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Fixed the 6502/65C02 false-read of 6522 issue for Willy Byte! (fixes #52)

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tomcw 2020-07-24 19:39:31 +01:00
parent 52ff9d5b99
commit b93de29ff1
1 changed files with 29 additions and 22 deletions
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51
source/Mockingboard.cpp
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@ -1682,6 +1682,31 @@ static BYTE __stdcall MB_Write(WORD PC, WORD nAddr, BYTE bWrite, BYTE nValue, UL
}
#endif
// Support 6502/65C02 false-reads of 6522 (GH#52)
if ( ((mem[(PC-2)&0xffff] == 0x91) && GetMainCpu() == CPU_6502) || // sta (zp),y - 6502 only (no-PX variant only) (UTAIIe:4-23)
(mem[(PC-3)&0xffff] == 0x99) || // sta abs16,y - 65C02: it's only the no-PX variant that does the false-read (UTAIIe:4-27)
(mem[(PC-3)&0xffff] == 0x9D) ) // sta abs16,x - 65C02: it's only the no-PX variant that does the false-read (UTAIIe:4-27)
{
WORD addr16;
if (mem[(PC-2)&0xffff] == 0x91)
{
BYTE zp = mem[(PC-1)&0xffff];
addr16 = (mem[zp] | (mem[(zp+1)&0xff]<<8)) + regs.y;
}
else
{
addr16 = mem[(PC-2)&0xffff] | (mem[(PC-1)&0xffff]<<8);
addr16 += (mem[(PC-3)&0xffff] == 0x99)? regs.y : regs.x;
}
_ASSERT(addr16 == nAddr);
if (addr16 == nAddr) // Check we've reverse looked-up the 6502 opcode correctly
{
if ( ((nAddr&0xf) == 4) || ((nAddr&0xf) == 8) ) // Only reading 6522 reg-4 or reg-8 actually has an effect
MB_Read(PC, nAddr, 0, 0, nExecutedCycles);
}
}
BYTE nMB = (nAddr>>8)&0xf - SLOT4;
BYTE nOffset = nAddr&0xff;
@ -1898,7 +1923,7 @@ void MB_PeriodicUpdate(UINT executedCycles)
//-----------------------------------------------------------------------------
static bool CheckTimerUnderflowAndIrq(USHORT& timerCounter, int& timerIrqDelay, const USHORT nClocks, bool* pTimerUnderflow=NULL)
static bool CheckTimerUnderflowAndIrq(USHORT& timerCounter, int& timerIrqDelay, const USHORT nClocks)
{
if (nClocks == 0)
return false;
@ -1920,9 +1945,6 @@ static bool CheckTimerUnderflowAndIrq(USHORT& timerCounter, int& timerIrqDelay,
if (oldTimer >= 0 && timer < 0) // Underflow occurs for 0x0000 -> 0xFFFF
{
if (pTimerUnderflow)
*pTimerUnderflow = true; // Just for Willy Byte!
if (timer <= -2) // TIMER = 0xFFFE (or less)
timerIrq = true;
else // TIMER = 0xFFFF
@ -1958,36 +1980,22 @@ bool MB_UpdateCycles(ULONG uExecutedCycles)
{
SY6522_AY8910* pMB = &g_MB[i];
bool bTimer1Underflow = false; // Just for Willy Byte!
bool bTimer1Irq = false;
bool bTimer1IrqOnLastCycle = false;
if (isOpcode)
{
bTimer1Irq = CheckTimerUnderflowAndIrq(pMB->sy6522.TIMER1_COUNTER.w, pMB->sy6522.timer1IrqDelay, nClocks-1, &bTimer1Underflow);
bTimer1IrqOnLastCycle = CheckTimerUnderflowAndIrq(pMB->sy6522.TIMER1_COUNTER.w, pMB->sy6522.timer1IrqDelay, 1, &bTimer1Underflow);
bTimer1Irq = CheckTimerUnderflowAndIrq(pMB->sy6522.TIMER1_COUNTER.w, pMB->sy6522.timer1IrqDelay, nClocks-1);
bTimer1IrqOnLastCycle = CheckTimerUnderflowAndIrq(pMB->sy6522.TIMER1_COUNTER.w, pMB->sy6522.timer1IrqDelay, 1);
bTimer1Irq = bTimer1Irq || bTimer1IrqOnLastCycle;
}
else
{
bTimer1Irq = CheckTimerUnderflowAndIrq(pMB->sy6522.TIMER1_COUNTER.w, pMB->sy6522.timer1IrqDelay, nClocks, &bTimer1Underflow);
bTimer1Irq = CheckTimerUnderflowAndIrq(pMB->sy6522.TIMER1_COUNTER.w, pMB->sy6522.timer1IrqDelay, nClocks);
}
const bool bTimer2Irq = CheckTimerUnderflowAndIrq(pMB->sy6522.TIMER2_COUNTER.w, pMB->sy6522.timer2IrqDelay, nClocks);
if (!pMB->bTimer1Active && bTimer1Underflow)
{
if ( (g_nMBTimerDevice == kTIMERDEVICE_INVALID) // StopTimer1() has been called
&& (pMB->sy6522.IFR & IxR_TIMER1) // Counter underflowed
&& ((pMB->sy6522.ACR & RUNMODE) == RM_ONESHOT) ) // One-shot mode
{
// Fix for Willy Byte - need to confirm that 6522 really does this!
// . It never accesses IER/IFR/TIMER1 regs to clear IRQ
// . NB. Willy Byte doesn't work with Phasor.
UpdateIFR(pMB, IxR_TIMER1); // Deassert the TIMER IRQ
}
}
if (pMB->bTimer1Active && bTimer1Irq)
{
UpdateIFR(pMB, 0, IxR_TIMER1);
@ -1999,7 +2007,6 @@ bool MB_UpdateCycles(ULONG uExecutedCycles)
{
// One-shot mode
// - Phasor's playback code uses one-shot mode
// - Willy Byte sets to one-shot to stop the timer IRQ
StopTimer1(pMB);
}
else