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Fixed the behavior of the JMP (ind) instruction in sim65 when it runs with the "6502X" CPU type.

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The JMP (ind) bug is present in the 6502 which is emulated by both the "6502" and "6502X"
emulation targets of sim65; specifically, the OPC_6502_6C handler. In the old code, the
bug-exhibiting code was not executed when the target was set to 6502X, which is incorrect.
the patch removes the (CPU == CPU_6502) check, which made no sense.

The JMP (ind) bug was actually fixed in the 65c02. Indeed, the OPC_65C02_6C opcode handler
has code that implements the 'right' behavior.
This commit is contained in:
Sidney Cadot
2024-11-30 12:36:35 +01:00
parent 05a653d3f9
commit 2abd66ea0c
1 changed files with 9 additions and 17 deletions
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10
src/sim65/6502.c
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@@ -1964,9 +1964,7 @@ static void OPC_6502_6C (void)
PC = Regs.PC;
Lo = MemReadWord (PC+1);
if (CPU == CPU_6502)
{
/* Emulate the 6502 bug */
/* Emulate the buggy 6502 behavior */
Cycles = 5;
Regs.PC = MemReadByte (Lo);
Hi = (Lo & 0xFF00) | ((Lo + 1) & 0xFF);
@@ -1978,12 +1976,6 @@ static void OPC_6502_6C (void)
Warning ("6502 indirect jump bug triggered at $%04X, ind addr = $%04X",
PC, Lo);
}
}
else
{
Cycles = 6;
Regs.PC = MemReadWord(Lo);
}
ParaVirtHooks (&Regs);
}