb.append(String.format(" $%02X,Y", op1));
break;
}
return sb.toString();
}
}
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