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425 lines
13 KiB
C++
425 lines
13 KiB
C++
//
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// 9918Base.hpp
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// Clock Signal
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//
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// Created by Thomas Harte on 14/12/2017.
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// Copyright 2017 Thomas Harte. All rights reserved.
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//
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#ifndef TMS9918Base_hpp
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#define TMS9918Base_hpp
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#include "ClockConverter.hpp"
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#include "../../../ClockReceiver/ClockReceiver.hpp"
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#include "../../../Numeric/BitReverse.hpp"
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#include "../../../Outputs/CRT/CRT.hpp"
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#include "PersonalityTraits.hpp"
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#include <array>
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#include <cassert>
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#include <cstdint>
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#include <cstring>
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#include <memory>
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#include <vector>
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namespace TI {
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namespace TMS {
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// Additional properties that correlate with personality.
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constexpr size_t memory_size(Personality p) {
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switch(p) {
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case TI::TMS::TMS9918A:
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case TI::TMS::SMSVDP:
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case TI::TMS::SMS2VDP:
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case TI::TMS::GGVDP: return 16 * 1024;
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case TI::TMS::MDVDP: return 64 * 1024;
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case TI::TMS::V9938: return 128 * 1024;
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case TI::TMS::V9958: return 192 * 1024;
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}
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}
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// The screen mode is a necessary predecessor to picking the line mode,
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// which is the thing latched per line.
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enum class ScreenMode {
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Blank,
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Text,
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MultiColour,
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ColouredText,
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Graphics,
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SMSMode4
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};
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enum class LineMode {
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Text,
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Character,
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Refresh,
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SMS
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};
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enum class MemoryAccess {
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Read, Write, None
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};
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// Temporary buffers collect a representation of each line prior to pixel serialisation.
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struct LineBuffer {
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// The line mode describes the proper timing diagram for this line.
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LineMode line_mode = LineMode::Text;
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// Holds the horizontal scroll position to apply to this line;
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// of those VDPs currently implemented, affects the Master System only.
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uint8_t latched_horizontal_scroll = 0;
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// The names array holds pattern names, as an offset into memory, and
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// potentially flags also.
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struct {
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size_t offset = 0;
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uint8_t flags = 0;
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} names[40];
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// The patterns array holds tile patterns, corresponding 1:1 with names.
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// Four bytes per pattern is the maximum required by any
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// currently-implemented VDP.
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uint8_t patterns[40][4];
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/*
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Horizontal layout (on a 342-cycle clock):
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15 cycles right border
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58 cycles blanking & sync
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13 cycles left border
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... i.e. to cycle 86, then:
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border up to first_pixel_output_column;
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pixels up to next_border_column;
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border up to the end.
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e.g. standard 256-pixel modes will want to set
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first_pixel_output_column = 86, next_border_column = 342.
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*/
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int first_pixel_output_column = 94;
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int next_border_column = 334;
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// An active sprite is one that has been selected for composition onto
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// this line.
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struct ActiveSprite {
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int index = 0; // The original in-table index of this sprite.
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int row = 0; // The row of the sprite that should be drawn.
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int x = 0; // The sprite's x position on screen.
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uint8_t image[4]; // Up to four bytes of image information.
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int shift_position = 0; // An offset representing how much of the image information has already been drawn.
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} active_sprites[8];
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int active_sprite_slot = 0; // A pointer to the slot into which a new active sprite will be deposited, if required.
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bool sprites_stopped = false; // A special TMS feature is that a sentinel value can be used to prevent any further sprites
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// being evaluated for display. This flag determines whether the sentinel has yet been reached.
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void reset_sprite_collection();
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};
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struct LineBufferPointer {
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int row, column;
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};
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constexpr uint8_t StatusInterrupt = 0x80;
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constexpr uint8_t StatusSpriteOverflow = 0x40;
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constexpr int StatusSpriteCollisionShift = 5;
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constexpr uint8_t StatusSpriteCollision = 0x20;
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template <Personality personality> struct Base {
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Base();
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static constexpr int output_lag = 11; // i.e. pixel output will occur 11 cycles
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// after corresponding data read.
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static constexpr uint32_t palette_pack(uint8_t r, uint8_t g, uint8_t b) {
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#if TARGET_RT_BIG_ENDIAN
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return uint32_t((r << 24) | (g << 16) | (b << 8));
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#else
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return uint32_t((b << 16) | (g << 8) | r);
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#endif
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}
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// The default TMS palette.
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static constexpr std::array<uint32_t, 16> palette {
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palette_pack(0, 0, 0),
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palette_pack(0, 0, 0),
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palette_pack(33, 200, 66),
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palette_pack(94, 220, 120),
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palette_pack(84, 85, 237),
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palette_pack(125, 118, 252),
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palette_pack(212, 82, 77),
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palette_pack(66, 235, 245),
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palette_pack(252, 85, 84),
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palette_pack(255, 121, 120),
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palette_pack(212, 193, 84),
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palette_pack(230, 206, 128),
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palette_pack(33, 176, 59),
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palette_pack(201, 91, 186),
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palette_pack(204, 204, 204),
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palette_pack(255, 255, 255)
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};
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Outputs::CRT::CRT crt_;
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TVStandard tv_standard_ = TVStandard::NTSC;
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// Personality-specific metrics and converters.
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ClockConverter<personality> clock_converter_;
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// This VDP's DRAM.
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std::array<uint8_t, memory_size(personality)> ram_;
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// State of the DRAM/CRAM-access mechanism.
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uint16_t ram_pointer_ = 0;
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uint8_t read_ahead_buffer_ = 0;
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MemoryAccess queued_access_ = MemoryAccess::None;
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int cycles_until_access_ = 0;
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int minimum_access_column_ = 0;
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// The main status register.
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uint8_t status_ = 0;
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// Current state of programmer input.
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bool write_phase_ = false; // Determines whether the VDP is expecting the low or high byte of a write.
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uint8_t low_write_ = 0; // Buffers the low byte of a write.
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// Various programmable flags.
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bool mode1_enable_ = false;
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bool mode2_enable_ = false;
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bool mode3_enable_ = false;
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bool blank_display_ = false;
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bool sprites_16x16_ = false;
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bool sprites_magnified_ = false;
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bool generate_interrupts_ = false;
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int sprite_height_ = 8;
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// Programmer-specified addresses.
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size_t pattern_name_address_ = 0; // i.e. address of the tile map.
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size_t colour_table_address_ = 0; // address of the colour map (if applicable).
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size_t pattern_generator_table_address_ = 0; // address of the tile contents.
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size_t sprite_attribute_table_address_ = 0; // address of the sprite list.
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size_t sprite_generator_table_address_ = 0; // address of the sprite contents.
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// Default colours.
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uint8_t text_colour_ = 0;
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uint8_t background_colour_ = 0;
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// Internal mechanisms for position tracking.
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int latched_column_ = 0;
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// A struct to contain timing information for the current mode.
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struct {
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/*
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Vertical layout:
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Lines 0 to [pixel_lines]: standard data fetch and drawing will occur.
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... to [first_vsync_line]: refresh fetches will occur and border will be output.
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.. to [2.5 or 3 lines later]: vertical sync is output.
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... to [total lines - 1]: refresh fetches will occur and border will be output.
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... for one line: standard data fetch will occur, without drawing.
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*/
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int total_lines = 262;
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int pixel_lines = 192;
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int first_vsync_line = 227;
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// Maximum number of sprite slots to populate;
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// if sprites beyond this number should be visible
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// then the appropriate status information will be set.
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int maximum_visible_sprites = 4;
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// Set the position, in cycles, of the two interrupts,
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// within a line.
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struct {
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int column = 4;
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int row = 193;
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} end_of_frame_interrupt_position;
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int line_interrupt_position = -1;
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// Enables or disabled the recognition of the sprite
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// list terminator, and sets the terminator value.
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bool allow_sprite_terminator = true;
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uint8_t sprite_terminator = 0xd0;
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} mode_timing_;
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uint8_t line_interrupt_target = 0xff;
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uint8_t line_interrupt_counter = 0;
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bool enable_line_interrupts_ = false;
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bool line_interrupt_pending_ = false;
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ScreenMode screen_mode_;
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LineBuffer line_buffers_[313];
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void posit_sprite(LineBuffer &buffer, int sprite_number, int sprite_y, int screen_row);
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// There is a delay between reading into the line buffer and outputting from there to the screen. That delay
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// is observeable because reading time affects availability of memory accesses and therefore time in which
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// to update sprites and tiles, but writing time affects when the palette is used and when the collision flag
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// may end up being set. So the two processes are slightly decoupled. The end of reading one line may overlap
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// with the beginning of writing the next, hence the two separate line buffers.
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LineBufferPointer read_pointer_, write_pointer_;
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// The SMS VDP has a programmer-set colour palette, with a dedicated patch of RAM. But the RAM is only exactly
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// fast enough for the pixel clock. So when the programmer writes to it, that causes a one-pixel glitch; there
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// isn't the bandwidth for the read both write to occur simultaneously. The following buffer therefore keeps
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// track of pending collisions, for visual reproduction.
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struct CRAMDot {
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LineBufferPointer location;
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uint32_t value;
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};
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std::vector<CRAMDot> upcoming_cram_dots_;
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// Extra information that affects the Master System output mode.
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struct {
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// Programmer-set flags.
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bool vertical_scroll_lock = false;
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bool horizontal_scroll_lock = false;
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bool hide_left_column = false;
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bool shift_sprites_8px_left = false;
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bool mode4_enable = false;
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uint8_t horizontal_scroll = 0;
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uint8_t vertical_scroll = 0;
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// The Master System's additional colour RAM.
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uint32_t colour_ram[32];
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bool cram_is_selected = false;
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// Holds the vertical scroll position for this frame; this is latched
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// once and cannot dynamically be changed until the next frame.
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uint8_t latched_vertical_scroll = 0;
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size_t pattern_name_address;
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size_t sprite_attribute_table_address;
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size_t sprite_generator_table_address;
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} master_system_;
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void set_current_screen_mode() {
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if(blank_display_) {
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screen_mode_ = ScreenMode::Blank;
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return;
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}
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if constexpr (is_sega_vdp(personality)) {
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if(master_system_.mode4_enable) {
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screen_mode_ = ScreenMode::SMSMode4;
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mode_timing_.maximum_visible_sprites = 8;
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return;
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}
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}
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mode_timing_.maximum_visible_sprites = 4;
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if(!mode1_enable_ && !mode2_enable_ && !mode3_enable_) {
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screen_mode_ = ScreenMode::ColouredText;
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return;
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}
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if(mode1_enable_ && !mode2_enable_ && !mode3_enable_) {
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screen_mode_ = ScreenMode::Text;
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return;
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}
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if(!mode1_enable_ && mode2_enable_ && !mode3_enable_) {
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screen_mode_ = ScreenMode::Graphics;
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return;
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}
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if(!mode1_enable_ && !mode2_enable_ && mode3_enable_) {
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screen_mode_ = ScreenMode::MultiColour;
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return;
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}
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// TODO: undocumented TMS modes.
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screen_mode_ = ScreenMode::Blank;
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}
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void do_external_slot(int access_column) {
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// Don't do anything if the required time for the access to become executable
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// has yet to pass.
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if(access_column < minimum_access_column_) {
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return;
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}
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switch(queued_access_) {
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default: return;
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case MemoryAccess::Write:
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if constexpr (is_sega_vdp(personality)) {
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if(master_system_.cram_is_selected) {
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// Adjust the palette. In a Master System blue has a slightly different
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// scale; cf. https://www.retrorgb.com/sega-master-system-non-linear-blue-channel-findings.html
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constexpr uint8_t rg_scale[] = {0, 85, 170, 255};
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constexpr uint8_t b_scale[] = {0, 104, 170, 255};
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master_system_.colour_ram[ram_pointer_ & 0x1f] = palette_pack(
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rg_scale[(read_ahead_buffer_ >> 0) & 3],
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rg_scale[(read_ahead_buffer_ >> 2) & 3],
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b_scale[(read_ahead_buffer_ >> 4) & 3]
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);
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// Schedule a CRAM dot; this is scheduled for wherever it should appear
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// on screen. So it's wherever the output stream would be now. Which
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// is output_lag cycles ago from the point of view of the input stream.
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CRAMDot &dot = upcoming_cram_dots_.emplace_back();
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dot.location.column = write_pointer_.column - output_lag;
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dot.location.row = write_pointer_.row;
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// Handle before this row conditionally; then handle after (or, more realistically,
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// exactly at the end of) naturally.
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if(dot.location.column < 0) {
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--dot.location.row;
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dot.location.column += 342;
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}
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dot.location.row += dot.location.column / 342;
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dot.location.column %= 342;
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dot.value = master_system_.colour_ram[ram_pointer_ & 0x1f];
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break;
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}
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}
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ram_[ram_pointer_ & 16383] = read_ahead_buffer_;
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break;
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case MemoryAccess::Read:
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read_ahead_buffer_ = ram_[ram_pointer_ & 16383];
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break;
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}
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++ram_pointer_;
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queued_access_ = MemoryAccess::None;
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}
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// Various fetchers.
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template<bool use_end> void fetch_tms_refresh(int start, int end);
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template<bool use_end> void fetch_tms_text(int start, int end);
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template<bool use_end> void fetch_tms_character(int start, int end);
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template<bool use_end> void fetch_yamaha_refresh(int start, int end);
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template<bool use_end> void fetch_yamaha_no_sprites(int start, int end);
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template<bool use_end> void fetch_yamaha_sprites(int start, int end);
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template<bool use_end> void fetch_sms(int start, int end);
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// A helper function to output the current border colour for
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// the number of cycles supplied.
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void output_border(int cycles, uint32_t cram_dot);
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// Output serialisation state.
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uint32_t *pixel_target_ = nullptr, *pixel_origin_ = nullptr;
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bool asked_for_write_area_ = false;
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// Output serialisers.
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void draw_tms_character(int start, int end);
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void draw_tms_text(int start, int end);
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void draw_sms(int start, int end, uint32_t cram_dot);
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};
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#include "Fetch.hpp"
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#include "Draw.hpp"
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}
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}
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#endif /* TMS9918Base_hpp */
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