private void recursiveTranversal(ushort addr, byte[] rom)
{
while (addr >= 0 && addr <= rom.Length)
{
if (!addrDecodeCheck[addr])
{
DecodedInstruction instruct = dissaembleInstruc((ushort)((rom[addr] << 8) | rom[addr + 1]), addr);
decodedRom.Add(instruct);
addrDecodeCheck[addr] = true;
byte opcode = Utli.getUpperByteHighNibble(instruct.Opcode);
//branch instruction check
if (opcode == 1) //non conditional jump
{
recursiveTranversal((ushort)((instruct.Opcode & 0x0FFF) - Chip8.ROM_BASE_ADDR), rom);
return;
}
else if (opcode == 2)// subroutine call,
{
//2 brances. first branch is the call, second is the return branch
recursiveTranversal((ushort)((instruct.Opcode & 0x0FFF) - Chip8.ROM_BASE_ADDR), rom);
recursiveTranversal((ushort)((instruct.AddrOfInstruc + 2)), rom);
return;
}
else if (instruct.Opcode == 0x00EE) //end subroutine
{
return;
}//3,5,4,9
else if (opcode == 3 || opcode == 5 || opcode == 4 || opcode == 9 || opcode == 0xE) //primitive conditional branching
{
recursiveTranversal((ushort)((instruct.AddrOfInstruc + 2)), rom);
recursiveTranversal((ushort)((instruct.AddrOfInstruc + 4)), rom);
return;
}
else
{
addr = (ushort)(addr + 2);
}
}
else
{
return;
}
}
}
public DecodedInstruction dissaembleInstruc(ushort opcode, ushort addr)
{
DecodedInstruction instruction = new DecodedInstruction();
//disassemble instruction params
string nnn = "0x" + ((opcode & 0x0FFF)).ToString("x2").ToUpper(); // address - 0nnn
string nn = "0x" + (Utli.getLowerByte(opcode)).ToString("x2").ToUpper(); // constant - 00nn
string n = "0x" + (Utli.getLowerByteLowNibble(opcode)).ToString("x2").ToUpper(); // constant - 000n
string x = (Utli.getUpperByteLowNibble(opcode)).ToString("x2").ToUpper(); // register # - 0x00
string y = (Utli.getLowerByteHighNibble(opcode)).ToString("x2").ToUpper(); // register # - 00y0
if (x.Substring(0, 1).Equals("0"))
{
x = x.Substring(1);
}
if (y.Substring(0, 1).Equals("0"))
{
y = y.Substring(1);
}
//decode
switch (Utli.getUpperByteHighNibble(opcode))
{
case 0x0:
{
if (Utli.getLowerByteHighNibble(opcode) == 0xE)
{
switch (Utli.getLowerByteLowNibble(opcode))
{
case 0x0: // Clears the screen.
instruction.AddrOfInstruc = addr;
instruction.Opcode = opcode;
instruction.MnemonicInstuc = "CLS";
instruction.Description = "Clears the screen.";
break;
case 0xE: //Returns from a subroutine.
instruction.AddrOfInstruc = addr;
instruction.Opcode = opcode;
instruction.MnemonicInstuc = "RET";
instruction.Description = "Returns from a subroutine.";
break;
default:
Console.WriteLine("Unknown Opcode - " + "0x" + opcode.ToString("x2"));
break;
}
}
else
{
if ((opcode & 0x0FFF) == 0)
{
instruction.AddrOfInstruc = addr;
instruction.Opcode = opcode;
instruction.MnemonicInstuc = "SYS";
instruction.Description = "Calls RCA 1802 program at address " + addr + " Not necessary for most ROMs.";
}
else
{
instruction.AddrOfInstruc = addr;
}
instruction.Opcode = opcode;
instruction.MnemonicInstuc = "UNKNOWN";
instruction.Description = "Unimplemented Opcode - " + "0x" + opcode.ToString("x2");
}
}
break;
case 0x1: //Jumps to address NNN.
instruction.AddrOfInstruc = addr;
instruction.Opcode = opcode;
instruction.MnemonicInstuc = "JP " + nnn;
instruction.Description = "Jumps to address " + nnn;
break;
case 0x2: //Calls subroutine at NNN.
instruction.AddrOfInstruc = addr;
instruction.Opcode = opcode;
instruction.MnemonicInstuc = "CALL " + nnn;
instruction.Description = "Calls subroutine at " + nnn;
break;
case 0x3: //3XNN Skips the next instruction if VX equals NN.
instruction.AddrOfInstruc = addr;
instruction.Opcode = opcode;
instruction.MnemonicInstuc = "SE V" + x + ", " + nn;
instruction.Description = "Skips the next instruction if V" + x + " equals " + nn;
break;
case 0x4: //4XNN Skips the next instruction if VX doesn't equal NN.
instruction.AddrOfInstruc = addr;
instruction.Opcode = opcode;
instruction.MnemonicInstuc = "SNE V" + x + ", " + nn;
instruction.Description = "Skips the next instruction if V" + x + " doesn't equal " + nn;
break;
case 0x5: //5XY0 Skips the next instruction if VX equals VY.
instruction.AddrOfInstruc = addr;
instruction.Opcode = opcode;
instruction.MnemonicInstuc = "SE V" + x + ", " + "V" + y;
instruction.Description = "Skips the next instruction if V" + x + " equals " + "V" + y;
break;
case 0x6: //6XNN Sets VX to NNX to NN.
instruction.AddrOfInstruc = addr;
instruction.Opcode = opcode;
instruction.MnemonicInstuc = "LD V" + x + ", " + nn;
instruction.Description = "Sets V" + x + " to " + nn;
break;
case 0x7: //7XNN Adds NN to VX.
instruction.AddrOfInstruc = addr;
instruction.Opcode = opcode;
instruction.MnemonicInstuc = "ADD V" + x + ", " + nn;
instruction.Description = "Adds " + nn + " to " + "V" + x;
break;
case 0x8:
{
switch (Utli.getLowerByteLowNibble(opcode))
{
case 0x0: // 8XY0 Sets VX to the value of VY.
instruction.AddrOfInstruc = addr;
instruction.Opcode = opcode;
instruction.MnemonicInstuc = "LD V" + x + ", " + "V" + y;
instruction.Description = "Sets V" + x + " to the value " + "V" + y;
break;
case 0x1: // 8XY1 Sets VX to VX or VY.
instruction.AddrOfInstruc = addr;
instruction.Opcode = opcode;
instruction.MnemonicInstuc = "OR V" + x + ", " + "V" + y;
instruction.Description = "Sets V" + x + " to " + "V" + x + " or " + "V" + y;
break;
case 0x2: // 8XY2 Sets VX to VX and VY.
instruction.AddrOfInstruc = addr;
instruction.Opcode = opcode;
instruction.MnemonicInstuc = "AND V" + x + ", " + "V" + y;
instruction.Description = "Sets V" + x + " to " + "V" + x + " and " + "V" + y;
break;
case 0x3: // 8XY3 Sets VX to VX xor VY.
instruction.AddrOfInstruc = addr;
instruction.Opcode = opcode;
instruction.MnemonicInstuc = "XOR V" + x + ", " + "V" + y;
instruction.Description = "Sets V" + x + " to " + "V" + x + " xor " + "V" + y;
break;
case 0x4: // 8XY4 Adds VY to VX. VF is set to 1 when there's a carry, and to 0 when there isn't.
{
instruction.AddrOfInstruc = addr;
instruction.Opcode = opcode;
instruction.MnemonicInstuc = "ADD V" + x + ", " + "V" + y;
instruction.Description = "Adds V" + y + " to " + "V" + x;
}
break;
case 0x5: //8XY5 VY is subtracted from VX. VF is set to 0 when there's a borrow, and 1 when there isn't.
{
instruction.AddrOfInstruc = addr;
instruction.Opcode = opcode;
instruction.MnemonicInstuc = "SUB V" + x + ", " + "V" + y;
instruction.Description = "V" + y + " is subtracted from " + "V" + x;
}
break;
case 0x6: //8XY6 Shifts VX right by one.
// VF is set to the value of the least significant bit of VX before the shift.
{
instruction.AddrOfInstruc = addr;
instruction.Opcode = opcode;
instruction.MnemonicInstuc = "SHR V" + x + "{, " + "V" + y + "}";
instruction.Description = "Shifts " + "V" + x + "right by one. " + " VF is set to the value of the least significant bit of "
+ "V" + x + " before the shift";
}
break;
case 0x7: //8XY7 Sets VX to VY minus VX. VF is set to 0 when there's a borrow, and 1 when there isn't.
{
instruction.AddrOfInstruc = addr;
instruction.Opcode = opcode;
instruction.MnemonicInstuc = "SUBN V" + x + ", " + "V" + y;
instruction.Description = "Sets V" + x + " to " + "V" + y + " minus " + "V" + x;
}
break;
case 0xE: //8XYE Shifts VX left by one. VF is set to the value of the
// most significant bit of VX before the shift.
{
instruction.AddrOfInstruc = addr;
instruction.Opcode = opcode;
instruction.MnemonicInstuc = "SHL V" + x + "{, " + "V" + y + "}";
instruction.Description = "Shifts " + "V" + x + "left by one. " + " VF is set to the value of the most significant bit of "
+ "V" + x + " before the shift";
}
break;
default:
instruction.AddrOfInstruc = addr;
instruction.Opcode = opcode;
instruction.MnemonicInstuc = "UNKNOWN";
instruction.Description = "Unimplemented Opcode - " + "0x" + opcode.ToString("x2");
break;
}
}
break;
case 0x9: //9XY0 Skips the next instruction if VX doesn't equal VY.
instruction.AddrOfInstruc = addr;
instruction.Opcode = opcode;
instruction.MnemonicInstuc = "SNE V" + x + ", " + "V" + y;
instruction.Description = "Skips the next instruction if V" + x + " dosen't equal " + "V" + y;
break;
case 0xA: //ANNN Sets Ireg to the address NNN.
instruction.AddrOfInstruc = addr;
instruction.Opcode = opcode;
instruction.MnemonicInstuc = "LD I, " + nnn;
instruction.Description = "Sets Ireg to the address " + nnn;
break;
case 0xB: //BNNN Jumps to the address NNN plus V0.
instruction.AddrOfInstruc = addr;
instruction.Opcode = opcode;
instruction.MnemonicInstuc = "JP V0, " + nnn;
instruction.Description = "Jumps to the address " + nnn + " plus V0";
break;
case 0xC: //CXNN Sets VX to the result of a bitwise and operation on a random number and NN.
instruction.AddrOfInstruc = addr;
instruction.Opcode = opcode;
instruction.MnemonicInstuc = "RND V" + x + ", " + nn;
instruction.Description = "Sets V" + x + " to the result of a bitwise and operation on a random number and " + nn;
break;
case 0xD:
{
//DXYN Draws a sprite at coordinate (VX, VY) that has a width of 8 pixels and a height of N pixels.
// Each row of 8 pixels is read as bit-coded starting from memory location Ireg;
// Ireg value doesn’t change after the execution of this instruction.
// As described above, VF is set to 1 if any screen pixels are flipped from set to unset when the sprite is drawn,
// and to 0 if that doesn’t happen
instruction.AddrOfInstruc = addr;
instruction.Opcode = opcode;
instruction.MnemonicInstuc = "DRW V" + x + ", " + "V" + y + ", " + n;
instruction.Description = "Draws a spirte at (V" + x + ", V" + y + ")" + " that has a width of 8 pixels and a height of " + n + "pixels";
}
break;
case 0xE:
{
switch (Utli.getLowerByte(opcode))
{
case 0x9E: //EX9E Skips the next instruction if the key stored in VX is pressed.
instruction.AddrOfInstruc = addr;
instruction.Opcode = opcode;
instruction.MnemonicInstuc = "SKP V" + x;
instruction.Description = "Skips the next instruction if the key stored in V" + x + " is pressed";
break;
case 0xA1: //EXA1 Skips the next instruction if the key stored in VX isn't pressed.
instruction.AddrOfInstruc = addr;
instruction.Opcode = opcode;
instruction.MnemonicInstuc = "SKNP V" + x;
instruction.Description = "Skips the next instruction if the key stored in V" + x + " isn't pressed";
break;
default:
instruction.AddrOfInstruc = addr;
instruction.Opcode = opcode;
instruction.MnemonicInstuc = "UNKNOWN";
instruction.Description = "Unimplemented Opcode - " + "0x" + opcode.ToString("x2");
break;
}
}
break;
case 0xF:
{
switch (Utli.getLowerByte(opcode))
{
case 0x07: //FX07 Sets VX to the value of the delay timer.
instruction.AddrOfInstruc = addr;
instruction.Opcode = opcode;
instruction.MnemonicInstuc = "LD V" + x + ", DT";
instruction.Description = "Sets V" + x + " to the value of the delay timer.";
break;
case 0x0A: //FX0A A key press is awaited, and then stored in VX.
{
instruction.AddrOfInstruc = addr;
instruction.Opcode = opcode;
instruction.MnemonicInstuc = "LD V" + x + ", K";
instruction.Description = "All execution stops until a key is pressed, then the value of that key is stored in V" + x;
}
break;
case 0x15: // FX15 Sets the delay timer to VX.
instruction.AddrOfInstruc = addr;
instruction.Opcode = opcode;
instruction.MnemonicInstuc = "LD DT, V" + x;
instruction.Description = "Sets the delay timer to V" + x;
break;
case 0x18: // FX18 Sets the sound timer to VX.
instruction.AddrOfInstruc = addr;
instruction.Opcode = opcode;
instruction.MnemonicInstuc = "LD ST, V" + x;
instruction.Description = "Sets the sound timer to V" + x;
break;
case 0x1E: //FX1E Adds VX to Ireg.
instruction.AddrOfInstruc = addr;
instruction.Opcode = opcode;
instruction.MnemonicInstuc = "ADD I, V" + x;
instruction.Description = "Adds V" + x + " to Ireg.";
break;
case 0x29: //FX29 Sets Ireg to the location of the sprite for the character in VX.
// Characters 0-F (in hexadecimal) are represented by a 4x5 font.
instruction.AddrOfInstruc = addr;
instruction.Opcode = opcode;
instruction.MnemonicInstuc = "LD F, V" + x;
instruction.Description = "Sets Ireg to the location of the sprite for character in V" + x;
break;
case 0x33: //FX33 Stores the binary-coded decimal representation of VX,
//with the most significant of three digits at the address in I,
//the middle digit at I plus 1, and the least significant digit at I plus 2.
instruction.AddrOfInstruc = addr;
instruction.Opcode = opcode;
instruction.MnemonicInstuc = "LD B, V" + x;
instruction.Description = "Stores the binary-coded decimal representation of V" + x + "(I, I+1, I+2)";
break;
case 0x55: //FX55 Stores V0 to VX (including VX) in memory starting at address Ireg.
//I is set to I + X + 1 after operation
instruction.AddrOfInstruc = addr;
instruction.Opcode = opcode;
instruction.MnemonicInstuc = "LD [I], V" + x;
instruction.Description = "Stores V0 to V" + x + " (including V" + x + ") in memory starting at address Ireg";
break;
case 0x65: //FX65 Fills V0 to VX (including VX) with values from memory starting at address Ireg.
instruction.AddrOfInstruc = addr;
instruction.Opcode = opcode;
instruction.MnemonicInstuc = "LD V" + x + ", [I]";
instruction.Description = "Fills V0 to V" + x + " (including V" + x + ") with values from memory starting at address Ireg";
break;
default:
instruction.AddrOfInstruc = addr;
instruction.Opcode = opcode;
instruction.MnemonicInstuc = "UNKNOWN";
instruction.Description = "Unimplemented Opcode - " + "0x" + opcode.ToString("x2");
break;
}
}
break;
default:
instruction.AddrOfInstruc = addr;
instruction.Opcode = opcode;
instruction.MnemonicInstuc = "UNKNOWN";
instruction.Description = "Unimplemented Opcode - " + "0x" + opcode.ToString("x2");
break;
}
return(instruction);
}
