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125 lines
3.9 KiB
C++
125 lines
3.9 KiB
C++
//
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// CartridgePitfall2.h
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// Clock Signal
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//
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// Created by Thomas Harte on 18/03/2017.
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// Copyright 2017 Thomas Harte. All rights reserved.
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//
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#pragma once
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namespace Atari2600::Cartridge {
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class Pitfall2: public BusExtender {
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public:
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Pitfall2(uint8_t *rom_base, std::size_t rom_size) :
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BusExtender(rom_base, rom_size),
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rom_ptr_(rom_base) {}
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void advance_cycles(int cycles) {
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cycles_since_audio_update_ += cycles;
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}
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void perform_bus_operation(CPU::MOS6502::BusOperation operation, uint16_t address, uint8_t *value) {
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address &= 0x1fff;
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if(!(address & 0x1000)) return;
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switch(address) {
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// MARK: - Reads
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// The random number generator
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case 0x1000: case 0x1001: case 0x1002: case 0x1003: case 0x1004:
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if(isReadOperation(operation)) {
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*value = random_number_generator_;
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}
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random_number_generator_ = uint8_t(
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(random_number_generator_ << 1) |
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(~( (random_number_generator_ >> 7) ^
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(random_number_generator_ >> 5) ^
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(random_number_generator_ >> 4) ^
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(random_number_generator_ >> 3)
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) & 1));
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break;
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case 0x1005: case 0x1006: case 0x1007:
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*value = update_audio();
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break;
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case 0x1008: case 0x1009: case 0x100a: case 0x100b: case 0x100c: case 0x100d: case 0x100e: case 0x100f:
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*value = rom_base_[8192 + address_for_counter(address & 7)];
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break;
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case 0x1010: case 0x1011: case 0x1012: case 0x1013: case 0x1014: case 0x1015: case 0x1016: case 0x1017:
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*value = rom_base_[8192 + address_for_counter(address & 7)] & mask_[address & 7];
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break;
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// MARK: - Writes
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case 0x1040: case 0x1041: case 0x1042: case 0x1043: case 0x1044: case 0x1045: case 0x1046: case 0x1047:
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top_[address & 7] = *value;
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break;
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case 0x1048: case 0x1049: case 0x104a: case 0x104b: case 0x104c: case 0x104d: case 0x104e: case 0x104f:
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bottom_[address & 7] = *value;
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break;
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case 0x1050: case 0x1051: case 0x1052: case 0x1053: case 0x1054: case 0x1055: case 0x1056: case 0x1057:
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featcher_address_[address & 7] = (featcher_address_[address & 7] & 0xff00) | *value;
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mask_[address & 7] = 0x00;
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break;
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case 0x1058: case 0x1059: case 0x105a: case 0x105b: case 0x105c: case 0x105d: case 0x105e: case 0x105f:
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featcher_address_[address & 7] = (featcher_address_[address & 7] & 0x00ff) | uint16_t(*value << 8);
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break;
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case 0x1070: case 0x1071: case 0x1072: case 0x1073: case 0x1074: case 0x1075: case 0x1076: case 0x1077:
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random_number_generator_ = 0;
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break;
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// MARK: - Paging
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case 0x1ff8: rom_ptr_ = rom_base_; break;
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case 0x1ff9: rom_ptr_ = rom_base_ + 4096; break;
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// MARK: - Business as usual
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default:
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if(isReadOperation(operation)) {
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*value = rom_ptr_[address & 4095];
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}
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break;
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}
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}
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private:
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inline uint16_t address_for_counter(int counter) {
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uint16_t fetch_address = (featcher_address_[counter] & 2047) ^ 2047;
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if((featcher_address_[counter] & 0xff) == top_[counter]) mask_[counter] = 0xff;
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if((featcher_address_[counter] & 0xff) == bottom_[counter]) mask_[counter] = 0x00;
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featcher_address_[counter]--;
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return fetch_address;
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}
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inline uint8_t update_audio() {
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const unsigned int clock_divisor = 57;
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int cycles_to_run_for = int(cycles_since_audio_update_.divide(clock_divisor).as_integral());
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int table_position = 0;
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for(int c = 0; c < 3; c++) {
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audio_channel_[c] = uint8_t((audio_channel_[c] + cycles_to_run_for) % (1 + top_[5 + c]));
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if((featcher_address_[5 + c] & 0x1000) && ((top_[5 + c] - audio_channel_[c]) > bottom_[5 + c])) {
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table_position |= 0x4 >> c;
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}
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}
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static uint8_t level_table[8] = { 0x0, 0x4, 0x5, 0x9, 0x6, 0xa, 0xb, 0xf };
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return level_table[table_position];
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}
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uint16_t featcher_address_[8] = {0, 0, 0, 0, 0, 0, 0, 0};
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uint8_t top_[8], bottom_[8], mask_[8] = {0, 0, 0, 0, 0, 0, 0, 0};
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uint8_t random_number_generator_ = 0;
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uint8_t *rom_ptr_;
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uint8_t audio_channel_[3];
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Cycles cycles_since_audio_update_ = 0;
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};
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}
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