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485 lines
15 KiB
C++
485 lines
15 KiB
C++
//
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// Video.hpp
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// Clock Signal
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//
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// Created by Thomas Harte on 20/03/2024.
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// Copyright © 2024 Thomas Harte. All rights reserved.
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//
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#pragma once
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#include "../../../Outputs/Log.hpp"
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#include "../../../Outputs/CRT/CRT.hpp"
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#include <array>
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#include <cstdint>
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#include <cstring>
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namespace Archimedes {
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template <typename InterruptObserverT, typename ClockRateObserverT, typename SoundT>
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struct Video {
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Video(InterruptObserverT &interrupt_observer, ClockRateObserverT &clock_rate_observer, SoundT &sound, const uint8_t *ram) :
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interrupt_observer_(interrupt_observer),
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clock_rate_observer_(clock_rate_observer),
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sound_(sound),
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ram_(ram),
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crt_(Outputs::Display::InputDataType::Red4Green4Blue4) {
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set_clock_divider(3);
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crt_.set_visible_area(Outputs::Display::Rect(0.06f, 0.07f, 0.9f, 0.9f));
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crt_.set_display_type(Outputs::Display::DisplayType::RGB);
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}
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static constexpr uint16_t colour(uint32_t value) {
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uint8_t packed[2]{};
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packed[0] = value & 0xf;
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packed[1] = (value & 0xf0) | ((value & 0xf00) >> 8);
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#if TARGET_RT_BIG_ENDIAN
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return static_cast<uint16_t>(packed[1] | (packed[0] << 8));
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#else
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return static_cast<uint16_t>(packed[0] | (packed[1] << 8));
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#endif
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};
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static constexpr uint16_t high_spread[] = {
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colour(0b0000'0000'0000), colour(0b0000'0000'1000), colour(0b0000'0100'0000), colour(0b0000'0100'1000),
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colour(0b0000'1000'0000), colour(0b0000'1000'1000), colour(0b0000'1100'0000), colour(0b0000'1100'1000),
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colour(0b1000'0000'0000), colour(0b1000'0000'1000), colour(0b1000'0100'0000), colour(0b1000'0100'1000),
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colour(0b1000'1000'0000), colour(0b1000'1000'1000), colour(0b1000'1100'0000), colour(0b1000'1100'1000),
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};
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void write(uint32_t value) {
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const auto target = (value >> 24) & 0xfc;
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const auto timing_value = [](uint32_t value) -> uint32_t {
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return (value >> 14) & 0x3ff;
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};
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switch(target) {
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case 0x00: case 0x04: case 0x08: case 0x0c:
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case 0x10: case 0x14: case 0x18: case 0x1c:
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case 0x20: case 0x24: case 0x28: case 0x2c:
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case 0x30: case 0x34: case 0x38: case 0x3c:
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colours_[target >> 2] = colour(value);
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break;
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case 0x40: border_colour_ = colour(value); break;
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case 0x44: case 0x48: case 0x4c:
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cursor_colours_[(target - 0x40) >> 2] = colour(value);
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break;
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case 0x80: horizontal_timing_.period = timing_value(value); break;
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case 0x84: horizontal_timing_.sync_width = timing_value(value); break;
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case 0x88: horizontal_timing_.border_start = timing_value(value); break;
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case 0x8c: horizontal_timing_.display_start = timing_value(value); break;
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case 0x90: horizontal_timing_.display_end = timing_value(value); break;
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case 0x94: horizontal_timing_.border_end = timing_value(value); break;
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case 0x98:
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horizontal_timing_.cursor_start = (value >> 13) & 0x7ff;
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cursor_shift_ = (value >> 11) & 3;
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break;
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case 0x9c:
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logger.error().append("TODO: Video horizontal interlace: %d", (value >> 14) & 0x3ff);
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break;
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case 0xa0: vertical_timing_.period = timing_value(value); break;
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case 0xa4: vertical_timing_.sync_width = timing_value(value); break;
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case 0xa8: vertical_timing_.border_start = timing_value(value); break;
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case 0xac: vertical_timing_.display_start = timing_value(value); break;
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case 0xb0: vertical_timing_.display_end = timing_value(value); break;
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case 0xb4: vertical_timing_.border_end = timing_value(value); break;
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case 0xb8: vertical_timing_.cursor_start = timing_value(value); break;
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case 0xbc: vertical_timing_.cursor_end = timing_value(value); break;
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case 0xe0:
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logger.error().append("TODO: video control: %08x", value);
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// Set pixel rate. This is the value that a 24Mhz clock should be divided
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// by to get half the pixel rate.
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switch(value & 0b11) {
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case 0b00: set_clock_divider(6); break; // i.e. pixel clock = 8Mhz.
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case 0b01: set_clock_divider(4); break; // 12Mhz.
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case 0b10: set_clock_divider(3); break; // 16Mhz.
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case 0b11: set_clock_divider(2); break; // 24Mhz.
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}
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// Set colour depth.
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colour_depth_ = Depth((value >> 2) & 0b11);
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break;
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//
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// Sound parameters.
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//
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case 0x60: case 0x64: case 0x68: case 0x6c:
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case 0x70: case 0x74: case 0x78: case 0x7c: {
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const uint8_t channel = ((value >> 26) + 7) & 7;
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sound_.set_stereo_image(channel, value & 7);
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} break;
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case 0xc0:
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sound_.set_frequency(value & 0x7f);
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break;
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default:
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logger.error().append("TODO: unrecognised VIDC write of %08x", value);
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break;
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}
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}
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void tick() {
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// Pick new horizontal state, possibly rolling over into the vertical.
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horizontal_state_.increment_position(horizontal_timing_);
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if(horizontal_state_.position == horizontal_timing_.period) {
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horizontal_state_.position = 0;
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vertical_state_.increment_position(vertical_timing_);
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pixel_count_ = 0;
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if(vertical_state_.position == vertical_timing_.period) {
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vertical_state_.position = 0;
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address_ = frame_start_;
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cursor_address_ = cursor_start_;
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entered_sync_ = true;
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interrupt_observer_.update_interrupts();
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}
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// Determine which next 8 bytes will be the cursor image for this line.
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// Pragmatically, updating cursor_address_ once per line avoids probable
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// errors in getting it to appear appropriately over both pixels and border.
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if(vertical_state_.cursor_active) {
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uint8_t *cursor_pixel = cursor_image_.data();
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for(int byte = 0; byte < 8; byte ++) {
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cursor_pixel[0] = (ram_[cursor_address_] >> 0) & 3;
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cursor_pixel[1] = (ram_[cursor_address_] >> 2) & 3;
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cursor_pixel[2] = (ram_[cursor_address_] >> 4) & 3;
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cursor_pixel[3] = (ram_[cursor_address_] >> 6) & 3;
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cursor_pixel += 4;
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++cursor_address_;
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}
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}
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cursor_pixel_ = 32;
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}
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// Update cursor pixel counter if applicable; this might mean triggering it
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// and it might just mean advancing it if it has already been triggered.
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if(vertical_state_.cursor_active) {
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const auto pixel_position = horizontal_state_.position << 1;
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if(pixel_position <= horizontal_timing_.cursor_start && (pixel_position + 2) > horizontal_timing_.cursor_start) {
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cursor_pixel_ = int(horizontal_timing_.cursor_start) - int(pixel_position);
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}
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}
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// Grab some more pixels if appropriate.
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const auto flush_pixels = [&]() {
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const auto duration = static_cast<int>(time_in_phase_);
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crt_.output_data(duration, static_cast<size_t>(time_in_phase_) * 2);
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time_in_phase_ = 0;
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pixels_ = nullptr;
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};
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if(phase_ == Phase::Display) {
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if(pixels_ && time_in_phase_ == PixelBufferSize/2) {
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flush_pixels();
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}
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if(!pixels_) {
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if(time_in_phase_) {
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flush_pixels();
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}
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pixels_ = reinterpret_cast<uint16_t *>(crt_.begin_data(PixelBufferSize));
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}
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const auto next_byte = [&]() -> uint8_t {
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const auto next = ram_[address_];
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++address_;
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// `buffer_end_` is the final address that a 16-byte block will be fetched from;
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// the +16 here papers over the fact that I'm not accurately implementing DMA.
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if(address_ == buffer_end_ + 16) {
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address_ = buffer_start_;
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}
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return next;
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};
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if(pixels_) {
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// Each tick in here is two ticks of the pixel clock, so:
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//
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// 8bpp mode: output two bytes;
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// 4bpp mode: output one byte;
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// 2bpp mode: output one byte every second tick;
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// 1bpp mode: output one byte every fourth tick.
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switch(colour_depth_) {
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case Depth::EightBPP: {
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uint8_t next = next_byte();
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pixels_[0] = (colours_[next & 0xf] & colour(0b0111'0011'0111)) | high_spread[next >> 4];
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next = next_byte();
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pixels_[1] = (colours_[next & 0xf] & colour(0b0111'0011'0111)) | high_spread[next >> 4];
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} break;
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case Depth::FourBPP: {
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const uint8_t next = next_byte();
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pixels_[0] = colours_[next & 0xf];
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pixels_[1] = colours_[next >> 4];
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} break;
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case Depth::TwoBPP: {
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if(!(pixel_count_&1)) {
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pixel_data_ = next_byte();
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}
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pixels_[0] = colours_[pixel_data_ & 3];
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pixels_[1] = colours_[(pixel_data_ >> 2) & 3];
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pixel_data_ >>= 4;
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} break;
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case Depth::OneBPP: {
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if(!(pixel_count_&3)) {
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pixel_data_ = next_byte();
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}
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pixels_[0] = colours_[pixel_data_ & 1];
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pixels_[1] = colours_[(pixel_data_ >> 1) & 1];
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pixel_data_ >>= 2;
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} break;
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}
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// Overlay cursor if applicable.
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// TODO: pull this so far out that the cursor can display over the border, too.
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if(cursor_pixel_ < 32) {
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if(cursor_pixel_ >= 0) {
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const auto pixel = cursor_image_[static_cast<size_t>(cursor_pixel_)];
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if(pixel) {
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pixels_[0] = cursor_colours_[pixel];
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}
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}
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if(cursor_pixel_ < 31) {
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const auto pixel = cursor_image_[static_cast<size_t>(cursor_pixel_ + 1)];
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if(pixel) {
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pixels_[1] = cursor_colours_[pixel];
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}
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}
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cursor_pixel_ += 2;
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}
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pixels_ += 2;
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} else {
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switch(colour_depth_) {
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case Depth::EightBPP:
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next_byte();
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next_byte();
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break;
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case Depth::FourBPP:
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next_byte();
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break;
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case Depth::TwoBPP:
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if(!(pixel_count_&1)) {
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next_byte();
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}
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break;
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case Depth::OneBPP:
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if(!(pixel_count_&3)) {
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next_byte();
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}
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break;
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}
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}
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++pixel_count_;
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}
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// Accumulate total phase.
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++time_in_phase_;
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// Determine current output phase.
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Phase new_phase;
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switch(vertical_state_.phase()) {
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case Phase::Sync: new_phase = Phase::Sync; break;
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case Phase::Blank: new_phase = Phase::Blank; break;
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case Phase::Border:
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new_phase = horizontal_state_.phase() == Phase::Display ? Phase::Border : horizontal_state_.phase();
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break;
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case Phase::Display:
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new_phase = horizontal_state_.phase();
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break;
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}
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// Possibly output something.
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if(new_phase != phase_) {
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if(time_in_phase_) {
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const auto duration = static_cast<int>(time_in_phase_);
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switch(phase_) {
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case Phase::Sync: crt_.output_sync(duration); break;
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case Phase::Blank: crt_.output_blank(duration); break;
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case Phase::Display: flush_pixels(); break;
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case Phase::Border: crt_.output_level<uint16_t>(duration, border_colour_); break;
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}
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time_in_phase_ = 0;
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}
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phase_ = new_phase;
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}
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}
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/// @returns @c true if a vertical retrace interrupt has been signalled since the last call to @c interrupt(); @c false otherwise.
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bool interrupt() {
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// Guess: edge triggered?
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const bool interrupt = entered_sync_;
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entered_sync_ = false;
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return interrupt;
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}
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void set_frame_start(uint32_t address) { frame_start_ = address; }
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void set_buffer_start(uint32_t address) { buffer_start_ = address; }
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void set_buffer_end(uint32_t address) { buffer_end_ = address; }
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void set_cursor_start(uint32_t address) { cursor_start_ = address; }
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Outputs::CRT::CRT &crt() { return crt_; }
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const Outputs::CRT::CRT &crt() const { return crt_; }
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int clock_divider() const {
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return static_cast<int>(clock_divider_);
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}
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private:
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Log::Logger<Log::Source::ARMIOC> logger;
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InterruptObserverT &interrupt_observer_;
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ClockRateObserverT &clock_rate_observer_;
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SoundT &sound_;
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// In the current version of this code, video DMA occurrs costlessly,
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// being deferred to the component itself.
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const uint8_t *ram_ = nullptr;
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Outputs::CRT::CRT crt_;
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// Horizontal and vertical timing.
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struct Timing {
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uint32_t period = 0;
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uint32_t sync_width = 0;
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uint32_t border_start = 0;
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uint32_t border_end = 0;
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uint32_t display_start = 0;
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uint32_t display_end = 0;
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uint32_t cursor_start = 0;
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uint32_t cursor_end = 0;
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};
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uint32_t cursor_shift_ = 0;
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Timing horizontal_timing_, vertical_timing_;
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// Current video state.
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enum class Phase {
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Sync, Blank, Border, Display,
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};
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struct State {
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uint32_t position = 0;
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void increment_position(const Timing &timing) {
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++position;
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if(position == 1024) position = 0;
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if(position == timing.period) {
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sync_active = timing.sync_width;
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display_started = !timing.display_start;
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display_ended = !timing.display_end;
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border_started = !timing.border_start;
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border_ended = !timing.border_end;
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cursor_active = !timing.cursor_start;
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} else {
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sync_active &= position != timing.sync_width;
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display_started |= position == timing.display_start;
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display_ended |= position == timing.display_end;
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border_started |= position == timing.border_start;
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border_ended |= position == timing.border_end;
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cursor_active |= position == timing.cursor_start;
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cursor_active &= position != timing.cursor_end;
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}
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}
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bool sync_active = true;
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bool border_started = false;
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bool border_ended = false;
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bool display_started = false;
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bool display_ended = false;
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bool cursor_active = false;
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Phase phase() const {
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if(sync_active) return Phase::Sync;
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if(display_started && !display_ended) return Phase::Display;
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if(border_started && !border_ended) return Phase::Border;
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return Phase::Blank;
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}
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};
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State horizontal_state_, vertical_state_;
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Phase phase_ = Phase::Sync;
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uint32_t time_in_phase_ = 0;
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uint32_t pixel_count_ = 0;
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uint16_t *pixels_ = nullptr;
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// It is elsewhere assumed that this size is a multiple of 8.
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static constexpr size_t PixelBufferSize = 320;
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// Programmer-set addresses.
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uint32_t buffer_start_ = 0;
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uint32_t buffer_end_ = 0;
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uint32_t frame_start_ = 0;
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uint32_t cursor_start_ = 0;
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// Ephemeral address state.
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uint32_t address_ = 0;
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// Horizontal cursor output state.
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uint32_t cursor_address_ = 0;
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int cursor_pixel_ = 0;
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std::array<uint8_t, 32> cursor_image_;
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// Ephemeral graphics data.
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uint8_t pixel_data_ = 0;
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// Colour palette, converted to internal format.
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uint16_t border_colour_;
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std::array<uint16_t, 16> colours_{};
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std::array<uint16_t, 4> cursor_colours_{};
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// An interrupt flag; more closely related to the interface by which
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// my implementation of the IOC picks up an interrupt request than
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// to hardware.
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bool entered_sync_ = false;
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// The divider that would need to be applied to a 24Mhz clock to
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// get half the current pixel clock; counting is in units of half
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// the pixel clock because that's the fidelity at which the programmer
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// places horizontal events — display start, end, sync period, etc.
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uint32_t clock_divider_ = 0;
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enum class Depth {
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OneBPP = 0b00,
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TwoBPP = 0b01,
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FourBPP = 0b10,
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EightBPP = 0b11,
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} colour_depth_;
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void set_clock_divider(uint32_t divider) {
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if(divider == clock_divider_) {
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return;
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}
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clock_divider_ = divider;
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const auto cycles_per_line = static_cast<int>(24'000'000 / (divider * 312 * 50));
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crt_.set_new_timing(
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cycles_per_line,
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312, /* Height of display. */
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Outputs::CRT::PAL::ColourSpace,
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Outputs::CRT::PAL::ColourCycleNumerator,
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Outputs::CRT::PAL::ColourCycleDenominator,
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Outputs::CRT::PAL::VerticalSyncLength,
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Outputs::CRT::PAL::AlternatesPhase);
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clock_rate_observer_.update_clock_rates();
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}
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};
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}
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