public void InterruptServiceRoutine()
{
byte bIF = Memory.DirectRead(IF);
byte bIE = Memory.DirectRead(IE);
int f = IRQLookup[bIF & bIE & 0x1F]; //-1 means no interrupt
if (IME)
{
if (f != -1)
{
//2 Internal delays
Board.AdvanceSystemTime(); //4
Board.AdvanceSystemTime(); //8
//PUSH PC
Board.AdvanceSystemTime(); //12
Memory.Write((byte)(Registers.PC >> 8), --Registers.SP);
Board.AdvanceSystemTime(); //16
Memory.Write((byte)Registers.PC, --Registers.SP);
//SERVE
bIF = ServeIRQ(f, bIF);
Board.AdvanceSystemTime(); //20
Memory.DirectWrite(bIF, IF);
if (GetCPU().Halt)
{
Board.AdvanceSystemTime(); //24
GetCPU().Halt = false;
}
SetIME(false);
}
}
else
{
if (f != -1)
{
if (GetCPU().Halt)
{
Board.AdvanceSystemTime(); //4
GetCPU().Halt = false;
GetCPU().DoubleInstructionExecutionBug = DoubleInstructionEnable;
DoubleInstructionEnable = true;
}
}
else
{
DoubleInstructionEnable = false;
}
}
if (Schedule)
{
IME = true;
Schedule = false;
}
}
public override void Update(int Clocks)
{
if (TransferSignal)
{
Clock -= Clocks;
if (Clock <= 0)
{
SC &= 0x7F;
SB = 0xFF;
Memory.DirectWrite((byte)(Memory.DirectRead(0xFF0F) | 0x8), 0xFF0F);
TransferSignal = false;
Clock = 4096;
}
}
}
/**
* "It (DIV) works by using an internal system 16 bit counter. The counter increases each clock (4 clocks per
* nop) and the value of DIV is the 8 upper bits of the counter: it increases every 256 oscillator clocks.
* The value of DIV is the actual bits of the system internal counter, not a mirror, not a register that
* increases with the system internal counter: The actual bits of the counter mapped to memory."
* Source: AntonioND, The Cycle-Accurate Game Boy Docs
*
* "The signal used to increase the TIMA register is generated in a weird way. It selects the actual value
* of one bit of the system internal counter, and performs an and operation with the enable bit in TAC.
* This means that writing to the DIV register affects the timer too (writing to timer registers doesn't
* affect the DIV register)."
* Source: AntonioND, The Cycle-Accurate Game Boy Docs
*
* Tima is not blackbox so we can actually implement what Antonio mentions in his Docs about TIMA and indeed:
* bool TIMASIGNAL = (((DIVREG & MASK) / MASK) & ((TACREG & 4) / 4)) != 0;
* or to avoid the costly divisions: TIMASIGNAL = (DIV & MASK) == MASK && (TAC & 4) == 4;
* TIMASIGNAL is true when the circuit is HI. TIMA increases if the FallingEdgeDetector
* detects a 1 -> 0 transition of TIMASIGNAL.
*/
public override void Update(int clocks)
{
DIV = (ushort)(clocks + DIV);
bool TIMASIGNAL = (DIV & MASK) == MASK && (TAC & 4) == 4;
if (ReleaseOverflow)
{
//TIME: 8
Overflowing = false;
ReleaseOverflow = false;
}
//After the brief period, TIMA will do its regular routine.
if (Overflowing)
{
//TIME: 4
TIMA = TMA;
Memory.DirectWrite((byte)(Memory.DirectRead(IF) | 0x4), IF);
TIMACARRY = false;
ReleaseOverflow = true;
}
if (FallingEdgeDetector.Check(TIMASIGNAL))
{
TIMA++;
//For a brief period (1 cycle or 4 clocks) TIMA has the value 0, and it's currently overflowing (AntonioND)
if (TIMA == 0x0 && TIMACARRY)
{
//TIME: 0
Overflowing = true;
}
else if (TIMA == 0xFF)
{
//about to overflow
TIMACARRY = true;
}
}
}
private void IRQ(byte BIT)
{
Memory.DirectWrite((byte)(Memory.DirectRead(0xFF0F) | BIT), 0xFF0F);
}
