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169 lines
3.8 KiB
C++
169 lines
3.8 KiB
C++
//
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// 65816Implementation.hpp
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// Clock Signal
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//
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// Created by Thomas Harte on 27/09/2020.
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// Copyright © 2020 Thomas Harte. All rights reserved.
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//
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template <typename BusHandler> void Processor<BusHandler>::run_for(const Cycles cycles) {
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// Temporary storage for the next bus cycle.
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uint32_t bus_address = 0;
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uint8_t *bus_value = nullptr;
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uint8_t throwaway = 0;
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BusOperation bus_operation = BusOperation::None;
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Cycles number_of_cycles = cycles + cycles_left_to_run_;
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while(number_of_cycles > Cycles(0)) {
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const MicroOp operation = *next_op_;
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++next_op_;
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switch(operation) {
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//
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// Scheduling.
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//
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case OperationMoveToNextProgram: {
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// The exception program will determine the appropriate way to respond
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// based on the pending exception if one exists; otherwise just do a
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// standard fetch-decode-execute.
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const auto offset = instructions[pending_exceptions_ ? size_t(OperationSlot::Exception) : size_t(OperationSlot::FetchDecodeExecute)].program_offsets[0];
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next_op_ = µ_ops_[offset];
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instruction_buffer_.clear();
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data_buffer_.clear();
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last_operation_pc_ = pc_;
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} continue;
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case OperationDecode: {
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// A VERY TEMPORARY piece of logging.
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printf("%02x\n", instruction_buffer_.value);
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active_instruction_ = &instructions[instruction_offset_ + instruction_buffer_.value];
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const auto size_flag = mx_flags_[active_instruction_->size_field];
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next_op_ = µ_ops_[active_instruction_->program_offsets[size_flag]];
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instruction_buffer_.clear();
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} continue;
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//
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// PC fetches.
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//
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case CycleFetchIncrementPC:
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case CycleFetchOpcode:
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bus_address = pc_ | program_bank_;
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bus_value = instruction_buffer_.next();
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bus_operation = (operation == CycleFetchOpcode) ? MOS6502Esque::ReadOpcode : MOS6502Esque::Read;
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// TODO: split this action when I'm happy that my route to bus accesses is settled, to avoid repeating the conditional
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// embedded into the `switch`.
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++pc_;
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break;
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case CycleFetchPC:
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bus_address = pc_ | program_bank_;
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bus_value = &throwaway;
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bus_operation = MOS6502Esque::Read;
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break;
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//
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// Data movement.
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//
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case OperationCopyPCToData:
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data_buffer_.size = 2;
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data_buffer_.value = pc_;
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break;
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case OperationCopyInstructionToData:
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data_buffer_ = instruction_buffer_;
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break;
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//
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// Performance.
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//
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case OperationPerform:
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switch(active_instruction_->operation) {
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//
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// Flag manipulation.
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//
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case CLD:
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decimal_flag_ = 0;
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break;
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//
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// Loads, stores and transfers
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//
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#define LD(dest, src, masks) dest.full = (dest.full & masks[0]) | (src & masks[1])
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case LDA:
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LD(a_, data_buffer_.value, m_masks_);
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break;
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case LDX:
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LD(x_, data_buffer_.value, x_masks_);
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break;
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case LDY:
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LD(y_, data_buffer_.value, x_masks_);
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break;
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case TXS:
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// TODO: does this transfer in full when in 8-bit index mode?
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LD(s_, x_.full, x_masks_);
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break;
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#undef LD
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default:
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assert(false);
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}
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break;
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default:
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assert(false);
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}
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number_of_cycles -= bus_handler_.perform_bus_operation(bus_operation, bus_address, bus_value);
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}
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cycles_left_to_run_ = number_of_cycles;
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}
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void ProcessorBase::set_power_on(bool active) {
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if(active) {
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pending_exceptions_ |= PowerOn;
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} else {
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pending_exceptions_ &= ~PowerOn;
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}
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}
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void ProcessorBase::set_irq_line(bool active) {
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if(active) {
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pending_exceptions_ |= IRQ;
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} else {
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pending_exceptions_ &= ~IRQ;
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}
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}
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void ProcessorBase::set_reset_line(bool active) {
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if(active) {
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pending_exceptions_ |= Reset;
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} else {
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pending_exceptions_ &= ~Reset;
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}
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}
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void ProcessorBase::set_nmi_line(bool active) {
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// This is edge triggered.
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if(active) {
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pending_exceptions_ |= NMI;
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}
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}
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// The 65816 can't jam.
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bool ProcessorBase::is_jammed() const { return false; }
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