Establish general pattern for selecting a performance phase and obtaining operands.

Processors/68000Mk2/68000Mk2.hpp

@@ -372,6 +372,7 @@ template <class BusHandler, bool dtack_is_implicit = true, bool permit_overrun =
 
 	private:
 		BusHandler &bus_handler_;
+		void setup_operation();
 };
 
 }

Processors/68000Mk2/Implementation/68000Mk2Implementation.hpp

@@ -10,6 +10,7 @@
 #define _8000Mk2Implementation_h
 
 #include <cassert>
+#include <cstdio>
 
 namespace CPU {
 namespace MC68000Mk2 {
@@ -145,6 +146,8 @@ void Processor<BusHandler, dtack_is_implicit, permit_overrun, signal_will_perfor
 	prefetch_.high = prefetch_.low;	\
 	ReadProgramWord(prefetch_.low)
 
+	using Mode = InstructionSet::M68k::AddressingMode;
+
 	// Otherwise continue for all time, until back in debt.
 	// Formatting is slightly obtuse here to make this look more like a coroutine.
 	while(true) { switch(state_) {
@@ -181,21 +184,38 @@ void Processor<BusHandler, dtack_is_implicit, permit_overrun, signal_will_perfor
 		case State::Decode:
 			opcode_ = prefetch_.high.w;
 			instruction_ = decoder_.decode(opcode_);
+			instruction_address_ = program_counter_.l - 4;
 
-			// TODO: it might be better to switch on instruction_.operation
+			// TODO: check for privilege and unrecognised instructions.
-			// and establish both the instruction pattern and the operand
-			// flags here?
-			operand_flags_ = InstructionSet::M68k::operand_flags<InstructionSet::M68k::Model::M68000>(instruction_.operation);
 
-			operand_ = 0;
+			// Obtain operand flags and pick a perform pattern.
+			setup_operation();
+
+			next_operand_ = 0;
 		[[fallthrough]];
 
 		// Check the operand flags to determine whether the operand at index
 		// operand_ needs to be fetched, and do so.
 		case State::FetchOperand:
+			switch(instruction_.mode(next_operand_)) {
+				case Mode::None:
+					state_ = perform_state_;
+				continue;
+
+				case Mode::AddressRegisterDirect:
+				case Mode::DataRegisterDirect:
+					operand_[next_operand_] = registers_[instruction_.lreg(next_operand_)];
+					++next_operand_;
+					state_ = next_operand_ == 2 ? perform_state_ : state_;
+				continue;
+
+				default:
+					assert(false);
+			}
 
 		[[fallthrough]];
 		default:
+			printf("Unhandled or unterminated state: %d\n", state_);
 			assert(false);
 	}}
 
@@ -214,6 +234,25 @@ void Processor<BusHandler, dtack_is_implicit, permit_overrun, signal_will_perfor
 
 }
 
+template <class BusHandler, bool dtack_is_implicit, bool permit_overrun, bool signal_will_perform>
+void Processor<BusHandler, dtack_is_implicit, permit_overrun, signal_will_perform>::setup_operation() {
+
+#define BIND(x, p)	\
+	case InstructionSet::M68k::Operation::x:			\
+		operand_flags_ = InstructionSet::M68k::operand_flags<InstructionSet::M68k::Model::M68000, InstructionSet::M68k::Operation::x>();	\
+		perform_state_ = State::p;	\
+	break;
+
+	switch(instruction_.operation) {
+		BIND(NBCD, Perform_np);
+
+		default:
+			assert(false);
+	}
+
+#undef BIND
+}
+
 template <class BusHandler, bool dtack_is_implicit, bool permit_overrun, bool signal_will_perform>
 CPU::MC68000Mk2::State Processor<BusHandler, dtack_is_implicit, permit_overrun, signal_will_perform>::get_state() {
 	return CPU::MC68000Mk2::State();

Processors/68000Mk2/Implementation/68000Mk2Storage.hpp

@@ -16,34 +16,76 @@ namespace CPU {
 namespace MC68000Mk2 {
 
 struct ProcessorBase {
+	/// States for the state machine which are named by
+	/// me for their purpose rather than automatically by file position.
+	/// These are negative to avoid ambiguity with the other group.
 	enum State: int {
 		Reset			= -1,
 		Decode	 		= -2,
 		WaitForDTACK	= -3,
 		FetchOperand	= -4,
+
+		// Various different effective address calculations.
+
+		CalculateAnDn	= -5,
+
+		// Various forms of perform; each of these will
+		// perform the current instruction, then do the
+		// indicated bus cycle.
+
+		Perform_np		= -6,
 	};
 	int state_ = State::Reset;
 
+	/// Counts time left on the clock before the current batch of processing
+	/// is complete; may be less than zero.
 	HalfCycles time_remaining_;
-	int post_dtack_state_ = 0;
+
+	/// Current supervisor state, for direct provision to the bus handler.
 	int is_supervisor_ = 1;
 
+	// A decoder for instructions, plus all collected information about the
+	// current instruction.
 	InstructionSet::M68k::Predecoder<InstructionSet::M68k::Model::M68000> decoder_;
 	InstructionSet::M68k::Preinstruction instruction_;
 	uint16_t opcode_;
 	uint8_t operand_flags_;
+	uint32_t instruction_address_;
 
+	// Register state.
 	InstructionSet::M68k::Status status_;
 	SlicedInt32 program_counter_;
 	SlicedInt32 registers_[16];		// D0–D7 followed by A0–A7.
 	SlicedInt32 stack_pointers_[2];
 
+	/// Current state of the DTACK input.
 	bool dtack_ = false;
+	/// Current state of the VPA input.
 	bool vpa_ = false;
+	/// Current state of the BERR input.
 	bool berr_ = false;
 
+	/// Contains the prefetch queue; the most-recently fetched thing is the
+	/// low portion of this word, and the thing fetched before that has
+	/// proceeded to the high portion.
 	SlicedInt32 prefetch_;
-	int operand_ = 0;
+
+	// Temporary storage for the current instruction's operands
+	// and the corresponding effective addresses.
+	CPU::SlicedInt32 operand_[2];
+	uint32_t effective_address_[2];
+
+	/// If currently in the wait-for-DTACK state, this indicates where to go
+	/// upon receipt of DTACK or VPA. BERR will automatically segue
+	/// into the proper exception.
+	int post_dtack_state_ = 0;
+
+	/// The perform state for this operation.
+	int perform_state_ = 0;
+
+	/// When fetching or storing operands, this is the next one to fetch
+	/// or store.
+	int next_operand_ = 0;
 };
 
 }