Merge pull request #456 from TomHarte/TristateSleeper

Commutes `Sleeper` to `ClockingHint::Source`

ClockReceiver/ClockReceiver.hpp

@@ -52,79 +52,79 @@
 */
 template <class T> class WrappedInt {
 	public:
-		inline WrappedInt(int l) : length_(l) {}
-		inline WrappedInt() : length_(0) {}
+		constexpr WrappedInt(int l) : length_(l) {}
+		constexpr WrappedInt() : length_(0) {}
 
-		inline T &operator =(const T &rhs) {
+		T &operator =(const T &rhs) {
 			length_ = rhs.length_;
 			return *this;
 		}
 
-		inline T &operator +=(const T &rhs) {
+		T &operator +=(const T &rhs) {
 			length_ += rhs.length_;
 			return *static_cast<T *>(this);
 		}
 
-		inline T &operator -=(const T &rhs) {
+		T &operator -=(const T &rhs) {
 			length_ -= rhs.length_;
 			return *static_cast<T *>(this);
 		}
 
-		inline T &operator ++() {
+		T &operator ++() {
 			++ length_;
 			return *static_cast<T *>(this);
 		}
 
-		inline T &operator ++(int) {
+		T &operator ++(int) {
 			length_ ++;
 			return *static_cast<T *>(this);
 		}
 
-		inline T &operator --() {
+		T &operator --() {
 			-- length_;
 			return *static_cast<T *>(this);
 		}
 
-		inline T &operator --(int) {
+		T &operator --(int) {
 			length_ --;
 			return *static_cast<T *>(this);
 		}
 
-		inline T &operator %=(const T &rhs) {
+		T &operator %=(const T &rhs) {
 			length_ %= rhs.length_;
 			return *static_cast<T *>(this);
 		}
 
-		inline T &operator &=(const T &rhs) {
+		T &operator &=(const T &rhs) {
 			length_ &= rhs.length_;
 			return *static_cast<T *>(this);
 		}
 
-		inline T operator +(const T &rhs) const			{	return T(length_ + rhs.length_);	}
-		inline T operator -(const T &rhs) const			{	return T(length_ - rhs.length_);	}
+		constexpr T operator +(const T &rhs) const			{	return T(length_ + rhs.length_);	}
+		constexpr T operator -(const T &rhs) const			{	return T(length_ - rhs.length_);	}
 
-		inline T operator %(const T &rhs) const			{	return T(length_ % rhs.length_);	}
-		inline T operator &(const T &rhs) const			{	return T(length_ & rhs.length_);	}
+		constexpr T operator %(const T &rhs) const			{	return T(length_ % rhs.length_);	}
+		constexpr T operator &(const T &rhs) const			{	return T(length_ & rhs.length_);	}
 
-		inline T operator -() const						{	return T(- length_);				}
+		constexpr T operator -() const						{	return T(- length_);				}
 
-		inline bool operator <(const T &rhs) const		{	return length_ < rhs.length_;		}
-		inline bool operator >(const T &rhs) const		{	return length_ > rhs.length_;		}
-		inline bool operator <=(const T &rhs) const		{	return length_ <= rhs.length_;		}
-		inline bool operator >=(const T &rhs) const		{	return length_ >= rhs.length_;		}
-		inline bool operator ==(const T &rhs) const		{	return length_ == rhs.length_;		}
-		inline bool operator !=(const T &rhs) const		{	return length_ != rhs.length_;		}
+		constexpr bool operator <(const T &rhs) const		{	return length_ < rhs.length_;		}
+		constexpr bool operator >(const T &rhs) const		{	return length_ > rhs.length_;		}
+		constexpr bool operator <=(const T &rhs) const		{	return length_ <= rhs.length_;		}
+		constexpr bool operator >=(const T &rhs) const		{	return length_ >= rhs.length_;		}
+		constexpr bool operator ==(const T &rhs) const		{	return length_ == rhs.length_;		}
+		constexpr bool operator !=(const T &rhs) const		{	return length_ != rhs.length_;		}
 
-		inline bool operator !() const					{	return !length_;					}
+		constexpr bool operator !() const					{	return !length_;					}
 		// bool operator () is not supported because it offers an implicit cast to int, which is prone silently to permit misuse
 
-		inline int as_int() const { return length_; }
+		constexpr int as_int() const { return length_; }
 
 		/*!
 			Severs from @c this the effect of dividing by @c divisor; @c this will end up with
 			the value of @c this modulo @c divisor and @c divided by @c divisor is returned.
 		*/
-		inline T divide(const T &divisor) {
+		T divide(const T &divisor) {
 			T result(length_ / divisor.length_);
 			length_ %= divisor.length_;
 			return result;
@@ -134,7 +134,7 @@ template <class T> class WrappedInt {
 			Flushes the value in @c this. The current value is returned, and the internal value
 			is reset to zero.
 		*/
-		inline T flush() {
+		T flush() {
 			T result(length_);
 			length_ = 0;
 			return result;
@@ -150,34 +150,34 @@ template <class T> class WrappedInt {
 /// Describes an integer number of whole cycles: pairs of clock signal transitions.
 class Cycles: public WrappedInt<Cycles> {
 	public:
-		inline Cycles(int l) : WrappedInt<Cycles>(l) {}
-		inline Cycles() : WrappedInt<Cycles>() {}
-		inline Cycles(const Cycles &cycles) : WrappedInt<Cycles>(cycles.length_) {}
+		constexpr Cycles(int l) : WrappedInt<Cycles>(l) {}
+		constexpr Cycles() : WrappedInt<Cycles>() {}
+		constexpr Cycles(const Cycles &cycles) : WrappedInt<Cycles>(cycles.length_) {}
 };
 
 /// Describes an integer number of half cycles: single clock signal transitions.
 class HalfCycles: public WrappedInt<HalfCycles> {
 	public:
-		inline HalfCycles(int l) : WrappedInt<HalfCycles>(l) {}
-		inline HalfCycles() : WrappedInt<HalfCycles>() {}
+		constexpr HalfCycles(int l) : WrappedInt<HalfCycles>(l) {}
+		constexpr HalfCycles() : WrappedInt<HalfCycles>() {}
 
-		inline HalfCycles(const Cycles cycles) : WrappedInt<HalfCycles>(cycles.as_int() * 2) {}
-		inline HalfCycles(const HalfCycles &half_cycles) : WrappedInt<HalfCycles>(half_cycles.length_) {}
+		constexpr HalfCycles(const Cycles cycles) : WrappedInt<HalfCycles>(cycles.as_int() * 2) {}
+		constexpr HalfCycles(const HalfCycles &half_cycles) : WrappedInt<HalfCycles>(half_cycles.length_) {}
 
 		/// @returns The number of whole cycles completely covered by this span of half cycles.
-		inline Cycles cycles() {
+		constexpr Cycles cycles() {
 			return Cycles(length_ >> 1);
 		}
 
 		/// Flushes the whole cycles in @c this, subtracting that many from the total stored here.
-		inline Cycles flush_cycles() {
+		Cycles flush_cycles() {
 			Cycles result(length_ >> 1);
 			length_ &= 1;
 			return result;
 		}
 
 		/// Flushes the half cycles in @c this, returning the number stored and setting this total to zero.
-		inline HalfCycles flush() {
+		HalfCycles flush() {
 			HalfCycles result(length_);
 			length_ = 0;
 			return result;
@@ -187,7 +187,7 @@ class HalfCycles: public WrappedInt<HalfCycles> {
 			Severs from @c this the effect of dividing by @c divisor; @c this will end up with
 			the value of @c this modulo @c divisor and @c divided by @c divisor is returned.
 		*/
-		inline Cycles divide_cycles(const Cycles &divisor) {
+		Cycles divide_cycles(const Cycles &divisor) {
 			HalfCycles half_divisor = HalfCycles(divisor);
 			Cycles result(length_ / half_divisor.length_);
 			length_ %= half_divisor.length_;
@@ -203,7 +203,6 @@ template <class T> class HalfClockReceiver: public T {
 	public:
 		using T::T;
 
-		using T::run_for;
 		inline void run_for(const HalfCycles half_cycles) {
 			half_cycles_ += half_cycles;
 			T::run_for(half_cycles_.flush_cycles());

ClockReceiver/ClockingHintSource.hpp

@@ -0,0 +1,88 @@
+//
+//  ClockingHintSource.h
+//  Clock Signal
+//
+//  Created by Thomas Harte on 20/08/2017.
+//  Copyright 2017 Thomas Harte. All rights reserved.
+//
+
+#ifndef ClockingHintSource_hpp
+#define ClockingHintSource_hpp
+
+namespace ClockingHint {
+
+enum class Preference {
+	/// The component doesn't currently require a clock signal.
+	None,
+	/// The component can be clocked only immediate prior to (explicit) accesses.
+	JustInTime,
+	/// The component require real-time clocking.
+	RealTime
+};
+
+class Source;
+
+struct Observer {
+	/// Called to inform an observer that the component @c component has changed its clocking requirements.
+	virtual void set_component_prefers_clocking(Source *component, Preference clocking) = 0;
+};
+
+/*!
+	An clocking hint source is any component that can provide hints as to the type of
+	clocking required for accurate emulation. A disk controller is an archetypal example.
+
+	Types of clocking are:
+
+		- none:
+			a component that acts and reacts to direct contact but does not have a state that autonomously evolves.
+			E.g. a ROM, RAM, or some kinds of disk controller when not in the process of performing a command.
+
+		- just-in-time:
+			a component that has an evolving state but can receive clock updates only immediately before a
+			direct contact. This is possibly the most common kind of component.
+
+		- real-time:
+			a component that needs to be clocked in 'real time' (i.e. in terms of the emulated machine). For example
+			so that it can announce an interrupt at the proper moment, because it is monitoring some aspect of
+			the machine rather than waiting to be called upon, or because there's some other non-obvious relationship
+			at play.
+
+	A clocking hint source can signal changes in preferred clocking to an observer.
+
+	This is intended to allow for performance improvements to machines with components that can be messaged selectively.
+	The observer callout is virtual so the intended use case is that a machine holds a component that might go through
+	periods of different clocking requirements.
+
+	Transitions should be sufficiently infrequent that a virtual call to announce them costs little enough that
+	the saved or deferred ::run_fors add up to a substantial amount.
+
+	The hint provided is just that: a hint. Owners may perform ::run_for at a greater frequency.
+*/
+class Source {
+	public:
+		/// Registers @c observer as the new clocking observer.
+		void set_clocking_hint_observer(Observer *observer) {
+			observer_ = observer;
+			update_clocking_observer();
+		}
+
+		/// @returns the current preferred clocking strategy.
+		virtual Preference preferred_clocking() = 0;
+
+	private:
+		Observer *observer_ = nullptr;
+
+	protected:
+		/*!
+			Provided for subclasses; call this whenever the clocking preference might have changed.
+			This will notify the observer if there is one.
+		*/
+		void update_clocking_observer() {
+			if(!observer_) return;
+			observer_->set_component_prefers_clocking(this, preferred_clocking());
+		}
+};
+
+}
+
+#endif /* ClockingHintSource_h */

ClockReceiver/Sleeper.hpp

@@ -1,60 +0,0 @@
-//
-//  Sleeper.h
-//  Clock Signal
-//
-//  Created by Thomas Harte on 20/08/2017.
-//  Copyright 2017 Thomas Harte. All rights reserved.
-//
-
-#ifndef Sleeper_hpp
-#define Sleeper_hpp
-
-/*!
-	A sleeper is any component that sometimes requires a clock but at other times is 'asleep', i.e. is not doing
-	any clock-derived work, so needn't receive a clock. A disk controller is an archetypal example.
-
-	A sleeper will signal sleeps and wakes to an observer.
-
-	This is intended to allow for performance improvements to machines with components that can sleep. The observer
-	callout is virtual so the intended use case is that a machine holds a component that might sleep. Its transitions
-	into and out of sleep are sufficiently infrequent that a virtual call to announce them costs sufficiently little that
-	the saved ::run_fors add up to a substantial amount.
-
-	By convention, sleeper components must be willing to accept ::run_for even after announcing sleep. It's a hint,
-	not a command.
-*/
-class Sleeper {
-	public:
-		Sleeper() : sleep_observer_(nullptr) {}
-
-		class SleepObserver {
-			public:
-				/// Called to inform an observer that the component @c component has either gone to sleep or become awake.
-				virtual void set_component_is_sleeping(Sleeper *component, bool is_sleeping) = 0;
-		};
-
-		/// Registers @c observer as the new sleep observer;
-		void set_sleep_observer(SleepObserver *observer) {
-			sleep_observer_ = observer;
-		}
-
-		/// @returns @c true if the component is currently sleeping; @c false otherwise.
-		virtual bool is_sleeping() = 0;
-
-	protected:
-		/// Provided for subclasses; send sleep announcements to the sleep_observer_.
-		SleepObserver *sleep_observer_;
-
-		/*!
-			Provided for subclasses; call this whenever is_sleeping might have changed, and the observer will be notified,
-			if one exists.
-
-			@c is_sleeping will be called only if there is an observer.
-		*/
-		void update_sleep_observer() {
-			if(!sleep_observer_) return;
-			sleep_observer_->set_component_is_sleeping(this, is_sleeping());
-		}
-};
-
-#endif /* Sleeper_h */

Components/1770/1770.hpp

@@ -43,7 +43,6 @@ class WD1770: public Storage::Disk::MFMController {
 
 		/// Runs the controller for @c number_of_cycles cycles.
 		void run_for(const Cycles cycles);
-		using Storage::Disk::Controller::run_for;
 
 		enum Flag: uint8_t {
 			NotReady		= 0x80,

Components/8272/i8272.cpp

@@ -83,8 +83,10 @@ i8272::i8272(BusHandler &bus_handler, Cycles clock_rate) :
 	posit_event(static_cast<int>(Event8272::CommandByte));
 }
 
-bool i8272::is_sleeping() {
-	return is_sleeping_ && Storage::Disk::MFMController::is_sleeping();
+ClockingHint::Preference i8272::preferred_clocking() {
+	const auto mfm_controller_preferred_clocking = Storage::Disk::MFMController::preferred_clocking();
+	if(mfm_controller_preferred_clocking != ClockingHint::Preference::None) return mfm_controller_preferred_clocking;
+	return is_sleeping_ ? ClockingHint::Preference::None : ClockingHint::Preference::JustInTime;
 }
 
 void i8272::run_for(Cycles cycles) {
@@ -159,7 +161,7 @@ void i8272::run_for(Cycles cycles) {
 	}
 
 	is_sleeping_ = !delay_time_ && !drives_seeking_ && !head_timers_running_;
-	if(is_sleeping_) update_sleep_observer();
+	if(is_sleeping_) update_clocking_observer();
 }
 
 void i8272::set_register(int address, uint8_t value) {
@@ -198,7 +200,7 @@ uint8_t i8272::get_register(int address) {
 
 #define MS_TO_CYCLES(x)			x * 8000
 #define WAIT_FOR_EVENT(mask)	resume_point_ = __LINE__; interesting_event_mask_ = static_cast<int>(mask); return; case __LINE__:
-#define WAIT_FOR_TIME(ms)		resume_point_ = __LINE__; interesting_event_mask_ = static_cast<int>(Event8272::Timer); delay_time_ = MS_TO_CYCLES(ms); is_sleeping_ = false; update_sleep_observer(); case __LINE__: if(delay_time_) return;
+#define WAIT_FOR_TIME(ms)		resume_point_ = __LINE__; interesting_event_mask_ = static_cast<int>(Event8272::Timer); delay_time_ = MS_TO_CYCLES(ms); is_sleeping_ = false; update_clocking_observer(); case __LINE__: if(delay_time_) return;
 
 #define PASTE(x, y) x##y
 #define CONCAT(x, y) PASTE(x, y)
@@ -257,7 +259,7 @@ uint8_t i8272::get_register(int address) {
 		if(drives_[active_drive_].head_unload_delay[active_head_] == 0) {	\
 			head_timers_running_++;	\
 			is_sleeping_ = false;	\
-			update_sleep_observer();	\
+			update_clocking_observer();	\
 		}	\
 		drives_[active_drive_].head_unload_delay[active_head_] = MS_TO_CYCLES(head_unload_time_);\
 	}
@@ -720,7 +722,7 @@ void i8272::posit_event(int event_type) {
 				if(drives_[drive].phase != Drive::Seeking) {
 					drives_seeking_++;
 					is_sleeping_ = false;
-					update_sleep_observer();
+					update_clocking_observer();
 				}
 
 				// Set currently seeking, with a step to occur right now (yes, it sounds like jamming these

Components/8272/i8272.hpp

@@ -39,7 +39,7 @@ class i8272: public Storage::Disk::MFMController {
 		void set_dma_acknowledge(bool dack);
 		void set_terminal_count(bool tc);
 
-		bool is_sleeping();
+		ClockingHint::Preference preferred_clocking() override;
 
 	protected:
 		virtual void select_drive(int number) = 0;
@@ -67,7 +67,7 @@ class i8272: public Storage::Disk::MFMController {
 			ResultEmpty = (1 << 5),
 			NoLongerReady = (1 << 6)
 		};
-		void posit_event(int type);
+		void posit_event(int type) override;
 		int interesting_event_mask_ = static_cast<int>(Event8272::CommandByte);
 		int resume_point_ = 0;
 		bool is_access_command_ = false;

Components/DiskII/DiskII.cpp

@@ -19,12 +19,13 @@ namespace  {
 	const uint8_t input_flux = 0x1;
 }
 
-DiskII::DiskII() :
+DiskII::DiskII(int clock_rate) :
+	clock_rate_(clock_rate),
 	inputs_(input_command),
-	drives_{{2045454, 300, 1}, {2045454, 300, 1}}
+	drives_{{static_cast<unsigned int>(clock_rate), 300, 1}, {static_cast<unsigned int>(clock_rate), 300, 1}}
 {
-	drives_[0].set_sleep_observer(this);
-	drives_[1].set_sleep_observer(this);
+	drives_[0].set_clocking_hint_observer(this);
+	drives_[1].set_clocking_hint_observer(this);
 	drives_[active_drive_].set_event_delegate(this);
 }
 
@@ -73,9 +74,8 @@ void DiskII::select_drive(int drive) {
 }
 
 void DiskII::run_for(const Cycles cycles) {
-	if(is_sleeping()) return;
+	if(preferred_clocking() == ClockingHint::Preference::None) return;
 
-	if(!controller_can_sleep_) {
 	int integer_cycles = cycles.as_int();
 	while(integer_cycles--) {
 		const int address = (state_ & 0xf0) | inputs_ | ((shift_register_&0x80) >> 6);
@@ -93,10 +93,10 @@ void DiskII::run_for(const Cycles cycles) {
 
 				// If the controller is in the sense write protect loop but the register will never change,
 				// short circuit further work and return now.
-					if(shift_register_ == is_write_protected() ? 0xff : 0x00) {
+				if(shift_register_ == (is_write_protected() ? 0xff : 0x00)) {
 					if(!drive_is_sleeping_[0]) drives_[0].run_for(Cycles(integer_cycles));
 					if(!drive_is_sleeping_[1]) drives_[1].run_for(Cycles(integer_cycles));
-						set_controller_can_sleep();
+					decide_clocking_preference();
 					return;
 				}
 			break;
@@ -110,34 +110,39 @@ void DiskII::run_for(const Cycles cycles) {
 			drives_[active_drive_].write_bit(!!((state_ ^ address) & 0x80));
 		}
 
-			// TODO: surely there's a less heavyweight solution than this?
+		// TODO: surely there's a less heavyweight solution than inline updates?
 		if(!drive_is_sleeping_[0]) drives_[0].run_for(Cycles(1));
 		if(!drive_is_sleeping_[1]) drives_[1].run_for(Cycles(1));
 	}
-	} else {
-		if(!drive_is_sleeping_[0]) drives_[0].run_for(cycles);
-		if(!drive_is_sleeping_[1]) drives_[1].run_for(cycles);
-	}
 
-	set_controller_can_sleep();
+	decide_clocking_preference();
 }
 
-void DiskII::set_controller_can_sleep() {
-	// Permit the controller to sleep if it's in sense write protect mode, and the shift register
-	// has already filled with the result of shifting eight times.
-	bool controller_could_sleep = controller_can_sleep_;
-	controller_can_sleep_ =
-		(
-			(inputs_ == input_flux) &&
-			!motor_is_enabled_ &&
-			!shift_register_
-		) ||
-		(
-			(inputs_ == (input_command | input_flux)) &&
-			(shift_register_ == (is_write_protected() ? 0xff : 0x00))
-		);
-	if(controller_could_sleep != controller_can_sleep_)
-		update_sleep_observer();
+void DiskII::decide_clocking_preference() {
+	ClockingHint::Preference prior_preference = clocking_preference_;
+
+	// If in read mode, clocking is either:
+	//
+	//	just-in-time, if drives are running or the shift register has any 1s in it or a flux event hasn't yet passed; or
+	//	none, given that drives are not running, the shift register has already emptied and there's no flux about to fire.
+	if(!(inputs_ & ~input_flux)) {
+		clocking_preference_ = (!motor_is_enabled_ && !shift_register_ && !(inputs_&input_flux)) ? ClockingHint::Preference::None : ClockingHint::Preference::JustInTime;
+	}
+
+	// If in writing mode, clocking is real time.
+	if(inputs_ & input_mode) {
+		clocking_preference_ = ClockingHint::Preference::RealTime;
+	}
+
+	// If in sense-write-protect mode, clocking is just-in-time if the shift register hasn't yet filled with the value that
+	// corresponds to the current write protect status. Otherwise it is none.
+	if((inputs_ & ~input_flux) == input_command) {
+		clocking_preference_ = (shift_register_ == (is_write_protected() ? 0xff : 0x00)) ? ClockingHint::Preference::None : ClockingHint::Preference::JustInTime;
+	}
+
+	// Announce a change if there was one.
+	if(prior_preference != clocking_preference_)
+		update_clocking_observer();
 }
 
 bool DiskII::is_write_protected() {
@@ -195,18 +200,18 @@ void DiskII::set_disk(const std::shared_ptr<Storage::Disk::Disk> &disk, int driv
 void DiskII::process_event(const Storage::Disk::Track::Event &event) {
 	if(event.type == Storage::Disk::Track::Event::FluxTransition) {
 		inputs_ &= ~input_flux;
-		set_controller_can_sleep();
+		decide_clocking_preference();
 	}
 }
 
-void DiskII::set_component_is_sleeping(Sleeper *component, bool is_sleeping) {
-	drive_is_sleeping_[0] = drives_[0].is_sleeping();
-	drive_is_sleeping_[1] = drives_[1].is_sleeping();
-	update_sleep_observer();
+void DiskII::set_component_prefers_clocking(ClockingHint::Source *component, ClockingHint::Preference preference) {
+	drive_is_sleeping_[0] = drives_[0].preferred_clocking() == ClockingHint::Preference::None;
+	drive_is_sleeping_[1] = drives_[1].preferred_clocking() == ClockingHint::Preference::None;
+	decide_clocking_preference();
 }
 
-bool DiskII::is_sleeping() {
-	return controller_can_sleep_ && drive_is_sleeping_[0] && drive_is_sleeping_[1];
+ClockingHint::Preference DiskII::preferred_clocking() {
+	return clocking_preference_;
 }
 
 void DiskII::set_data_input(uint8_t input) {
@@ -243,11 +248,11 @@ int DiskII::read_address(int address) {
 		break;
 		case 0xf:
 			if(!(inputs_ & input_mode))
-				drives_[active_drive_].begin_writing(Storage::Time(1, 2045454), false);
+				drives_[active_drive_].begin_writing(Storage::Time(1, clock_rate_), false);
 			inputs_ |= input_mode;
 		break;
 	}
-	set_controller_can_sleep();
+	decide_clocking_preference();
 	return (address & 1) ? 0xff : shift_register_;
 }
 

Components/DiskII/DiskII.hpp

@@ -10,7 +10,7 @@
 #define DiskII_hpp
 
 #include "../../ClockReceiver/ClockReceiver.hpp"
-#include "../../ClockReceiver/Sleeper.hpp"
+#include "../../ClockReceiver/ClockingHintSource.hpp"
 
 #include "../../Storage/Disk/Disk.hpp"
 #include "../../Storage/Disk/Drive.hpp"
@@ -28,10 +28,10 @@ namespace Apple {
 */
 class DiskII:
 	public Storage::Disk::Drive::EventDelegate,
-	public Sleeper::SleepObserver,
-	public Sleeper {
+	public ClockingHint::Source,
+	public ClockingHint::Observer {
 	public:
-		DiskII();
+		DiskII(int clock_rate);
 
 		/// Sets the current external value of the data bus.
 		void set_data_input(uint8_t input);
@@ -76,7 +76,7 @@ class DiskII:
 		void set_disk(const std::shared_ptr<Storage::Disk::Disk> &disk, int drive);
 
 		// As per Sleeper.
-		bool is_sleeping() override;
+		ClockingHint::Preference preferred_clocking() override;
 
 		// The Disk II functions as a potential target for @c Activity::Sources.
 		void set_activity_observer(Activity::Observer *observer);
@@ -95,7 +95,9 @@ class DiskII:
 
 		uint8_t trigger_address(int address, uint8_t value);
 		void process_event(const Storage::Disk::Track::Event &event) override;
-		void set_component_is_sleeping(Sleeper *component, bool is_sleeping) override;
+		void set_component_prefers_clocking(ClockingHint::Source *component, ClockingHint::Preference preference) override;
+
+		const int clock_rate_ = 0;
 
 		uint8_t state_ = 0;
 		uint8_t inputs_ = 0;
@@ -108,11 +110,11 @@ class DiskII:
 		std::array<uint8_t, 256> state_machine_;
 		Storage::Disk::Drive drives_[2];
 		bool drive_is_sleeping_[2];
-		bool controller_can_sleep_ = false;
 		int active_drive_ = 0;
 		bool motor_is_enabled_ = false;
 
-		void set_controller_can_sleep();
+		void decide_clocking_preference();
+		ClockingHint::Preference clocking_preference_ = ClockingHint::Preference::RealTime;
 
 		uint8_t data_input_ = 0;
 };

Machines/AmstradCPC/AmstradCPC.cpp

@@ -694,7 +694,7 @@ class ConcreteMachine:
 	public KeyboardMachine::Machine,
 	public Utility::TypeRecipient,
 	public CPU::Z80::BusHandler,
-	public Sleeper::SleepObserver,
+	public ClockingHint::Observer,
 	public Machine,
 	public Activity::Source {
 	public:
@@ -714,11 +714,8 @@ class ConcreteMachine:
 			Memory::Fuzz(ram_, sizeof(ram_));
 
 			// register this class as the sleep observer for the FDC and tape
-			fdc_.set_sleep_observer(this);
-			fdc_is_sleeping_ = fdc_.is_sleeping();
-
-			tape_player_.set_sleep_observer(this);
-			tape_player_is_sleeping_ = tape_player_.is_sleeping();
+			fdc_.set_clocking_hint_observer(this);
+			tape_player_.set_clocking_hint_observer(this);
 
 			ay_.ay().set_port_handler(&key_state_);
 		}
@@ -749,7 +746,7 @@ class ConcreteMachine:
 			ay_.run_for(cycle.length);
 
 			// Clock the FDC, if connected, using a lazy scale by two
-			if(has_fdc_ && !fdc_is_sleeping_) fdc_.run_for(Cycles(cycle.length.as_int()));
+			time_since_fdc_update_ += cycle.length;
 
 			// Update typing activity
 			if(typer_) typer_->run_for(cycle.length);
@@ -796,11 +793,13 @@ class ConcreteMachine:
 
 					// Check for an FDC access
 					if(has_fdc_ && (address & 0x580) == 0x100) {
+						flush_fdc();
 						fdc_.set_register(address & 1, *cycle.value);
 					}
 
 					// Check for a disk motor access
 					if(has_fdc_ && !(address & 0x580)) {
+						flush_fdc();
 						fdc_.set_motor_on(!!(*cycle.value));
 					}
 				break;
@@ -815,6 +814,7 @@ class ConcreteMachine:
 
 					// Check for an FDC access
 					if(has_fdc_ && (address & 0x580) == 0x100) {
+						flush_fdc();
 						*cycle.value &= fdc_.get_register(address & 1);
 					}
 
@@ -858,6 +858,7 @@ class ConcreteMachine:
 			// Just flush the AY.
 			ay_.update();
 			ay_.flush();
+			flush_fdc();
 		}
 
 		/// A CRTMachine function; indicates that outputs should be created now.
@@ -967,9 +968,10 @@ class ConcreteMachine:
 			return true;
 		}
 
-		void set_component_is_sleeping(Sleeper *component, bool is_sleeping) override final {
-			fdc_is_sleeping_ = fdc_.is_sleeping();
-			tape_player_is_sleeping_ = tape_player_.is_sleeping();
+		void set_component_prefers_clocking(ClockingHint::Source *component, ClockingHint::Preference clocking) override final {
+			fdc_is_sleeping_ = fdc_.preferred_clocking() == ClockingHint::Preference::None;
+			tape_player_is_sleeping_ = tape_player_.preferred_clocking() == ClockingHint::Preference::None;
+			printf("FDC: %s, tape %s\n", fdc_is_sleeping_ ? "sleeping" : "regular", tape_player_is_sleeping_ ? "sleeping" : "regular");
 		}
 
 // MARK: - Keyboard
@@ -1063,6 +1065,14 @@ class ConcreteMachine:
 		Intel::i8255::i8255<i8255PortHandler> i8255_;
 
 		FDC fdc_;
+		HalfCycles time_since_fdc_update_;
+		void flush_fdc() {
+			// Clock the FDC, if connected, using a lazy scale by two
+			if(has_fdc_ && !fdc_is_sleeping_) {
+				fdc_.run_for(Cycles(time_since_fdc_update_.as_int()));
+			}
+			time_since_fdc_update_ = HalfCycles(0);
+		}
 
 		InterruptTimer interrupt_timer_;
 		Storage::Tape::BinaryTapePlayer tape_player_;

Machines/AppleII/AppleII.cpp

@@ -24,6 +24,8 @@
 #include "DiskIICard.hpp"
 #include "Video.hpp"
 
+#include "../../ClockReceiver/ForceInline.hpp"
+
 #include "../../Analyser/Static/AppleII/Target.hpp"
 
 #include <algorithm>
@@ -203,7 +205,7 @@ class ConcreteMachine:
 			return &speaker_;
 		}
 
-		Cycles perform_bus_operation(CPU::MOS6502::BusOperation operation, uint16_t address, uint8_t *value) {
+		forceinline Cycles perform_bus_operation(CPU::MOS6502::BusOperation operation, uint16_t address, uint8_t *value) {
 			++ cycles_since_video_update_;
 			++ cycles_since_card_update_;
 			cycles_since_audio_update_ += Cycles(7);

Machines/AppleII/DiskIICard.cpp

@@ -10,7 +10,7 @@
 
 using namespace AppleII;
 
-DiskIICard::DiskIICard(const ROMMachine::ROMFetcher &rom_fetcher, bool is_16_sector) {
+DiskIICard::DiskIICard(const ROMMachine::ROMFetcher &rom_fetcher, bool is_16_sector) : diskii_(2045454) {
 	auto roms = rom_fetcher(
 		"DiskII",
 		{
@@ -20,7 +20,7 @@ DiskIICard::DiskIICard(const ROMMachine::ROMFetcher &rom_fetcher, bool is_16_sec
 	boot_ = std::move(*roms[0]);
 	diskii_.set_state_machine(*roms[1]);
 	set_select_constraints(None);
-	diskii_.set_sleep_observer(this);
+	diskii_.set_clocking_hint_observer(this);
 }
 
 void DiskIICard::perform_bus_operation(Select select, bool is_read, uint16_t address, uint8_t *value) {
@@ -41,7 +41,7 @@ void DiskIICard::perform_bus_operation(Select select, bool is_read, uint16_t add
 }
 
 void DiskIICard::run_for(Cycles cycles, int stretches) {
-	if(diskii_is_sleeping_) return;
+	if(diskii_clocking_preference_ == ClockingHint::Preference::None) return;
 	diskii_.run_for(Cycles(cycles.as_int() * 2));
 }
 
@@ -53,7 +53,7 @@ void DiskIICard::set_activity_observer(Activity::Observer *observer) {
 	diskii_.set_activity_observer(observer);
 }
 
-void DiskIICard::set_component_is_sleeping(Sleeper *component, bool is_sleeping) {
-	diskii_is_sleeping_ = is_sleeping;
-	set_select_constraints(is_sleeping ? (IO | Device) : 0);
+void DiskIICard::set_component_prefers_clocking(ClockingHint::Source *component, ClockingHint::Preference preference) {
+	diskii_clocking_preference_ = preference;
+	set_select_constraints((preference != ClockingHint::Preference::RealTime) ? (IO | Device) : 0);
 }

Machines/AppleII/DiskIICard.hpp

@@ -14,7 +14,7 @@
 
 #include "../../Components/DiskII/DiskII.hpp"
 #include "../../Storage/Disk/Disk.hpp"
-#include "../../ClockReceiver/Sleeper.hpp"
+#include "../../ClockReceiver/ClockingHintSource.hpp"
 
 #include <cstdint>
 #include <memory>
@@ -22,7 +22,7 @@
 
 namespace AppleII {
 
-class DiskIICard: public Card, public Sleeper::SleepObserver {
+class DiskIICard: public Card, public ClockingHint::Observer {
 	public:
 		DiskIICard(const ROMMachine::ROMFetcher &rom_fetcher, bool is_16_sector);
 
@@ -34,10 +34,10 @@ class DiskIICard: public Card, public Sleeper::SleepObserver {
 		void set_disk(const std::shared_ptr<Storage::Disk::Disk> &disk, int drive);
 
 	private:
-		void set_component_is_sleeping(Sleeper *component, bool is_sleeping) override;
+		void set_component_prefers_clocking(ClockingHint::Source *component, ClockingHint::Preference clocking) override;
 		std::vector<uint8_t> boot_;
 		Apple::DiskII diskii_;
-		bool diskii_is_sleeping_ = false;
+		ClockingHint::Preference diskii_clocking_preference_ = ClockingHint::Preference::RealTime;
 };
 
 }

Machines/Commodore/Vic-20/Vic20.cpp

@@ -304,7 +304,7 @@ class ConcreteMachine:
 	public Utility::TypeRecipient,
 	public Storage::Tape::BinaryTapePlayer::Delegate,
 	public Machine,
-	public Sleeper::SleepObserver,
+	public ClockingHint::Observer,
 	public Activity::Source {
 	public:
 		ConcreteMachine() :
@@ -331,7 +331,7 @@ class ConcreteMachine:
 			user_port_via_port_handler_->set_interrupt_delegate(this);
 			keyboard_via_port_handler_->set_interrupt_delegate(this);
 			tape_->set_delegate(this);
-			tape_->set_sleep_observer(this);
+			tape_->set_clocking_hint_observer(this);
 
 			// install a joystick
 			joysticks_.emplace_back(new Joystick(*user_port_via_port_handler_, *keyboard_via_port_handler_));
@@ -749,8 +749,8 @@ class ConcreteMachine:
 			return selection_set;
 		}
 
-		void set_component_is_sleeping(Sleeper *component, bool is_sleeping) override {
-			tape_is_sleeping_ = is_sleeping;
+		void set_component_prefers_clocking(ClockingHint::Source *component, ClockingHint::Preference clocking) override {
+			tape_is_sleeping_ = clocking == ClockingHint::Preference::None;
 			set_use_fast_tape();
 		}
 

Machines/MSX/MSX.cpp

@@ -88,7 +88,7 @@ class ConcreteMachine:
 	public KeyboardMachine::Machine,
 	public Configurable::Device,
 	public MemoryMap,
-	public Sleeper::SleepObserver,
+	public ClockingHint::Observer,
 	public Activity::Source {
 	public:
 		ConcreteMachine():
@@ -108,7 +108,7 @@ class ConcreteMachine:
 
 			ay_.set_port_handler(&ay_port_handler_);
 			speaker_.set_input_rate(3579545.0f / 2.0f);
-			tape_player_.set_sleep_observer(this);
+			tape_player_.set_clocking_hint_observer(this);
 
 			// Set the AY to 50% of available volume, the toggle to 10% and leave 40% for an SCC.
 			mixer_.set_relative_volumes({0.5f, 0.1f, 0.4f});
@@ -555,8 +555,8 @@ class ConcreteMachine:
 		}
 
 		// MARK: - Sleeper
-		void set_component_is_sleeping(Sleeper *component, bool is_sleeping) override {
-			tape_player_is_sleeping_ = tape_player_.is_sleeping();
+		void set_component_prefers_clocking(ClockingHint::Source *component, ClockingHint::Preference clocking) override {
+			tape_player_is_sleeping_ = tape_player_.preferred_clocking() == ClockingHint::Preference::None;
 			set_use_fast_tape();
 		}
 

Machines/Oric/Microdisc.hpp

@@ -28,7 +28,6 @@ class Microdisc: public WD::WD1770 {
 		bool get_interrupt_request_line();
 
 		void run_for(const Cycles cycles);
-		using WD::WD1770::run_for;
 
 		enum PagingFlags {
 			/// Indicates that the BASIC ROM should be disabled; if this is set then either
@@ -52,8 +51,9 @@ class Microdisc: public WD::WD1770 {
 
 	private:
 		void set_control_register(uint8_t control, uint8_t changes);
-		void set_head_load_request(bool head_load);
+		void set_head_load_request(bool head_load) override;
 		bool get_drive_is_ready();
+
 		std::array<std::shared_ptr<Storage::Disk::Drive>, 4> drives_;
 		size_t selected_drive_;
 		bool irq_enable_ = false;

Machines/Oric/Oric.cpp

@@ -201,7 +201,7 @@ template <Analyser::Static::Oric::Target::DiskInterface disk_interface> class Co
 	public Utility::TypeRecipient,
 	public Storage::Tape::BinaryTapePlayer::Delegate,
 	public Microdisc::Delegate,
-	public Sleeper::SleepObserver,
+	public ClockingHint::Observer,
 	public Activity::Source,
 	public Machine {
 
@@ -212,14 +212,15 @@ template <Analyser::Static::Oric::Target::DiskInterface disk_interface> class Co
 				ay8910_(audio_queue_),
 				speaker_(ay8910_),
 				via_port_handler_(audio_queue_, ay8910_, speaker_, tape_player_, keyboard_),
-				via_(via_port_handler_) {
+				via_(via_port_handler_),
+				diskii_(2000000) {
 			set_clock_rate(1000000);
 			via_port_handler_.set_interrupt_delegate(this);
 			tape_player_.set_delegate(this);
 			Memory::Fuzz(ram_, sizeof(ram_));
 
 			if(disk_interface == Analyser::Static::Oric::Target::DiskInterface::Pravetz) {
-				diskii_.set_sleep_observer(this);
+				diskii_.set_clocking_hint_observer(this);
 			}
 		}
 
@@ -410,6 +411,7 @@ template <Analyser::Static::Oric::Target::DiskInterface disk_interface> class Co
 										}
 									}
 								} else {
+									flush_diskii();
 									const int disk_value = diskii_.read_address(address);
 									if(isReadOperation(operation) && disk_value != diskii_.DidNotLoad) *value = static_cast<uint8_t>(disk_value);
 								}
@@ -444,9 +446,11 @@ template <Analyser::Static::Oric::Target::DiskInterface disk_interface> class Co
 					microdisc_.run_for(Cycles(8));
 				break;
 				case Analyser::Static::Oric::Target::DiskInterface::Pravetz:
-					if(!diskii_is_sleeping_) {
+					if(diskii_clocking_preference_ == ClockingHint::Preference::RealTime) {
 						diskii_.set_data_input(*value);
 						diskii_.run_for(Cycles(2));
+					} else {
+						cycles_since_diskii_update_ += Cycles(2);
 					}
 				break;
 			}
@@ -457,6 +461,7 @@ template <Analyser::Static::Oric::Target::DiskInterface disk_interface> class Co
 		forceinline void flush() {
 			update_video();
 			via_port_handler_.flush();
+			flush_diskii();
 		}
 
 		// to satisfy CRTMachine::Machine
@@ -571,8 +576,8 @@ template <Analyser::Static::Oric::Target::DiskInterface disk_interface> class Co
 			}
 		}
 
-		void set_component_is_sleeping(Sleeper *component, bool is_sleeping) override final {
-			diskii_is_sleeping_ = diskii_.is_sleeping();
+		void set_component_prefers_clocking(ClockingHint::Source *component, ClockingHint::Preference preference) override final {
+			diskii_clocking_preference_ = diskii_.preferred_clocking();
 		}
 
 	private:
@@ -617,9 +622,13 @@ template <Analyser::Static::Oric::Target::DiskInterface disk_interface> class Co
 
 		// the Pravetz/Disk II, if in use
 		Apple::DiskII diskii_;
+		Cycles cycles_since_diskii_update_;
+		void flush_diskii() {
+			diskii_.run_for(cycles_since_diskii_update_.flush());
+		}
 		std::vector<uint8_t> pravetz_rom_;
 		std::size_t pravetz_rom_base_pointer_ = 0;
-		bool diskii_is_sleeping_ = false;
+		ClockingHint::Preference diskii_clocking_preference_ = ClockingHint::Preference::RealTime;
 
 		// Overlay RAM
 		uint16_t ram_top_ = basic_visible_ram_top_;

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

@@ -1037,7 +1037,7 @@
 		4BB06B211F316A3F00600C7A /* ForceInline.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = ForceInline.hpp; sourceTree = "<group>"; };
 		4BB0A6592044FD3000FB3688 /* SN76489.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = SN76489.cpp; sourceTree = "<group>"; };
 		4BB0A65A2044FD3000FB3688 /* SN76489.hpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.h; path = SN76489.hpp; sourceTree = "<group>"; };
-		4BB146C61F49D7D700253439 /* Sleeper.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = Sleeper.hpp; sourceTree = "<group>"; };
+		4BB146C61F49D7D700253439 /* ClockingHintSource.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = ClockingHintSource.hpp; sourceTree = "<group>"; };
 		4BB17D4C1ED7909F00ABD1E1 /* tests.expected.json */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = text.json; name = tests.expected.json; path = FUSE/tests.expected.json; sourceTree = "<group>"; };
 		4BB17D4D1ED7909F00ABD1E1 /* tests.in.json */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = text.json; name = tests.in.json; path = FUSE/tests.in.json; sourceTree = "<group>"; };
 		4BB297E51B587D8300A49093 /*  start */ = {isa = PBXFileReference; lastKnownFileType = file; path = " start"; sourceTree = "<group>"; };
@@ -3124,7 +3124,7 @@
 			children = (
 				4BF6606A1F281573002CB053 /* ClockReceiver.hpp */,
 				4BB06B211F316A3F00600C7A /* ForceInline.hpp */,
-				4BB146C61F49D7D700253439 /* Sleeper.hpp */,
+				4BB146C61F49D7D700253439 /* ClockingHintSource.hpp */,
 				4B449C942063389900A095C8 /* TimeTypes.hpp */,
 			);
 			name = ClockReceiver;

Storage/Disk/Controller/DiskController.cpp

@@ -22,12 +22,12 @@ Controller::Controller(Cycles clock_rate) :
 	set_drive(empty_drive_);
 }
 
-void Controller::set_component_is_sleeping(Sleeper *component, bool is_sleeping) {
-	update_sleep_observer();
+void Controller::set_component_prefers_clocking(ClockingHint::Source *component, ClockingHint::Preference clocking) {
+	update_clocking_observer();
 }
 
-bool Controller::is_sleeping() {
-	return !drive_ || drive_->is_sleeping();
+ClockingHint::Preference Controller::preferred_clocking() {
+	return (!drive_ || (drive_->preferred_clocking() == ClockingHint::Preference::None)) ? ClockingHint::Preference::None : ClockingHint::Preference::RealTime;
 }
 
 void Controller::run_for(const Cycles cycles) {
@@ -77,23 +77,23 @@ void Controller::digital_phase_locked_loop_output_bit(int value) {
 
 void Controller::set_drive(std::shared_ptr<Drive> drive) {
 	if(drive_ != drive) {
-		bool was_sleeping = is_sleeping();
+		ClockingHint::Preference former_prefernece = preferred_clocking();
 //		invalidate_track();
 
 		if(drive_) {
 			drive_->set_event_delegate(nullptr);
-			drive_->set_sleep_observer(nullptr);
+			drive_->set_clocking_hint_observer(nullptr);
 		}
 		drive_ = drive;
 		if(drive_) {
 			drive_->set_event_delegate(this);
-			drive_->set_sleep_observer(this);
+			drive_->set_clocking_hint_observer(this);
 		} else {
 			drive_ = empty_drive_;
 		}
 
-		if(is_sleeping() != was_sleeping) {
-			update_sleep_observer();
+		if(preferred_clocking() != former_prefernece) {
+			update_clocking_observer();
 		}
 	}
 }

Storage/Disk/Controller/DiskController.hpp

@@ -15,7 +15,7 @@
 #include "../Track/PCMPatchedTrack.hpp"
 
 #include "../../../ClockReceiver/ClockReceiver.hpp"
-#include "../../../ClockReceiver/Sleeper.hpp"
+#include "../../../ClockReceiver/ClockingHintSource.hpp"
 
 namespace Storage {
 namespace Disk {
@@ -29,7 +29,11 @@ namespace Disk {
 
 	TODO: communication of head size and permissible stepping extents, appropriate simulation of gain.
 */
-class Controller: public DigitalPhaseLockedLoop::Delegate, public Drive::EventDelegate, public Sleeper, public Sleeper::SleepObserver {
+class Controller:
+	public DigitalPhaseLockedLoop::Delegate,
+	public Drive::EventDelegate,
+	public ClockingHint::Source,
+	public ClockingHint::Observer {
 	protected:
 		/*!
 			Constructs a @c Controller that will be run at @c clock_rate.
@@ -65,7 +69,7 @@ class Controller: public DigitalPhaseLockedLoop::Delegate, public Drive::EventDe
 			Should be implemented by subclasses if they implement writing; communicates that
 			all bits supplied to write_bit have now been written.
 		*/
-		virtual void process_write_completed();
+		virtual void process_write_completed() override;
 
 		/*!
 			Puts the controller and the drive returned by get_drive() into write mode, supplying to
@@ -97,9 +101,9 @@ class Controller: public DigitalPhaseLockedLoop::Delegate, public Drive::EventDe
 		Drive &get_drive();
 
 		/*!
-			As per Sleeper.
+			As per ClockingHint::Source.
 		*/
-		bool is_sleeping();
+		ClockingHint::Preference preferred_clocking() override;
 
 	private:
 		Time bit_length_;
@@ -113,14 +117,15 @@ class Controller: public DigitalPhaseLockedLoop::Delegate, public Drive::EventDe
 
 		std::shared_ptr<Drive> empty_drive_;
 
-		void set_component_is_sleeping(Sleeper *component, bool is_sleeping);
+		// ClockingHint::Observer.
+		void set_component_prefers_clocking(ClockingHint::Source *component, ClockingHint::Preference clocking) override;
 
 		// for Drive::EventDelegate
-		void process_event(const Track::Event &event);
-		void advance(const Cycles cycles);
+		void process_event(const Track::Event &event) override;
+		void advance(const Cycles cycles) override ;
 
 		// to satisfy DigitalPhaseLockedLoop::Delegate
-		void digital_phase_locked_loop_output_bit(int value);
+		void digital_phase_locked_loop_output_bit(int value) override;
 };
 
 }

Storage/Disk/Drive.cpp

@@ -46,15 +46,15 @@ void Drive::set_disk(const std::shared_ptr<Disk> &disk) {
 	has_disk_ = !!disk_;
 
 	invalidate_track();
-	update_sleep_observer();
+	update_clocking_observer();
 }
 
 bool Drive::has_disk() {
 	return has_disk_;
 }
 
-bool Drive::is_sleeping() {
-	return !motor_is_on_ || !has_disk_;
+ClockingHint::Preference Drive::preferred_clocking() {
+	return (!motor_is_on_ || !has_disk_) ? ClockingHint::Preference::None : ClockingHint::Preference::JustInTime;
 }
 
 bool Drive::get_is_track_zero() {
@@ -119,7 +119,7 @@ void Drive::set_motor_on(bool motor_is_on) {
 		ready_index_count_ = 0;
 		if(disk_) disk_->flush_tracks();
 	}
-	update_sleep_observer();
+	update_clocking_observer();
 }
 
 bool Drive::get_motor_on() {

Storage/Disk/Drive.hpp

@@ -15,14 +15,14 @@
 
 #include "../TimedEventLoop.hpp"
 #include "../../Activity/Observer.hpp"
-#include "../../ClockReceiver/Sleeper.hpp"
+#include "../../ClockReceiver/ClockingHintSource.hpp"
 
 #include <memory>
 
 namespace Storage {
 namespace Disk {
 
-class Drive: public Sleeper, public TimedEventLoop {
+class Drive: public ClockingHint::Source, public TimedEventLoop {
 	public:
 		Drive(unsigned int input_clock_rate, int revolutions_per_minute, int number_of_heads);
 		~Drive();
@@ -121,7 +121,7 @@ class Drive: public Sleeper, public TimedEventLoop {
 		void set_event_delegate(EventDelegate *);
 
 		// As per Sleeper.
-		bool is_sleeping();
+		ClockingHint::Preference preferred_clocking() override;
 
 		/// Adds an activity observer; it'll be notified of disk activity.
 		/// The caller can specify whether to add an LED based on disk motor.
@@ -171,9 +171,9 @@ class Drive: public Sleeper, public TimedEventLoop {
 		Time cycles_per_bit_;
 
 		// TimedEventLoop call-ins and state.
-		void process_next_event();
+		void process_next_event() override;
 		void get_next_event(const Time &duration_already_passed);
-		void advance(const Cycles cycles);
+		void advance(const Cycles cycles) override;
 		Track::Event current_event_;
 
 		// Helper for track changes.

Storage/Tape/Tape.cpp

@@ -65,15 +65,15 @@ void Tape::set_offset(uint64_t offset) {
 
 // MARK: - Player
 
-bool TapePlayer::is_sleeping() {
-	return !tape_ || tape_->is_at_end();
+ClockingHint::Preference TapePlayer::preferred_clocking() {
+	return (!tape_ || tape_->is_at_end()) ? ClockingHint::Preference::None : ClockingHint::Preference::JustInTime;
 }
 
 void TapePlayer::set_tape(std::shared_ptr<Storage::Tape::Tape> tape) {
 	tape_ = tape;
 	reset_timer();
 	get_next_pulse();
-	update_sleep_observer();
+	update_clocking_observer();
 }
 
 std::shared_ptr<Storage::Tape::Tape> TapePlayer::get_tape() {
@@ -88,7 +88,7 @@ void TapePlayer::get_next_pulse() {
 	// get the new pulse
 	if(tape_) {
 		current_pulse_ = tape_->get_next_pulse();
-		if(tape_->is_at_end()) update_sleep_observer();
+		if(tape_->is_at_end()) update_clocking_observer();
 	} else {
 		current_pulse_.length.length = 1;
 		current_pulse_.length.clock_rate = 1;
@@ -119,14 +119,15 @@ BinaryTapePlayer::BinaryTapePlayer(unsigned int input_clock_rate) :
 	TapePlayer(input_clock_rate)
 {}
 
-bool BinaryTapePlayer::is_sleeping() {
-	return !motor_is_running_ || TapePlayer::is_sleeping();
+ClockingHint::Preference BinaryTapePlayer::preferred_clocking() {
+	if(!motor_is_running_) return ClockingHint::Preference::None;
+	return TapePlayer::preferred_clocking();
 }
 
 void BinaryTapePlayer::set_motor_control(bool enabled) {
 	if(motor_is_running_ != enabled) {
 		motor_is_running_ = enabled;
-		update_sleep_observer();
+		update_clocking_observer();
 	}
 }
 

Storage/Tape/Tape.hpp

@@ -12,7 +12,7 @@
 #include <memory>
 
 #include "../../ClockReceiver/ClockReceiver.hpp"
-#include "../../ClockReceiver/Sleeper.hpp"
+#include "../../ClockReceiver/ClockingHintSource.hpp"
 
 #include "../TimedEventLoop.hpp"
 
@@ -95,7 +95,7 @@ class Tape {
 	Will call @c process_input_pulse instantaneously upon reaching *the end* of a pulse. Therefore a subclass
 	can decode pulses into data within process_input_pulse, using the supplied pulse's @c length and @c type.
 */
-class TapePlayer: public TimedEventLoop, public Sleeper {
+class TapePlayer: public TimedEventLoop, public ClockingHint::Source {
 	public:
 		TapePlayer(unsigned int input_clock_rate);
 
@@ -107,10 +107,10 @@ class TapePlayer: public TimedEventLoop, public Sleeper {
 
 		void run_for_input_pulse();
 
-		bool is_sleeping();
+		ClockingHint::Preference preferred_clocking() override;
 
 	protected:
-		virtual void process_next_event();
+		virtual void process_next_event() override;
 		virtual void process_input_pulse(const Tape::Pulse &pulse) = 0;
 
 	private:
@@ -145,11 +145,11 @@ class BinaryTapePlayer: public TapePlayer {
 		};
 		void set_delegate(Delegate *delegate);
 
-		bool is_sleeping();
+		ClockingHint::Preference preferred_clocking() override;
 
 	protected:
 		Delegate *delegate_ = nullptr;
-		virtual void process_input_pulse(const Storage::Tape::Tape::Pulse &pulse);
+		void process_input_pulse(const Storage::Tape::Tape::Pulse &pulse) override;
 		bool input_level_ = false;
 		bool motor_is_running_ = false;
 };