Abstracted the concept of an Acorn shifter away from being a PLLParser. The Acorn tape parser now skips using that class and uses the shifter. The actual Electron also uses the shifter. So the two are completely aligned. Net result: the Electron should successfully load exactly when static analysis was successful.

Machines/Electron/Tape.cpp

@@ -17,7 +17,9 @@ Tape::Tape() :
 		delegate_(nullptr),
 		output_({.bits_remaining_until_empty = 0, .cycles_into_pulse = 0}),
 		last_posted_interrupt_status_(0),
-		interrupt_status_(0) {}
+		interrupt_status_(0) {
+	shifter_.set_delegate(this);
+}
 
 void Tape::push_tape_bit(uint16_t bit) {
 	data_register_ = (uint16_t)((data_register_ >> 1) | (bit << 10));
@@ -71,30 +73,11 @@ uint8_t Tape::get_data_register() {
 }
 
 void Tape::process_input_pulse(Storage::Tape::Tape::Pulse pulse) {
-	crossings_[0] = crossings_[1];
-	crossings_[1] = crossings_[2];
-	crossings_[2] = crossings_[3];
+	shifter_.process_pulse(pulse);
+}
 
-	crossings_[3] = Tape::Unrecognised;
-	if(pulse.type != Storage::Tape::Tape::Pulse::Zero) {
-		float pulse_length = (float)pulse.length.length / (float)pulse.length.clock_rate;
-		if(pulse_length >= 0.35 / 2400.0 && pulse_length < 0.7 / 1200.0) {
-			crossings_[3] = pulse_length > 1.0 / 3000.0 ? Tape::Long : Tape::Short;
-		}
-//		if(pulse_length >= 0.35 / 2400.0 && pulse_length < 0.7 / 2400.0) crossings_[3] = Tape::Short;
-//		if(pulse_length >= 0.35 / 1200.0 && pulse_length < 0.7 / 1200.0) crossings_[3] = Tape::Long;
-	}
-
-	if(crossings_[0] == Tape::Long && crossings_[1] == Tape::Long) {
-		push_tape_bit(0);
-		crossings_[0] = crossings_[1] = Tape::Recognised;
-	} else {
-		if(crossings_[0] == Tape::Short && crossings_[1] == Tape::Short && crossings_[2] == Tape::Short && crossings_[3] == Tape::Short) {
-			push_tape_bit(1);
-			crossings_[0] = crossings_[1] =
-			crossings_[2] = crossings_[3] = Tape::Recognised;
-		}
-	}
+void Tape::acorn_shifter_output_bit(int value) {
+	push_tape_bit((uint16_t)value);
 }
 
 void Tape::run_for_cycles(unsigned int number_of_cycles) {

Machines/Electron/Tape.hpp

@@ -10,13 +10,16 @@
 #define Electron_Tape_h
 
 #include "../../Storage/Tape/Tape.hpp"
+#include "../../Storage/Tape/Parsers/Acorn.hpp"
 #include "Interrupts.hpp"
 
 #include <cstdint>
 
 namespace Electron {
 
-class Tape: public Storage::Tape::TapePlayer {
+class Tape:
+	public Storage::Tape::TapePlayer,
+	public Storage::Tape::Acorn::Shifter::Delegate {
 	public:
 		Tape();
 
@@ -39,6 +42,8 @@ class Tape: public Storage::Tape::TapePlayer {
 		inline void set_is_enabled(bool is_enabled) { is_enabled_ = is_enabled; }
 		void set_is_in_input_mode(bool is_in_input_mode);
 
+		void acorn_shifter_output_bit(int value);
+
 	private:
 		void process_input_pulse(Storage::Tape::Tape::Pulse pulse);
 		inline void push_tape_bit(uint16_t bit);
@@ -62,9 +67,7 @@ class Tape: public Storage::Tape::TapePlayer {
 		uint8_t interrupt_status_, last_posted_interrupt_status_;
 		Delegate *delegate_;
 
-		enum {
-			Long, Short, Unrecognised, Recognised
-		} crossings_[4];
+		::Storage::Tape::Acorn::Shifter shifter_;
 };
 
 }

Storage/Tape/Parsers/Acorn.cpp

@@ -14,9 +14,9 @@ namespace {
 const int PLLClockRate = 1920000;
 }
 
-Parser::Parser() :
-	::Storage::Tape::PLLParser<SymbolType>(PLLClockRate, PLLClockRate / 4800),
-	crc_(0x1021, 0x0000) {}
+Parser::Parser() : crc_(0x1021, 0x0000) {
+	shifter_.set_delegate(this);
+}
 
 int Parser::get_next_bit(const std::shared_ptr<Storage::Tape::Tape> &tape) {
 	SymbolType symbol = get_next_symbol(tape);
@@ -56,14 +56,38 @@ int Parser::get_next_word(const std::shared_ptr<Storage::Tape::Tape> &tape) {
 void Parser::reset_crc()	{	crc_.reset();				}
 uint16_t Parser::get_crc()	{	return crc_.get_value();	}
 
-bool Parser::did_update_shifter(int new_value, int length) {
-	if(length < 4) return false;
+void Parser::acorn_shifter_output_bit(int value) {
+	push_symbol(value ? SymbolType::One : SymbolType::Zero);
+}
 
-	switch(new_value & 0xf) {
-		case 0x5:	printf("0"); push_symbol(SymbolType::Zero);	return true;
-		case 0xf:	printf("1"); push_symbol(SymbolType::One);	return true;
-		default:
-			printf("?");
-		return false;
+void Parser::process_pulse(const Storage::Tape::Tape::Pulse &pulse) {
+	shifter_.process_pulse(pulse);
+}
+
+
+Shifter::Shifter() :
+	pll_(PLLClockRate / 4800, 15),
+	was_high_(false),
+	input_pattern_(0),
+	input_bit_counter_(0) {
+	pll_.set_delegate(this);
+}
+
+void Shifter::process_pulse(const Storage::Tape::Tape::Pulse &pulse) {
+	pll_.run_for_cycles((int)((float)PLLClockRate * pulse.length.get_float()));
+
+	bool is_high = pulse.type == Storage::Tape::Tape::Pulse::High;
+	if(is_high != was_high_) {
+		pll_.add_pulse();
+	}
+	was_high_ = is_high;
+}
+
+void Shifter::digital_phase_locked_loop_output_bit(int value) {
+	input_pattern_ = ((input_pattern_ << 1) | (unsigned int)value) & 0xf;
+	switch(input_pattern_) {
+		case 0x5:	delegate_->acorn_shifter_output_bit(0); input_pattern_ = 0;	break;
+		case 0xf:	delegate_->acorn_shifter_output_bit(1); input_pattern_ = 0;	break;
+		default:	break;;
 	}
 }

Storage/Tape/Parsers/Acorn.hpp

@@ -17,11 +17,37 @@ namespace Storage {
 namespace Tape {
 namespace Acorn {
 
+class Shifter: public Storage::DigitalPhaseLockedLoop::Delegate {
+	public:
+		Shifter();
+
+		void process_pulse(const Storage::Tape::Tape::Pulse &pulse);
+
+		class Delegate {
+			public:
+				virtual void acorn_shifter_output_bit(int value) = 0;
+		};
+		void set_delegate(Delegate *delegate) {
+			delegate_ = delegate;
+		}
+
+		void digital_phase_locked_loop_output_bit(int value);
+
+	private:
+		Storage::DigitalPhaseLockedLoop pll_;
+		bool was_high_;
+
+		unsigned int input_pattern_;
+		unsigned int input_bit_counter_;
+
+		Delegate *delegate_;
+};
+
 enum class SymbolType {
 	One, Zero
 };
 
-class Parser: public Storage::Tape::PLLParser<SymbolType> {
+class Parser: public Storage::Tape::Parser<SymbolType>, public Shifter::Delegate  {
 	public:
 		Parser();
 
@@ -32,10 +58,13 @@ class Parser: public Storage::Tape::PLLParser<SymbolType> {
 		void reset_crc();
 		uint16_t get_crc();
 
-		bool did_update_shifter(int new_value, int length);
+		void acorn_shifter_output_bit(int value);
+		void process_pulse(const Storage::Tape::Tape::Pulse &pulse);
 
 	private:
+		bool did_update_shifter(int new_value, int length);
 		NumberTheory::CRC16 crc_;
+		Shifter shifter_;
 };
 
 }