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426 lines
13 KiB
C++
426 lines
13 KiB
C++
//
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// Video.cpp
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// Clock Signal
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//
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// Created by Thomas Harte on 04/10/2019.
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// Copyright © 2019 Thomas Harte. All rights reserved.
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//
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#include "Video.hpp"
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#include "../../Outputs/Log.hpp"
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#include <algorithm>
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using namespace Atari::ST;
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namespace {
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/*!
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Defines the line counts at which mode-specific events will occur:
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vertical enable being set and being reset, and the line on which
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the frame will end.
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*/
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struct VerticalParams {
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const int set_enable;
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const int reset_enable;
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const int height;
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} vertical_params[3] = {
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{63, 263, 313}, // 47 rather than 63 on early machines.
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{34, 234, 263},
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{1, 401, 500} // 72 Hz mode: who knows?
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};
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/// @returns The correct @c VerticalParams for output at @c frequency.
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const VerticalParams &vertical_parameters(FieldFrequency frequency) {
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return vertical_params[int(frequency)];
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}
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/*!
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Defines the horizontal counts at which mode-specific events will occur:
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horizontal enable being set and being reset, blank being set and reset, and the
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intended length of this ine.
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The caller should:
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* latch line length at cycle 54 (TODO: also for 72Hz mode?);
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* at (line length - 50), start sync and reset enable (usually for the second time);
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* at (line length - 10), disable sync.
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*/
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struct HorizontalParams {
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const int set_enable;
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const int reset_enable;
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const int set_blank;
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const int reset_blank;
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const int length;
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} modes[3] = {
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{56*2, 376*2, 450*2, 28*2, 512*2},
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{52*2, 372*2, 450*2, 24*2, 508*2},
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{4*2, 164*2, 184*2, 2*2, 224*2}
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};
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const HorizontalParams &horizontal_parameters(FieldFrequency frequency) {
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return modes[int(frequency)];
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}
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}
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Video::Video() :
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crt_(1024, 1, Outputs::Display::Type::PAL50, Outputs::Display::InputDataType::Red4Green4Blue4) {
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crt_.set_visible_area(crt_.get_rect_for_area(43, 240, 120, 784, 4.0f / 3.0f));
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}
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void Video::set_ram(uint16_t *ram, size_t size) {
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ram_ = ram;
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}
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void Video::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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void Video::run_for(HalfCycles duration) {
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const auto horizontal_timings = horizontal_parameters(field_frequency_);
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const auto vertical_timings = vertical_parameters(field_frequency_);
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int integer_duration = int(duration.as_integral());
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while(integer_duration) {
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// Seed next event to end of line.
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int next_event = line_length_;
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// Check the explicitly-placed events.
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if(horizontal_timings.reset_blank > x) next_event = std::min(next_event, horizontal_timings.reset_blank);
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if(horizontal_timings.set_blank > x) next_event = std::min(next_event, horizontal_timings.set_blank);
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if(horizontal_timings.reset_enable > x) next_event = std::min(next_event, horizontal_timings.reset_enable);
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if(horizontal_timings.set_enable > x) next_event = std::min(next_event, horizontal_timings.set_enable);
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// Check for events that are relative to existing latched state.
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if(line_length_ - 50 > x) next_event = std::min(next_event, line_length_ - 50);
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if(line_length_ - 10 > x) next_event = std::min(next_event, line_length_ - 10);
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// Determine current output mode and number of cycles to output for.
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const int run_length = std::min(integer_duration, next_event - x);
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enum class OutputMode {
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Sync, Blank, Border, Pixels
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} output_mode;
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if(horizontal_.sync || vertical_.sync) {
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// Output sync.
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output_mode = OutputMode::Sync;
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} else if(horizontal_.blank || vertical_.blank) {
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// Output blank.
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output_mode = OutputMode::Blank;
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} else if(!vertical_.enable) {
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// There can be no pixels this line, just draw border.
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output_mode = OutputMode::Border;
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} else {
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output_mode = horizontal_.enable ? OutputMode::Pixels : OutputMode::Border;
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}
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// Flush any lingering pixels.
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if(
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(pixel_buffer_.output_bpp != output_bpp_) || // Buffer is now of wrong density.
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(output_mode != OutputMode::Pixels && pixel_buffer_.pixels_output)) { // Buffering has stopped for now.
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pixel_buffer_.flush(crt_);
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}
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switch(output_mode) {
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case OutputMode::Sync: crt_.output_sync(run_length); break;
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case OutputMode::Blank:
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data_latch_position_ = 0;
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crt_.output_blank(run_length);
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break;
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case OutputMode::Border: {
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if(!output_shifter_) {
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output_border(run_length);
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} else {
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if(run_length < 32) {
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shift_out(run_length); // TODO: this might end up overrunning.
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if(!output_shifter_) pixel_buffer_.flush(crt_);
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} else {
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shift_out(32);
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output_shifter_ = 0;
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pixel_buffer_.flush(crt_);
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output_border(run_length - 32);
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}
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}
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} break;
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default:
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// There will be pixels this line, subject to the shifter pipeline.
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// Divide into 8-[half-]cycle windows; at the start of each window fetch a word,
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// and during the rest of the window, shift out.
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int start_column = x >> 3;
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const int end_column = (x + run_length) >> 3;
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// Rules obeyed below:
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//
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// Video fetches occur as the first act of business in a column. Each
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// fetch is then followed by 8 shift clocks. Whether or not the shifter
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// was reloaded by the fetch depends on the FIFO.
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if(start_column == end_column) {
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shift_out(run_length);
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} else {
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// Continue the current column if partway across.
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if(x&7) {
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// If at least one column boundary is crossed, complete this column.
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// Otherwise the run_length is clearly less than 8 and within this column,
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// so go for the entirety of it.
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shift_out(8 - (x & 7));
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++start_column;
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latch_word();
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}
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// Run for all columns that have their starts in this time period.
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int complete_columns = end_column - start_column;
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while(complete_columns--) {
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shift_out(8);
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latch_word();
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}
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// Output the start of the next column, if necessary.
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if(start_column != end_column && (x + run_length) & 7) {
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shift_out((x + run_length) & 7);
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}
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}
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break;
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}
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// Check for whether line length should have been latched during this run.
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if(x <= 54 && (x + run_length) > 54) line_length_ = horizontal_timings.length;
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// Apply the next event.
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x += run_length;
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integer_duration -= run_length;
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if(horizontal_timings.reset_blank == x) horizontal_.blank = false;
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if(horizontal_timings.set_blank == x) horizontal_.blank = true;
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if(horizontal_timings.reset_enable == x) horizontal_.enable = false;
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if(horizontal_timings.set_enable == x) horizontal_.enable = true;
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if(line_length_ - 50 == x) horizontal_.sync = true;
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if(line_length_ - 10 == x) horizontal_.sync = false;
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// Check whether the terminating event was end-of-line; if so then advance
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// the vertical bits of state.
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if(x == line_length_) {
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x = 0;
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++y;
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// Use vertical_parameters to get parameters for the current output frequency.
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if(y == vertical_timings.set_enable) {
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vertical_.enable = true;
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} else if(y == vertical_timings.reset_enable) {
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vertical_.enable = false;
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} else if(y == vertical_timings.height) {
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y = 0;
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vertical_.sync = true;
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current_address_ = base_address_ >> 1;
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} else if(y == 3) {
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vertical_.sync = false;
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}
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}
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}
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}
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void Video::latch_word() {
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data_latch_[data_latch_position_] = ram_[current_address_ & 262143];
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++current_address_;
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++data_latch_position_;
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if(data_latch_position_ == 4) {
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data_latch_position_ = 0;
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output_shifter_ =
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(uint64_t(data_latch_[0]) << 48) |
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(uint64_t(data_latch_[1]) << 32) |
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(uint64_t(data_latch_[2]) << 16) |
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uint64_t(data_latch_[3]);
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}
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}
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void Video::shift_out(int length) {
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if(!pixel_buffer_.pixel_pointer) pixel_buffer_.allocate(crt_);
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pixel_buffer_.cycles_output += length;
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switch(output_bpp_) {
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case OutputBpp::One: {
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int pixels = length << 1;
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pixel_buffer_.pixels_output += pixels;
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if(pixel_buffer_.pixel_pointer) {
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while(pixels--) {
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*pixel_buffer_.pixel_pointer = ((output_shifter_ >> 63) & 1) * 0xffff;
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output_shifter_ <<= 1;
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++pixel_buffer_.pixel_pointer;
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}
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} else {
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output_shifter_ <<= pixels;
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}
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} break;
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case OutputBpp::Two:
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pixel_buffer_.pixels_output += length;
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if(pixel_buffer_.pixel_pointer) {
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while(length--) {
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*pixel_buffer_.pixel_pointer = palette_[
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((output_shifter_ >> 63) & 1) |
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((output_shifter_ >> 46) & 2)
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];
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// This ensures that the top two words shift one to the left;
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// their least significant bits are fed from the most significant bits
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// of the bottom two words, respectively.
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shifter_halves_[1] = (shifter_halves_[1] << 1) & 0xfffefffe;
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shifter_halves_[1] |= (shifter_halves_[0] & 0x80008000) >> 15;
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shifter_halves_[0] = (shifter_halves_[0] << 1) & 0xfffefffe;
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++pixel_buffer_.pixel_pointer;
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}
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} else {
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while(length--) {
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shifter_halves_[1] = (shifter_halves_[1] << 1) & 0xfffefffe;
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shifter_halves_[1] |= (shifter_halves_[0] & 0x80008000) >> 15;
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shifter_halves_[0] = (shifter_halves_[0] << 1) & 0xfffefffe;
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}
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}
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break;
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default:
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case OutputBpp::Four:
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pixel_buffer_.pixels_output += length >> 1;
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if(pixel_buffer_.pixel_pointer) {
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while(length) {
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*pixel_buffer_.pixel_pointer = palette_[
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((output_shifter_ >> 63) & 1) |
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((output_shifter_ >> 46) & 2) |
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((output_shifter_ >> 29) & 4) |
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((output_shifter_ >> 12) & 8)
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];
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output_shifter_ = (output_shifter_ << 1) & 0xfffefffefffefffe;
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++pixel_buffer_.pixel_pointer;
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length -= 2;
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}
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} else {
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while(length) {
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output_shifter_ = (output_shifter_ << 1) & 0xfffefffefffefffe;
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length -= 2;
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}
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}
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break;
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}
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// Check for buffer being full. Buffers are allocated as 328 pixels, and this method is
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// never called for more than 8 pixels, so there's no chance of overrun.
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if(pixel_buffer_.pixels_output >= 320) pixel_buffer_.flush(crt_);
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}
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void Video::output_border(int duration) {
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uint16_t *colour_pointer = reinterpret_cast<uint16_t *>(crt_.begin_data(1));
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if(colour_pointer) *colour_pointer = palette_[0];
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crt_.output_level(duration);
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}
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bool Video::hsync() {
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return horizontal_.sync;
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}
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bool Video::vsync() {
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return vertical_.sync;
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}
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bool Video::display_enabled() {
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return horizontal_.enable && vertical_.enable;
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}
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HalfCycles Video::get_next_sequence_point() {
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// The next sequence point will be whenever display_enabled, vsync or hsync next changes.
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// If this is a vertically-enabled line, and right now is either before graphics display,
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// or during it, then it's display enabled that will change next.
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const auto horizontal_timings = horizontal_parameters(field_frequency_);
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if(vertical_.enable) {
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if(x < horizontal_timings.set_enable) {
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return HalfCycles(horizontal_timings.set_enable - x);
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} else if(x < horizontal_timings.reset_enable) {
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return HalfCycles(horizontal_timings.reset_enable - x);
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}
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}
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// Otherwise, if this is before or during horizontal sync then that's the next event.
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if(x < line_length_ - 50) return HalfCycles(line_length_ - 50 - x);
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else if(x < line_length_ - 10) return HalfCycles(line_length_ - 10 - x);
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// Okay, then, it depends on the next line. If the next line is the start or end of vertical sync,
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// it's that. Otherwise it's the beginning of display enable on the next line.
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const auto vertical_timings = horizontal_parameters(field_frequency_);
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if(y+1 == vertical_timings.length || y+1 == 3) return HalfCycles(line_length_ - x);
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return HalfCycles(line_length_ + horizontal_timings.set_enable - x);
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}
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// MARK: - IO dispatch
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uint16_t Video::read(int address) {
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LOG("[Video] read " << PADHEX(2) << (address & 0x3f));
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address &= 0x3f;
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switch(address) {
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default:
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break;
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case 0x00: return uint16_t(0xff00 | (base_address_ >> 16));
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case 0x01: return uint16_t(0xff00 | (base_address_ >> 8));
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case 0x02: return uint16_t(0xff00 | (current_address_ >> 16));
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case 0x03: return uint16_t(0xff00 | (current_address_ >> 8));
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case 0x04: return uint16_t(0xff00 | (current_address_));
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case 0x05: return sync_mode_ | 0xfcff;
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case 0x30: return video_mode_ | 0xfcff;
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}
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return 0xff;
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}
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void Video::write(int address, uint16_t value) {
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LOG("[Video] write " << PADHEX(2) << int(value) << " to " << PADHEX(2) << (address & 0x3f));
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address &= 0x3f;
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switch(address) {
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default: break;
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// Start address.
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case 0x00: base_address_ = (base_address_ & 0x00ffff) | ((value & 0xff) << 16); break;
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case 0x01: base_address_ = (base_address_ & 0xff00ff) | ((value & 0xff) << 8); break;
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// Sync mode and pixel mode.
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case 0x05:
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sync_mode_ = value;
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update_output_mode();
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break;
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case 0x30:
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video_mode_ = value;
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update_output_mode();
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break;
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// Palette.
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case 0x20: case 0x21: case 0x22: case 0x23:
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case 0x24: case 0x25: case 0x26: case 0x27:
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case 0x28: case 0x29: case 0x2a: case 0x2b:
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case 0x2c: case 0x2d: case 0x2e: case 0x2f: {
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uint8_t *const entry = reinterpret_cast<uint8_t *>(&palette_[address - 0x20]);
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entry[0] = uint8_t((value & 0x700) >> 7);
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entry[1] = uint8_t((value & 0x77) << 1);
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} break;
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}
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}
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void Video::update_output_mode() {
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// If this is black and white mode, that's that.
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switch((video_mode_ >> 8) & 3) {
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default:
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case 0: output_bpp_ = OutputBpp::Four; break;
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case 1: output_bpp_ = OutputBpp::Two; break;
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// 1bpp mode ignores the otherwise-programmed frequency.
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case 2:
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output_bpp_ = OutputBpp::One;
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field_frequency_ = FieldFrequency::SeventyTwo;
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return;
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}
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field_frequency_ = (sync_mode_ & 0x200) ? FieldFrequency::Fifty : FieldFrequency::Sixty;
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}
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