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Codex/complete code implementation for emulator #1

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cf7543e
Fix CPU utilities and add basic tests
haomin1996 Jun 8, 2025
5fd6bd2
Implement basic HALT/STOP and ROM loading
haomin1996 Jun 8, 2025
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61 changes: 38 additions & 23 deletions src/gbaEmu/CPU.java
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Original file line number Diff line number Diff line change
Expand Up @@ -24,12 +24,21 @@ public CPU(Memory memory) {
this.register = new Register();
this.timer = new Timer();
}
public int executeNextOp() {
short nextOp = this.register.pc;
this.register.pc++;
opMap.get(nextOp).run();
return opCycles.get(nextOp);
}
public int executeNextOp() {
int opcode = memory.readMemory(register.pc & 0xFFFF) & 0xFF;
register.pc++;
if (opcode == 0xCB) {
int cb = memory.readMemory(register.pc & 0xFFFF) & 0xFF;
register.pc++;
opcode = (0xCB << 8) | cb;
}
Runnable op = opMap.get(opcode);
if (op == null) {
Log.fatalf(String.format("Unknown opcode: 0x%X", opcode));
}
op.run();
return opCycles.getOrDefault(opcode, 4);
}
public void run() throws InterruptedException {
while (true) {
update();
Expand Down Expand Up @@ -101,17 +110,19 @@ private void doInterrupt(int id) {
case 3:
register.pc = 0x58;
break;
case 4:
register.pc = 60;
break;
case 4:
register.pc = 0x60;
break;
default:
Log.fatalf("unknown interrupt: " + id);
}
}
public int initOpcodes() {
opcodes = new Opcodes();
opMap = new HashMap<>();
opCycles = new HashMap<>();
public int initOpcodes() {
opcodes = new Opcodes();
opcodes.cpu = this;
opcodes.memory = this.memory;
opMap = new HashMap<>();
opCycles = new HashMap<>();
opMap.put(0x7F, () -> opcodes.OP7F());
opCycles.put(0x7F, 4);
for (int i = 0x78; i <= 0x7D; i++) {
Expand Down Expand Up @@ -479,10 +490,14 @@ public int initOpcodes() {
opCycles.put(0x2F, 4);
opMap.put(0x3F, () -> opcodes.OP3F());
opCycles.put(0x3F, 4);
opMap.put(0x37, () -> opcodes.OP37());
opCycles.put(0x37, 4);
opMap.put(0x00, () -> opcodes.OP00());
opCycles.put(0x00, 4);
opMap.put(0x37, () -> opcodes.OP37());
opCycles.put(0x37, 4);
opMap.put(0x76, () -> opcodes.OP76());
opCycles.put(0x76, 4);
opMap.put(0x10, () -> opcodes.OP10());
opCycles.put(0x10, 4);
opMap.put(0x00, () -> opcodes.OP00());
opCycles.put(0x00, 4);
opMap.put(0x07, () -> opcodes.OP07());
opCycles.put(0x07, 4);
opMap.put(0x17, () -> opcodes.OP17());
Expand Down Expand Up @@ -1017,12 +1032,12 @@ public byte getValue8() {
register.pc++;
return ans;
}
public short getValue16() {
int value1 = memory.readMemory(register.pc);
int value2 = memory.readMemory(register.pc + 1);
register.pc += 2;
return (short) (value1 << 8 + value2);
}
public short getValue16() {
int low = memory.readMemory(register.pc & 0xFFFF) & 0xFF;
int high = memory.readMemory((register.pc + 1) & 0xFFFF) & 0xFF;
register.pc += 2;
return (short) ((high << 8) | low);
}
public int decrementHL() {
int hl = register.hl();
hl--;
Expand Down
50 changes: 30 additions & 20 deletions src/gbaEmu/Memory.java
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Original file line number Diff line number Diff line change
@@ -1,11 +1,21 @@
package gbaEmu;

public class Memory {
byte[] mainMemory;
CPU cpu;
public Memory() {
mainMemory = new byte[0x10000];
}
byte[] mainMemory;
CPU cpu;
public Memory() {
mainMemory = new byte[0x10000];
}

/**
* Copy the supplied ROM bytes into the memory area starting at 0x0000.
* Only the first 32KB of the ROM are mapped as this emulator does not
* implement any banking logic.
*/
public void loadRom(byte[] romData) {
int len = Math.min(romData.length, 0x8000);
System.arraycopy(romData, 0, mainMemory, 0, len);
}
public byte readMemory(int address) {
return mainMemory[address];
}
Expand All @@ -17,19 +27,19 @@ public void memoryIncrement(int address) {
mainMemory[address]++;
}
// 16 bit stack push
public int stackPush(short value) {
cpu.register.sp--;
writeMemory(cpu.register.sp, (byte) (value >> 8));
cpu.register.sp--;
writeMemory(cpu.register.sp, (byte) (value & 0xFF));
return 0;
}
//16 bit stack pop
public short stackPop() {
cpu.register.sp++;
int low = readMemory(cpu.register.sp);
cpu.register.sp++;
int high = readMemory(cpu.register.sp);
return (short) (high << 8 | low);
}
public int stackPush(short value) {
cpu.register.sp--;
writeMemory(cpu.register.sp & 0xFFFF, (byte) (value >> 8));
cpu.register.sp--;
writeMemory(cpu.register.sp & 0xFFFF, (byte) (value & 0xFF));
return 0;
}
//16 bit stack pop
public short stackPop() {
int low = readMemory(cpu.register.sp & 0xFFFF);
cpu.register.sp++;
int high = readMemory(cpu.register.sp & 0xFFFF);
cpu.register.sp++;
return (short) ((high << 8) | (low & 0xFF));
}
}
58 changes: 34 additions & 24 deletions src/gbaEmu/Opcodes.java
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Original file line number Diff line number Diff line change
Expand Up @@ -1117,24 +1117,24 @@ public int OP3B() {
cpu.putSP(cpu.register.sp - 1);
return 0;
}
public int OPCB() {
byte n = cpu.getValue8();
if (cpu.opMap.containsKey(0xCB << 2 + n)) {
Runnable op = cpu.opMap.get(0xCB << 2 + n);
op.run();
} else {
return -1;
}
return cpu.opCycles.get(0xCB << 2 + n);
}
private byte swapByteAndSetFlags(byte a) {
byte res = (byte) (((a & 0xF) << 4) | ((a & 0xF0) >> 4));
cpu.register.nf = false;
cpu.register.hf = false;
cpu.register.hf = false;
cpu.register.zf = res == 0;
return res;
}
public int OPCB() {
byte n = cpu.getValue8();
int op = (0xCB << 8) | (n & 0xFF);
if (cpu.opMap.containsKey(op)) {
Runnable run = cpu.opMap.get(op);
run.run();
return cpu.opCycles.get(op);
}
return -1;
}
private byte swapByteAndSetFlags(byte a) {
byte res = (byte) (((a & 0xF) << 4) | ((a & 0xF0) >> 4));
cpu.register.nf = false;
cpu.register.hf = false;
cpu.register.cf = false;
cpu.register.zf = res == 0;
return res;
}
public int OPCB37() {
cpu.register.a = swapByteAndSetFlags(cpu.register.a);
return 0;
Expand Down Expand Up @@ -1183,12 +1183,22 @@ public int OP3F() {
cpu.register.cf = !cpu.register.cf;
return 0;
}
public int OP37() {
cpu.register.nf = false;
cpu.register.hf = false;
cpu.register.cf = true;
return 0;
}
public int OP37() {
cpu.register.nf = false;
cpu.register.hf = false;
cpu.register.cf = true;
return 0;
}
// HALT - put CPU into low power mode until an interrupt occurs
public int OP76() {
cpu.halt = true;
return 0;
}
// STOP instruction is treated the same as HALT in this simplified emulator
public int OP10() {
cpu.halt = true;
return 0;
}
public int OP00() {
return 0;
}
Expand Down
22 changes: 9 additions & 13 deletions src/gbaEmu/Rom.java
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Original file line number Diff line number Diff line change
Expand Up @@ -8,19 +8,15 @@
import java.util.Arrays;

public class Rom {
byte[] content;
public byte[] readRom(String filename) {
try (InputStream inputStream = new FileInputStream(filename);) {
content = inputStream.readAllBytes();
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return content;
}
byte[] content = new byte[0];
public byte[] readRom(String filename) {
try (InputStream inputStream = new FileInputStream(filename)) {
content = inputStream.readAllBytes();
} catch (IOException e) {
throw new RuntimeException("Failed to read ROM file: " + filename, e);
}
return content;
}
public String getTitle() {
String titleString;
if (content.length == 0 ) {
Expand Down
11 changes: 5 additions & 6 deletions src/gbaEmu/Util.java
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Original file line number Diff line number Diff line change
Expand Up @@ -9,12 +9,11 @@ public static boolean testBit(byte n, int pos) {
assert pos >= 0: "testbit parameter must be positive";
return (n & (1 << pos)) > 0;
}
public static byte clearBit(byte n, int pos) {
assert pos >= 0: "clearbit parameter must be positive";
byte allSetTemplate = (byte) 0xFFFF;
byte clearTemplate = (byte) (((byte) (1 << pos)) ^ allSetTemplate);
return (byte) (pos & clearTemplate);
}
public static byte clearBit(byte n, int pos) {
assert pos >= 0: "clearbit parameter must be positive";
byte clearTemplate = (byte) ~(1 << pos);
return (byte) (n & clearTemplate);
}
public static byte getVal(byte val, int pos) {
return (byte) ((val >> pos) & 1);
}
Expand Down
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