mirror of
https://github.com/TomHarte/CLK.git
synced 2024-11-29 12:50:28 +00:00
434 lines
13 KiB
C++
434 lines
13 KiB
C++
//
|
||
// CRTC6845.hpp
|
||
// Clock Signal
|
||
//
|
||
// Created by Thomas Harte on 31/07/2017.
|
||
// Copyright 2017 Thomas Harte. All rights reserved.
|
||
//
|
||
|
||
#pragma once
|
||
|
||
#include "../../ClockReceiver/ClockReceiver.hpp"
|
||
|
||
#include <cstdint>
|
||
#include <cstdio>
|
||
|
||
namespace Motorola::CRTC {
|
||
|
||
struct BusState {
|
||
bool display_enable = false;
|
||
bool hsync = false;
|
||
bool vsync = false;
|
||
bool cursor = false;
|
||
uint16_t refresh_address = 0;
|
||
uint16_t row_address = 0;
|
||
|
||
// Not strictly part of the bus state; provided because the partition between 6845 and bus handler
|
||
// doesn't quite hold up in some emulated systems where the two are integrated and share more state.
|
||
int field_count = 0;
|
||
};
|
||
|
||
class BusHandler {
|
||
public:
|
||
void perform_bus_cycle(const BusState &) {}
|
||
};
|
||
|
||
enum class Personality {
|
||
HD6845S, // Type 0 in CPC parlance. Zero-width HSYNC available, no status, programmable VSYNC length.
|
||
// Considered exactly identical to the UM6845, so this enum covers both.
|
||
UM6845R, // Type 1 in CPC parlance. Status register, fixed-length VSYNC.
|
||
MC6845, // Type 2. No status register, fixed-length VSYNC, no zero-length HSYNC.
|
||
AMS40226, // Type 3. Status is get register, fixed-length VSYNC, no zero-length HSYNC.
|
||
|
||
EGA, // Extended EGA-style CRTC; uses 16-bit addressing throughout.
|
||
};
|
||
|
||
constexpr bool is_egavga(Personality p) {
|
||
return p >= Personality::EGA;
|
||
}
|
||
|
||
// https://www.pcjs.org/blog/2018/03/20/ advises that "the behavior of bits 5 and 6 [of register 10, the cursor start
|
||
// register is really card specific".
|
||
//
|
||
// This enum captures those specifics.
|
||
enum class CursorType {
|
||
/// No cursor signal is generated.
|
||
None,
|
||
/// MDA style: 00 => symmetric blinking; 01 or 10 => no blinking; 11 => short on, long off.
|
||
MDA,
|
||
/// EGA style: ignore the bits completely.
|
||
EGA,
|
||
};
|
||
|
||
// TODO UM6845R and R12/R13; see http://www.cpcwiki.eu/index.php/CRTC#CRTC_Differences
|
||
|
||
template <class BusHandlerT, Personality personality, CursorType cursor_type> class CRTC6845 {
|
||
public:
|
||
CRTC6845(BusHandlerT &bus_handler) noexcept :
|
||
bus_handler_(bus_handler), status_(0) {}
|
||
|
||
void select_register(uint8_t r) {
|
||
selected_register_ = r;
|
||
}
|
||
|
||
uint8_t get_status() {
|
||
switch(personality) {
|
||
case Personality::UM6845R: return status_ | (bus_state_.vsync ? 0x20 : 0x00);
|
||
case Personality::AMS40226: return get_register();
|
||
default: return 0xff;
|
||
}
|
||
return 0xff;
|
||
}
|
||
|
||
uint8_t get_register() {
|
||
if(selected_register_ == 31) status_ &= ~0x80;
|
||
if(selected_register_ == 16 || selected_register_ == 17) status_ &= ~0x40;
|
||
|
||
if(personality == Personality::UM6845R && selected_register_ == 31) return dummy_register_;
|
||
if(selected_register_ < 12 || selected_register_ > 17) return 0xff;
|
||
return registers_[selected_register_];
|
||
}
|
||
|
||
void set_register(uint8_t value) {
|
||
static constexpr bool is_ega = is_egavga(personality);
|
||
|
||
const auto load_low = [value](uint16_t &target) {
|
||
target = (target & 0xff00) | value;
|
||
};
|
||
const auto load_high = [value](uint16_t &target) {
|
||
constexpr uint8_t mask = RefreshMask >> 8;
|
||
target = uint16_t((target & 0x00ff) | ((value & mask) << 8));
|
||
};
|
||
|
||
switch(selected_register_) {
|
||
case 0: layout_.horizontal.total = value; break;
|
||
case 1: layout_.horizontal.displayed = value; break;
|
||
case 2: layout_.horizontal.start_sync = value; break;
|
||
case 3:
|
||
layout_.horizontal.sync_width = value & 0xf;
|
||
layout_.vertical.sync_lines = value >> 4;
|
||
// TODO: vertical sync lines:
|
||
// "(0 means 16 on some CRTC. Not present on all CRTCs, fixed to 16 lines on these)"
|
||
break;
|
||
case 4: layout_.vertical.total = value & 0x7f; break;
|
||
case 5: layout_.vertical.adjust = value & 0x1f; break;
|
||
case 6: layout_.vertical.displayed = value & 0x7f; break;
|
||
case 7: layout_.vertical.start_sync = value & 0x7f; break;
|
||
case 8:
|
||
switch(value & 3) {
|
||
default: layout_.interlace_mode_ = InterlaceMode::Off; break;
|
||
case 0b01: layout_.interlace_mode_ = InterlaceMode::InterlaceSync; break;
|
||
case 0b11: layout_.interlace_mode_ = InterlaceMode::InterlaceSyncAndVideo; break;
|
||
}
|
||
|
||
// Per CPC documentation, skew doesn't work on a "type 1 or 2", i.e. an MC6845 or a UM6845R.
|
||
if(personality != Personality::UM6845R && personality != Personality::MC6845) {
|
||
switch((value >> 4)&3) {
|
||
default: display_skew_mask_ = 1; break;
|
||
case 1: display_skew_mask_ = 2; break;
|
||
case 2: display_skew_mask_ = 4; break;
|
||
}
|
||
}
|
||
break;
|
||
case 9: layout_.vertical.end_row = value & 0x1f; break;
|
||
case 10:
|
||
layout_.vertical.start_cursor = value & 0x1f;
|
||
layout_.cursor_flags = (value >> 5) & 3;
|
||
break;
|
||
case 11:
|
||
layout_.vertical.end_cursor = value & 0x1f;
|
||
break;
|
||
case 12: load_high(layout_.start_address); break;
|
||
case 13: load_low(layout_.start_address); break;
|
||
case 14: load_high(layout_.cursor_address); break;
|
||
case 15: load_low(layout_.cursor_address); break;
|
||
}
|
||
|
||
static constexpr uint8_t masks[] = {
|
||
0xff, // Horizontal total.
|
||
0xff, // Horizontal display end.
|
||
0xff, // Start horizontal blank.
|
||
0xff, //
|
||
// EGA: b0–b4: end of horizontal blank;
|
||
// b5–b6: "Number of character clocks to delay start of display after Horizontal Total has been reached."
|
||
|
||
is_ega ? 0xff : 0x7f, // Start horizontal retrace.
|
||
0x1f, 0x7f, 0x7f,
|
||
0xff, 0x1f, 0x7f, 0x1f,
|
||
uint8_t(RefreshMask >> 8), uint8_t(RefreshMask),
|
||
uint8_t(RefreshMask >> 8), uint8_t(RefreshMask),
|
||
};
|
||
|
||
if(selected_register_ < 16) {
|
||
registers_[selected_register_] = value & masks[selected_register_];
|
||
}
|
||
if(selected_register_ == 31 && personality == Personality::UM6845R) {
|
||
dummy_register_ = value;
|
||
}
|
||
}
|
||
|
||
void trigger_light_pen() {
|
||
registers_[17] = bus_state_.refresh_address & 0xff;
|
||
registers_[16] = bus_state_.refresh_address >> 8;
|
||
status_ |= 0x40;
|
||
}
|
||
|
||
void run_for(Cycles cycles) {
|
||
auto cyles_remaining = cycles.as_integral();
|
||
while(cyles_remaining--) {
|
||
// Intention of code below: all conditionals are evaluated as if functional; they should be
|
||
// ordered so that whatever assignments result don't affect any subsequent conditionals
|
||
|
||
|
||
// Do bus work.
|
||
bus_state_.cursor = is_cursor_line_ &&
|
||
bus_state_.refresh_address == layout_.cursor_address;
|
||
bus_state_.display_enable = character_is_visible_ && line_is_visible_;
|
||
bus_handler_.perform_bus_cycle(bus_state_);
|
||
|
||
//
|
||
// Shared, stateless signals.
|
||
//
|
||
const bool character_total_hit = character_counter_ == layout_.horizontal.total;
|
||
const uint8_t lines_per_row = layout_.interlace_mode_ == InterlaceMode::InterlaceSyncAndVideo ? layout_.vertical.end_row & ~1 : layout_.vertical.end_row;
|
||
const bool row_end_hit = bus_state_.row_address == lines_per_row && !is_in_adjustment_period_;
|
||
const bool was_eof = eof_latched_;
|
||
const bool new_frame =
|
||
character_total_hit && was_eof &&
|
||
(
|
||
layout_.interlace_mode_ == InterlaceMode::Off ||
|
||
!odd_field_
|
||
);
|
||
|
||
//
|
||
// Horizontal.
|
||
//
|
||
|
||
// Update horizontal sync.
|
||
if(bus_state_.hsync) {
|
||
++hsync_counter_;
|
||
bus_state_.hsync = hsync_counter_ != layout_.horizontal.sync_width;
|
||
}
|
||
if(character_counter_ == layout_.horizontal.start_sync) {
|
||
hsync_counter_ = 0;
|
||
bus_state_.hsync = true;
|
||
}
|
||
|
||
// Check for end-of-line.
|
||
character_reset_history_ <<= 1;
|
||
if(character_total_hit) {
|
||
character_counter_ = 0;
|
||
character_is_visible_ = true;
|
||
character_reset_history_ |= 1;
|
||
} else {
|
||
character_counter_++;
|
||
}
|
||
|
||
// Check for end of visible characters.
|
||
if(character_counter_ == layout_.horizontal.displayed) {
|
||
character_is_visible_ = false;
|
||
}
|
||
|
||
//
|
||
// End-of-frame.
|
||
//
|
||
|
||
if(character_total_hit) {
|
||
if(was_eof) {
|
||
eof_latched_ = eom_latched_ = is_in_adjustment_period_ = false;
|
||
adjustment_counter_ = 0;
|
||
} else if(is_in_adjustment_period_) {
|
||
adjustment_counter_ = (adjustment_counter_ + 1) & 31;
|
||
}
|
||
}
|
||
|
||
if(character_reset_history_ & 2) {
|
||
eom_latched_ |= row_end_hit && row_counter_ == layout_.vertical.total;
|
||
}
|
||
|
||
if(character_reset_history_ & 4 && eom_latched_) {
|
||
// TODO: I don't believe the "add 1 for interlaced" test here is accurate; others represent the extra scanline as
|
||
// additional state, presumably because adjust total might be reprogrammed at any time.
|
||
const auto adjust_length = layout_.vertical.adjust + (layout_.interlace_mode_ != InterlaceMode::Off && odd_field_ ? 1 : 0);
|
||
is_in_adjustment_period_ |= adjustment_counter_ != adjust_length;
|
||
eof_latched_ |= adjustment_counter_ == adjust_length;
|
||
}
|
||
|
||
//
|
||
// Vertical.
|
||
//
|
||
|
||
// Sync.
|
||
const bool vsync_horizontal =
|
||
(!odd_field_ && !character_counter_) ||
|
||
(odd_field_ && character_counter_ == (layout_.horizontal.total >> 1));
|
||
if(vsync_horizontal) {
|
||
if((row_counter_ == layout_.vertical.start_sync && !bus_state_.row_address) || bus_state_.vsync) {
|
||
bus_state_.vsync = true;
|
||
vsync_counter_ = (vsync_counter_ + 1) & 0xf;
|
||
} else {
|
||
vsync_counter_ = 0;
|
||
}
|
||
|
||
if(vsync_counter_ == layout_.vertical.sync_lines) {
|
||
bus_state_.vsync = false;
|
||
}
|
||
}
|
||
|
||
// Row address.
|
||
if(character_total_hit) {
|
||
if(was_eof) {
|
||
bus_state_.row_address = 0;
|
||
eof_latched_ = eom_latched_ = false;
|
||
} else if(row_end_hit) {
|
||
bus_state_.row_address = 0;
|
||
} else if(layout_.interlace_mode_ == InterlaceMode::InterlaceSyncAndVideo) {
|
||
bus_state_.row_address = (bus_state_.row_address + 2) & ~1 & 31;
|
||
} else {
|
||
bus_state_.row_address = (bus_state_.row_address + 1) & 31;
|
||
}
|
||
}
|
||
|
||
// Row counter.
|
||
row_counter_ = next_row_counter_;
|
||
if(new_frame) {
|
||
next_row_counter_ = 0;
|
||
is_first_scanline_ = true;
|
||
} else {
|
||
next_row_counter_ = row_end_hit && character_total_hit ? (next_row_counter_ + 1) : next_row_counter_;
|
||
is_first_scanline_ &= !row_end_hit;
|
||
}
|
||
|
||
// Vertical display enable.
|
||
if(is_first_scanline_) {
|
||
line_is_visible_ = true;
|
||
odd_field_ = bus_state_.field_count & 1;
|
||
} else if(line_is_visible_ && row_counter_ == layout_.vertical.displayed) {
|
||
line_is_visible_ = false;
|
||
++bus_state_.field_count;
|
||
}
|
||
|
||
|
||
// Cursor.
|
||
if constexpr (cursor_type != CursorType::None) {
|
||
// Check for cursor enable.
|
||
is_cursor_line_ |= bus_state_.row_address == layout_.vertical.start_cursor;
|
||
is_cursor_line_ &= bus_state_.row_address != layout_.vertical.end_cursor;
|
||
|
||
switch(cursor_type) {
|
||
// MDA-style blinking.
|
||
// https://retrocomputing.stackexchange.com/questions/27803/what-are-the-blinking-rates-of-the-caret-and-of-blinking-text-on-pc-graphics-car
|
||
// gives an 8/8 pattern for regular blinking though mode 11 is then just a guess.
|
||
case CursorType::MDA:
|
||
switch(layout_.cursor_flags) {
|
||
case 0b11: is_cursor_line_ &= (bus_state_.field_count & 8) < 3; break;
|
||
case 0b00: is_cursor_line_ &= bool(bus_state_.field_count & 8); break;
|
||
case 0b01: is_cursor_line_ = false; break;
|
||
case 0b10: is_cursor_line_ = true; break;
|
||
default: break;
|
||
}
|
||
break;
|
||
}
|
||
}
|
||
|
||
//
|
||
// Addressing.
|
||
//
|
||
|
||
if(new_frame) {
|
||
bus_state_.refresh_address = layout_.start_address;
|
||
} else if(character_total_hit) {
|
||
bus_state_.refresh_address = line_address_;
|
||
} else {
|
||
bus_state_.refresh_address = (bus_state_.refresh_address + 1) & RefreshMask;
|
||
}
|
||
|
||
if(new_frame) {
|
||
line_address_ = layout_.start_address;
|
||
} else if(character_counter_ == layout_.horizontal.displayed && row_end_hit) {
|
||
line_address_ = bus_state_.refresh_address;
|
||
}
|
||
}
|
||
}
|
||
|
||
const BusState &get_bus_state() const {
|
||
return bus_state_;
|
||
}
|
||
|
||
private:
|
||
static constexpr uint16_t RefreshMask = (personality >= Personality::EGA) ? 0xffff : 0x3fff;
|
||
|
||
BusHandlerT &bus_handler_;
|
||
BusState bus_state_;
|
||
|
||
enum class InterlaceMode {
|
||
Off,
|
||
InterlaceSync,
|
||
InterlaceSyncAndVideo,
|
||
};
|
||
enum class BlinkMode {
|
||
// TODO.
|
||
};
|
||
struct {
|
||
struct {
|
||
uint8_t total;
|
||
uint8_t displayed;
|
||
uint8_t start_sync;
|
||
uint8_t sync_width;
|
||
} horizontal;
|
||
|
||
struct {
|
||
uint8_t total;
|
||
uint8_t displayed;
|
||
uint8_t start_sync;
|
||
uint8_t sync_lines;
|
||
uint8_t adjust;
|
||
|
||
uint8_t end_row;
|
||
uint8_t start_cursor;
|
||
uint8_t end_cursor;
|
||
} vertical;
|
||
|
||
InterlaceMode interlace_mode_ = InterlaceMode::Off;
|
||
uint8_t end_row() const {
|
||
return interlace_mode_ == InterlaceMode::InterlaceSyncAndVideo ? vertical.end_row & ~1 : vertical.end_row;
|
||
}
|
||
|
||
uint16_t start_address;
|
||
uint16_t cursor_address;
|
||
uint16_t light_pen_address;
|
||
uint8_t cursor_flags;
|
||
} layout_;
|
||
|
||
uint8_t registers_[18]{};
|
||
uint8_t dummy_register_ = 0;
|
||
int selected_register_ = 0;
|
||
|
||
uint8_t character_counter_ = 0;
|
||
uint32_t character_reset_history_ = 0;
|
||
uint8_t row_counter_ = 0, next_row_counter_ = 0;
|
||
uint8_t adjustment_counter_ = 0;
|
||
|
||
bool character_is_visible_ = false;
|
||
bool line_is_visible_ = false;
|
||
bool is_first_scanline_ = false;
|
||
bool is_cursor_line_ = false;
|
||
|
||
int hsync_counter_ = 0;
|
||
int vsync_counter_ = 0;
|
||
bool is_in_adjustment_period_ = false;
|
||
|
||
uint16_t line_address_ = 0;
|
||
uint8_t status_ = 0;
|
||
|
||
int display_skew_mask_ = 1;
|
||
unsigned int character_is_visible_shifter_ = 0;
|
||
|
||
bool eof_latched_ = false;
|
||
bool eom_latched_ = false;
|
||
uint16_t next_row_address_ = 0;
|
||
bool odd_field_ = false;
|
||
};
|
||
|
||
}
|