copy reference implementation

1 files changed, 1358 insertions, 0 deletions

diff --git a/lib/nes/ref/cpu.cc b/lib/nes/ref/cpu.cc
new file mode 100644
index 0000000..79b0c56
--- /dev/null
+++ b/lib/nes/ref/cpu.cc
@@ -0,0 +1,1358 @@
+#include "nes/ref/cpu.hh"
+#include "nes/ref/ppu.hh"
+#include "nes/ref/controller.hh"
+#include "nes/ref/mapper.hh"
+#include "nes/util/snapshot.hh"
+
+namespace nes::ref
+{
+	cpu::cpu(ppu& ppu, mapper& mapper, controller& controller_1, controller& controller_2)
+		: ppu_{ ppu }
+		, mapper_{ mapper }
+		, controller_1_{ controller_1 }
+		, controller_2_{ controller_2 }
+	{
+		registers_.pc = read16(address{ 0xFFFC });
+	}
+
+	auto cpu::build_snapshot(snapshot& snapshot) -> void
+	{
+		snapshot.cpu_cycle = current_cycles_;
+		snapshot.ram = std::vector(std::begin(ram_), std::end(ram_));
+		snapshot.registers.pc = registers_.pc;
+		snapshot.registers.sp = registers_.sp;
+		snapshot.registers.a = registers_.a;
+		snapshot.registers.x = registers_.x;
+		snapshot.registers.y = registers_.y;
+		snapshot.registers.p = registers_.p;
+		snapshot.registers.c = registers_.c;
+		snapshot.registers.z = registers_.z;
+		snapshot.registers.i = registers_.i;
+		snapshot.registers.d = registers_.d;
+		snapshot.registers.b = registers_.b;
+		snapshot.registers.v = registers_.v;
+		snapshot.registers.n = registers_.n;
+	}
+
+	auto cpu::stall_cycles(cycle_count const count) -> void
+	{
+		current_cycles_ += count;
+	}
+
+	auto cpu::trigger_nmi() -> void
+	{
+		nmi_pending_ = true;
+	}
+
+	auto cpu::step() -> void
+	{
+		// See https://www.nesdev.org/wiki/CPU_unofficial_opcodes
+
+#ifdef NES_ENABLE_PPU
+		if (nmi_pending_)
+		{
+			execute_interrupt(address{ 0xFFFA });
+			nmi_pending_ = false;
+		}
+#endif
+
+		auto const opcode = advance_pc8();
+		switch (opcode)
+		{
+			case 0x00: run_brk<addressing_mode::immediate>(); break;
+			case 0x01: run_ora<addressing_mode::indexed_indirect>(); break;
+			case 0x02: run_stp(); break;
+			case 0x03: run_slo<addressing_mode::indexed_indirect>(); break;
+			case 0x04: run_nop<addressing_mode::zero_page>(); break;
+			case 0x05: run_ora<addressing_mode::zero_page>(); break;
+			case 0x06: run_asl<addressing_mode::zero_page>(); break;
+			case 0x07: run_slo<addressing_mode::zero_page>(); break;
+			case 0x08: run_php(); break;
+			case 0x09: run_ora<addressing_mode::immediate>(); break;
+			case 0x0A: run_asl<addressing_mode::accumulator>(); break;
+			case 0x0B: run_anc<addressing_mode::immediate>(); break;
+			case 0x0C: run_nop<addressing_mode::absolute>(); break;
+			case 0x0D: run_ora<addressing_mode::absolute>(); break;
+			case 0x0E: run_asl<addressing_mode::absolute>(); break;
+			case 0x0F: run_slo<addressing_mode::absolute>(); break;
+			case 0x10: run_bpl<addressing_mode::relative>(); break;
+			case 0x11: run_ora<addressing_mode::indirect_indexed>(); break;
+			case 0x12: run_stp(); break;
+			case 0x13: run_slo<addressing_mode::indirect_indexed>(); break;
+			case 0x14: run_nop<addressing_mode::zero_page_indexed_x>(); break;
+			case 0x15: run_ora<addressing_mode::zero_page_indexed_x>(); break;
+			case 0x16: run_asl<addressing_mode::zero_page_indexed_x>(); break;
+			case 0x17: run_slo<addressing_mode::zero_page_indexed_x>(); break;
+			case 0x18: run_clc(); break;
+			case 0x19: run_ora<addressing_mode::absolute_indexed_y>(); break;
+			case 0x1A: run_nop(); break;
+			case 0x1B: run_slo<addressing_mode::absolute_indexed_y>(); break;
+			case 0x1C: run_nop<addressing_mode::absolute_indexed_x>(); break;
+			case 0x1D: run_ora<addressing_mode::absolute_indexed_x>(); break;
+			case 0x1E: run_asl<addressing_mode::absolute_indexed_x>(); break;
+			case 0x1F: run_slo<addressing_mode::absolute_indexed_x>(); break;
+			case 0x20: run_jsr<addressing_mode::absolute>(); break;
+			case 0x21: run_and<addressing_mode::indexed_indirect>(); break;
+			case 0x22: run_stp(); break;
+			case 0x23: run_rla<addressing_mode::indexed_indirect>(); break;
+			case 0x24: run_bit<addressing_mode::zero_page>(); break;
+			case 0x25: run_and<addressing_mode::zero_page>(); break;
+			case 0x26: run_rol<addressing_mode::zero_page>(); break;
+			case 0x27: run_rla<addressing_mode::zero_page>(); break;
+			case 0x28: run_plp(); break;
+			case 0x29: run_and<addressing_mode::immediate>(); break;
+			case 0x2A: run_rol<addressing_mode::accumulator>(); break;
+			case 0x2B: run_anc<addressing_mode::immediate>(); break;
+			case 0x2C: run_bit<addressing_mode::absolute>(); break;
+			case 0x2D: run_and<addressing_mode::absolute>(); break;
+			case 0x2E: run_rol<addressing_mode::absolute>(); break;
+			case 0x2F: run_rla<addressing_mode::absolute>(); break;
+			case 0x30: run_bmi<addressing_mode::relative>(); break;
+			case 0x31: run_and<addressing_mode::indirect_indexed>(); break;
+			case 0x32: run_stp(); break;
+			case 0x33: run_rla<addressing_mode::indirect_indexed>(); break;
+			case 0x34: run_nop<addressing_mode::zero_page_indexed_x>(); break;
+			case 0x35: run_and<addressing_mode::zero_page_indexed_x>(); break;
+			case 0x36: run_rol<addressing_mode::zero_page_indexed_x>(); break;
+			case 0x37: run_rla<addressing_mode::zero_page_indexed_x>(); break;
+			case 0x38: run_sec(); break;
+			case 0x39: run_and<addressing_mode::absolute_indexed_y>(); break;
+			case 0x3A: run_nop(); break;
+			case 0x3B: run_rla<addressing_mode::absolute_indexed_y>(); break;
+			case 0x3C: run_nop<addressing_mode::absolute_indexed_x>(); break;
+			case 0x3D: run_and<addressing_mode::absolute_indexed_x>(); break;
+			case 0x3E: run_rol<addressing_mode::absolute_indexed_x>(); break;
+			case 0x3F: run_rla<addressing_mode::absolute_indexed_x>(); break;
+			case 0x40: run_rti(); break;
+			case 0x41: run_eor<addressing_mode::indexed_indirect>(); break;
+			case 0x42: run_stp(); break;
+			case 0x43: run_sre<addressing_mode::indexed_indirect>(); break;
+			case 0x44: run_nop<addressing_mode::zero_page>(); break;
+			case 0x45: run_eor<addressing_mode::zero_page>(); break;
+			case 0x46: run_lsr<addressing_mode::zero_page>(); break;
+			case 0x47: run_sre<addressing_mode::zero_page>(); break;
+			case 0x48: run_pha(); break;
+			case 0x49: run_eor<addressing_mode::immediate>(); break;
+			case 0x4A: run_lsr<addressing_mode::accumulator>(); break;
+			case 0x4B: run_alr<addressing_mode::immediate>(); break;
+			case 0x4C: run_jmp<addressing_mode::absolute>(); break;
+			case 0x4D: run_eor<addressing_mode::absolute>(); break;
+			case 0x4E: run_lsr<addressing_mode::absolute>(); break;
+			case 0x4F: run_sre<addressing_mode::absolute>(); break;
+			case 0x50: run_bvc<addressing_mode::relative>(); break;
+			case 0x51: run_eor<addressing_mode::indirect_indexed>(); break;
+			case 0x52: run_stp(); break;
+			case 0x53: run_sre<addressing_mode::indirect_indexed>(); break;
+			case 0x54: run_nop<addressing_mode::zero_page_indexed_x>(); break;
+			case 0x55: run_eor<addressing_mode::zero_page_indexed_x>(); break;
+			case 0x56: run_lsr<addressing_mode::zero_page_indexed_x>(); break;
+			case 0x57: run_sre<addressing_mode::zero_page_indexed_x>(); break;
+			case 0x58: run_cli(); break;
+			case 0x59: run_eor<addressing_mode::absolute_indexed_y>(); break;
+			case 0x5A: run_nop(); break;
+			case 0x5B: run_sre<addressing_mode::absolute_indexed_y>(); break;
+			case 0x5C: run_nop<addressing_mode::absolute_indexed_x>(); break;
+			case 0x5D: run_eor<addressing_mode::absolute_indexed_x>(); break;
+			case 0x5E: run_lsr<addressing_mode::absolute_indexed_x>(); break;
+			case 0x5F: run_sre<addressing_mode::absolute_indexed_x>(); break;
+			case 0x60: run_rts(); break;
+			case 0x61: run_adc<addressing_mode::indexed_indirect>(); break;
+			case 0x62: run_stp(); break;
+			case 0x63: run_rra<addressing_mode::indexed_indirect>(); break;
+			case 0x64: run_nop<addressing_mode::zero_page>(); break;
+			case 0x65: run_adc<addressing_mode::zero_page>(); break;
+			case 0x66: run_ror<addressing_mode::zero_page>(); break;
+			case 0x67: run_rra<addressing_mode::zero_page>(); break;
+			case 0x68: run_pla(); break;
+			case 0x69: run_adc<addressing_mode::immediate>(); break;
+			case 0x6A: run_ror<addressing_mode::accumulator>(); break;
+			case 0x6B: run_arr<addressing_mode::immediate>(); break;
+			case 0x6C: run_jmp<addressing_mode::indirect>(); break;
+			case 0x6D: run_adc<addressing_mode::absolute>(); break;
+			case 0x6E: run_ror<addressing_mode::absolute>(); break;
+			case 0x6F: run_rra<addressing_mode::absolute>(); break;
+			case 0x70: run_bvs<addressing_mode::relative>(); break;
+			case 0x71: run_adc<addressing_mode::indirect_indexed>(); break;
+			case 0x72: run_stp(); break;
+			case 0x73: run_rra<addressing_mode::indirect_indexed>(); break;
+			case 0x74: run_nop<addressing_mode::zero_page_indexed_x>(); break;
+			case 0x75: run_adc<addressing_mode::zero_page_indexed_x>(); break;
+			case 0x76: run_ror<addressing_mode::zero_page_indexed_x>(); break;
+			case 0x77: run_rra<addressing_mode::zero_page_indexed_x>(); break;
+			case 0x78: run_sei(); break;
+			case 0x79: run_adc<addressing_mode::absolute_indexed_y>(); break;
+			case 0x7A: run_nop(); break;
+			case 0x7B: run_rra<addressing_mode::absolute_indexed_y>(); break;
+			case 0x7C: run_nop<addressing_mode::absolute_indexed_x>(); break;
+			case 0x7D: run_adc<addressing_mode::absolute_indexed_x>(); break;
+			case 0x7E: run_ror<addressing_mode::absolute_indexed_x>(); break;
+			case 0x7F: run_rra<addressing_mode::absolute_indexed_x>(); break;
+			case 0x80: run_nop<addressing_mode::immediate>(); break;
+			case 0x81: run_sta<addressing_mode::indexed_indirect>(); break;
+			case 0x82: run_nop<addressing_mode::immediate>(); break;
+			case 0x83: run_sax<addressing_mode::indexed_indirect>(); break;
+			case 0x84: run_sty<addressing_mode::zero_page>(); break;
+			case 0x85: run_sta<addressing_mode::zero_page>(); break;
+			case 0x86: run_stx<addressing_mode::zero_page>(); break;
+			case 0x87: run_sax<addressing_mode::zero_page>(); break;
+			case 0x88: run_dey(); break;
+			case 0x89: run_nop<addressing_mode::immediate>(); break;
+			case 0x8A: run_txa(); break;
+			case 0x8B: run_xaa<addressing_mode::immediate>(); break;
+			case 0x8C: run_sty<addressing_mode::absolute>(); break;
+			case 0x8D: run_sta<addressing_mode::absolute>(); break;
+			case 0x8E: run_stx<addressing_mode::absolute>(); break;
+			case 0x8F: run_sax<addressing_mode::absolute>(); break;
+			case 0x90: run_bcc<addressing_mode::relative>(); break;
+			case 0x91: run_sta<addressing_mode::indirect_indexed>(); break;
+			case 0x92: run_stp(); break;
+			case 0x93: run_ahx<addressing_mode::indirect_indexed>(); break;
+			case 0x94: run_sty<addressing_mode::zero_page_indexed_x>(); break;
+			case 0x95: run_sta<addressing_mode::zero_page_indexed_x>(); break;
+			case 0x96: run_stx<addressing_mode::zero_page_indexed_y>(); break;
+			case 0x97: run_sax<addressing_mode::zero_page_indexed_y>(); break;
+			case 0x98: run_tya(); break;
+			case 0x99: run_sta<addressing_mode::absolute_indexed_y>(); break;
+			case 0x9A: run_txs(); break;
+			case 0x9B: run_tas<addressing_mode::absolute_indexed_y>(); break;
+			case 0x9C: run_shy<addressing_mode::absolute_indexed_x>(); break;
+			case 0x9D: run_sta<addressing_mode::absolute_indexed_x>(); break;
+			case 0x9E: run_shx<addressing_mode::absolute_indexed_y>(); break;
+			case 0x9F: run_ahx<addressing_mode::absolute_indexed_y>(); break;
+			case 0xA0: run_ldy<addressing_mode::immediate>(); break;
+			case 0xA1: run_lda<addressing_mode::indexed_indirect>(); break;
+			case 0xA2: run_ldx<addressing_mode::immediate>(); break;
+			case 0xA3: run_lax<addressing_mode::indexed_indirect>(); break;
+			case 0xA4: run_ldy<addressing_mode::zero_page>(); break;
+			case 0xA5: run_lda<addressing_mode::zero_page>(); break;
+			case 0xA6: run_ldx<addressing_mode::zero_page>(); break;
+			case 0xA7: run_lax<addressing_mode::zero_page>(); break;
+			case 0xA8: run_tay(); break;
+			case 0xA9: run_lda<addressing_mode::immediate>(); break;
+			case 0xAA: run_tax(); break;
+			case 0xAB: run_lax<addressing_mode::immediate>(); break;
+			case 0xAC: run_ldy<addressing_mode::absolute>(); break;
+			case 0xAD: run_lda<addressing_mode::absolute>(); break;
+			case 0xAE: run_ldx<addressing_mode::absolute>(); break;
+			case 0xAF: run_lax<addressing_mode::absolute>(); break;
+			case 0xB0: run_bcs<addressing_mode::relative>(); break;
+			case 0xB1: run_lda<addressing_mode::indirect_indexed>(); break;
+			case 0xB2: run_stp(); break;
+			case 0xB3: run_lax<addressing_mode::indirect_indexed>(); break;
+			case 0xB4: run_ldy<addressing_mode::zero_page_indexed_x>(); break;
+			case 0xB5: run_lda<addressing_mode::zero_page_indexed_x>(); break;
+			case 0xB6: run_ldx<addressing_mode::zero_page_indexed_y>(); break;
+			case 0xB7: run_lax<addressing_mode::zero_page_indexed_y>(); break;
+			case 0xB8: run_clv(); break;
+			case 0xB9: run_lda<addressing_mode::absolute_indexed_y>(); break;
+			case 0xBA: run_tsx(); break;
+			case 0xBB: run_las<addressing_mode::absolute_indexed_y>(); break;
+			case 0xBC: run_ldy<addressing_mode::absolute_indexed_x>(); break;
+			case 0xBD: run_lda<addressing_mode::absolute_indexed_x>(); break;
+			case 0xBE: run_ldx<addressing_mode::absolute_indexed_y>(); break;
+			case 0xBF: run_lax<addressing_mode::absolute_indexed_y>(); break;
+			case 0xC0: run_cpy<addressing_mode::immediate>(); break;
+			case 0xC1: run_cmp<addressing_mode::indexed_indirect>(); break;
+			case 0xC2: run_nop<addressing_mode::immediate>(); break;
+			case 0xC3: run_dcp<addressing_mode::indexed_indirect>(); break;
+			case 0xC4: run_cpy<addressing_mode::zero_page>(); break;
+			case 0xC5: run_cmp<addressing_mode::zero_page>(); break;
+			case 0xC6: run_dec<addressing_mode::zero_page>(); break;
+			case 0xC7: run_dcp<addressing_mode::zero_page>(); break;
+			case 0xC8: run_iny(); break;
+			case 0xC9: run_cmp<addressing_mode::immediate>(); break;
+			case 0xCA: run_dex(); break;
+			case 0xCB: run_axs<addressing_mode::immediate>(); break;
+			case 0xCC: run_cpy<addressing_mode::absolute>(); break;
+			case 0xCD: run_cmp<addressing_mode::absolute>(); break;
+			case 0xCE: run_dec<addressing_mode::absolute>(); break;
+			case 0xCF: run_dcp<addressing_mode::absolute>(); break;
+			case 0xD0: run_bne<addressing_mode::relative>(); break;
+			case 0xD1: run_cmp<addressing_mode::indirect_indexed>(); break;
+			case 0xD2: run_stp(); break;
+			case 0xD3: run_dcp<addressing_mode::indirect_indexed>(); break;
+			case 0xD4: run_nop<addressing_mode::zero_page_indexed_x>(); break;
+			case 0xD5: run_cmp<addressing_mode::zero_page_indexed_x>(); break;
+			case 0xD6: run_dec<addressing_mode::zero_page_indexed_x>(); break;
+			case 0xD7: run_dcp<addressing_mode::zero_page_indexed_x>(); break;
+			case 0xD8: run_cld(); break;
+			case 0xD9: run_cmp<addressing_mode::absolute_indexed_y>(); break;
+			case 0xDA: run_nop(); break;
+			case 0xDB: run_dcp<addressing_mode::absolute_indexed_y>(); break;
+			case 0xDC: run_nop<addressing_mode::absolute_indexed_x>(); break;
+			case 0xDD: run_cmp<addressing_mode::absolute_indexed_x>(); break;
+			case 0xDE: run_dec<addressing_mode::absolute_indexed_x>(); break;
+			case 0xDF: run_dcp<addressing_mode::absolute_indexed_x>(); break;
+			case 0xE0: run_cpx<addressing_mode::immediate>(); break;
+			case 0xE1: run_sbc<addressing_mode::indexed_indirect>(); break;
+			case 0xE2: run_nop<addressing_mode::immediate>(); break;
+			case 0xE3: run_isc<addressing_mode::indexed_indirect>(); break;
+			case 0xE4: run_cpx<addressing_mode::zero_page>(); break;
+			case 0xE5: run_sbc<addressing_mode::zero_page>(); break;
+			case 0xE6: run_inc<addressing_mode::zero_page>(); break;
+			case 0xE7: run_isc<addressing_mode::zero_page>(); break;
+			case 0xE8: run_inx(); break;
+			case 0xE9: run_sbc<addressing_mode::immediate>(); break;
+			case 0xEA: run_nop(); break;
+			case 0xEB: run_sbc<addressing_mode::immediate>(); break;
+			case 0xEC: run_cpx<addressing_mode::absolute>(); break;
+			case 0xED: run_sbc<addressing_mode::absolute>(); break;
+			case 0xEE: run_inc<addressing_mode::absolute>(); break;
+			case 0xEF: run_isc<addressing_mode::absolute>(); break;
+			case 0xF0: run_beq<addressing_mode::relative>(); break;
+			case 0xF1: run_sbc<addressing_mode::indirect_indexed>(); break;
+			case 0xF2: run_stp(); break;
+			case 0xF3: run_isc<addressing_mode::indirect_indexed>(); break;
+			case 0xF4: run_nop<addressing_mode::zero_page_indexed_x>(); break;
+			case 0xF5: run_sbc<addressing_mode::zero_page_indexed_x>(); break;
+			case 0xF6: run_inc<addressing_mode::zero_page_indexed_x>(); break;
+			case 0xF7: run_isc<addressing_mode::zero_page_indexed_x>(); break;
+			case 0xF8: run_sed(); break;
+			case 0xF9: run_sbc<addressing_mode::absolute_indexed_y>(); break;
+			case 0xFA: run_nop(); break;
+			case 0xFB: run_isc<addressing_mode::absolute_indexed_y>(); break;
+			case 0xFC: run_nop<addressing_mode::absolute_indexed_x>(); break;
+			case 0xFD: run_sbc<addressing_mode::absolute_indexed_x>(); break;
+			case 0xFE: run_inc<addressing_mode::absolute_indexed_x>(); break;
+			case 0xFF: run_isc<addressing_mode::absolute_indexed_x>(); break;
+			default: std::abort();
+		}
+	}
+
+	// -----------------------------------------------------------------------------------------------------------------
+	// Instructions
+	// -----------------------------------------------------------------------------------------------------------------
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_brk() -> void
+	{
+		// BRK: Break
+		fetch_operand<Mode>();
+		execute_interrupt(address{ 0xFFFE });
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_ora() -> void
+	{
+		// ORA: Logical Inclusive OR
+		auto operand = fetch_operand<Mode>();
+		eval_ora(operand.read());
+		current_cycles_ += operand.get_cycles();
+	}
+
+	auto cpu::run_stp() -> void
+	{
+		// TODO: Proper STP handling
+		std::abort();
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_slo() -> void
+	{
+		// SLO: ASL + ORA
+		auto operand = fetch_operand<Mode>(force_page_crossing::yes);
+		auto const tmp = eval_asl(operand.read());
+		operand.write(tmp);
+		eval_ora(tmp);
+		current_cycles_ += operand.get_cycles() + cycle_count::from_cpu(2);
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_nop() -> void
+	{
+		// NOP: NOP
+		auto operand = fetch_operand<Mode>();
+		current_cycles_ += operand.get_cycles();
+	}
+
+	auto cpu::run_nop() -> void
+	{
+		// NOP: NOP
+		current_cycles_ += cycle_count::from_cpu(2);
+	}
+
+	auto cpu::run_php() -> void
+	{
+		// PHP: Push Processor Status
+		eval_php();
+		current_cycles_ += cycle_count::from_cpu(3);
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_asl() -> void
+	{
+		// ASL: Arithmetic Shift Left
+		auto operand = fetch_operand<Mode>();
+		operand.write(eval_asl(operand.read()));
+		current_cycles_ += shift_cycle_count<Mode>();
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_anc() -> void
+	{
+		// ANC: AND #i + copy N to C
+		auto operand = fetch_operand<Mode>();
+		eval_and(operand.read());
+		registers_.c = registers_.n;
+		current_cycles_ += operand.get_cycles();
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_bpl() -> void
+	{
+		// BPL: Break If Positive
+		branch<Mode>(!registers_.n);
+	}
+
+	auto cpu::run_clc() -> void
+	{
+		// CLC: Clear Carry Flag
+		registers_.c = false;
+		current_cycles_ += cycle_count::from_cpu(2);
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_jsr() -> void
+	{
+		// JSR: Jump to Subroutine
+		static_assert(Mode == addressing_mode::absolute, "JSR only supports absolute addressing.");
+
+		push_stack16(registers_.pc + 1);
+
+		auto operand = fetch_operand<Mode>();
+		registers_.pc = operand.get_address().get_absolute();
+		current_cycles_ += cycle_count::from_cpu(6);
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_and() -> void
+	{
+		// AND: Logical AND
+		auto operand = fetch_operand<Mode>();
+		eval_and(operand.read());
+		current_cycles_ += operand.get_cycles();
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_rla() -> void
+	{
+		// RLA: ROL + AND
+		auto operand = fetch_operand<Mode>(force_page_crossing::yes);
+		auto const tmp = eval_rol(operand.read());
+		operand.write(tmp);
+		eval_and(tmp);
+		current_cycles_ += operand.get_cycles() + cycle_count::from_cpu(2);
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_bit() -> void
+	{
+		// BIT: Bit Test
+		auto operand = fetch_operand<Mode>();
+		auto const arg = operand.read();
+		auto const res = (registers_.a & arg) != 0;
+		registers_.z = res == 0;
+		registers_.v = (arg & 0x40) != 0;
+		registers_.n = (arg & 0x80) != 0;
+		current_cycles_ += operand.get_cycles();
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_rol() -> void
+	{
+		// ROR: Rotate Left
+		auto operand = fetch_operand<Mode>();
+		auto const result = eval_rol(operand.read());
+		operand.write(result);
+		current_cycles_ += shift_cycle_count<Mode>();
+	}
+
+	auto cpu::run_plp() -> void
+	{
+		// PLP: Pull Processor Status
+		eval_plp();
+		current_cycles_ += cycle_count::from_cpu(4);
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_bmi() -> void
+	{
+		branch<Mode>(registers_.n);
+	}
+
+	auto cpu::run_sec() -> void
+	{
+		// SEC: Set Carry Flag
+		registers_.c = true;
+		current_cycles_ += cycle_count::from_cpu(2);
+	}
+
+	auto cpu::run_rti() -> void
+	{
+		// RTI: Return From Interrupt
+		eval_plp();
+		registers_.pc = pop_stack16();
+		current_cycles_ += cycle_count::from_cpu(6);
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_eor() -> void
+	{
+		// EOR: Exclusive OR
+		auto operand = fetch_operand<Mode>();
+		eval_eor(operand.read());
+		current_cycles_ += operand.get_cycles();
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_sre() -> void
+	{
+		// SRE: LSR + EOR
+		auto operand = fetch_operand<Mode>(force_page_crossing::yes);
+		auto const tmp = eval_lsr(operand.read());
+		operand.write(tmp);
+		eval_eor(tmp);
+		current_cycles_ += operand.get_cycles() + cycle_count::from_cpu(2);
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_lsr() -> void
+	{
+		// LSR: Logical Shift Right
+		auto operand = fetch_operand<Mode>();
+		auto const old_val = operand.read();
+		auto const new_val = static_cast<std::uint8_t>(old_val >> 1);
+		operand.write(new_val);
+		registers_.c = (old_val & 0x1) != 0;
+		update_zn(new_val);
+		current_cycles_ += shift_cycle_count<Mode>();
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_alr() -> void
+	{
+		// ALR: AND #i + LSR A
+		auto operand = fetch_operand<Mode>();
+		eval_and(operand.read());
+		registers_.a = eval_lsr(registers_.a);
+		current_cycles_ += operand.get_cycles();
+	}
+
+	auto cpu::run_pha() -> void
+	{
+		// PHA: Push Accumulator
+		push_stack8(registers_.a);
+		current_cycles_ += cycle_count::from_cpu(3);
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_jmp() -> void
+	{
+		// JMP: Jump
+		auto operand = fetch_operand<Mode>();
+		registers_.pc = operand.get_address().get_absolute();
+		current_cycles_ += jump_cycle_count<Mode>();
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_bvc() -> void
+	{
+		// BVC: Branch If Overflow Clear
+		branch<Mode>(!registers_.v);
+	}
+
+	auto cpu::run_cli() -> void
+	{
+		// CLI: Clear Interrupt Disable
+		registers_.i = false;
+		current_cycles_ += cycle_count::from_cpu(2);
+	}
+
+	auto cpu::run_rts() -> void
+	{
+		// RTS: Return from Subroutine
+		auto const addr = address{ pop_stack16() } + 1;
+		registers_.pc = addr.get_absolute();
+		current_cycles_ += cycle_count::from_cpu(6);
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_adc() -> void
+	{
+		// ADC: Add With Carry
+		auto operand = fetch_operand<Mode>();
+		eval_adc(operand.read());
+		current_cycles_ += operand.get_cycles();
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_rra() -> void
+	{
+		// RRA: ROR + ADC
+		auto operand = fetch_operand<Mode>(force_page_crossing::yes);
+		auto const tmp = eval_ror(operand.read());
+		operand.write(tmp);
+		eval_adc(tmp);
+		current_cycles_ += operand.get_cycles() + cycle_count::from_cpu(2);
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_ror() -> void
+	{
+		// ROR: Rotate Right
+		auto operand = fetch_operand<Mode>();
+		auto const result = eval_ror(operand.read());
+		operand.write(result);
+		current_cycles_ += shift_cycle_count<Mode>();
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_arr() -> void
+	{
+		// ARR: AND #i + ROR A but with different flags
+		// TODO
+		std::abort();
+	}
+
+	auto cpu::run_pla() -> void
+	{
+		// PLA: Pull Accumulator
+		registers_.a = pop_stack8();
+		update_zn(registers_.a);
+		current_cycles_ += cycle_count::from_cpu(4);
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_bvs() -> void
+	{
+		// BVS: Branch If Overflow Set
+		branch<Mode>(registers_.v);
+	}
+
+	auto cpu::run_sei() -> void
+	{
+		// SEI: Set Interrupt Disable
+		registers_.i = true;
+		current_cycles_ += cycle_count::from_cpu(2);
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_sta() -> void
+	{
+		// STA: Store Accumulator
+		auto operand = fetch_operand<Mode>(force_page_crossing::yes);
+		operand.write(registers_.a);
+		current_cycles_ += operand.get_cycles();
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_ahx() -> void
+	{
+		// AHX: ???
+		// TODO
+		std::abort();
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_sax() -> void
+	{
+		// SAX: AND A X
+		auto operand = fetch_operand<Mode>();
+		auto const result = static_cast<std::uint8_t>(registers_.a & registers_.x);
+		operand.write(result);
+		current_cycles_ += operand.get_cycles();
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_sty() -> void
+	{
+		// STX: Store Y
+		auto operand = fetch_operand<Mode>();
+		operand.write(registers_.y);
+		current_cycles_ += operand.get_cycles();
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_stx() -> void
+	{
+		// STX: Store X
+		auto operand = fetch_operand<Mode>();
+		operand.write(registers_.x);
+		current_cycles_ += operand.get_cycles();
+	}
+
+	auto cpu::run_dey() -> void
+	{
+		// DEY: Decrement Y Register
+		registers_.y -= 1;
+		update_zn(registers_.y);
+		current_cycles_ += cycle_count::from_cpu(2);
+	}
+
+	auto cpu::run_txa() -> void
+	{
+		// TXA: Transfer X to Accumulator
+		registers_.a = registers_.x;
+		update_zn(registers_.a);
+		current_cycles_ += cycle_count::from_cpu(2);
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_xaa() -> void
+	{
+		// XAA: Depends on analog behavior.
+		run_stp();
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_bcc() -> void
+	{
+		// BCC: Branch If Carry Clear
+		branch<Mode>(!registers_.c);
+	}
+
+	auto cpu::run_tya() -> void
+	{
+		// TYA: Transfer Y to Accumulator
+		registers_.a = registers_.y;
+		update_zn(registers_.a);
+		current_cycles_ += cycle_count::from_cpu(2);
+	}
+
+	auto cpu::run_txs() -> void
+	{
+		// TXS: Transfer X to Stack Pointer
+		registers_.sp = registers_.x;
+		current_cycles_ += cycle_count::from_cpu(2);
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_tas() -> void
+	{
+		// TAS: ???
+		// TODO
+		std::abort();
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_shy() -> void
+	{
+		// SHY: ???
+		// TODO
+		std::abort();
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_shx() -> void
+	{
+		// SHY: ???
+		// TODO
+		std::abort();
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_ldy() -> void
+	{
+		// LDY: Load Y Register
+		auto operand = fetch_operand<Mode>();
+		registers_.y = operand.read();
+		update_zn(registers_.y);
+		current_cycles_ += operand.get_cycles();
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_lda() -> void
+	{
+		// LDA: Load Accumulator
+		auto operand = fetch_operand<Mode>();
+		registers_.a = operand.read();
+		update_zn(registers_.a);
+		current_cycles_ += operand.get_cycles();
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_ldx() -> void
+	{
+		// LDX: Load X Register
+		auto operand = fetch_operand<Mode>();
+		registers_.x = operand.read();
+		update_zn(registers_.x);
+		current_cycles_ += operand.get_cycles();
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_lax() -> void
+	{
+		// LAX: LDA + TAX
+		auto operand = fetch_operand<Mode>();
+		registers_.x = registers_.a = operand.read();
+		update_zn(registers_.a);
+		current_cycles_ += operand.get_cycles();
+	}
+
+	auto cpu::run_tay() -> void
+	{
+		// TAY: Transfer Accumulator to Y
+		registers_.y = registers_.a;
+		update_zn(registers_.y);
+		current_cycles_ += cycle_count::from_cpu(2);
+	}
+
+	auto cpu::run_tax() -> void
+	{
+		// TAX: Transfer Accumulator to X
+		registers_.x = registers_.a;
+		update_zn(registers_.x);
+		current_cycles_ += cycle_count::from_cpu(2);
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_bcs() -> void
+	{
+		// BCS: Branch If Carry Set
+		branch<Mode>(registers_.c);
+	}
+
+	auto cpu::run_clv() -> void
+	{
+		// CLV: Clear Overflow Flag
+		registers_.v = false;
+		current_cycles_ += cycle_count::from_cpu(2);
+	}
+
+	auto cpu::run_tsx() -> void
+	{
+		// TSX: Transfer Stack Pointer to X
+		registers_.x = registers_.sp;
+		update_zn(registers_.x);
+		current_cycles_ += cycle_count::from_cpu(2);
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_las() -> void
+	{
+		// LAS: ???
+		// TODO
+		std::abort();
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_cpy() -> void
+	{
+		// CPY: Compare Y Register
+		auto operand = fetch_operand<Mode>();
+		eval_cmp(registers_.y, operand.read());
+		current_cycles_ += operand.get_cycles();
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_axs() -> void
+	{
+		// AXS: Set X to ((A AND X) - #value without borrow), updates NZC
+		// TODO
+		std::abort();
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_cmp() -> void
+	{
+		// CMP: Compare
+		auto operand = fetch_operand<Mode>();
+		eval_cmp(registers_.a, operand.read());
+		current_cycles_ += operand.get_cycles();
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_dcp() -> void
+	{
+		// DCP: DEC + CMP
+		auto operand = fetch_operand<Mode>(force_page_crossing::yes);
+		auto const tmp = static_cast<std::uint8_t>(operand.read() - 1);
+		operand.write(tmp);
+		eval_cmp(registers_.a, tmp);
+		current_cycles_ += operand.get_cycles() + cycle_count::from_cpu(2);
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_dec() -> void
+	{
+		// DEC: Decrement Memory
+		auto operand = fetch_operand<Mode>();
+		auto const old_val = read8(operand.get_address());
+		auto const new_val = static_cast<std::uint8_t>(old_val - 1);
+		write8(operand.get_address(), new_val);
+		update_zn(new_val);
+		current_cycles_ += inc_dec_cycle_count<Mode>();
+	}
+
+	auto cpu::run_iny() -> void
+	{
+		// INY: Increment Y
+		registers_.y += 1;
+		update_zn(registers_.y);
+		current_cycles_ += cycle_count::from_cpu(2);
+	}
+
+	auto cpu::run_dex() -> void
+	{
+		// DEX: Decrement X Register
+		registers_.x -= 1;
+		update_zn(registers_.x);
+		current_cycles_ += cycle_count::from_cpu(2);
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_bne() -> void
+	{
+		// BNE: Branch If Not Equal
+		branch<Mode>(!registers_.z);
+	}
+
+	auto cpu::run_cld() -> void
+	{
+		// CLD: Clear Decimal Mode
+		registers_.d = false;
+		current_cycles_ += cycle_count::from_cpu(2);
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_cpx() -> void
+	{
+		// CPX: Compare X Register
+		auto operand = fetch_operand<Mode>();
+		eval_cmp(registers_.x, operand.read());
+		current_cycles_ += operand.get_cycles();
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_sbc() -> void
+	{
+		// SBC: Subtract With Carry
+		auto operand = fetch_operand<Mode>();
+		eval_adc(~operand.read());
+		current_cycles_ += operand.get_cycles();
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_isc() -> void
+	{
+		// ISC: INC + SBC
+		auto operand = fetch_operand<Mode>(force_page_crossing::yes);
+		auto const tmp = static_cast<std::uint8_t>(operand.read() + 1);
+		operand.write(tmp);
+		eval_adc(~tmp);
+		current_cycles_ += operand.get_cycles() + cycle_count::from_cpu(2);
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_inc() -> void
+	{
+		// INC: Increment Memory
+		auto operand = fetch_operand<Mode>();
+		auto const old_val = read8(operand.get_address());
+		auto const new_val = static_cast<std::uint8_t>(old_val + 1);
+		write8(operand.get_address(), new_val);
+		update_zn(new_val);
+		current_cycles_ += inc_dec_cycle_count<Mode>();
+	}
+
+	auto cpu::run_inx() -> void
+	{
+		// INX: Increment X
+		registers_.x += 1;
+		update_zn(registers_.x);
+		current_cycles_ += cycle_count::from_cpu(2);
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::run_beq() -> void
+	{
+		// BEQ: Branch If Equal
+		branch<Mode>(registers_.z);
+	}
+
+	auto cpu::run_sed() -> void
+	{
+		// SED: Set Decimal Flag
+		registers_.d = true;
+		current_cycles_ += cycle_count::from_cpu(2);
+	}
+	
+	// -----------------------------------------------------------------------------------------------------------------
+	// Helpers
+	// -----------------------------------------------------------------------------------------------------------------
+
+	auto cpu::advance_pc8() -> std::uint8_t
+	{
+		auto const val = read8(address{ registers_.pc });
+		registers_.pc += 1;
+		return val;
+	}
+
+	auto cpu::advance_pc16() -> std::uint16_t
+	{
+		auto const val = read16(address{ registers_.pc });
+		registers_.pc += 2;
+		return val;
+	}
+
+	auto cpu::push_stack8(std::uint8_t const value) -> void
+	{
+		write8(stack_offset + registers_.sp, value);
+		registers_.sp -= 1;
+	}
+
+	auto cpu::push_stack16(std::uint16_t const value) -> void
+	{
+		auto const low = static_cast<std::uint8_t>(value >> 0 & 0xFF);
+		auto const high = static_cast<std::uint8_t>(value >> 8 & 0xFF);
+		push_stack8(high);
+		push_stack8(low);
+	}
+
+	auto cpu::pop_stack8() -> std::uint8_t
+	{
+		registers_.sp += 1;
+		return read8(stack_offset + registers_.sp);
+	}
+
+	auto cpu::pop_stack16() -> std::uint16_t
+	{
+		auto const low = pop_stack8();
+		auto const high = pop_stack8();
+		return static_cast<std::uint16_t>((high << 8) | (low << 0));
+	}
+
+	auto cpu::update_zn(std::uint8_t const value) -> void
+	{
+		registers_.z = value == 0;
+		registers_.n = (value & 0x80) != 0;
+	}
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::branch(bool const condition) -> void
+	{
+		static_assert(Mode == addressing_mode::relative, "Branch should only be used with relative operands.");
+
+		auto operand = fetch_operand<Mode>();
+		if (condition)
+		{
+			registers_.pc = operand.get_address().get_absolute();
+			current_cycles_ += operand.get_cycles();
+		}
+		else
+		{
+			current_cycles_ += cycle_count::from_cpu(2);
+		}
+	}
+
+	auto cpu::execute_interrupt(address const vector) -> void
+	{
+		push_stack16(registers_.pc);
+		eval_php();
+		registers_.pc = read16(vector);
+		registers_.i = true;
+		current_cycles_ += cycle_count::from_cpu(7);
+	}
+
+	auto cpu::eval_ror(std::uint8_t const arg) -> std::uint8_t
+	{
+		auto const res = static_cast<std::uint8_t>((registers_.c << 7) | (arg >> 1));
+		registers_.c = (arg & 0x1) != 0;
+		update_zn(res);
+		return res;
+	}
+
+	auto cpu::eval_rol(std::uint8_t const arg) -> std::uint8_t
+	{
+		auto const res = static_cast<std::uint8_t>((arg << 1) | (registers_.c ? 1 : 0));
+		registers_.c = (arg & 0x80) != 0;
+		update_zn(res);
+		return res;
+	}
+
+	auto cpu::eval_asl(std::uint8_t const arg) -> std::uint8_t
+	{
+		auto const new_val = static_cast<std::uint8_t>(arg << 1);
+		registers_.c = (arg & 0x80) != 0;
+		update_zn(new_val);
+		return new_val;
+	}
+
+	auto cpu::eval_lsr(std::uint8_t const arg) -> std::uint8_t
+	{
+		auto const new_val = static_cast<std::uint8_t>(arg >> 1);
+		registers_.c = (arg & 0x01) != 0;
+		update_zn(new_val);
+		return new_val;
+	}
+
+	auto cpu::eval_adc(std::uint8_t const arg) -> void
+	{
+		auto const old_val = registers_.a;
+		auto const tmp = old_val + arg + (registers_.c ? 1 : 0);
+		auto const new_val = static_cast<std::uint8_t>(tmp);
+
+		registers_.a = new_val;
+		registers_.c = tmp > 0xFF;
+		registers_.v = ((old_val ^ arg) & 0x80) == 0 && ((old_val ^ new_val) & 0x80) != 0;
+		update_zn(registers_.a);
+	}
+
+	auto cpu::eval_and(std::uint8_t const arg) -> void
+	{
+		registers_.a &= arg;
+		update_zn(registers_.a);
+	}
+
+	auto cpu::eval_ora(std::uint8_t const arg) -> void
+	{
+		registers_.a |= arg;
+		update_zn(registers_.a);
+	}
+
+	auto cpu::eval_eor(std::uint8_t const arg) -> void
+	{
+		registers_.a ^= arg;
+		update_zn(registers_.a);
+	}
+
+	auto cpu::eval_cmp(std::uint8_t const a, std::uint8_t const b) -> void
+	{
+		update_zn(a - b);
+		registers_.c = a >= b;
+	}
+
+	auto cpu::eval_plp() -> void
+	{
+		// Ignore bits 4 and 5
+		registers_.p =
+			(pop_stack8() & 0b11001111) |
+			(registers_.p & 0b00110000);
+	}
+
+	auto cpu::eval_php() -> void
+	{
+		// Always set bits 4 and 5.
+		push_stack8(registers_.p | 0b00110000);
+	}
+
+	// -----------------------------------------------------------------------------------------------------------------
+	// Operands
+	// -----------------------------------------------------------------------------------------------------------------
+
+	//
+	// See: https://www.nesdev.org/wiki/CPU_addressing_modes
+	//
+
+	template<cpu::addressing_mode Mode>
+	auto cpu::fetch_operand(force_page_crossing const force_page_crossing) -> operand<Mode>
+	{
+		auto addr = address{};
+		auto cycles = cycle_count{};
+
+		switch (Mode)
+		{
+			case addressing_mode::immediate: static_assert(Mode != addressing_mode::immediate);
+			case addressing_mode::accumulator: static_assert(Mode != addressing_mode::accumulator);
+			case addressing_mode::zero_page:
+			{
+				addr = address{ advance_pc8() };
+				cycles = cycle_count::from_cpu(3);
+				break;
+			}
+			case addressing_mode::absolute:
+			{
+				addr = address{ advance_pc16() };
+				cycles = cycle_count::from_cpu(4);
+				break;
+			}
+			case addressing_mode::relative:
+			{
+				auto const offset = static_cast<std::int8_t>(advance_pc8());
+				auto const base = address{ registers_.pc };
+				addr = address{ static_cast<std::uint16_t>(registers_.pc + offset) };
+				auto const page_crossing =
+					base.get_page() != addr.get_page() || force_page_crossing == force_page_crossing::yes;
+				cycles = cycle_count::from_cpu(page_crossing ? 4 : 3);
+				break;
+			}
+			case addressing_mode::indirect:
+			{
+				auto const arg = address{ advance_pc16() };
+				// Account for buggy indirect read: https://www.nesdev.org/wiki/Errata
+				addr = arg.get_offset() == 0xFF
+					? address{ read8(address{ arg.get_page(), 0x00 }), read8(arg) }
+					: address{ read16(arg) };
+				cycles = cycle_count::from_cpu(6);
+				break;
+			}
+			case addressing_mode::zero_page_indexed_x:
+			{
+				// PEEK((arg + X) % 256)
+				addr = address{ 0x00, static_cast<std::uint8_t>(advance_pc8() + registers_.x) };
+				cycles = cycle_count::from_cpu(4);
+				break;
+			}
+			case addressing_mode::zero_page_indexed_y:
+			{
+				// PEEK((arg + Y) % 256)
+				addr = address{ 0x00, static_cast<std::uint8_t>(advance_pc8() + registers_.y) };
+				cycles = cycle_count::from_cpu(4);
+				break;
+			}
+			case addressing_mode::absolute_indexed_x:
+			{
+				// PEEK(arg + X)
+				auto const arg = address{ advance_pc16() };
+				addr = arg + registers_.x;
+				auto const page_crossing =
+					addr.get_page() != arg.get_page() || force_page_crossing == force_page_crossing::yes;
+				cycles = cycle_count::from_cpu(page_crossing ? 5 : 4);
+				break;
+			}
+			case addressing_mode::absolute_indexed_y:
+			{
+				// PEEK(arg + Y)
+				auto const arg = address{ advance_pc16() };
+				addr = arg + registers_.y;
+				auto const page_crossing =
+					addr.get_page() != arg.get_page() || force_page_crossing == force_page_crossing::yes;
+				cycles = cycle_count::from_cpu(page_crossing ? 5 : 4);
+				break;
+			}
+			case addressing_mode::indexed_indirect:
+			{
+				// PEEK(PEEK((arg + X) % 256) + PEEK((arg + X + 1) % 256) * 256)
+				auto const arg = advance_pc8();
+				auto const page = read8(address{ 0x00, static_cast<std::uint8_t>(arg + registers_.x + 1) });
+				auto const offset = read8(address{ 0x00, static_cast<std::uint8_t>(arg + registers_.x) });
+				addr = address{ page, offset };
+				cycles = cycle_count::from_cpu(6);
+				break;
+			}
+			case addressing_mode::indirect_indexed:
+			{
+				// PEEK(PEEK(arg) + PEEK((arg + 1) % 256) * 256 + Y)
+				auto const arg = advance_pc8();
+				auto const page = read8(address{ 0x00, static_cast<std::uint8_t>(arg + 1) });
+				auto const offset = read8(address{ 0x00, static_cast<std::uint8_t>(arg) });
+				auto const base = address{ page, offset };
+				addr = base + registers_.y;
+				auto const page_crossing =
+					addr.get_page() != base.get_page() || force_page_crossing == force_page_crossing::yes;
+				cycles = cycle_count::from_cpu(page_crossing ? 6 : 5);
+				break;
+			}
+		}
+
+		return operand<Mode>{ *this, addr, cycles };
+	}
+
+	template<>
+	auto cpu::fetch_operand<cpu::addressing_mode::accumulator>(force_page_crossing)
+		-> operand<addressing_mode::accumulator>
+	{
+		return operand<addressing_mode::accumulator>{ *this };
+	}
+
+	template<>
+	auto cpu::fetch_operand<cpu::addressing_mode::immediate>(force_page_crossing)
+		-> operand<addressing_mode::immediate>
+	{
+		return operand<addressing_mode::immediate>{ advance_pc8() };
+	}
+
+	// -----------------------------------------------------------------------------------------------------------------
+	// Memory Access
+	// -----------------------------------------------------------------------------------------------------------------
+
+	//
+	// See: https://www.nesdev.org/wiki/CPU_memory_map
+	//
+
+	auto cpu::read8(address const addr) -> std::uint8_t
+	{
+		if (addr <= address{ 0x1FFF }) { return ram_[addr.get_absolute() % ram_size]; }
+		if (addr <= address{ 0x3FFF })
+		{
+#ifdef NES_ENABLE_PPU
+			switch (addr.get_absolute() % 8)
+			{
+				case 0: return ppu_.read_latch();
+				case 1: return ppu_.read_latch();
+				case 2: return ppu_.read_ppustatus();
+				case 3: return ppu_.read_latch();
+				case 4: return ppu_.read_oamdata();
+				case 5: return ppu_.read_latch();
+				case 6: return ppu_.read_latch();
+				case 7: return ppu_.read_ppudata();
+				default: return 0x0;
+			}
+#else
+			return 0x0;
+#endif
+		}
+		if (addr <= address{ 0x4013 }) { return 0x0; } // TODO: APU registers
+#ifdef NES_ENABLE_PPU
+		if (addr == address{ 0x4014 }) { return ppu_.read_latch(); }
+#else
+		if (addr == address{ 0x4014 }) { return 0x0; }
+#endif
+		if (addr == address{ 0x4015 }) { return 0x0; } // TODO: APU registers
+		if (addr == address{ 0x4016 }) { return controller_1_.read(); }
+		if (addr == address{ 0x4017 }) { return controller_2_.read(); }
+		if (addr <= address{ 0x401F }) { return 0x0; }
+		return mapper_.read_cpu(addr);
+	}
+
+	auto cpu::read16(address const addr) -> std::uint16_t
+	{
+		auto const low = read8(addr + 0);
+		auto const high = read8(addr + 1);
+		return static_cast<std::uint16_t>((high << 8) | (low << 0));
+	}
+
+	auto cpu::write8(address const addr, std::uint8_t const value) -> void
+	{
+		if (addr <= address{ 0x1FFF }) { ram_[addr.get_absolute() % ram_size] = value; return; }
+		if (addr <= address{ 0x3FFF })
+		{
+#ifdef NES_ENABLE_PPU
+			switch (addr.get_absolute() % 8)
+			{
+				case 0: ppu_.write_ppuctrl(value); return;
+				case 1: ppu_.write_ppumask(value); return;
+				case 2: ppu_.write_latch(value); return;
+				case 3: ppu_.write_oamaddr(value); return;
+				case 4: ppu_.write_oamdata(value); return;
+				case 5: ppu_.write_ppuscroll(value); return;
+				case 6: ppu_.write_ppuaddr(value); return;
+				case 7: ppu_.write_ppudata(value); return;
+				default: return;
+			}
+#else
+			return;
+#endif
+		}
+		if (addr <= address{ 0x4013 }) { return; } // TODO: APU registers
+#ifdef NES_ENABLE_PPU
+		if (addr == address{ 0x4014 }) { ppu_.write_oamdma(value); return; }
+#else
+		if (addr == address{ 0x4014 }) { return; }
+#endif
+		if (addr == address{ 0x4015 }) { return; } // TODO: APU registers
+		if (addr == address{ 0x4016 }) { controller_1_.write(value); return; }
+		if (addr == address{ 0x4017 }) { controller_2_.write(value); return; }
+		if (addr <= address{ 0x401F }) { return; }
+		mapper_.write_cpu(addr, value);
+	}
+
+	auto cpu::write16(address const addr, std::uint16_t const value) -> void
+	{
+		auto const low = static_cast<std::uint8_t>(value >> 0 & 0xFF);
+		auto const high = static_cast<std::uint8_t>(value >> 8 & 0xFF);
+		write8(addr + 0, low);
+		write8(addr + 1, high);
+	}
+} // namespace nes::ref
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