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Implement fast modify path; fix more NOPs.

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This commit is contained in:
Thomas Harte
2025-10-24 16:43:57 -04:00
parent 7d6b7a5874
commit 2e0e89c494
2 changed files with 35 additions and 8 deletions
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22
Processors/6502Mk2/Decoder.hpp
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@@ -49,6 +49,7 @@ enum class AddressingMode {
Absolute,
AbsoluteIndexed,
FastAbsoluteIndexedModify,
Zero,
ZeroIndexed,
ZeroIndirect,
@@ -556,14 +557,19 @@ struct Decoder<model, std::enable_if_t<model == Model::Synertek65C02>> {
case 0x3c: return {AbsoluteIndexed, Operation::BIT};
case 0x9c: return {Absolute, Operation::STZ};
case 0x1f: return {AbsoluteIndexed, Operation::NOP};
case 0x3f: return {AbsoluteIndexed, Operation::NOP};
case 0x5f: return {AbsoluteIndexed, Operation::NOP};
case 0x7f: return {AbsoluteIndexed, Operation::NOP};
case 0x9f: return {AbsoluteIndexed, Operation::NOP};
case 0xbf: return {AbsoluteIndexed, Operation::NOP};
case 0xdf: return {AbsoluteIndexed, Operation::NOP};
case 0xff: return {AbsoluteIndexed, Operation::NOP};
case 0x1e: return {FastAbsoluteIndexedModify, Operation::ASL};
case 0x3e: return {FastAbsoluteIndexedModify, Operation::ROL};
case 0x5e: return {FastAbsoluteIndexedModify, Operation::LSR};
case 0x7e: return {FastAbsoluteIndexedModify, Operation::ROR};
case 0x1f: return {AbsoluteIndexed, Operation::FastNOP};
case 0x3f: return {AbsoluteIndexed, Operation::FastNOP};
case 0x5f: return {AbsoluteIndexed, Operation::FastNOP};
case 0x7f: return {AbsoluteIndexed, Operation::FastNOP};
case 0x9f: return {AbsoluteIndexed, Operation::FastNOP};
case 0xbf: return {AbsoluteIndexed, Operation::FastNOP};
case 0xdf: return {AbsoluteIndexed, Operation::FastNOP};
case 0xff: return {AbsoluteIndexed, Operation::FastNOP};
}
}
};

21
Processors/6502Mk2/Implementation/6502.hpp
View File

@@ -323,6 +323,27 @@ void Processor<model, Traits>::run_for(const Cycles cycles) {
access(BusOperation::Read, Literal(registers.pc.full), throwaway);
goto access_absolute;
// MARK: - Fast absolute indexed modify, which is a 65c02 improvement but not applied universally.
case access_program(FastAbsoluteIndexedModify):
++registers.pc.full;
// Read top half of address.
Storage::address_.halves.low = Storage::operand_;
check_interrupt();
access(BusOperation::Read, Literal(registers.pc.full), Storage::address_.halves.high);
// If this is a read and the top byte doesn't need adjusting, skip that cycle.
Storage::operand_ = Storage::address_.halves.high;
Storage::address_.full += index();
if(Storage::address_.halves.high == Storage::operand_) {
goto access_absolute;
}
check_interrupt();
access(BusOperation::Read, Literal(registers.pc.full), throwaway);
goto access_absolute;
// MARK: - Indexed indirect.
case access_program(IndexedIndirect):