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580 lines
20 KiB
C++
580 lines
20 KiB
C++
//
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// 68000Storage.hpp
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// Clock Signal
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//
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// Created by Thomas Harte on 08/03/2019.
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// Copyright © 2019 Thomas Harte. All rights reserved.
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//
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#ifndef MC68000Storage_h
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#define MC68000Storage_h
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class ProcessorStorage {
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public:
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ProcessorStorage();
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protected:
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RegisterPair32 data_[8];
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RegisterPair32 address_[8];
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RegisterPair32 program_counter_;
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RegisterPair32 stack_pointers_[2]; // [0] = user stack pointer; [1] = supervisor; the values from here
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// are copied into/out of address_[7] upon mode switches.
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RegisterPair32 prefetch_queue_; // Each word will go into the low part of the word, then proceed upward.
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// Generic sources and targets for memory operations;
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// by convention: effective_address_[0] = source, [1] = destination.
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//
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// These, and the various register contents above, should be kept
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// close to the top of this class so that small-integer offsets can be
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// used in instances of Program (see below).
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RegisterPair32 effective_address_[2];
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RegisterPair32 source_bus_data_;
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RegisterPair32 destination_bus_data_;
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enum class ExecutionState {
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/// The normal mode, this means the 68000 is expending processing effort.
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Executing,
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/// The 68000 is in a holding loop, waiting for either DTack or to be notified of a bus error.
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WaitingForDTack,
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/// Occurs after executing a STOP instruction; the processor will idle waiting for an interrupt or reset.
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Stopped,
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/// Occurs at the end of the current bus cycle after detection of the HALT input, continuing until
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/// HALT is no longer signalled.
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Halted,
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/// Signals a transition from some other straight directly to cueing up an interrupt.
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WillBeginInterrupt,
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} execution_state_ = ExecutionState::Executing;
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Microcycle dtack_cycle_;
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Microcycle stop_cycle_;
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// Various status parts.
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int is_supervisor_;
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int interrupt_level_;
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uint_fast32_t zero_result_; // The zero flag is set if this value is zero.
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uint_fast32_t carry_flag_; // The carry flag is set if this value is non-zero.
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uint_fast32_t extend_flag_; // The extend flag is set if this value is non-zero.
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uint_fast32_t overflow_flag_; // The overflow flag is set if this value is non-zero.
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uint_fast32_t negative_flag_; // The negative flag is set if this value is non-zero.
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uint_fast32_t trace_flag_; // The trace flag is set if this value is non-zero.
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uint_fast32_t last_trace_flag_ = 0;
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// Bus inputs.
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int bus_interrupt_level_ = 0;
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bool dtack_ = false;
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bool is_peripheral_address_ = false;
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bool bus_error_ = false;
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bool bus_request_ = false;
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bool bus_acknowledge_ = false;
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bool halt_ = false;
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// Holds the interrupt level that should be serviced at the next instruction
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// dispatch, if any.
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int pending_interrupt_level_ = 0;
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// Holds the interrupt level that is currently being serviced.
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// TODO: surely this doesn't need to be distinct from the pending_interrupt_level_?
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int accepted_interrupt_level_ = 0;
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bool is_starting_interrupt_ = false;
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HalfCycles half_cycles_left_to_run_;
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HalfCycles e_clock_phase_;
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enum class Operation: uint8_t {
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None,
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ABCD, SBCD, NBCD,
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ADDb, ADDw, ADDl,
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ADDQb, ADDQw, ADDQl,
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ADDAw, ADDAl,
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ADDQAw, ADDQAl,
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ADDXb, ADDXw, ADDXl,
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SUBb, SUBw, SUBl,
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SUBQb, SUBQw, SUBQl,
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SUBAw, SUBAl,
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SUBQAw, SUBQAl,
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SUBXb, SUBXw, SUBXl,
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MOVEb, MOVEw, MOVEl, MOVEq,
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MOVEAw, MOVEAl,
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PEA,
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MOVEtoSR, MOVEfromSR,
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MOVEtoCCR,
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ORItoSR, ORItoCCR,
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ANDItoSR, ANDItoCCR,
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EORItoSR, EORItoCCR,
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BTSTb, BTSTl,
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BCLRl, BCLRb,
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CMPb, CMPw, CMPl,
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CMPAw,
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TSTb, TSTw, TSTl,
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JMP, RTS,
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BRA, Bcc,
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DBcc,
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Scc,
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CLRb, CLRw, CLRl,
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NEGXb, NEGXw, NEGXl,
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NEGb, NEGw, NEGl,
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ASLb, ASLw, ASLl, ASLm,
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ASRb, ASRw, ASRl, ASRm,
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LSLb, LSLw, LSLl, LSLm,
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LSRb, LSRw, LSRl, LSRm,
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ROLb, ROLw, ROLl, ROLm,
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RORb, RORw, RORl, RORm,
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ROXLb, ROXLw, ROXLl, ROXLm,
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ROXRb, ROXRw, ROXRl, ROXRm,
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MOVEMtoRl, MOVEMtoRw,
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MOVEMtoMl, MOVEMtoMw,
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MOVEPtoRl, MOVEPtoRw,
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MOVEPtoMl, MOVEPtoMw,
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ANDb, ANDw, ANDl,
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EORb, EORw, EORl,
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NOTb, NOTw, NOTl,
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ORb, ORw, ORl,
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MULU, MULS,
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DIVU, DIVS,
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RTE_RTR,
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TRAP, TRAPV,
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CHK,
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EXG, SWAP,
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BCHGl, BCHGb,
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BSETl, BSETb,
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TAS,
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EXTbtow, EXTwtol,
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LINK, UNLINK,
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STOP,
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};
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/*!
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Bus steps are sequences of things to communicate to the bus.
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Standard behaviour is: (i) perform microcycle; (ii) perform action.
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*/
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struct BusStep {
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Microcycle microcycle;
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enum class Action {
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None,
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/// Performs effective_address_[0] += 2.
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IncrementEffectiveAddress0,
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/// Performs effective_address_[1] += 2.
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IncrementEffectiveAddress1,
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/// Performs effective_address_[0] -= 2.
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DecrementEffectiveAddress0,
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/// Performs effective_address_[1] -= 2.
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DecrementEffectiveAddress1,
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/// Performs program_counter_ += 2.
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IncrementProgramCounter,
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/// Copies prefetch_queue_[1] to prefetch_queue_[0].
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AdvancePrefetch,
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/// Performs effective_address_[0] += 2 and zeroes the final bit of the stack pointer.
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IncrementEffectiveAddress0AlignStackPointer,
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/*!
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Terminates an atomic program; if nothing else is pending, schedules the next instruction.
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This action is special in that it usurps any included microcycle. So any Step with this
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as its action acts as an end-of-list sentinel.
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*/
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ScheduleNextProgram
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} action = Action::None;
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forceinline bool operator ==(const BusStep &rhs) const {
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if(action != rhs.action) return false;
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return microcycle == rhs.microcycle;
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}
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forceinline bool is_terminal() const {
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return action == Action::ScheduleNextProgram;
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}
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};
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/*!
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A micro-op is: (i) an action to take; and (ii) a sequence of bus operations
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to perform after taking the action.
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NOTE: this therefore has the opposite order of behaviour compared to a BusStep,
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the action occurs BEFORE the bus operations, not after.
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A nullptr bus_program terminates a sequence of micro operations; the is_terminal
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test should be used to query for that. The action on the final operation will
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be performed.
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*/
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struct MicroOp {
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enum class Action: uint8_t {
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None,
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/// Does whatever this instruction says is the main operation.
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PerformOperation,
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/*
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All of the below will honour the source and destination masks
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in deciding where to apply their actions.
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*/
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/// Subtracts 1 from the [source/destination]_address.
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Decrement1,
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/// Subtracts 2 from the [source/destination]_address.
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Decrement2,
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/// Subtracts 4 from the [source/destination]_address.
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Decrement4,
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/// Adds 1 from the [source/destination]_address.
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Increment1,
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/// Adds 2 from the [source/destination]_address.
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Increment2,
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/// Adds 4 from the [source/destination]_address.
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Increment4,
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/// Copies the source and/or destination to effective_address_.
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CopyToEffectiveAddress,
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/// Peeking into the end of the prefetch queue, calculates the proper target of (d16,An) addressing.
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CalcD16An,
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/// Peeking into the end of the prefetch queue, calculates the proper target of (d8,An,Xn) addressing.
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CalcD8AnXn,
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/// Peeking into the prefetch queue, calculates the proper target of (d16,PC) addressing,
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/// adjusting as though it had been performed after the proper PC fetches. The source
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/// and destination mask flags affect only the destination of the result.
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CalcD16PC,
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/// Peeking into the prefetch queue, calculates the proper target of (d8,An,Xn) addressing,
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/// adjusting as though it had been performed after the proper PC fetches. The source
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/// and destination mask flags affect only the destination of the result.
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CalcD8PCXn,
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/// Sets the high word according to the MSB of the low word.
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SignExtendWord,
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/// Sets the high three bytes according to the MSB of the low byte.
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SignExtendByte,
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/// From the next word in the prefetch queue assembles a sign-extended long word in either or
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/// both of effective_address_[0] and effective_address_[1].
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AssembleWordAddressFromPrefetch,
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/// From the next word in the prefetch queue assembles a 0-padded 32-bit long word in either or
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/// both of bus_data_[0] and bus_data_[1].
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AssembleWordDataFromPrefetch,
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/// Copies the next two prefetch words into one of the effective_address_.
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AssembleLongWordAddressFromPrefetch,
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/// Copies the next two prefetch words into one of the bus_data_.
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AssembleLongWordDataFromPrefetch,
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/// Copies the low part of the prefetch queue into next_word_.
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CopyNextWord,
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/// Performs write-back of post-increment address and/or sign extensions as necessary.
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MOVEMtoRComplete,
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/// Performs write-back of pre-decrement address.
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MOVEMtoMComplete,
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// (i) inspects the prefetch queue to determine the length of this instruction and copies the next PC to destination_bus_data_;
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// (ii) copies the stack pointer minus 4 to effective_address_[1];
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// (iii) decrements the stack pointer by four.
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PrepareJSR,
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PrepareBSR,
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// (i) copies the stack pointer to effective_address_[0];
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// (ii) increments the stack pointer by four.
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PrepareRTS,
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// (i) fills in the proper stack addresses to the bus steps for this micro-op; and
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// (ii) adjusts the stack pointer appropriately.
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PrepareRTE_RTR,
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// Performs the necessary status word substitution for the current interrupt level,
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// and does the first part of initialising the trap steps.
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PrepareINT,
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// Observes the bus_error_, valid_peripheral_address_ and/or the value currently in
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// source_bus_data_ to determine an interrupt vector, and fills in the final trap
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// steps detail appropriately.
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PrepareINTVector,
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};
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static_assert(uint8_t(Action::PrepareINTVector) < 32); // i.e. will fit into five bits.
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static constexpr int SourceMask = 1 << 5;
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static constexpr int DestinationMask = 1 << 6;
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uint8_t action = uint8_t(Action::None); // Requires 7 bits at present; sizeof(Action) + the two flags above.
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static constexpr uint16_t NoBusProgram = std::numeric_limits<uint16_t>::max();
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uint16_t bus_program = NoBusProgram; // Empirically requires 11 bits at present.
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MicroOp(): action(uint8_t(Action::None)), bus_program(NoBusProgram) {}
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MicroOp(uint8_t action) : action(action), bus_program(NoBusProgram) {}
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MicroOp(uint8_t action, uint16_t bus_program) : action(action), bus_program(bus_program) {}
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MicroOp(Action action) : MicroOp(uint8_t(action)) {}
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MicroOp(Action action, uint16_t bus_program) : MicroOp(uint8_t(action), bus_program) {}
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forceinline bool is_terminal() const {
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return bus_program == NoBusProgram;
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}
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};
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/*!
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A program represents the implementation of a particular opcode, as a sequence
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of micro-ops and, separately, the operation to perform plus whatever other
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fields the operation requires.
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Some of the fields are slightly convoluted in how they identify the information
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they reference; this is done to keep this struct as small as possible due to
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concerns about cache size.
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On the 64-bit Intel processor this emulator was developed on, the struct below
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adds up to 8 bytes; four for the initial uint32_t and then one each for the
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remaining fields, with no additional padding being inserted by the compiler.
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*/
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struct Program {
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Program() {
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// Initialisers for bitfields aren't available until C++20. So, yuck, do it manually.
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requires_supervisor = 0;
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source = 0;
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dest = 0;
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destination_offset = 0;
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source_offset = 0;
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}
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static constexpr uint32_t NoSuchProgram = std::numeric_limits<uint32_t>::max();
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/// The offset into the all_micro_ops_ at which micro-ops for this instruction begin,
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/// or std::numeric_limits<uint32_t>::max() if this is an invalid Program.
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uint32_t micro_operations = NoSuchProgram;
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/// The overarching operation applied by this program when the moment comes.
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Operation operation;
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/// The number of bytes after the beginning of an instance of ProcessorStorage that the RegisterPair32 containing
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/// a source value for this operation lies at.
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uint8_t source_offset: 7;
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/// The number of bytes after the beginning of an instance of ProcessorStorage that the RegisterPair32 containing
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/// a destination value for this operation lies at.
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uint8_t destination_offset: 7;
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/// Set if this program requires supervisor mode.
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bool requires_supervisor: 1;
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/// The source address register (for pre-decrement and post-increment actions).
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uint8_t source: 3;
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/// Destination address register.
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uint8_t dest: 3;
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void set_source_address([[maybe_unused]] ProcessorStorage &storage, int index) {
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source = uint8_t(index);
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assert(int(source) == index);
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}
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void set_destination_address([[maybe_unused]] ProcessorStorage &storage, int index) {
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dest = uint8_t(index);
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assert(int(dest) == index);
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}
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void set_requires_supervisor(bool req) {
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requires_supervisor = req;
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assert(requires_supervisor == req);
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}
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void set_source(ProcessorStorage &storage, RegisterPair32 *target) {
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source_offset = decltype(source_offset)(reinterpret_cast<uint8_t *>(target) - reinterpret_cast<uint8_t *>(&storage));
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// Test that destination_offset could be stored fully within the integer size provided for source_offset.
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assert(source_offset == (reinterpret_cast<uint8_t *>(target) - reinterpret_cast<uint8_t *>(&storage)));
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}
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void set_destination(ProcessorStorage &storage, RegisterPair32 *target) {
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destination_offset = decltype(destination_offset)(reinterpret_cast<uint8_t *>(target) - reinterpret_cast<uint8_t *>(&storage));
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// Test that destination_offset could be stored fully within the integer size provided for destination_offset.
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assert(destination_offset == (reinterpret_cast<uint8_t *>(target) - reinterpret_cast<uint8_t *>(&storage)));
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}
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void set_source(ProcessorStorage &storage, int mode, int reg) {
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set_source_address(storage, reg);
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switch(mode) {
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case 0: set_source(storage, &storage.data_[reg]); break;
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case 1: set_source(storage, &storage.address_[reg]); break;
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default: set_source(storage, &storage.source_bus_data_); break;
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}
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}
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void set_destination(ProcessorStorage &storage, int mode, int reg) {
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set_destination_address(storage, reg);
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switch(mode) {
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case 0: set_destination(storage, &storage.data_[reg]); break;
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case 1: set_destination(storage, &storage.address_[reg]); break;
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default: set_destination(storage, &storage.destination_bus_data_); break;
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}
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}
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};
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// Storage for all the sequences of bus steps and micro-ops used throughout
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// the 68000.
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std::vector<BusStep> all_bus_steps_;
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std::vector<MicroOp> all_micro_ops_;
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// A lookup table from instructions to implementations.
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Program instructions[65536];
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// Special steps and programs for exception handlers.
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BusStep *reset_bus_steps_;
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MicroOp *long_exception_micro_ops_; // i.e. those that leave 14 bytes on the stack — bus error and address error.
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MicroOp *short_exception_micro_ops_; // i.e. those that leave 6 bytes on the stack — everything else (other than interrupts).
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MicroOp *interrupt_micro_ops_;
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// Special micro-op sequences and storage for conditionals.
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BusStep *branch_taken_bus_steps_;
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BusStep *branch_byte_not_taken_bus_steps_;
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BusStep *branch_word_not_taken_bus_steps_;
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BusStep *bsr_bus_steps_;
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uint32_t dbcc_false_address_;
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BusStep *dbcc_condition_true_steps_;
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BusStep *dbcc_condition_false_no_branch_steps_;
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BusStep *dbcc_condition_false_branch_steps_;
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BusStep *movem_read_steps_;
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BusStep *movem_write_steps_;
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// These two are dynamically modified depending on the particular
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// TRAP and bus error.
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BusStep *trap_steps_;
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BusStep *bus_error_steps_;
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// Current bus step pointer, and outer program pointer.
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const Program *active_program_ = nullptr;
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const MicroOp *active_micro_op_ = nullptr;
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const BusStep *active_step_ = nullptr;
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RegisterPair16 decoded_instruction_ = 0;
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uint16_t next_word_ = 0;
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/// Copies address_[7] to the proper stack pointer based on current mode.
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void write_back_stack_pointer();
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/// Sets or clears the supervisor flag, ensuring the stack pointer is properly updated.
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void set_is_supervisor(bool);
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// Transient storage for MOVEM, TRAP and others.
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RegisterPair16 throwaway_value_;
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uint32_t movem_final_address_;
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uint32_t precomputed_addresses_[65]; // This is a big chunk of rarely-used storage. It's placed last deliberately.
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/*!
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Evaluates the conditional described by @c code and returns @c true or @c false to
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indicate the result of that evaluation.
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*/
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forceinline bool evaluate_condition(uint8_t code) {
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switch(code & 0xf) {
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default:
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case 0x00: return true; // true
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|
case 0x01: return false; // false
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|
case 0x02: return zero_result_ && !carry_flag_; // high
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|
case 0x03: return !zero_result_ || carry_flag_; // low or same
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|
case 0x04: return !carry_flag_; // carry clear
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|
case 0x05: return carry_flag_; // carry set
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|
case 0x06: return zero_result_; // not equal
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|
case 0x07: return !zero_result_; // equal
|
|
case 0x08: return !overflow_flag_; // overflow clear
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|
case 0x09: return overflow_flag_; // overflow set
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|
case 0x0a: return !negative_flag_; // positive
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|
case 0x0b: return negative_flag_; // negative
|
|
case 0x0c: // greater than or equal
|
|
return (negative_flag_ && overflow_flag_) || (!negative_flag_ && !overflow_flag_);
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|
case 0x0d: // less than
|
|
return (negative_flag_ && !overflow_flag_) || (!negative_flag_ && overflow_flag_);
|
|
case 0x0e: // greater than
|
|
return zero_result_ && ((negative_flag_ && overflow_flag_) || (!negative_flag_ && !overflow_flag_));
|
|
case 0x0f: // less than or equal
|
|
return !zero_result_ || (negative_flag_ && !overflow_flag_) || (!negative_flag_ && overflow_flag_);
|
|
}
|
|
}
|
|
|
|
/*!
|
|
Fills in the appropriate addresses and values to complete the TRAP steps — those
|
|
representing a short-form exception — and mutates the status register as if one
|
|
were beginning.
|
|
*/
|
|
forceinline void populate_trap_steps(uint32_t vector, uint16_t status) {
|
|
// Fill in the status word value.
|
|
destination_bus_data_.full = status;
|
|
|
|
// Switch to supervisor mode, disable the trace bit.
|
|
set_is_supervisor(true);
|
|
trace_flag_ = last_trace_flag_ = 0;
|
|
|
|
// Pick a vector.
|
|
effective_address_[0].full = vector << 2;
|
|
|
|
// Schedule the proper stack activity.
|
|
precomputed_addresses_[0] = address_[7].full - 2; // PC.l
|
|
precomputed_addresses_[1] = address_[7].full - 6; // status word (in destination_bus_data_)
|
|
precomputed_addresses_[2] = address_[7].full - 4; // PC.h
|
|
address_[7].full -= 6;
|
|
|
|
// Set the default timing.
|
|
trap_steps_->microcycle.length = HalfCycles(8);
|
|
}
|
|
|
|
forceinline void populate_bus_error_steps(uint32_t vector, uint16_t status, uint16_t bus_status, RegisterPair32 faulting_address) {
|
|
// Fill in the status word value.
|
|
destination_bus_data_.halves.low.full = status;
|
|
destination_bus_data_.halves.high.full = bus_status;
|
|
effective_address_[1] = faulting_address;
|
|
|
|
// Switch to supervisor mode, disable the trace bit.
|
|
set_is_supervisor(true);
|
|
trace_flag_ = last_trace_flag_ = 0;
|
|
|
|
// Pick a vector.
|
|
effective_address_[0].full = vector << 2;
|
|
|
|
// Schedule the proper stack activity.
|
|
precomputed_addresses_[0] = address_[7].full - 2; // PC.l
|
|
precomputed_addresses_[1] = address_[7].full - 6; // status word
|
|
precomputed_addresses_[2] = address_[7].full - 4; // PC.h
|
|
precomputed_addresses_[3] = address_[7].full - 8; // current instruction
|
|
precomputed_addresses_[4] = address_[7].full - 10; // fault address.l
|
|
precomputed_addresses_[5] = address_[7].full - 14; // bus cycle status word
|
|
precomputed_addresses_[6] = address_[7].full - 12; // fault address.h
|
|
address_[7].full -= 14;
|
|
}
|
|
|
|
inline uint16_t get_status() const;
|
|
inline void set_status(uint16_t);
|
|
|
|
private:
|
|
friend struct ProcessorStorageConstructor;
|
|
friend class ProcessorStorageTests;
|
|
friend struct State;
|
|
};
|
|
|
|
#endif /* MC68000Storage_h */
|