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239 lines
6.9 KiB
C++
239 lines
6.9 KiB
C++
//
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// Nick.cpp
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// Clock Signal
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//
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// Created by Thomas Harte on 14/06/2021.
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// Copyright © 2021 Thomas Harte. All rights reserved.
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//
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#include "Nick.hpp"
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#include <cstdio>
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namespace {
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uint16_t mapped_colour(uint8_t source) {
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// On the Enterprise, red and green are 3-bit quantities; blue is a 2-bit quantity.
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const int red = ((source&0x01) << 2) | ((source&0x08) >> 2) | ((source&0x40) >> 6);
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const int green = ((source&0x02) << 1) | ((source&0x10) >> 3) | ((source&0x80) >> 7);
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const int blue = ((source&0x04) >> 1) | ((source&0x20) >> 5);
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// Duplicate bits where necessary to map to a full 4-bit range per channel.
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return uint16_t(
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(red << 9) + ((red&0x4) << 6) +
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(green << 5) + ((green&0x4) << 2) +
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(blue << 2) + blue
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);
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}
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}
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using namespace Enterprise;
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Nick::Nick(const uint8_t *ram) :
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crt_(57, 1, Outputs::Display::Type::PAL50, Outputs::Display::InputDataType::Red4Green4Blue4),
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ram_(ram) {
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// Just use RGB for now.
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crt_.set_display_type(Outputs::Display::DisplayType::RGB);
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}
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void Nick::write(uint16_t address, uint8_t value) {
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printf("Nick write: %02x -> %d\n", value, address & 3);
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switch(address & 3) {
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default:
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printf("Unhandled\n");
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break;
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case 1:
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flush_border();
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border_colour_ = mapped_colour(value);
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break;
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case 2:
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line_parameter_base_ = uint16_t((line_parameter_base_ & 0xf000) | (value << 4));
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break;
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case 3:
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line_parameter_base_ = uint16_t((line_parameter_base_ & 0x0ff0) | (value << 12));
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// Still a mystery to me: the exact meaning of the top two bits here. For now
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// just treat a 0 -> 1 transition of the MSB as a forced frame restart.
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if((value^line_parameter_control_) & value & 0x80) {
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printf("Should restart frame from %04x\n", line_parameter_base_);
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// For now: just force this to be the final line of this mode block.
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// I'm unclear whether I should also reset the horizontal counter
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// (i.e. completely abandon current video phase).
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lines_remaining_ = 0xff;
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line_parameters_[1] |= 1;
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}
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line_parameter_control_ = value & 0xc0;
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break;
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}
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}
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uint8_t Nick::read([[maybe_unused]] uint16_t address) {
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return 0xff;
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}
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void Nick::run_for(HalfCycles duration) {
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constexpr int line_length = 912;
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int clocks_remaining = duration.as<int>();
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while(clocks_remaining) {
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// Determine how many cycles are left this line.
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const int clocks_this_line = std::min(clocks_remaining, line_length - horizontal_counter_);
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// Convert that into a [start/current] and end window.
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int window = horizontal_counter_ >> 4;
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const int end_window = (horizontal_counter_ + clocks_this_line) >> 4;
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// Advance the line counters.
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clocks_remaining -= clocks_this_line;
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horizontal_counter_ = (horizontal_counter_ + clocks_this_line) % line_length;
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// Do nothing if a window boundary isn't crossed.
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if(window == end_window) continue;
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// If this is within the first 8 cycles of the line, [possibly] fetch
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// the relevant part of the line parameters.
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if(should_reload_line_parameters_ && window < 8) {
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int fetch_spot = window;
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while(fetch_spot < end_window && fetch_spot < 8) {
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line_parameters_[(fetch_spot << 1)] = ram_[line_parameter_pointer_];
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line_parameters_[(fetch_spot << 1) + 1] = ram_[line_parameter_pointer_ + 1];
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line_parameter_pointer_ += 2;
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++fetch_spot;
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}
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// If all parameters have been loaded, set appropriate fields.
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if(fetch_spot == 8) {
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should_reload_line_parameters_ = false;
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// Set length of mode line.
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lines_remaining_ = line_parameters_[0];
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// Determine the line data pointers.
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line_data_pointer_[0] = uint16_t(line_parameters_[4] | (line_parameters_[5] << 8));
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line_data_pointer_[1] = uint16_t(line_parameters_[6] | (line_parameters_[7] << 8));
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// Set the output mode and margin.
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mode_ = Mode((line_parameters_[1] >> 1)&7);
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left_margin_ = line_parameters_[2] & 0x3f;
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right_margin_ = line_parameters_[3] & 0x3f;
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if(mode_ == Mode::Vsync) {
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state_ = State::Blank;
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} else {
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// The first ten windows are occupied by the horizontal sync and
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// colour burst; if left signalled before then, begin in pixels.
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state_ = left_margin_ > 10 ? State::Border : State::Pixels;
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}
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}
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}
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// HSYNC is signalled for four windows at the start of the line.
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if(window < 4 && end_window >= 4) {
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crt_.output_sync(4);
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window = 4;
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}
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// Deal with vsync mode out here.
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if(mode_ == Mode::Vsync) {
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while(window < end_window) {
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int next_event = end_window;
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if(window < left_margin_) next_event = std::min(next_event, left_margin_);
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if(window < right_margin_) next_event = std::min(next_event, right_margin_);
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if(state_ == State::Blank) {
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crt_.output_blank(next_event - window);
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} else {
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crt_.output_sync(next_event - window);
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}
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window = next_event;
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if(window == left_margin_) state_ = State::Sync;
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if(window == right_margin_) state_ = State::Blank;
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}
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} else {
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// If present then the colour burst is output for the period from
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// the start of window 6 to the end of window 10.
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if(window < 10 && end_window >= 10) {
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crt_.output_blank(2);
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crt_.output_colour_burst(4, 0); // TODO: try to determine actual phase.
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window = 10;
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}
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while(window < end_window) {
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int next_event = end_window;
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if(window < left_margin_) next_event = std::min(next_event, left_margin_);
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if(window < right_margin_) next_event = std::min(next_event, right_margin_);
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if(state_ == State::Border) {
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border_duration_ += next_event - window;
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} else {
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// TODO: something proper here.
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uint16_t *const colour_pointer = reinterpret_cast<uint16_t *>(crt_.begin_data(1));
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if(colour_pointer) *colour_pointer = 0xfff;
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crt_.output_level(next_event - window);
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}
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window = next_event;
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if(window == left_margin_) {
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flush_border();
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state_ = State::Pixels;
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// TODO: probably allocate some pixels here?
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}
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if(window == right_margin_) {
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state_ = State::Border;
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// TODO: probably output pixels here?
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}
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}
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// Finish up the line.
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if(!horizontal_counter_) {
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if(state_ == State::Border) {
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flush_border();
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} else {
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// TODO: output pixels.
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}
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}
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}
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// Check for end of line.
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if(!horizontal_counter_) {
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++lines_remaining_;
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if(!lines_remaining_) {
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should_reload_line_parameters_ = true;
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// Check for end-of-frame.
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if(line_parameters_[1] & 1) {
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line_parameter_pointer_ = line_parameter_base_;
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}
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}
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// TODO: should reload line data pointers?
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}
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}
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}
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void Nick::flush_border() {
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if(!border_duration_) return;
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uint16_t *const colour_pointer = reinterpret_cast<uint16_t *>(crt_.begin_data(1));
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if(colour_pointer) *colour_pointer = border_colour_;
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crt_.output_level(border_duration_);
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border_duration_ = 0;
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}
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// MARK: - CRT passthroughs.
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void Nick::set_scan_target(Outputs::Display::ScanTarget *scan_target) {
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crt_.set_scan_target(scan_target);
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}
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Outputs::Display::ScanStatus Nick::get_scaled_scan_status() const {
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return crt_.get_scaled_scan_status();
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}
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