Merge pull request #43 from TomHarte/NonSkippingTracks

Sought to prevent a reset of angular position when changing tracks

NumberTheory/Factors.cpp

@@ -29,6 +29,8 @@ unsigned int NumberTheory::greatest_common_divisor(unsigned int a, unsigned int
 
 unsigned int NumberTheory::least_common_multiple(unsigned int a, unsigned int b)
 {
+	if(a == b) return a;
+
 	unsigned int gcd = greatest_common_divisor(a, b);
-	return (a / gcd) * (b / gcd);
+	return (a / gcd) * (b / gcd) * gcd;
 }

Storage/Disk/Disk.hpp

@@ -37,9 +37,16 @@ class Track {
 		};
 
 		/*!
-			Returns the next event that will be detected during rotation of this disk.
+			@returns the next event that will be detected during rotation of this disk.
 		*/
 		virtual Event get_next_event() = 0;
+
+		/*!
+			Jumps to the event latest offset that is less than or equal to the input time.
+
+			@returns the time jumped to.
+		*/
+		virtual Time seek_to(Time time_since_index_hole) = 0;
 };
 
 /*!

Storage/Disk/DiskDrive.cpp

@@ -17,7 +17,11 @@ DiskDrive::DiskDrive(unsigned int clock_rate, unsigned int clock_rate_multiplier
 	_head_position(0),
 
 	TimedEventLoop(clock_rate * clock_rate_multiplier)
-{}
+{
+	_rotational_multiplier.length = 60;
+	_rotational_multiplier.clock_rate = revolutions_per_minute;
+	_rotational_multiplier.simplify();
+}
 
 void DiskDrive::set_expected_bit_length(Time bit_length)
 {
@@ -33,7 +37,7 @@ void DiskDrive::set_expected_bit_length(Time bit_length)
 void DiskDrive::set_disk(std::shared_ptr<Disk> disk)
 {
 	_disk = disk;
-	set_track();
+	set_track(Time());
 }
 
 bool DiskDrive::has_disk()
@@ -49,14 +53,32 @@ bool DiskDrive::get_is_track_zero()
 void DiskDrive::step(int direction)
 {
 	_head_position = std::max(_head_position + direction, 0);
-	set_track();
+	Time extra_time = get_time_into_next_event() / _rotational_multiplier;
+	extra_time.simplify();
+	_time_into_track += extra_time;
+	set_track(_time_into_track);
 }
 
-void DiskDrive::set_track()
+void DiskDrive::set_track(Time initial_offset)
 {
 	_track = _disk->get_track_at_position((unsigned int)_head_position);
+	// TODO: probably a better implementation of the empty track?
+	Time offset;
+	if(_track && _time_into_track.length > 0)
+	{
+		Time time_found = _track->seek_to(_time_into_track).simplify();
+		offset = (_time_into_track - time_found).simplify();
+		_time_into_track = time_found;
+	}
+	else
+	{
+		offset = _time_into_track;
+		_time_into_track.set_zero();
+	}
+
 	reset_timer();
 	get_next_event();
+	reset_timer_to_offset(offset * _rotational_multiplier);
 }
 
 void DiskDrive::run_for_cycles(int number_of_cycles)
@@ -88,11 +110,7 @@ void DiskDrive::get_next_event()
 
 	// divide interval, which is in terms of a rotation of the disk, by rotation speed, and
 	// convert it into revolutions per second
-	Time event_interval = _current_event.length;
-	event_interval.length *= 60;
-	event_interval.clock_rate *= _revolutions_per_minute;
-	event_interval.simplify();
-	set_next_event_time_interval(event_interval);
+	set_next_event_time_interval(_current_event.length * _rotational_multiplier);
 }
 
 void DiskDrive::process_next_event()
@@ -101,9 +119,11 @@ void DiskDrive::process_next_event()
 	{
 		case Track::Event::FluxTransition:
 			_pll->add_pulse();
+			_time_into_track += _current_event.length;
 		break;
 		case Track::Event::IndexHole:
 			_cycles_since_index_hole = 0;
+			_time_into_track.set_zero();
 			process_index_hole();
 		break;
 	}

Storage/Disk/DiskDrive.hpp

@@ -93,16 +93,18 @@ class DiskDrive: public DigitalPhaseLockedLoop::Delegate, public TimedEventLoop
 		unsigned int _clock_rate;
 		unsigned int _clock_rate_multiplier;
 		unsigned int _revolutions_per_minute;
+		Time _rotational_multiplier;
 
 		std::shared_ptr<DigitalPhaseLockedLoop> _pll;
 		std::shared_ptr<Disk> _disk;
 		std::shared_ptr<Track> _track;
 		int _head_position;
 		unsigned int _cycles_since_index_hole;
-		void set_track();
+		void set_track(Time initial_offset);
 
 		inline void get_next_event();
 		Track::Event _current_event;
+		Time _time_into_track;
 };
 
 }

Storage/Disk/PCMTrack.cpp

@@ -61,6 +61,45 @@ PCMTrack::Event PCMTrack::get_next_event()
 	return _next_event;
 }
 
+Time PCMTrack::seek_to(Time time_since_index_hole)
+{
+	_segment_pointer = 0;
+
+	// pick a common clock rate for counting time on this track and multiply up the time being sought appropriately
+	Time time_so_far;
+	time_so_far.clock_rate = NumberTheory::least_common_multiple(_next_event.length.clock_rate, time_since_index_hole.clock_rate);
+	time_since_index_hole.length *= time_so_far.clock_rate / time_since_index_hole.clock_rate;
+	time_since_index_hole.clock_rate = time_so_far.clock_rate;
+
+	while(_segment_pointer < _segments.size())
+	{
+		// determine how long this segment is in terms of the master clock
+		unsigned int clock_multiplier = time_so_far.clock_rate / _next_event.length.clock_rate;
+		unsigned int bit_length = ((clock_multiplier / _track_clock_rate) / _segments[_segment_pointer].length_of_a_bit.clock_rate) * _segments[_segment_pointer].length_of_a_bit.length;
+		unsigned int time_in_this_segment = bit_length * _segments[_segment_pointer].number_of_bits;
+
+		// if this segment goes on longer than the time being sought, end here
+		unsigned int time_remaining = time_since_index_hole.length - time_so_far.length;
+		if(time_in_this_segment >= time_remaining)
+		{
+			// get the amount of time actually to move into this segment
+			unsigned int time_found = time_remaining - (time_remaining % bit_length);
+
+			// resolve that into the stateful bit count
+			_bit_pointer = 1 + (time_remaining / bit_length);
+
+			// update and return the time sought to
+			time_so_far.length += time_found;
+			return time_so_far;
+		}
+
+		// otherwise, accumulate time and keep moving
+		time_so_far.length += time_in_this_segment;
+		_segment_pointer++;
+	}
+	return time_since_index_hole;
+}
+
 void PCMTrack::fix_length()
 {
 	// find the least common multiple of all segment clock rates

Storage/Disk/PCMTrack.hpp

@@ -47,6 +47,7 @@ class PCMTrack: public Track {
 
 		// as per @c Track
 		Event get_next_event();
+		Time seek_to(Time time_since_index_hole);
 
 	private:
 		// storage for the segments that describe this track

Storage/Storage.hpp

@@ -19,27 +19,109 @@ namespace Storage {
 */
 struct Time {
 	unsigned int length, clock_rate;
+	Time() : length(0), clock_rate(1) {}
 
 	/*!
 		Reduces this @c Time to its simplest form — eliminates all common factors from @c length
 		and @c clock_rate.
 	*/
-	inline void simplify()
+	inline Time &simplify()
 	{
 		unsigned int common_divisor = NumberTheory::greatest_common_divisor(length, clock_rate);
 		length /= common_divisor;
 		clock_rate /= common_divisor;
+		return *this;
 	}
 
 	/*!
-		Returns the floating point conversion of this @c Time. This will often be less precise.
+		@returns the floating point conversion of this @c Time. This will often be less precise.
 	*/
 	inline float get_float()
 	{
 		return (float)length / (float)clock_rate;
 	}
+
+	inline bool operator < (Time other)
+	{
+		return other.clock_rate * length < clock_rate * other.length;
+	}
+
+	inline Time operator + (Time other)
+	{
+		Time result;
+		result.clock_rate = NumberTheory::least_common_multiple(clock_rate, other.clock_rate);
+		result.length = length * (result.clock_rate / clock_rate) + other.length * (result.clock_rate / other.clock_rate);
+		return result;
+	}
+
+	inline Time &operator += (Time other)
+	{
+		unsigned int combined_clock_rate = NumberTheory::least_common_multiple(clock_rate, other.clock_rate);
+		length = length * (combined_clock_rate / clock_rate) + other.length * (combined_clock_rate / other.clock_rate);
+		clock_rate = combined_clock_rate;
+		return *this;
+	}
+
+	inline Time operator - (Time other)
+	{
+		Time result;
+		result.clock_rate = NumberTheory::least_common_multiple(clock_rate, other.clock_rate);
+		result.length = length * (result.clock_rate / clock_rate) - other.length * (result.clock_rate / other.clock_rate);
+		return result;
+	}
+
+	inline Time operator -= (Time other)
+	{
+		unsigned int combined_clock_rate = NumberTheory::least_common_multiple(clock_rate, other.clock_rate);
+		length = length * (combined_clock_rate / clock_rate) - other.length * (combined_clock_rate / other.clock_rate);
+		clock_rate = combined_clock_rate;
+		return *this;
+	}
+
+	inline Time operator * (Time other)
+	{
+		Time result;
+		result.clock_rate = clock_rate * other.clock_rate;
+		result.length = length * other.length;
+		return result;
+	}
+
+	inline Time &operator *= (Time other)
+	{
+		length *= other.length;
+		clock_rate *= other.clock_rate;
+		return *this;
+	}
+
+	inline Time operator / (Time other)
+	{
+		Time result;
+		result.clock_rate = clock_rate * other.length;
+		result.length = length * other.clock_rate;
+		return result;
+	}
+
+	inline Time &operator /= (Time other)
+	{
+		length *= other.clock_rate;
+		clock_rate *= other.length;
+		return *this;
+	}
+
+	inline void set_zero()
+	{
+		length = 0;
+		clock_rate = 1;
+	}
+
+	inline void set_one()
+	{
+		length = 1;
+		clock_rate = 1;
+	}
 };
 
+
 }
 
 #endif /* Storage_h */

Storage/TimedEventLoop.cpp

@@ -29,6 +29,18 @@ void TimedEventLoop::reset_timer()
 	_stepper.reset();
 }
 
+void TimedEventLoop::reset_timer_to_offset(Time offset)
+{
+	unsigned int common_clock_rate = NumberTheory::least_common_multiple(offset.clock_rate, _event_interval.clock_rate);
+	_time_into_interval = offset.length * (common_clock_rate / offset.clock_rate);
+	_event_interval.length *= common_clock_rate / _event_interval.clock_rate;
+	_event_interval.clock_rate = common_clock_rate;
+	if(common_clock_rate != _stepper->get_output_rate())
+	{
+		_stepper.reset(new SignalProcessing::Stepper(_event_interval.clock_rate, _input_clock_rate));
+	}
+}
+
 void TimedEventLoop::jump_to_next_event()
 {
 	reset_timer();
@@ -70,3 +82,10 @@ void TimedEventLoop::set_next_event_time_interval(Time interval)
 		_stepper.reset(new SignalProcessing::Stepper(_event_interval.clock_rate, _input_clock_rate));
 	}
 }
+
+Time TimedEventLoop::get_time_into_next_event()
+{
+	Time result = _event_interval;
+	result.length = _time_into_interval;
+	return result;
+}

Storage/TimedEventLoop.hpp

@@ -66,6 +66,11 @@ namespace Storage {
 			*/
 			void reset_timer();
 
+			/*!
+				Sets the amount of time into the current event to @c offset.
+			*/
+			void reset_timer_to_offset(Time offset);
+
 			/*!
 				Causes an immediate call to @c process_next_event and a call to @c reset_timer with the
 				net effect of processing the current event immediately and fast forwarding exactly to the
@@ -73,6 +78,12 @@ namespace Storage {
 			*/
 			void jump_to_next_event();
 
+			/*!
+				@returns the amount of time that has passed since the last call to @c set_next_time_interval,
+				which will always be less than or equal to the time that was supplied to @c set_next_time_interval.
+			*/
+			Time get_time_into_next_event();
+
 		private:
 			unsigned int _input_clock_rate;
 			Time _event_interval;