Begins keyboard sketches and notes.

Machines/Amiga/Keyboard.cpp

@@ -0,0 +1,92 @@
+//
+//  Keyboard.cpp
+//  Clock Signal
+//
+//  Created by Thomas Harte on 29/07/2021.
+//  Copyright © 2021 Thomas Harte. All rights reserved.
+//
+
+#include "Keyboard.hpp"
+
+// Notes to self:
+//
+//
+// Before
+// the transmission starts, both KCLK and KDAT are high.  The keyboard starts
+// the transmission by putting out the first data bit (on KDAT), followed by
+// a pulse on KCLK (low then high); then it puts out the second data bit and
+// pulses KCLK until all eight data bits have been sent.
+//
+// When the computer has received the eighth bit, it must pulse KDAT low for
+// at least 1 (one) microsecond, as a handshake signal to the keyboard. The
+// keyboard must be able to detect pulses greater than or equal
+// to 1 microsecond.  Software MUST pulse the line low for 85 microseconds to
+// ensure compatibility with all keyboard models.
+//
+//
+// If the handshake pulse does not arrive within
+// 143 ms of the last clock of the transmission, the keyboard will assume
+// that the computer is still waiting for the rest of the transmission and is
+// therefore out of sync.  The keyboard will then attempt to restore sync by
+// going into "resync mode."  In this mode, the keyboard clocks out a 1 and
+// waits for a handshake pulse. If none arrives within 143 ms, it clocks out
+// another 1 and waits again.
+//
+// The keyboard Hard Resets the Amiga by pulling KCLK low and starting a 500
+// millisecond timer.   When one or more of the keys is released and 500
+// milliseconds have passed, the keyboard will release KCLK.
+//
+// The usual sequence of events will therefore be:  power-up; synchronize;
+// transmit "initiate power-up key stream" ($FD); transmit "terminate key
+// stream" ($FE).
+
+using namespace Amiga;
+
+uint8_t Keyboard::update(uint8_t input) {
+	// If a bit transmission is ongoing, continue that, up to and including
+	// the handshake. If no handshake comes, set a macro state of synchronising.
+	switch(shift_state_) {
+		case ShiftState::Shifting:
+			// The keyboard processor sets the KDAT line about 20 microseconds before it
+			// pulls KCLK low.  KCLK stays low for about 20 microseconds, then goes high
+			// again.  The processor waits another 20 microseconds before changing KDAT.
+			switch(bit_phase_) {
+				default: break;
+				case 0:		lines_ = Lines::Clock | (shift_sequence_ & 1);	break;
+				case 20:	lines_ = (shift_sequence_ & 1);					break;
+				case 40:	lines_ = Lines::Clock | (shift_sequence_ & 1);	break;
+			}
+			bit_phase_ = (bit_phase_ + 1) % 60;
+
+			if(!bit_phase_) {
+				--bits_remaining_;
+				shift_sequence_ >>= 1;
+				if(!bits_remaining_) {
+					shift_state_ = ShiftState::AwaitingHandshake;
+				}
+			}
+		return lines_;
+
+		case ShiftState::AwaitingHandshake:
+			if(!(input & Lines::Data)) {
+				shift_state_ = ShiftState::Idle;
+			}
+			++bit_phase_;
+			if(bit_phase_ == 143) {
+//				shift_state_ = ShiftState::Synchronising;
+			}
+		return lines_;
+
+		default: break;
+	}
+
+	switch(state_) {
+		case State::Startup:
+			bit_phase_ = 0;
+			shift_sequence_ = 0xff;
+			shift_state_ = ShiftState::Shifting;
+		break;
+	}
+
+	return lines_;
+}

Machines/Amiga/Keyboard.hpp

@@ -0,0 +1,45 @@
+//
+//  Keyboard.hpp
+//  Clock Signal
+//
+//  Created by Thomas Harte on 29/07/2021.
+//  Copyright © 2021 Thomas Harte. All rights reserved.
+//
+
+#ifndef Keyboard_hpp
+#define Keyboard_hpp
+
+#include <cstdint>
+
+namespace Amiga {
+
+class Keyboard {
+	public:
+		enum Lines: uint8_t {
+			Data = (1 << 0),
+			Clock = (1 << 1),
+		};
+
+		uint8_t update(uint8_t);
+
+	private:
+		enum class ShiftState {
+			Shifting,
+			AwaitingHandshake,
+			Idle,
+		} shift_state_ = ShiftState::Idle;
+
+		enum class State {
+			Startup,
+		} state_ = State::Startup;
+
+		int bit_phase_ = 0;
+		uint32_t shift_sequence_ = 0;
+		int bits_remaining_ = 0;
+
+		uint8_t lines_ = 0;
+};
+
+}
+
+#endif /* Keyboard_hpp */

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

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@@ -4275,9 +4279,11 @@
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 				4B9EC0E126AA27BA0060A31F /* Blitter.cpp */,
 				4B9EC0E426AA4A660060A31F /* Chipset.cpp */,
+				4B9EC0E826B384080060A31F /* Keyboard.cpp */,
 				4BC080D726A25ADA00D03FD8 /* Amiga.hpp */,
 				4B9EC0E026AA260C0060A31F /* Blitter.hpp */,
 				4B9EC0E526AA4A660060A31F /* Chipset.hpp */,
+				4B9EC0E926B384080060A31F /* Keyboard.hpp */,
 			);
 			path = Amiga;
 			sourceTree = "<group>";
@@ -5286,6 +5292,7 @@
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 				4B0E04F11FC9EA9500F43484 /* MSX.cpp in Sources */,
 				4B055AD51FAE9B0B0060FFFF /* Video.cpp in Sources */,
+				4B9EC0EB26B384080060A31F /* Keyboard.cpp in Sources */,
 				4B894521201967B4007DE474 /* StaticAnalyser.cpp in Sources */,
 				4B8318B522D3E548006DB630 /* Macintosh.cpp in Sources */,
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 				4B1B58FF246E19FD009C171E /* State.cpp in Sources */,
 				4B2B3A4C1F9B8FA70062DABF /* MemoryFuzzer.cpp in Sources */,
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