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Add undocumented 6502 instruction: ISB

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Signed-off-by: Adrian Conlon <Adrian.conlon@gmail.com>
This commit is contained in:
Adrian Conlon 2018-01-04 21:47:50 +00:00
parent 12565966de
commit cb89eb8c82
3 changed files with 43 additions and 7 deletions
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12
M6502/inc/mos6502.h
View File

@ -572,9 +572,15 @@ namespace EightBit {
}
void DCP(int bbb) {
const auto result = AM_11_x(bbb) - 1;
setByte(result);
CMP(A(), result);
auto operand = AM_11_x(bbb);
setByte(--operand);
CMP(A(), operand);
}
void ISB(int bbb) {
auto operand = AM_01(bbb);
setByte(++operand);
A() = SBC(A(), operand);
}
void ROR(uint8_t& output);

17
M6502/src/Disassembly.cpp
View File

@ -399,7 +399,22 @@ std::string EightBit::Disassembly::disassemble(uint16_t current) const {
output << disassemble_AM_11_x(bbb, "*DCP");
break;
case 0b111:
output << disassemble_AM_11(bbb, "*SBC");
switch (bbb) {
case 0b000: // *ISB
case 0b001:
case 0b011:
case 0b100:
case 0b101:
case 0b110:
case 0b111:
output << disassemble_AM_01(bbb, "*ISB");
break;
case 0b010:
output << disassemble_AM_11(bbb, "*SBC");
break;
default:
UNREACHABLE;
}
break;
default:
throw std::domain_error("Illegal instruction group");

21
M6502/src/mos6502.cpp
View File

@ -19,8 +19,8 @@ EightBit::MOS6502::MOS6502(Bus& bus)
/* B */ 2, 5, 0, 5, 4, 4, 4, 4, 2, 4, 2, 0, 4, 4, 4, 4,
/* C */ 2, 6, 0, 8, 3, 3, 5, 5, 2, 2, 2, 0, 4, 4, 6, 6,
/* D */ 2, 5, 0, 7, 4, 4, 6, 6, 2, 4, 2, 6, 4, 4, 7, 6,
/* E */ 2, 6, 0, 0, 3, 3, 5, 0, 2, 2, 2, 2, 4, 4, 6, 0,
/* F */ 2, 5, 0, 0, 4, 4, 6, 0, 2, 4, 2, 0, 4, 4, 7, 0,
/* E */ 2, 6, 0, 8, 3, 3, 5, 5, 2, 2, 2, 2, 4, 4, 6, 6,
/* F */ 2, 5, 0, 7, 4, 4, 6, 6, 2, 4, 2, 6, 4, 4, 7, 6,
};
@ -421,7 +421,22 @@ int EightBit::MOS6502::execute(uint8_t cell) {
DCP(decoded.bbb);
break;
case 0b111: // *SBC
A() = SBC(A(), AM_11(decoded.bbb));
switch (decoded.bbb) {
case 0b000: // *ISB
case 0b001:
case 0b011:
case 0b100:
case 0b101:
case 0b110:
case 0b111:
ISB(decoded.bbb);
break;
case 0b010:
A() = SBC(A(), AM_11(decoded.bbb));
break;
default:
UNREACHABLE;
}
break;
default:
throw std::domain_error("Illegal instruction group");