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236 lines
6.7 KiB
C++
236 lines
6.7 KiB
C++
//
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// MDA.hpp
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// Clock Signal
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//
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// Created by Thomas Harte on 05/12/2023.
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// Copyright © 2023 Thomas Harte. All rights reserved.
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//
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#pragma once
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#include "../../Components/6845/CRTC6845.hpp"
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#include "../../Outputs/CRT/CRT.hpp"
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#include "../../Machines/Utility/ROMCatalogue.hpp"
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namespace PCCompatible {
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class MDA {
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public:
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MDA() : crtc_(outputter_) {}
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static constexpr uint32_t BaseAddress = 0xb'0000;
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static constexpr auto FontROM = ROM::Name::PCCompatibleMDAFont;
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void set_source(const uint8_t *ram, std::vector<uint8_t> font) {
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outputter_.ram = ram;
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outputter_.font = font;
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}
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void run_for(Cycles cycles) {
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// Input rate is the PIT rate of 1,193,182 Hz.
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// MDA is actually clocked at 16.257 MHz; which is treated internally as 1,806,333.333333333333333... Hz
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//
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// The GCD of those two numbers is... 2. Oh well.
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full_clock_ += 8'128'500 * cycles.as<int>();
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crtc_.run_for(Cycles(full_clock_ / (596'591 * 9)));
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full_clock_ %= (596'591 * 9);
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}
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template <int address>
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void write(uint8_t value) {
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switch(address) {
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case 0: case 2: case 4: case 6:
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crtc_.select_register(value);
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break;
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case 1: case 3: case 5: case 7:
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crtc_.set_register(value);
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break;
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case 0x8:
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outputter_.set_control(value);
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break;
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default: break;
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}
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}
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template <int address>
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uint8_t read() {
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switch(address) {
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case 1: case 3: case 5: case 7:
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return crtc_.get_register();
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case 0x8: return outputter_.control();
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default: return 0xff;
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}
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}
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// MARK: - Call-ins for ScanProducer.
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void set_scan_target(Outputs::Display::ScanTarget *scan_target) {
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outputter_.crt.set_scan_target(scan_target);
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}
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Outputs::Display::ScanStatus get_scaled_scan_status() const {
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return outputter_.crt.get_scaled_scan_status() * 596591.0f / 8128500.0f;
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}
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// MARK: - Display type configuration.
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void set_display_type(Outputs::Display::DisplayType) {}
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Outputs::Display::DisplayType get_display_type() const {
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return outputter_.crt.get_display_type();
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}
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private:
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struct CRTCOutputter {
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CRTCOutputter() :
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crt(882, 9, 370, 3, Outputs::Display::InputDataType::Red2Green2Blue2)
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// TODO: really this should be a Luminance8 and set an appropriate modal tint colour;
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// consider whether that's worth building into the scan target.
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{
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crt.set_visible_area(Outputs::Display::Rect(0.028f, 0.025f, 0.98f, 0.98f));
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crt.set_display_type(Outputs::Display::DisplayType::RGB);
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}
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void set_control(uint8_t control) {
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// b0: 'high resolution' (probably breaks if not 1)
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// b3: video enable
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// b5: enable blink
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control_ = control;
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}
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uint8_t control() {
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return control_;
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}
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void perform_bus_cycle(const Motorola::CRTC::BusState &state) {
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// Determine new output state.
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const OutputState new_state =
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(state.hsync | state.vsync) ? OutputState::Sync :
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((state.display_enable && control_&0x08) ? OutputState::Pixels : OutputState::Border);
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// Upon either a state change or just having accumulated too much local time...
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if(new_state != output_state || count > 882) {
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// (1) flush preexisting state.
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if(count) {
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switch(output_state) {
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case OutputState::Sync: crt.output_sync(count); break;
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case OutputState::Border: crt.output_blank(count); break;
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case OutputState::Pixels:
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crt.output_data(count);
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pixels = pixel_pointer = nullptr;
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break;
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}
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}
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// (2) adopt new state.
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output_state = new_state;
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count = 0;
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}
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// Collect pixels if applicable.
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if(output_state == OutputState::Pixels) {
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if(!pixels) {
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pixel_pointer = pixels = crt.begin_data(DefaultAllocationSize);
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// Flush any period where pixels weren't recorded due to back pressure.
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if(pixels && count) {
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crt.output_blank(count);
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count = 0;
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}
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}
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if(pixels) {
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static constexpr uint8_t high_intensity = 0x0d;
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static constexpr uint8_t low_intensity = 0x09;
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static constexpr uint8_t off = 0x00;
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if(state.cursor) {
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pixel_pointer[0] = pixel_pointer[1] = pixel_pointer[2] = pixel_pointer[3] =
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pixel_pointer[4] = pixel_pointer[5] = pixel_pointer[6] = pixel_pointer[7] =
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pixel_pointer[8] = low_intensity;
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} else {
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const uint8_t attributes = ram[((state.refresh_address << 1) + 1) & 0xfff];
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const uint8_t glyph = ram[((state.refresh_address << 1) + 0) & 0xfff];
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uint8_t row = font[(glyph * 14) + state.row_address];
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const uint8_t intensity = (attributes & 0x08) ? high_intensity : low_intensity;
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uint8_t blank = off;
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// Handle irregular attributes.
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// Cf. http://www.seasip.info/VintagePC/mda.html#memmap
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switch(attributes) {
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case 0x00: case 0x08: case 0x80: case 0x88:
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row = 0;
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break;
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case 0x70: case 0x78: case 0xf0: case 0xf8:
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row ^= 0xff;
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blank = intensity;
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break;
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}
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// Apply blink if enabled.
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if((control_ & 0x20) && (attributes & 0x80) && (state.field_count & 16)) {
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row ^= 0xff;
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blank = (blank == off) ? intensity : off;
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}
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if(((attributes & 7) == 1) && state.row_address == 13) {
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// Draw as underline.
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std::fill(pixel_pointer, pixel_pointer + 9, intensity);
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} else {
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// Draw according to ROM contents, possibly duplicating final column.
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pixel_pointer[0] = (row & 0x80) ? intensity : off;
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pixel_pointer[1] = (row & 0x40) ? intensity : off;
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pixel_pointer[2] = (row & 0x20) ? intensity : off;
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pixel_pointer[3] = (row & 0x10) ? intensity : off;
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pixel_pointer[4] = (row & 0x08) ? intensity : off;
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pixel_pointer[5] = (row & 0x04) ? intensity : off;
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pixel_pointer[6] = (row & 0x02) ? intensity : off;
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pixel_pointer[7] = (row & 0x01) ? intensity : off;
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pixel_pointer[8] = (glyph >= 0xc0 && glyph < 0xe0) ? pixel_pointer[7] : blank;
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}
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}
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pixel_pointer += 9;
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}
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}
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// Advance.
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count += 9;
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// Output pixel row prematurely if storage is exhausted.
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if(output_state == OutputState::Pixels && pixel_pointer == pixels + DefaultAllocationSize) {
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crt.output_data(count);
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count = 0;
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pixels = pixel_pointer = nullptr;
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}
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}
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Outputs::CRT::CRT crt;
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enum class OutputState {
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Sync, Pixels, Border
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} output_state = OutputState::Sync;
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int count = 0;
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uint8_t *pixels = nullptr;
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uint8_t *pixel_pointer = nullptr;
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static constexpr size_t DefaultAllocationSize = 720;
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const uint8_t *ram = nullptr;
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std::vector<uint8_t> font;
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uint8_t control_ = 0;
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} outputter_;
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Motorola::CRTC::CRTC6845<
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CRTCOutputter,
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Motorola::CRTC::Personality::HD6845S,
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Motorola::CRTC::CursorType::MDA> crtc_;
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int full_clock_ = 0;
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};
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}
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