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MB false read of 6522: limit to only the no-PX variants

This commit is contained in:
tomcw 2020-08-22 16:06:26 +01:00
parent f13d220203
commit 06f8ccb384
1 changed files with 14 additions and 9 deletions
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23
source/Mockingboard.cpp
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@ -1684,26 +1684,31 @@ static BYTE __stdcall MB_Write(WORD PC, WORD nAddr, BYTE bWrite, BYTE nValue, UL
// 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)
(mem[(PC-3)&0xffff] == 0x99) || // sta abs16,y - 6502/65C02, but for 65C02 only the no-PX variant that does the false-read (UTAIIe:4-27)
(mem[(PC-3)&0xffff] == 0x9D) ) // sta abs16,x - 6502/65C02, but for 65C02 only the no-PX variant that does the false-read (UTAIIe:4-27)
{
WORD base;
WORD addr16;
if (mem[(PC-2)&0xffff] == 0x91)
{
BYTE zp = mem[(PC-1)&0xffff];
addr16 = (mem[zp] | (mem[(zp+1)&0xff]<<8)) + regs.y;
base = (mem[zp] | (mem[(zp+1)&0xff]<<8));
addr16 = base + regs.y;
}
else
{
addr16 = mem[(PC-2)&0xffff] | (mem[(PC-1)&0xffff]<<8);
addr16 += (mem[(PC-3)&0xffff] == 0x99)? regs.y : regs.x;
base = mem[(PC-2)&0xffff] | (mem[(PC-1)&0xffff]<<8);
addr16 = base + ((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 (((base ^ addr16) >> 8) == 0) // Only the no-PX variant does the false read (to the same I/O SELECT page)
{
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);
_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);
}
}
}