/// <summary>
/// Get the amount of ticks to be run before the opcode execution
/// </summary>
/// <returns>cpu ticks</returns>
private byte GetPreClocks()
{
byte ticks = 0;
// We return the ticks that the instruction took
if (!_state.CurrentInstruction.CB)
{
ticks = CPUInstructionPreClocks.Get((byte)_state.CurrentInstruction.OpCode);
}
else
{
ticks = CPUCBInstructionPreClocks.Get((byte)_state.CurrentInstruction.OpCode);
}
return(ticks);
}
private Instruction InterruptHandler(Interrupts interrupt)
{
// Handle interrupt with a CALL instruction to the interrupt handler
Instruction instruction = new Instruction();
instruction.OpCode = 0xCD; // CALL!
byte lowOpcode = (byte)instruction.OpCode;
instruction.Length = CPUInstructionLengths.Get(lowOpcode);
instruction.Literal = this.interruptHandlers[(Interrupts)interrupt];
instruction.Ticks = CPUInstructionPreClocks.Get(lowOpcode);
instruction.Name = CPUInstructionNames.Get(lowOpcode);
instruction.Description = CPUInstructionDescriptions.Get(lowOpcode);
// Disable interrupts during interrupt handling and clear the current one
this._interruptController.InterruptMasterEnable = false;
byte IF = this._memory.LowLevelRead((ushort)MMR.IF);
IF &= (byte)~(byte)interrupt;
this._memory.LowLevelWrite((ushort)MMR.IF, IF);
return(instruction);
}
/// <summary>
/// Fetches and Decodes an instruction
/// </summary>
/// <param name="instruction">
/// As FetchAndDecode gets called *several* times a frame (and many times during
/// disassembly), it is better to have a pre-allocated instruction and to replace
/// the values, instead of getting the overhead of allocating a new Instrucion
/// everytime.
/// </param>
/// <param name="instructionAddress"></param>
/// <param name="haltLoad"></param>
/// <returns></returns>
internal Instruction FetchAndDecode(ref Instruction instruction,
ushort instructionAddress, bool haltLoad = false)
{
instruction.Address = instructionAddress;
byte opcode = this._memory.LowLevelRead(instructionAddress);
instruction.OpCode = opcode;
if (instruction.OpCode != 0xCB)
{
instruction.CB = false;
byte lowOpcode = (byte)instruction.OpCode;
if (_instructionHistogram[lowOpcode] < ushort.MaxValue)
{
_instructionHistogram[lowOpcode]++;
}
// Normal instructions
instruction.Length = CPUInstructionLengths.Get(lowOpcode);
// Extract literal
if (instruction.Length == 2)
{
// 8 bit literal
instruction.Operands[0] = this._memory.LowLevelRead((ushort)(instructionAddress + 1));
if (haltLoad)
{
instruction.Operands[0] = opcode;
}
instruction.Literal = (byte)instruction.Operands[0];
}
else if (instruction.Length == 3)
{
// 16 bit literal, little endian
instruction.Operands[0] = this._memory.LowLevelRead((ushort)(instructionAddress + 2));
instruction.Operands[1] = this._memory.LowLevelRead((ushort)(instructionAddress + 1));
if (haltLoad)
{
instruction.Operands[1] = instruction.Operands[0];
instruction.Operands[0] = opcode;
}
instruction.Literal = (byte)instruction.Operands[1];
instruction.Literal += (ushort)(instruction.Operands[0] << 8);
}
instruction.Ticks = CPUInstructionPreClocks.Get(lowOpcode);
instruction.Name = CPUInstructionNames.Get(lowOpcode);
instruction.Description = CPUInstructionDescriptions.Get(lowOpcode);
}
else
{
instruction.CB = true;
// CB instructions block
instruction.OpCode <<= 8;
if (!haltLoad)
{
instruction.OpCode += this._memory.LowLevelRead((ushort)(instructionAddress + 1));
}
else
{
instruction.OpCode += 0xCB; // The first byte is duplicated
}
byte lowOpcode = (byte)instruction.OpCode;
if (_cbInstructionHistogram[lowOpcode] < ushort.MaxValue)
{
_cbInstructionHistogram[lowOpcode]++;
}
instruction.Length = CPUCBInstructionLengths.Get(lowOpcode);
// There is no literal in CB instructions!
//instruction.Lambda = this.CBInstructionLambdas[lowOpcode];
instruction.Ticks = CPUCBInstructionPreClocks.Get(lowOpcode);
instruction.Name = CPUCBInstructionNames.Get(lowOpcode);
instruction.Description = CPUCBInstructionDescriptions.Get(lowOpcode);
}
// NOTE(Cristian): On haltLoad (HALT with IME disabled), the next byte after the HALT opcode
// is "duplicated". This is a hardware bug.
if (haltLoad)
{
instruction.Length--;
}
return(instruction);
}
