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Add extra cycle to immediate decimal arithmetic.

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This commit is contained in:
Thomas Harte
2025-10-24 21:39:14 -04:00
parent 76a5872d17
commit fe79a1231d
1 changed files with 23 additions and 18 deletions
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41
Processors/6502Mk2/Implementation/6502.hpp
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@@ -76,6 +76,14 @@ void Processor<model, Traits>::run_for(const Cycles cycles) {
Storage::opcode_
);
};
const auto needs_65c02_extra_arithmetic_cycle = [&] {
return
is_65c02(model) &&
(
Storage::decoded_.operation == Operation::ADC ||
Storage::decoded_.operation == Operation::SBC
) && registers.flags.decimal;
};
using Literal = Address::Literal;
using ZeroPage = Address::ZeroPage;
@@ -101,15 +109,8 @@ void Processor<model, Traits>::run_for(const Cycles cycles) {
}
// ADC and SBC decimal take an extra cycle on the 65c02.
if constexpr (is_65c02(model)) {
if(
(
Storage::decoded_.operation == Operation::ADC ||
Storage::decoded_.operation == Operation::SBC
) && registers.flags.decimal
) {
goto access_zero_65c02_decimal;
}
if(needs_65c02_extra_arithmetic_cycle()) {
goto access_zero_65c02_decimal;
}
// Read.
@@ -156,15 +157,8 @@ void Processor<model, Traits>::run_for(const Cycles cycles) {
}
// ADC and SBC decimal take an extra cycle on the 65c02.
if constexpr (is_65c02(model)) {
if(
(
Storage::decoded_.operation == Operation::ADC ||
Storage::decoded_.operation == Operation::SBC
) && registers.flags.decimal
) {
goto access_absolute_65c02_decimal;
}
if(needs_65c02_extra_arithmetic_cycle()) {
goto access_absolute_65c02_decimal;
}
// Read.
@@ -235,6 +229,9 @@ void Processor<model, Traits>::run_for(const Cycles cycles) {
// MARK: - Immediate, Implied, Accumulator.
case access_program(Immediate):
if(needs_65c02_extra_arithmetic_cycle()) {
goto immediate_65c02_decimal;
}
++registers.pc.full;
[[fallthrough]];
@@ -242,6 +239,14 @@ void Processor<model, Traits>::run_for(const Cycles cycles) {
perform_operation();
goto fetch_decode;
immediate_65c02_decimal:
check_interrupt();
access(BusOperation::Read, Literal(registers.pc.full), Storage::operand_);
++registers.pc.full;
perform_operation();
goto fetch_decode;
case access_program(Accumulator):
CPU::MOS6502Mk2::perform<model>(
Storage::decoded_.operation,