Drives can now deliver activity events.

Activity/Observer.hpp

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+//
+//  ActivityObserver.h
+//  Clock Signal
+//
+//  Created by Thomas Harte on 07/05/2018.
+//  Copyright © 2018 Thomas Harte. All rights reserved.
+//
+
+#ifndef ActivityObserver_h
+#define ActivityObserver_h
+
+#include <string>
+
+namespace Activity {
+
+/*!
+	Provides a purely virtual base class for anybody that wants to receive notifications of
+	'activity' — any feedback from an emulated system which a user could perceive other than
+	through the machine's native audio and video outputs.
+
+	So: status LEDs, drive activity, etc. A receiver may choose to make appropriate noises
+	and/or to show or unshow status indicators.
+*/
+class Observer {
+	public:
+		/// Announces to the receiver that there is an LED of name @c name.
+		virtual void register_led(const std::string &name) = 0;
+
+		/// Announces to the receiver that there is a drive of name @c name.
+		virtual void register_drive(const std::string &name) = 0;
+
+		/// Informs the receiver of the new state of the LED with name @c name.
+		virtual void set_led_status(const std::string &name, bool lit) = 0;
+
+		enum class DriveEvent {
+			Step,
+			StepBelowZero,
+			StepBeyondMaximum
+		};
+
+		/// Informs the receiver that the named event just occurred for the drive with name @c name.
+		virtual void announce_drive_event(const std::string &name, DriveEvent event) = 0;
+
+		/// Informs the receiver of the motor-on status of the drive with name @c name.
+		virtual void set_drive_motor_status(const std::string &name, bool is_on) = 0;
+
+};
+
+}
+
+#endif /* ActivityObserver_h */

Activity/Source.hpp

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+//
+//  ActivitySource.h
+//  Clock Signal
+//
+//  Created by Thomas Harte on 07/05/2018.
+//  Copyright © 2018 Thomas Harte. All rights reserved.
+//
+
+#ifndef ActivitySource_h
+#define ActivitySource_h
+
+#include "Observer.hpp"
+
+namespace Activity {
+
+class Source {
+	public:
+		virtual void set_activity_observer(Observer *observer) = 0;
+};
+
+}
+
+
+#endif /* ActivitySource_h */