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- Continued refactoring of address decoding.

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- Device read and write may now throw MemoryAccessException, and appropriate
  throws clauses have been added throughout the code.
This commit is contained in:
Seth J. Morabito committed 2010-01-09 16:53:04 -08:00
1 parent a01090a16e
commit ac88786df7
21 files changed
+465 -446
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src/main/java/com/loomcom/symon/Cpu.java
+116 -117
View File
@@ -1,6 +1,7 @@
package com.loomcom.symon;
import java.util.Arrays;
import com.loomcom.symon.InstructionTable;
import com.loomcom.symon.exceptions.MemoryAccessException;
/**
* Main 6502 CPU Simulation.
@@ -46,7 +47,6 @@ public class Cpu implements InstructionTable {
/* Scratch space for addressing mode and effective address
* calculations */
private int irOpCode; // Bits 0-2 of IR: [X|X|X| | | | | ]
private int irAddressMode; // Bits 3-5 of IR: [ | | |X|X|X| | ]
private int irOpMode; // Bits 6-7 of IR: [ | | | | | |X|X]
private int effectiveAddress;
@@ -93,7 +93,7 @@ public class Cpu implements InstructionTable {
/**
* Reset the CPU to known initial values.
*/
public void reset() {
public void reset() throws MemoryAccessException {
// Registers
sp = 0xff;
@@ -114,7 +114,7 @@ public class Cpu implements InstructionTable {
opTrap = false;
}
public void step(int num) {
public void step(int num) throws MemoryAccessException {
for (int i = 0; i < num; i++) {
step();
}
@@ -123,26 +123,25 @@ public class Cpu implements InstructionTable {
/**
* Performs an individual machine cycle.
*/
public void step() {
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);
irOpCode = (ir >> 5) & 0x07;
irAddressMode = (ir >> 2) & 0x07;
irOpMode = ir & 0x03;
// Increment PC
incrementPC();
// Clear the illegal opcode trap.
clearOpTrap();
// Clear the illegal opcode trap.
clearOpTrap();
// Decode the instruction and operands
instSize = Cpu.instructionSizes[ir];
for (int i = 0; i < instSize-1; i++) {
operands[i] = bus.read(pc);
args[i] = bus.read(pc);
// Increment PC after reading
incrementPC();
}
@@ -162,36 +161,36 @@ public class Cpu implements InstructionTable {
switch(irAddressMode) {
case 0: // (Zero Page,X)
// TODO: UNIT TESTS
effectiveAddress = bus.read(zpxAddress(operands[0]));
effectiveAddress = bus.read(zpxAddress(args[0]));
effectiveData = bus.read(effectiveAddress);
break;
case 1: // Zero Page
effectiveAddress = operands[0];
effectiveAddress = args[0];
effectiveData = bus.read(effectiveAddress);
break;
case 2: // #Immediate
effectiveAddress = -1;
effectiveData = operands[0];
effectiveData = args[0];
break;
case 3: // Absolute
effectiveAddress = address(operands[0], operands[1]);
effectiveAddress = address(args[0], args[1]);
effectiveData = bus.read(effectiveAddress);
break;
case 4: // (Zero Page),Y
// TODO: UNIT TESTS
effectiveAddress = yAddress(bus.read(operands[0]), getYRegister());
effectiveAddress = yAddress(bus.read(args[0]), getYRegister());
effectiveData = bus.read(effectiveAddress);
break;
case 5: // Zero Page, X
effectiveAddress = zpxAddress(operands[0]);
effectiveAddress = zpxAddress(args[0]);
effectiveData = bus.read(effectiveAddress);
break;
case 6: // Absolute, Y
effectiveAddress = yAddress(operands[0], operands[1]);
effectiveAddress = yAddress(args[0], args[1]);
effectiveData = bus.read(effectiveAddress);
break;
case 7: // Absolute, X
effectiveAddress = xAddress(operands[0], operands[1]);
effectiveAddress = xAddress(args[0], args[1]);
effectiveData = bus.read(effectiveAddress);
break;
}
@@ -200,24 +199,24 @@ public class Cpu implements InstructionTable {
case 2:
switch(irAddressMode) {
case 0: // #Immediate
efectiveAddress = -1;
effectiveData = operands[0];
effectiveAddress = -1;
effectiveData = args[0];
break;
case 1: // Zero Page
effectiveAddress = operands[0];
effectiveData = bus.read(effectiveeAddress);
effectiveAddress = args[0];
effectiveData = bus.read(effectiveAddress);
break;
case 2: // Accumulator - ignored
break;
case 3: // Absolute
effectiveAddress = address(operands[0], operands[1]);
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(operands[0]);
effectiveAddress = zpyAddress(args[0]);
} else {
effectiveAddress = zpxAddress(operands[0]);
effectiveAddress = zpxAddress(args[0]);
}
effectiveData = bus.read(effectiveAddress);
case 7: // Absolute,X / Absolute,Y
@@ -252,7 +251,7 @@ public class Cpu implements InstructionTable {
break;
case 0x10: // BPL - Branch if Positive - Relative
if (!getNegativeFlag()) {
pc = relAddress(operands[0]);
pc = relAddress(args[0]);
}
break;
case 0x18: // CLC - Clear Carry Flag - Implied
@@ -261,14 +260,14 @@ public class Cpu implements InstructionTable {
case 0x20: // JSR - Jump to Subroutine - Implied
stackPush((pc-1 >> 8) & 0xff); // PC high byte
stackPush(pc-1 & 0xff); // PC low byte
pc = address(operands[0], operands[1]);
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(operands[0]);
pc = relAddress(args[0]);
}
break;
case 0x38: // SEC - Set Carry Flag - Implied
@@ -285,7 +284,7 @@ public class Cpu implements InstructionTable {
break;
case 0x50: // BVC - Branch if Overflow Clear - Relative
if (!getOverflowFlag()) {
pc = relAddress(operands[0]);
pc = relAddress(args[0]);
}
break;
case 0x58: // CLI - Clear Interrupt Disable - Implied
@@ -302,7 +301,7 @@ public class Cpu implements InstructionTable {
break;
case 0x70: // BVS - Branch if Overflow Set - Relative
if (getOverflowFlag()) {
pc = relAddress(operands[0]);
pc = relAddress(args[0]);
}
break;
case 0x78: // SEI - Set Interrupt Disable - Implied
@@ -318,7 +317,7 @@ public class Cpu implements InstructionTable {
break;
case 0x90: // BCC - Branch if Carry Clear - Relative
if (!getCarryFlag()) {
pc = relAddress(operands[0]);
pc = relAddress(args[0]);
}
break;
case 0x98: // TYA - Transfer Y to Accumulator - Implied
@@ -338,7 +337,7 @@ public class Cpu implements InstructionTable {
break;
case 0xb0: // BCS - Branch if Carry Set - Relative
if (getCarryFlag()) {
pc = relAddress(operands[0]);
pc = relAddress(args[0]);
}
break;
case 0xb8: // CLV - Clear Overflow Flag - Implied
@@ -358,7 +357,7 @@ public class Cpu implements InstructionTable {
break;
case 0xd0: // BNE - Branch if Not Equal to Zero - Relative
if (!getZeroFlag()) {
pc = relAddress(operands[0]);
pc = relAddress(args[0]);
}
break;
case 0xd8: // CLD - Clear Decimal Mode - Implied
@@ -373,7 +372,7 @@ public class Cpu implements InstructionTable {
break;
case 0xf0: // BEQ - Branch if Equal to Zero - Relative
if (getZeroFlag()) {
pc = relAddress(operands[0]);
pc = relAddress(args[0]);
}
break;
case 0xf8: // SED - Set Decimal Flag - Implied
@@ -382,10 +381,10 @@ public class Cpu implements InstructionTable {
/** JMP *****************************************************************/
case 0x4c: // JMP - Absolute
pc = address(operands[0], operands[1]);
pc = address(args[0], args[1]);
break;
case 0x6c: // JMP - Indirect
lo = address(operands[0], operands[1]); // Address of low byte
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
@@ -423,41 +422,41 @@ public class Cpu implements InstructionTable {
setArithmeticFlags(a);
break;
case 0x06: // ASL - Zero Page
j = bus.read(operands[0]);
j = bus.read(args[0]);
k = asl(j);
bus.write(operands[0], k);
bus.write(args[0], k);
setArithmeticFlags(k);
break;
case 0x0e: // ASL - Absolute
j = bus.read(address(operands[0], operands[1]));
j = bus.read(address(args[0], args[1]));
k = asl(j);
bus.write(address(operands[0], operands[1]), k);
bus.write(address(args[0], args[1]), k);
setArithmeticFlags(k);
break;
case 0x16: // ASL - Zero Page,X
j = bus.read(zpxAddress(operands[0]));
j = bus.read(zpxAddress(args[0]));
k = asl(j);
bus.write(zpxAddress(operands[0]), k);
bus.write(zpxAddress(args[0]), k);
setArithmeticFlags(k);
break;
case 0x1e: // ASL - Absolute,X
j = bus.read(xAddress(operands[0], operands[1]));
j = bus.read(xAddress(args[0], args[1]));
k = asl(j);
bus.write(xAddress(operands[0], operands[1]), k);
bus.write(xAddress(args[0], args[1]), k);
setArithmeticFlags(k);
break;
/** BIT - Bit Test ******************************************************/
case 0x24: // BIT - Zero Page
j = bus.read(operands[0]);
j = bus.read(args[0]);
k = a & j;
setZeroFlag(k == 0);
setNegativeFlag((k & 0x80) != 0);
setOverflowFlag((k & 0x40) != 0);
break;
case 0x2c: // BIT - Absolute
j = bus.read(address(operands[0], operands[1]));
j = bus.read(address(args[0], args[1]));
k = a & j;
setZeroFlag(k == 0);
setNegativeFlag((k & 0x80) != 0);
@@ -469,33 +468,33 @@ public class Cpu implements InstructionTable {
case 0x21: // AND - (Zero Page,X)
break;
case 0x25: // AND - Zero Page
j = bus.read(operands[0]);
j = bus.read(args[0]);
a &= j;
setArithmeticFlags(a);
break;
case 0x29: // AND - #Immediate
a &= operands[0];
a &= args[0];
setArithmeticFlags(a);
break;
case 0x2d: // AND - Absolute
j = bus.read(address(operands[0], operands[1]));
j = bus.read(address(args[0], args[1]));
a &= j;
setArithmeticFlags(a);
break;
case 0x31: // AND - (Zero Page),Y
break;
case 0x35: // AND - Zero Page,X
j = bus.read(zpxAddress(operands[0]));
j = bus.read(zpxAddress(args[0]));
a &= j;
setArithmeticFlags(a);
break;
case 0x39: // AND - Absolute,Y
j = bus.read(yAddress(operands[0], operands[1]));
j = bus.read(yAddress(args[0], args[1]));
a &= j;
setArithmeticFlags(a);
break;
case 0x3d: // AND - Absolute,X
j = bus.read(xAddress(operands[0], operands[1]));
j = bus.read(xAddress(args[0], args[1]));
a &= j;
setArithmeticFlags(a);
break;
@@ -503,9 +502,9 @@ public class Cpu implements InstructionTable {
/** ROL - Rotate Left ***************************************************/
case 0x26: // ROL - Zero Page
j = bus.read(operands[0]);
j = bus.read(args[0]);
k = rol(j);
bus.write(operands[0], k);
bus.write(args[0], k);
setArithmeticFlags(k);
break;
case 0x2a: // ROL - Accumulator
@@ -513,21 +512,21 @@ public class Cpu implements InstructionTable {
setArithmeticFlags(a);
break;
case 0x2e: // ROL - Absolute
j = bus.read(address(operands[0], operands[1]));
j = bus.read(address(args[0], args[1]));
k = rol(j);
bus.write(address(operands[0], operands[1]), k);
bus.write(address(args[0], args[1]), k);
setArithmeticFlags(k);
break;
case 0x36: // ROL - Zero Page,X
j = bus.read(zpxAddress(operands[0]));
j = bus.read(zpxAddress(args[0]));
k = rol(j);
bus.write(zpxAddress(operands[0]), k);
bus.write(zpxAddress(args[0]), k);
setArithmeticFlags(k);
break;
case 0x3e: // ROL - Absolute,X
j = bus.read(xAddress(operands[0], operands[1]));
j = bus.read(xAddress(args[0], args[1]));
k = rol(j);
bus.write(xAddress(operands[0], operands[1]), k);
bus.write(xAddress(args[0], args[1]), k);
setArithmeticFlags(k);
break;
@@ -548,8 +547,8 @@ public class Cpu implements InstructionTable {
/** LSR - Logical Shift Right *******************************************/
case 0x46: // LSR - Zero Page
k = lsr(bus.read(operands[0]));
bus.write(operands[0], k);
k = lsr(bus.read(args[0]));
bus.write(args[0], k);
setArithmeticFlags(k);
break;
case 0x4a: // LSR - Accumulator
@@ -557,18 +556,18 @@ public class Cpu implements InstructionTable {
setArithmeticFlags(a);
break;
case 0x4e: // LSR - Absolute
k = lsr(bus.read(address(operands[0], operands[1])));
bus.write(address(operands[0], operands[1]), k);
k = lsr(bus.read(address(args[0], args[1])));
bus.write(address(args[0], args[1]), k);
setArithmeticFlags(k);
break;
case 0x56: // LSR - Zero Page,X
k = lsr(bus.read(zpxAddress(operands[0])));
bus.write(zpxAddress(operands[0]), k);
k = lsr(bus.read(zpxAddress(args[0])));
bus.write(zpxAddress(args[0]), k);
setArithmeticFlags(k);
break;
case 0x5e: // LSR - Absolute,X
k = lsr(bus.read(xAddress(operands[0], operands[1])));
bus.write(xAddress(operands[0], operands[1]), k);
k = lsr(bus.read(xAddress(args[0], args[1])));
bus.write(xAddress(args[0], args[1]), k);
setArithmeticFlags(k);
break;
@@ -592,9 +591,9 @@ public class Cpu implements InstructionTable {
/** ROR - Rotate Right **************************************************/
case 0x66: // ROR - Zero Page
j = bus.read(operands[0]);
j = bus.read(args[0]);
k = ror(j);
bus.write(operands[0], k);
bus.write(args[0], k);
setArithmeticFlags(k);
break;
case 0x6a: // ROR - Accumulator
@@ -602,21 +601,21 @@ public class Cpu implements InstructionTable {
setArithmeticFlags(a);
break;
case 0x6e: // ROR - Absolute
j = bus.read(address(operands[0], operands[1]));
j = bus.read(address(args[0], args[1]));
k = ror(j);
bus.write(address(operands[0], operands[1]), k);
bus.write(address(args[0], args[1]), k);
setArithmeticFlags(k);
break;
case 0x76: // ROR - Zero Page,X
j = bus.read(zpxAddress(operands[0]));
j = bus.read(zpxAddress(args[0]));
k = ror(j);
bus.write(zpxAddress(operands[0]), k);
bus.write(zpxAddress(args[0]), k);
setArithmeticFlags(k);
break;
case 0x7e: // ROR - Absolute,X
j = bus.read(xAddress(operands[0], operands[1]));
j = bus.read(xAddress(args[0], args[1]));
k = ror(j);
bus.write(xAddress(operands[0], operands[1]), k);
bus.write(xAddress(args[0], args[1]), k);
setArithmeticFlags(k);
break;
@@ -636,76 +635,76 @@ public class Cpu implements InstructionTable {
/** STY - Store Y Register **********************************************/
case 0x84: // STY - Store Y Register - Zero Page
bus.write(operands[0], y);
bus.write(args[0], y);
setArithmeticFlags(y);
break;
case 0x8c: // STY - Store Y Register - Absolute
bus.write(address(operands[0], operands[1]), y);
bus.write(address(args[0], args[1]), y);
setArithmeticFlags(y);
break;
case 0x94: // STY - Store Y Register - Zero Page,X
bus.write(zpxAddress(operands[0]), y);
bus.write(zpxAddress(args[0]), y);
setArithmeticFlags(y);
break;
/** STX - Store X Register **********************************************/
case 0x86: // STX - Zero Page
bus.write(operands[0], x);
bus.write(args[0], x);
setArithmeticFlags(x);
break;
case 0x8e: // STX - Absolute
bus.write(address(operands[0], operands[1]), x);
bus.write(address(args[0], args[1]), x);
setArithmeticFlags(x);
break;
case 0x96: // STX - Zero Page,Y
bus.write(zpyAddress(operands[0]), x);
bus.write(zpyAddress(args[0]), x);
setArithmeticFlags(x);
break;
/** LDY - Load Y Register ***********************************************/
case 0xa0: // LDY - Immediate
y = operands[0];
y = args[0];
setArithmeticFlags(y);
break;
case 0xa4: // LDY - Zero Page
y = bus.read(operands[0]);
y = bus.read(args[0]);
setArithmeticFlags(y);
break;
case 0xac: // LDY - Absolute
y = bus.read(address(operands[0], operands[1]));
y = bus.read(address(args[0], args[1]));
setArithmeticFlags(y);
break;
case 0xb4: // LDY - Zero Page,X
y = bus.read(zpxAddress(operands[0]));
y = bus.read(zpxAddress(args[0]));
setArithmeticFlags(y);
break;
case 0xbc: // LDY - Absolute,X
y = bus.read(xAddress(operands[0], operands[1]));
y = bus.read(xAddress(args[0], args[1]));
setArithmeticFlags(y);
break;
/** LDX - Load X Register ***********************************************/
case 0xa2: // LDX - Immediate
x = operands[0];
x = args[0];
setArithmeticFlags(x);
break;
case 0xa6: // LDX - Zero Page
x = bus.read(operands[0]);
x = bus.read(args[0]);
setArithmeticFlags(x);
break;
case 0xae: // LDX - Absolute
x = bus.read(address(operands[0], operands[1]));
x = bus.read(address(args[0], args[1]));
setArithmeticFlags(x);
break;
case 0xb6: // LDX - Zero Page,Y
x = bus.read(zpyAddress(operands[0]));
x = bus.read(zpyAddress(args[0]));
setArithmeticFlags(x);
break;
case 0xbe: // LDX - Absolute,Y
x = bus.read(yAddress(operands[0], operands[1]));
x = bus.read(yAddress(args[0], args[1]));
setArithmeticFlags(x);
break;
@@ -726,13 +725,13 @@ public class Cpu implements InstructionTable {
/** CPY - Compare Y Register ********************************************/
case 0xc0: // CPY - Immediate
cmp(y, operands[0]);
cmp(y, args[0]);
break;
case 0xc4: // CPY - Zero Page
cmp(y, bus.read(operands[0]));
cmp(y, bus.read(args[0]));
break;
case 0xcc: // CPY - Absolute
cmp(y, bus.read(address(operands[0], operands[1])));
cmp(y, bus.read(address(args[0], args[1])));
break;
@@ -751,40 +750,40 @@ public class Cpu implements InstructionTable {
/** DEC - Decrement Memory **********************************************/
case 0xc6: // DEC - Zero Page
j = bus.read(operands[0]);
j = bus.read(args[0]);
k = --j & 0xff;
bus.write(operands[0], k);
bus.write(args[0], k);
setArithmeticFlags(k);
break;
case 0xce: // DEC - Absolute
j = bus.read(address(operands[0], operands[1]));
j = bus.read(address(args[0], args[1]));
k = --j & 0xff;
bus.write(address(operands[0], operands[1]), k);
bus.write(address(args[0], args[1]), k);
setArithmeticFlags(k);
break;
case 0xd6: // DEC - Zero Page, X
j = bus.read(zpxAddress(operands[0]));
j = bus.read(zpxAddress(args[0]));
k = --j & 0xff;
bus.write(zpxAddress(operands[0]), k);
bus.write(zpxAddress(args[0]), k);
setArithmeticFlags(k);
break;
case 0xde: // DEC - Absolute,X
j = bus.read(xAddress(operands[0], operands[1]));
j = bus.read(xAddress(args[0], args[1]));
k = --j & 0xff;
bus.write(xAddress(operands[0], operands[1]), k);
bus.write(xAddress(args[0], args[1]), k);
setArithmeticFlags(k);
break;
/** CPX - Compare X Register ********************************************/
case 0xe0: // CPX - Immediate
cmp(x, operands[0]);
cmp(x, args[0]);
break;
case 0xe4: // CPX - Zero Page
cmp(x, bus.read(operands[0]));
cmp(x, bus.read(args[0]));
break;
case 0xec: // CPX - Absolute
cmp(x, bus.read(address(operands[0], operands[1])));
cmp(x, bus.read(address(args[0], args[1])));
break;
@@ -807,27 +806,27 @@ public class Cpu implements InstructionTable {
/** INC - Increment Memory **********************************************/
case 0xe6: // INC - Zero Page
j = bus.read(operands[0]);
j = bus.read(args[0]);
k = ++j & 0xff;
bus.write(operands[0], k);
bus.write(args[0], k);
setArithmeticFlags(k);
break;
case 0xee: // INC - Absolute
j = bus.read(address(operands[0], operands[1]));
j = bus.read(address(args[0], args[1]));
k = ++j & 0xff;
bus.write(address(operands[0], operands[1]), k);
bus.write(address(args[0], args[1]), k);
setArithmeticFlags(k);
break;
case 0xf6: // INC - Zero Page,X
j = bus.read(zpxAddress(operands[0]));
j = bus.read(zpxAddress(args[0]));
k = ++j & 0xff;
bus.write(zpxAddress(operands[0]), k);
bus.write(zpxAddress(args[0]), k);
setArithmeticFlags(k);
break;
case 0xfe: // INC - Absolute,X
j = bus.read(xAddress(operands[0], operands[1]));
j = bus.read(xAddress(args[0], args[1]));
k = ++j & 0xff;
bus.write(xAddress(operands[0], operands[1]), k);
bus.write(xAddress(args[0], args[1]), k);
setArithmeticFlags(k);
break;
@@ -1478,7 +1477,7 @@ public class Cpu implements InstructionTable {
* Returns a string representing the CPU state.
*/
public String toString() {
String opcode = opcode(ir, operands[0], operands[1]);
String opcode = opcode(ir, args[0], args[1]);
StringBuffer sb = new StringBuffer(String.format("$%04X", addr) +
" ");
sb.append(String.format("%-14s", opcode));
@@ -1494,7 +1493,7 @@ public class Cpu implements InstructionTable {
* 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) {
void stackPush(int data) throws MemoryAccessException {
bus.write(0x100+sp, data);
if (sp == 0)
@@ -1507,7 +1506,7 @@ public class Cpu implements InstructionTable {
/**
* Pre-increment the stack pointer, and return the top of the stack.
*/
int stackPop() {
int stackPop() throws MemoryAccessException {
if (sp == 0xff)
sp = 0x00;
else
@@ -1521,7 +1520,7 @@ public class Cpu implements InstructionTable {
/**
* Peek at the value currently at the top of the stack
*/
int stackPeek() {
int stackPeek() throws MemoryAccessException {
return bus.read(0x100+sp+1);
}