Merge pull request #1574 from TomHarte/SAA5050

Add SAA5050 and hence BBC Mode 7.

Components/SAA5050/SAA5050.cpp

@@ -0,0 +1,365 @@
+//
+//  SAA5050.cpp
+//  Clock Signal
+//
+//  Created by Thomas Harte on 24/09/2025.
+//  Copyright © 2025 Thomas Harte. All rights reserved.
+//
+
+#include "SAA5050.hpp"
+
+#include <algorithm>
+#include <cstdint>
+
+namespace {
+// SAA5050 font, padded out to one byte per row. The least-significant five bits of each byte
+// are the meaningful pixels for that row, with the LSB being on the right.
+constexpr uint8_t font[][10] = {
+	{0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, },	// Character 32.
+	{0x00, 0x04, 0x04, 0x04, 0x04, 0x04, 0x00, 0x04, 0x00, 0x00, },
+	{0x00, 0x0a, 0x0a, 0x0a, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, },
+	{0x00, 0x06, 0x09, 0x08, 0x1c, 0x08, 0x08, 0x1f, 0x00, 0x00, },
+	{0x00, 0x0e, 0x15, 0x14, 0x0e, 0x05, 0x15, 0x0e, 0x00, 0x00, },
+	{0x00, 0x18, 0x19, 0x02, 0x04, 0x08, 0x13, 0x03, 0x00, 0x00, },
+	{0x00, 0x08, 0x14, 0x14, 0x08, 0x15, 0x12, 0x0d, 0x00, 0x00, },
+	{0x00, 0x04, 0x04, 0x04, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, },
+	{0x00, 0x02, 0x04, 0x08, 0x08, 0x08, 0x04, 0x02, 0x00, 0x00, },
+	{0x00, 0x08, 0x04, 0x02, 0x02, 0x02, 0x04, 0x08, 0x00, 0x00, },
+	{0x00, 0x04, 0x15, 0x0e, 0x04, 0x0e, 0x15, 0x04, 0x00, 0x00, },
+	{0x00, 0x00, 0x04, 0x04, 0x1f, 0x04, 0x04, 0x00, 0x00, 0x00, },
+	{0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x04, 0x04, 0x08, 0x00, },
+	{0x00, 0x00, 0x00, 0x00, 0x0e, 0x00, 0x00, 0x00, 0x00, 0x00, },
+	{0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x04, 0x00, 0x00, },
+	{0x00, 0x00, 0x01, 0x02, 0x04, 0x08, 0x10, 0x00, 0x00, 0x00, },
+	{0x00, 0x04, 0x0a, 0x11, 0x11, 0x11, 0x0a, 0x04, 0x00, 0x00, },
+	{0x00, 0x04, 0x0c, 0x04, 0x04, 0x04, 0x04, 0x0e, 0x00, 0x00, },
+	{0x00, 0x0e, 0x11, 0x01, 0x06, 0x08, 0x10, 0x1f, 0x00, 0x00, },
+	{0x00, 0x1f, 0x01, 0x02, 0x06, 0x01, 0x11, 0x0e, 0x00, 0x00, },
+	{0x00, 0x02, 0x06, 0x0a, 0x12, 0x1f, 0x02, 0x02, 0x00, 0x00, },
+	{0x00, 0x1f, 0x10, 0x1e, 0x01, 0x01, 0x11, 0x0e, 0x00, 0x00, },
+	{0x00, 0x06, 0x08, 0x10, 0x1e, 0x11, 0x11, 0x0e, 0x00, 0x00, },
+	{0x00, 0x1f, 0x01, 0x02, 0x04, 0x08, 0x08, 0x08, 0x00, 0x00, },
+	{0x00, 0x0e, 0x11, 0x11, 0x0e, 0x11, 0x11, 0x0e, 0x00, 0x00, },
+	{0x00, 0x0e, 0x11, 0x11, 0x0f, 0x01, 0x02, 0x0c, 0x00, 0x00, },
+	{0x00, 0x00, 0x00, 0x04, 0x00, 0x00, 0x00, 0x04, 0x00, 0x00, },
+	{0x00, 0x00, 0x00, 0x04, 0x00, 0x00, 0x04, 0x04, 0x08, 0x00, },
+	{0x00, 0x02, 0x04, 0x08, 0x10, 0x08, 0x04, 0x02, 0x00, 0x00, },
+	{0x00, 0x00, 0x00, 0x1f, 0x00, 0x1f, 0x00, 0x00, 0x00, 0x00, },
+	{0x00, 0x08, 0x04, 0x02, 0x01, 0x02, 0x04, 0x08, 0x00, 0x00, },
+	{0x00, 0x0e, 0x11, 0x02, 0x04, 0x04, 0x00, 0x04, 0x00, 0x00, },
+	{0x00, 0x0e, 0x11, 0x17, 0x15, 0x17, 0x10, 0x0e, 0x00, 0x00, },
+	{0x00, 0x04, 0x0a, 0x11, 0x11, 0x1f, 0x11, 0x11, 0x00, 0x00, },
+	{0x00, 0x1e, 0x11, 0x11, 0x1e, 0x11, 0x11, 0x1e, 0x00, 0x00, },
+	{0x00, 0x0e, 0x11, 0x10, 0x10, 0x10, 0x11, 0x0e, 0x00, 0x00, },
+	{0x00, 0x1e, 0x11, 0x11, 0x11, 0x11, 0x11, 0x1e, 0x00, 0x00, },
+	{0x00, 0x1f, 0x10, 0x10, 0x1e, 0x10, 0x10, 0x1f, 0x00, 0x00, },
+	{0x00, 0x1f, 0x10, 0x10, 0x1e, 0x10, 0x10, 0x10, 0x00, 0x00, },
+	{0x00, 0x0e, 0x11, 0x10, 0x10, 0x13, 0x11, 0x0f, 0x00, 0x00, },
+	{0x00, 0x11, 0x11, 0x11, 0x1f, 0x11, 0x11, 0x11, 0x00, 0x00, },
+	{0x00, 0x0e, 0x04, 0x04, 0x04, 0x04, 0x04, 0x0e, 0x00, 0x00, },
+	{0x00, 0x01, 0x01, 0x01, 0x01, 0x01, 0x11, 0x0e, 0x00, 0x00, },
+	{0x00, 0x11, 0x12, 0x14, 0x18, 0x14, 0x12, 0x11, 0x00, 0x00, },
+	{0x00, 0x10, 0x10, 0x10, 0x10, 0x10, 0x10, 0x1f, 0x00, 0x00, },
+	{0x00, 0x11, 0x1b, 0x15, 0x15, 0x11, 0x11, 0x11, 0x00, 0x00, },
+	{0x00, 0x11, 0x11, 0x19, 0x15, 0x13, 0x11, 0x11, 0x00, 0x00, },
+	{0x00, 0x0e, 0x11, 0x11, 0x11, 0x11, 0x11, 0x0e, 0x00, 0x00, },
+	{0x00, 0x1e, 0x11, 0x11, 0x1e, 0x10, 0x10, 0x10, 0x00, 0x00, },
+	{0x00, 0x0e, 0x11, 0x11, 0x11, 0x15, 0x12, 0x0d, 0x00, 0x00, },
+	{0x00, 0x1e, 0x11, 0x11, 0x1e, 0x14, 0x12, 0x11, 0x00, 0x00, },
+	{0x00, 0x0e, 0x11, 0x10, 0x0e, 0x01, 0x11, 0x0e, 0x00, 0x00, },
+	{0x00, 0x1f, 0x04, 0x04, 0x04, 0x04, 0x04, 0x04, 0x00, 0x00, },
+	{0x00, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x0e, 0x00, 0x00, },
+	{0x00, 0x11, 0x11, 0x11, 0x0a, 0x0a, 0x04, 0x04, 0x00, 0x00, },
+	{0x00, 0x11, 0x11, 0x11, 0x15, 0x15, 0x15, 0x0a, 0x00, 0x00, },
+	{0x00, 0x11, 0x11, 0x0a, 0x04, 0x0a, 0x11, 0x11, 0x00, 0x00, },
+	{0x00, 0x11, 0x11, 0x0a, 0x04, 0x04, 0x04, 0x04, 0x00, 0x00, },
+	{0x00, 0x1f, 0x01, 0x02, 0x04, 0x08, 0x10, 0x1f, 0x00, 0x00, },
+	{0x00, 0x00, 0x04, 0x08, 0x1f, 0x08, 0x04, 0x00, 0x00, 0x00, },
+	{0x00, 0x10, 0x10, 0x10, 0x10, 0x16, 0x01, 0x02, 0x04, 0x07, },
+	{0x00, 0x00, 0x04, 0x02, 0x1f, 0x02, 0x04, 0x00, 0x00, 0x00, },
+	{0x00, 0x00, 0x04, 0x0e, 0x15, 0x04, 0x04, 0x00, 0x00, 0x00, },
+	{0x00, 0x0a, 0x0a, 0x1f, 0x0a, 0x1f, 0x0a, 0x0a, 0x00, 0x00, },
+	{0x00, 0x00, 0x00, 0x00, 0x1f, 0x00, 0x00, 0x00, 0x00, 0x00, },
+	{0x00, 0x00, 0x00, 0x0e, 0x01, 0x0f, 0x11, 0x0f, 0x00, 0x00, },
+	{0x00, 0x10, 0x10, 0x1e, 0x11, 0x11, 0x11, 0x1e, 0x00, 0x00, },
+	{0x00, 0x00, 0x00, 0x0f, 0x10, 0x10, 0x10, 0x0f, 0x00, 0x00, },
+	{0x00, 0x01, 0x01, 0x0f, 0x11, 0x11, 0x11, 0x0f, 0x00, 0x00, },
+	{0x00, 0x00, 0x00, 0x0e, 0x11, 0x1f, 0x10, 0x0e, 0x00, 0x00, },
+	{0x00, 0x02, 0x04, 0x04, 0x0e, 0x04, 0x04, 0x04, 0x00, 0x00, },
+	{0x00, 0x00, 0x00, 0x0f, 0x11, 0x11, 0x11, 0x0f, 0x01, 0x0e, },
+	{0x00, 0x10, 0x10, 0x1e, 0x11, 0x11, 0x11, 0x11, 0x00, 0x00, },
+	{0x00, 0x04, 0x00, 0x0c, 0x04, 0x04, 0x04, 0x0e, 0x00, 0x00, },
+	{0x00, 0x04, 0x00, 0x04, 0x04, 0x04, 0x04, 0x04, 0x04, 0x08, },
+	{0x00, 0x08, 0x08, 0x09, 0x0a, 0x0c, 0x0a, 0x09, 0x00, 0x00, },
+	{0x00, 0x0c, 0x04, 0x04, 0x04, 0x04, 0x04, 0x0e, 0x00, 0x00, },
+	{0x00, 0x00, 0x00, 0x1a, 0x15, 0x15, 0x15, 0x15, 0x00, 0x00, },
+	{0x00, 0x00, 0x00, 0x1e, 0x11, 0x11, 0x11, 0x11, 0x00, 0x00, },
+	{0x00, 0x00, 0x00, 0x0e, 0x11, 0x11, 0x11, 0x0e, 0x00, 0x00, },
+	{0x00, 0x00, 0x00, 0x1e, 0x11, 0x11, 0x11, 0x1e, 0x10, 0x10, },
+	{0x00, 0x00, 0x00, 0x0f, 0x11, 0x11, 0x11, 0x0f, 0x01, 0x01, },
+	{0x00, 0x00, 0x00, 0x0b, 0x0c, 0x08, 0x08, 0x08, 0x00, 0x00, },
+	{0x00, 0x00, 0x00, 0x0f, 0x10, 0x0e, 0x01, 0x1e, 0x00, 0x00, },
+	{0x00, 0x04, 0x04, 0x0e, 0x04, 0x04, 0x04, 0x02, 0x00, 0x00, },
+	{0x00, 0x00, 0x00, 0x11, 0x11, 0x11, 0x11, 0x0f, 0x00, 0x00, },
+	{0x00, 0x00, 0x00, 0x11, 0x11, 0x0a, 0x0a, 0x04, 0x00, 0x00, },
+	{0x00, 0x00, 0x00, 0x11, 0x11, 0x15, 0x15, 0x0a, 0x00, 0x00, },
+	{0x00, 0x00, 0x00, 0x11, 0x0a, 0x04, 0x0a, 0x11, 0x00, 0x00, },
+	{0x00, 0x00, 0x00, 0x11, 0x11, 0x11, 0x11, 0x0f, 0x01, 0x0e, },
+	{0x00, 0x00, 0x00, 0x1f, 0x02, 0x04, 0x08, 0x1f, 0x00, 0x00, },
+	{0x00, 0x10, 0x10, 0x10, 0x10, 0x11, 0x03, 0x05, 0x07, 0x01, },
+	{0x00, 0x0a, 0x0a, 0x0a, 0x0a, 0x0a, 0x0a, 0x0a, 0x00, 0x00, },
+	{0x00, 0x18, 0x04, 0x18, 0x04, 0x19, 0x03, 0x05, 0x07, 0x01, },
+	{0x00, 0x00, 0x04, 0x00, 0x1f, 0x00, 0x04, 0x00, 0x00, 0x00, },
+	{0x00, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x00, 0x00, },
+};
+
+constexpr uint16_t scale(const uint8_t top, const uint8_t bottom) {
+	// Adapted from old ElectrEm source; my original provenance for this being the correct logic is unknown.
+	uint16_t wide =
+		((top & 0b00001) ? 0b0000'0000'0011 : 0) |
+		((top & 0b00010) ? 0b0000'0000'1100 : 0) |
+		((top & 0b00100) ? 0b0000'0011'0000 : 0) |
+		((top & 0b01000) ? 0b0000'1100'0000 : 0) |
+		((top & 0b10000) ? 0b0011'0000'0000 : 0);
+
+	if((top & 0b10000) && (bottom & 0b11000) == 0b01000) wide |= 0b0000'1000'0000;
+	if((top & 0b01000) && (bottom & 0b01100) == 0b00100) wide |= 0b0000'0010'0000;
+	if((top & 0b00100) && (bottom & 0b00110) == 0b00010) wide |= 0b0000'0000'1000;
+	if((top & 0b00010) && (bottom & 0b00011) == 0b00001) wide |= 0b0000'0000'0010;
+
+	if((top & 0b01000) && (bottom & 0b11000) == 0b10000) wide |= 0b0001'0000'0000;
+	if((top & 0b00100) && (bottom & 0b01100) == 0b01000) wide |= 0b0000'0100'0000;
+	if((top & 0b00010) && (bottom & 0b00110) == 0b00100) wide |= 0b0000'0001'0000;
+	if((top & 0b00001) && (bottom & 0b00011) == 0b00010) wide |= 0b0000'0000'0100;
+
+	return wide;
+}
+
+enum ControlCode: uint8_t {
+	RedAlpha = 0x01,
+	GreenAlpha = 0x02,
+	YellowAlpha = 0x03,
+	BlueAlpha = 0x04,
+	MagentaAlpha = 0x05,
+	CyanAlpha = 0x06,
+	WhiteAlpha = 0x07,
+
+	Flash = 0x08,
+	Steady = 0x09,
+
+	RedGraphics = 0x11,
+	GreenGraphics = 0x12,
+	YellowGraphics = 0x13,
+	BlueGraphics = 0x14,
+	MagentaGraphics = 0x15,
+	CyanGraphics = 0x16,
+	WhiteGraphics = 0x17,
+
+	Conceal = 0x18,
+
+	ContinuousGraphics = 0x19,
+	SeparatedGraphics = 0x1a,
+
+	NormalHeight = 0xc,
+	DoubleHeight = 0xd,
+
+	BlackBackground = 0x1c,
+	NewBackground = 0x1d,
+
+	HoldGraphics = 0x1e,
+	ReleaseGraphics = 0x1f,
+};}
+
+using namespace Mullard;
+
+void SAA5050Serialiser::begin_frame(const bool is_odd) {
+	line_ = -2;
+	row_ = 0;
+	odd_frame_ = is_odd;
+
+	row_has_double_height_ = false;
+	double_height_offset_ = 0;
+
+	++frame_counter_;
+}
+
+void SAA5050Serialiser::begin_line() {
+	line_ += 2;
+	if(line_ == 20) {
+		line_ = 0;
+		++row_;
+
+		if(row_has_double_height_) {
+			double_height_offset_ = (double_height_offset_ + 5) % 10;
+		}
+		row_has_double_height_ = false;
+	}
+
+	output_.pixels = 0;
+	has_output_ = false;
+
+	apply_control(ControlCode::WhiteAlpha);
+	apply_control(ControlCode::Steady);
+	apply_control(ControlCode::NormalHeight);
+	apply_control(ControlCode::ContinuousGraphics);
+	apply_control(ControlCode::BlackBackground);
+	apply_control(ControlCode::ReleaseGraphics);
+}
+
+bool SAA5050Serialiser::has_output() const {
+	return has_output_;
+}
+
+SAA5050Serialiser::Output SAA5050Serialiser::output() {
+	has_output_ = false;
+	return output_;
+}
+
+void SAA5050Serialiser::apply_control(const uint8_t value) {
+	const auto set_alpha = [&](const uint8_t colour) {
+		alpha_mode_ = true;
+		conceal_ = false;
+		output_.alpha = colour;
+		hold_graphics_ = false;
+	};
+
+	const auto set_graphics = [&](const uint8_t colour) {
+		alpha_mode_ = false;
+		conceal_ = false;
+		output_.alpha = colour;
+		hold_graphics_ = false;
+	};
+
+	switch(value) {
+		default: break;
+
+		case RedAlpha:				set_alpha(0b100);									break;
+		case GreenAlpha:			set_alpha(0b010);									break;
+		case YellowAlpha:			set_alpha(0b110);									break;
+		case BlueAlpha:				set_alpha(0b001);									break;
+		case MagentaAlpha:			set_alpha(0b101);									break;
+		case CyanAlpha:				set_alpha(0b011);									break;
+		case WhiteAlpha:			set_alpha(0b111);									break;
+
+		case Flash:					flash_ = true;										break;
+		case Steady:				flash_ = false;										break;
+
+		case RedGraphics:			set_graphics(0b100);								break;
+		case GreenGraphics:			set_graphics(0b010);								break;
+		case YellowGraphics:		set_graphics(0b110);								break;
+		case BlueGraphics:			set_graphics(0b001);								break;
+		case MagentaGraphics:		set_graphics(0b101);								break;
+		case CyanGraphics:			set_graphics(0b011);								break;
+		case WhiteGraphics:			set_graphics(0b111);								break;
+
+		case Conceal:				conceal_ = true;									break;
+
+		case ContinuousGraphics:	separated_graphics_ = false;						break;
+		case SeparatedGraphics:		separated_graphics_ = true;							break;
+
+		case NormalHeight:			double_height_ = false;								break;
+		case DoubleHeight:			double_height_ = row_has_double_height_ = true;		break;
+
+		case BlackBackground:		output_.background = 0;								break;
+		case NewBackground:			output_.background = output_.alpha;					break;
+
+		case HoldGraphics:			hold_graphics_ = true;								break;
+		case ReleaseGraphics:		hold_graphics_ = false; last_graphic_ = 32;			break;
+	}
+}
+
+void SAA5050Serialiser::set_reveal(const bool reveal) {
+	reveal_ = reveal;
+}
+
+void SAA5050Serialiser::add(const Numeric::SizedCounter<7> c) {
+	has_output_ = true;
+	if(c.get() < 32) {
+		output_.pixels = hold_graphics_ ? pixels(last_graphic_) : 0;
+		apply_control(c.get());
+		return;
+	}
+	output_.pixels = pixels(c.get());
+}
+
+uint16_t SAA5050Serialiser:: pixels(const uint8_t c) {
+	if(flash_ && frame_counter_&16) {
+		return 0;
+	}
+
+	if(conceal_ && !reveal_) {
+		return 0;
+	}
+
+	// Divert into graphics only if both the mode and the character code allows it.
+	if(!alpha_mode_ && (c & (1 << 5))) {
+		last_graphic_ = c;
+
+		// Graphics layout:
+		//
+		//	|----|----|
+		//	|    |    |
+		//	| b0 | b1 |
+		//	|    |    |
+		//	|----|----|
+		//	|    |    |
+		//	| b2 | b3 |
+		//	|    |    |
+		//	|----|----|
+		//	|    |    |
+		//	| b4 | b6 |
+		//	|    |    |
+		//	|----|----|
+
+		if(separated_graphics_ && (line_ == 6 || line_ == 12 || line_ == 18)) {
+			return 0;
+		}
+
+		uint16_t pixels;
+		if(line_ < 6) {
+			pixels =
+				((c & 1) ? 0b1111'1100'0000 : 0) |
+				((c & 2) ? 0b0000'0011'1111 : 0);
+		} else if(line_ < 12) {
+			pixels =
+				((c & 4) ? 0b1111'1100'0000 : 0) |
+				((c & 8) ? 0b0000'0011'1111 : 0);
+		} else {
+			pixels =
+				((c & 16) ? 0b1111'1100'0000 : 0) |
+				((c & 64) ? 0b0000'0011'1111 : 0);
+		}
+
+		if(separated_graphics_) {
+			pixels &= 0b0111'1101'1111;
+		}
+
+		return pixels;
+	}
+
+	if(double_height_) {
+		const auto top_address = (line_ >> 2) + double_height_offset_;
+		const uint8_t top = font[c - 32][top_address];
+		const uint8_t bottom = font[c - 32][std::min(9, top_address + 1)];
+
+		if(line_ & 2) {
+			return scale(bottom, top);
+		} else {
+			return scale(top, bottom);
+		}
+	} else {
+		if(double_height_offset_) {
+			return 0;
+		} else {
+			const auto top_address = line_ >> 1;
+			const uint8_t top = font[c - 32][top_address];
+			const uint8_t bottom = font[c - 32][std::min(9, top_address + 1)];
+
+			if(odd_frame_) {
+				return scale(bottom, top);
+			} else {
+				return scale(top, bottom);
+			}
+		}
+	}
+}

Components/SAA5050/SAA5050.hpp

@@ -0,0 +1,63 @@
+//
+//  SAA5050.hpp
+//  Clock Signal
+//
+//  Created by Thomas Harte on 24/09/2025.
+//  Copyright © 2025 Thomas Harte. All rights reserved.
+//
+
+#pragma once
+
+#include <cstdint>
+#include "Numeric/SizedCounter.hpp"
+
+namespace Mullard {
+
+struct SAA5050Serialiser {
+public:
+	void begin_frame(bool is_odd);
+	void begin_line();
+
+	void add(Numeric::SizedCounter<7>);
+
+	struct Output {
+		// The low twelve bits of this word provide 1bpp pixels.
+		uint16_t pixels;
+
+		// Colours for set and background pixels.
+		uint8_t alpha;
+		uint8_t background;
+	};
+	bool has_output() const;
+	Output output();
+
+	void set_reveal(bool);
+
+private:
+	Output output_;
+	bool has_output_ = false;
+
+	int row_, line_;
+	bool odd_frame_;
+
+	bool flash_ = false;
+	int frame_counter_ = 0;
+
+	bool reveal_ = false;
+	bool conceal_ = false;
+
+	bool alpha_mode_ = true;
+	bool separated_graphics_ = false;
+
+	bool double_height_ = false;
+	bool row_has_double_height_ = false;
+	int double_height_offset_ = 0;
+
+	bool hold_graphics_ = false;
+	uint8_t last_graphic_ = 0;
+
+	uint16_t pixels(const uint8_t);
+	void apply_control(const uint8_t);
+};
+
+}

Machines/Acorn/BBCMicro/BBCMicro.cpp

@@ -17,8 +17,9 @@
 
 #include "Components/6522/6522.hpp"
 #include "Components/6845/CRTC6845.hpp"
-#include "Components/SN76489/SN76489.hpp"
 #include "Components/6850/6850.hpp"
+#include "Components/SAA5050/SAA5050.hpp"
+#include "Components/SN76489/SN76489.hpp"
 #include "Components/uPD7002/uPD7002.hpp"
 
 // TODO: factor this more appropriately.
@@ -306,10 +307,6 @@ public:
 
 		active_collation_.pixels_per_clock = 1 << ((value >> 2) & 0x03);
 		active_collation_.is_teletext = value & 0x02;
-		if(active_collation_.is_teletext) {
-			Logger::error().append("TODO: video control => teletext %d", bool(value & 0x02));
-		}
-
 		flash_mask_ = value & 0x01 ? 7 : 0;
 		cursor_mask_ = value & 0b1110'0000;
 	}
@@ -327,15 +324,13 @@ public:
 		system_via_.set_control_line_input<MOS::MOS6522::Port::A, MOS::MOS6522::Line::One>(state.vsync);
 
 		// Count cycles since horizontal sync to insert a colour burst.
-		if(state.hsync) {
-			++cycles_into_hsync_;
-		} else {
-			cycles_into_hsync_ = 0;
-		}
-		const bool is_colour_burst = cycles_into_hsync_ >= 5 && cycles_into_hsync_ < 9;
-
-		// Sync is taken to override pixels, and is combined as a simple OR.
-		const bool is_sync = state.hsync || state.vsync;
+		// TODO: this is copy/pasted from the CPC. How does the BBC do it?
+//		if(state.hsync) {
+//			++cycles_into_hsync_;
+//		} else {
+//			cycles_into_hsync_ = 0;
+//		}
+//		const bool is_colour_burst = cycles_into_hsync_ >= 5 && cycles_into_hsync_ < 9;
 
 		// Check for a cursor leading edge.
 		cursor_shifter_ >>= 4;
@@ -349,17 +344,64 @@ public:
 			previous_cursor_enabled_ = state.cursor;
 		}
 
-		OutputMode output_mode;
-		const bool should_fetch = state.display_enable && (active_collation_.is_teletext || !(state.line.get() & 8));
-		if(is_sync) {
-			output_mode = OutputMode::Sync;
-		} else if(is_colour_burst) {
-			output_mode = OutputMode::ColourBurst;
-		} else if(should_fetch || cursor_shifter_) {
-			output_mode = OutputMode::Pixels;
-		} else {
-			output_mode = OutputMode::Blank;
+		// Consider some SAA5050 signalling.
+		if(!state.vsync && previous_vsync_) {
+			// Complete fiction here; the SAA5050 field flag is set by peeking inside CRTC state.
+			// TODO: what really sets CRS for the SAA5050? Time since hsync maybe?
+			saa5050_serialiser_.begin_frame(state.field_count.bit<0>());
 		}
+		previous_vsync_ = state.vsync;
+
+		if(state.display_enable && !previous_display_enabled_) {
+			saa5050_serialiser_.begin_line();
+		}
+		previous_display_enabled_ = state.display_enable;
+
+		// Grab 5050 output, if any.
+		bool has_5050_output_ = saa5050_serialiser_.has_output();
+		const auto saa_50505_output_ = saa5050_serialiser_.output();
+
+		// Fetch, possibly.
+		const bool should_fetch = state.display_enable && (active_collation_.is_teletext || !(state.line.get() & 8));
+		if(should_fetch) {
+			const uint16_t address = [&] {
+				// Teletext address generation.
+				if(state.refresh.get() & (1 << 13)) {
+					return uint16_t(
+						0x3c00 |
+						((state.refresh.get() & 0x800) << 3) |
+						(state.refresh.get() & 0x3ff)
+					);
+				}
+
+				uint16_t address = uint16_t((state.refresh.get() << 3) | (state.line.get() & 7));
+				if(address & 0x8000) {
+					address = (address + video_base_) & 0x7fff;
+				}
+				return address;
+			} ();
+			const uint8_t fetched = ram_[address];
+			pixel_shifter_ = fetched;
+			saa5050_serialiser_.add(fetched);
+		}
+
+		// Pick new output mode.
+		const OutputMode output_mode = [&] {
+			if(state.hsync || state.vsync) {
+				return OutputMode::Sync;
+			}
+//			if(is_colour_burst) {
+//				return OutputMode::ColourBurst;
+//			}
+			if(
+				(should_fetch && !active_collation_.is_teletext) ||
+				(has_5050_output_ && active_collation_.is_teletext) ||
+				cursor_shifter_
+			) {
+				return OutputMode::Pixels;
+			}
+			return OutputMode::Blank;
+		} ();
 
 		// If a transition between sync/border/pixels just occurred, flush whatever was
 		// in progress to the CRT and reset counting. Also flush if this mode has just been effective
@@ -379,11 +421,8 @@ public:
 			previous_output_mode_ = output_mode;
 		}
 
-		// Increment cycles since state changed.
-		cycles_ += crtc_clock_multiplier_ << 3;
-
 		// Collect some more pixels if output is ongoing.
-		if(previous_output_mode_ == OutputMode::Pixels) {
+		if(output_mode == OutputMode::Pixels) {
 			// Flush the current buffer pixel if full; the CRTC allows many different display
 			// widths so it's not necessarily possible to predict the correct number in advance
 			// and using the upper bound could lead to inefficient behaviour.
@@ -396,30 +435,20 @@ public:
 			if(!pixel_data_) {
 				pixel_pointer_ = pixel_data_ = crt_.begin_data(PixelAllocationUnit, 8);
 			}
-			if(pixel_pointer_) {
-				uint16_t address;
 
-				if(state.refresh.get() & (1 << 13)) {
-					// Teletext address generation mode.
-					address = uint16_t(
-						0x3c00 |
-						((state.refresh.get() & 0x800) << 3) |
-						(state.refresh.get() & 0x3ff)
-					);
-					// TODO: wraparound? Does that happen on Mode 7?
-				} else {
-					address = uint16_t((state.refresh.get() << 3) | (state.line.get() & 7));
-					if(address & 0x8000) {
-						address = (address + video_base_) & 0x7fff;
-					}
-				}
-
-				pixel_shifter_ = should_fetch ? ram_[address] : 0;
+			if(pixel_data_) {
 				if(active_collation_.is_teletext) {
-					// TODO: output meaningful teletext pixels.
-					for(int c = 0; c < 12; c++) {
-						*pixel_pointer_++ = (pixel_shifter_ & 0x80 ? 0xff : 0x00) ^ cursor_mask_;
-						pixel_shifter_ <<= 1;
+					if(has_5050_output_) {
+						uint16_t pixels = saa_50505_output_.pixels;
+						for(int c = 0; c < 12; c++) {
+							*pixel_pointer_++ =
+								((pixels & 0b1000'0000'0000) ? saa_50505_output_.alpha : saa_50505_output_.background)
+									^ uint8_t(cursor_shifter_);
+							pixels <<= 1;
+						}
+					} else {
+						std::fill(pixel_pointer_, pixel_pointer_ + 12, 0);
+						pixel_pointer_ += 12;
 					}
 				} else {
 					switch(crtc_clock_multiplier_ * active_collation_.pixels_per_clock) {
@@ -433,6 +462,9 @@ public:
 				}
 			}
 		}
+
+		// Increment cycles since state changed.
+		cycles_ += crtc_clock_multiplier_ << 3;
 	}
 
 	/// Sets the destination for output.
@@ -499,6 +531,9 @@ private:
 	uint32_t cursor_shifter_ = 0;
 	bool previous_cursor_enabled_ = false;
 
+	bool previous_display_enabled_ = false;
+	bool previous_vsync_ = false;
+
 	template <int count> void shift_pixels(const uint8_t cursor_mask) {
 		for(int c = 0; c < count; c++) {
 			const uint8_t colour =
@@ -513,6 +548,8 @@ private:
 
 	const uint8_t *const ram_ = nullptr;
 	SystemVIA &system_via_;
+
+	Mullard::SAA5050Serialiser saa5050_serialiser_;
 };
 using CRTC = Motorola::CRTC::CRTC6845<
 	CRTCBusHandler,

OSBindings/Mac/Clock Signal.xcodeproj/project.pbxproj

@@ -641,6 +641,9 @@
 		4B882F5B2C2F9C7700D84031 /* Shaker in Resources */ = {isa = PBXBuildFile; fileRef = 4B882F5A2C2F9C7700D84031 /* Shaker */; };
 		4B882F5C2C32199400D84031 /* MachineForTarget.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4B055ABE1FAE98000060FFFF /* MachineForTarget.cpp */; };
 		4B882F5D2C3219A400D84031 /* AmstradCPC.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4B38F3461F2EC11D00D9235D /* AmstradCPC.cpp */; };
+		4B8855A52E84D51B00E251DD /* SAA5050.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4B8855A32E84D51B00E251DD /* SAA5050.cpp */; };
+		4B8855A62E84D51B00E251DD /* SAA5050.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4B8855A32E84D51B00E251DD /* SAA5050.cpp */; };
+		4B8855A72E84D51B00E251DD /* SAA5050.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4B8855A32E84D51B00E251DD /* SAA5050.cpp */; };
 		4B89449520194CB3007DE474 /* MachineForTarget.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4B055ABE1FAE98000060FFFF /* MachineForTarget.cpp */; };
 		4B894518201967B4007DE474 /* ConfidenceCounter.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4B8944E6201967B4007DE474 /* ConfidenceCounter.cpp */; };
 		4B894519201967B4007DE474 /* ConfidenceCounter.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4B8944E6201967B4007DE474 /* ConfidenceCounter.cpp */; };
@@ -1795,6 +1798,8 @@
 		4B882F582C2F9C6900D84031 /* CPCShakerTests.mm */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.objcpp; path = CPCShakerTests.mm; sourceTree = "<group>"; };
 		4B882F5A2C2F9C7700D84031 /* Shaker */ = {isa = PBXFileReference; lastKnownFileType = folder; path = Shaker; sourceTree = "<group>"; };
 		4B88559C2E8185BF00E251DD /* SizedCounter.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = SizedCounter.hpp; sourceTree = "<group>"; };
+		4B8855A22E84D51B00E251DD /* SAA5050.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = SAA5050.hpp; sourceTree = "<group>"; };
+		4B8855A32E84D51B00E251DD /* SAA5050.cpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.cpp; path = SAA5050.cpp; sourceTree = "<group>"; };
 		4B89449220194A47007DE474 /* CSStaticAnalyser+TargetVector.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; name = "CSStaticAnalyser+TargetVector.h"; path = "StaticAnalyser/CSStaticAnalyser+TargetVector.h"; sourceTree = "<group>"; };
 		4B8944E4201967B4007DE474 /* ConfidenceSummary.hpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.h; path = ConfidenceSummary.hpp; sourceTree = "<group>"; };
 		4B8944E5201967B4007DE474 /* ConfidenceSource.hpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.h; path = ConfidenceSource.hpp; sourceTree = "<group>"; };
@@ -3847,6 +3852,15 @@
 			path = Data;
 			sourceTree = "<group>";
 		};
+		4B8855A42E84D51B00E251DD /* SAA5050 */ = {
+			isa = PBXGroup;
+			children = (
+				4B8855A22E84D51B00E251DD /* SAA5050.hpp */,
+				4B8855A32E84D51B00E251DD /* SAA5050.cpp */,
+			);
+			path = SAA5050;
+			sourceTree = "<group>";
+		};
 		4B8944E2201967B4007DE474 /* Analyser */ = {
 			isa = PBXGroup;
 			children = (
@@ -5089,6 +5103,7 @@
 				4B4B1A39200198C900A0F866 /* KonamiSCC */,
 				4BC23A212467600E001A6030 /* OPx */,
 				4BF0BC6E2973318E00CCA2B5 /* RP5C01 */,
+				4B8855A42E84D51B00E251DD /* SAA5050 */,
 				4B0ACBFF237756EC008902D0 /* Serial */,
 				4BB0A6582044FD3000FB3688 /* SN76489 */,
 				4B47F3B42E7B9A14005D4DEC /* uPD7002 */,
@@ -6301,6 +6316,7 @@
 				4B302185208A550100773308 /* DiskII.cpp in Sources */,
 				42EB81292B23AAC300429AF4 /* IMD.cpp in Sources */,
 				4B051CB1267C1CA200CA44E8 /* Keyboard.cpp in Sources */,
+				4B8855A72E84D51B00E251DD /* SAA5050.cpp in Sources */,
 				4B0F1BB32602645900B85C66 /* StaticAnalyser.cpp in Sources */,
 				4B055A931FAE85B50060FFFF /* BinaryDump.cpp in Sources */,
 				4B89452D201967B4007DE474 /* Tape.cpp in Sources */,
@@ -6397,6 +6413,7 @@
 				4B4DC82B1D2C27A4003C5BF8 /* SerialBus.cpp in Sources */,
 				4BE8EB6625C750B50040BC40 /* DAT.cpp in Sources */,
 				4BBFFEE61F7B27F1005F3FEB /* TrackSerialiser.cpp in Sources */,
+				4B8855A52E84D51B00E251DD /* SAA5050.cpp in Sources */,
 				4BAE49582032881E004BE78E /* CSZX8081.mm in Sources */,
 				4B0333AF2094081A0050B93D /* AppleDSK.cpp in Sources */,
 				4B894518201967B4007DE474 /* ConfidenceCounter.cpp in Sources */,
@@ -6628,6 +6645,7 @@
 				4B778F3123A5F0CB0000D260 /* Keyboard.cpp in Sources */,
 				4B778F4A23A5F1FB0000D260 /* StaticAnalyser.cpp in Sources */,
 				4B7752AB28217E560073E2C5 /* SZX.cpp in Sources */,
+				4B8855A62E84D51B00E251DD /* SAA5050.cpp in Sources */,
 				4BD91D772401C2B8007BDC91 /* PatrikRakTests.swift in Sources */,
 				4B06AAE22C645F970034D014 /* PCBooter.cpp in Sources */,
 				4B1082C32C1A87CA00B07C5D /* CSL.cpp in Sources */,

OSBindings/Qt/clksignal.pro

@@ -76,6 +76,7 @@ SOURCES += \
 	$$SRC/Components/KonamiSCC/*.cpp \
 	$$SRC/Components/OPx/*.cpp \
 	$$SRC/Components/RP5C01/*.cpp \
+	$$SRC/Components/SAA5050/*.cpp \
 	$$SRC/Components/Serial/*.cpp \
 	$$SRC/Components/SN76489/*.cpp \
 	$$SRC/Components/uPD7002/*.cpp \
@@ -212,6 +213,7 @@ HEADERS += \
 	$$SRC/Components/OPx/*.hpp \
 	$$SRC/Components/OPx/Implementation/*.hpp \
 	$$SRC/Components/RP5C01/*.hpp \
+	$$SRC/Components/SAA5050/*.hpp \
 	$$SRC/Components/Serial/*.hpp \
 	$$SRC/Components/SN76489/*.hpp \
 	$$SRC/Components/uPD7002/*.hpp \

OSBindings/SDL/SConstruct

@@ -60,6 +60,7 @@ SOURCES += glob.glob('../../Components/I2C/*.cpp')
 SOURCES += glob.glob('../../Components/KonamiSCC/*.cpp')
 SOURCES += glob.glob('../../Components/OPx/*.cpp')
 SOURCES += glob.glob('../../Components/RP5C01/*.cpp')
+SOURCES += glob.glob('../../Components/SAA5050/*.cpp')
 SOURCES += glob.glob('../../Components/SN76489/*.cpp')
 SOURCES += glob.glob('../../Components/Serial/*.cpp')
 SOURCES += glob.glob('../../Components/uPD7002/*.cpp')

cmake/CLK_SOURCES.cmake

@@ -58,6 +58,7 @@ set(CLK_SOURCES
 	Components/KonamiSCC/KonamiSCC.cpp
 	Components/OPx/OPLL.cpp
 	Components/RP5C01/RP5C01.cpp
+	Components/SAA5050/SAA5050.cpp
 	Components/SN76489/SN76489.cpp
 	Components/Serial/Line.cpp
 	Components/uPD7002/uPD7002.cpp