From 064fe7658cb35a035872c83329487d11f78e1d84 Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Fri, 12 Mar 2021 18:43:20 -0500
Subject: [PATCH] Adds necessary interface to inherit a CPC tape-speed byte.

---
 Storage/Tape/Parsers/Spectrum.cpp | 19 +++++++++++++++----
 Storage/Tape/Parsers/Spectrum.hpp |  7 +++++++
 2 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/Storage/Tape/Parsers/Spectrum.cpp b/Storage/Tape/Parsers/Spectrum.cpp
index bcf18194c..4a884875a 100644
--- a/Storage/Tape/Parsers/Spectrum.cpp
+++ b/Storage/Tape/Parsers/Spectrum.cpp
@@ -82,10 +82,7 @@ void Parser::process_pulse(const Storage::Tape::Tape::Pulse &pulse) {
 					case MachineType::AmstradCPC:
 						// CPC: pilot tone is length of bit 1; bit 0 is half that.
 						// So no more detecting formal pilot waves.
-						is_one_ = mean * 0.75f;
-						too_long_ = mean * 1.0f / 0.75f;
-						too_short_ = is_one_ * 0.5f;
-						is_pilot_ = too_long_;
+						set_cpc_one_zero_boundary(mean * 0.75f);
 					break;
 
 					case MachineType::Enterprise:
@@ -132,6 +129,20 @@ void Parser::process_pulse(const Storage::Tape::Tape::Pulse &pulse) {
 	push_wave(t_states > is_one_ ? WaveType::One : WaveType::Zero);
 }
 
+void Parser::set_cpc_read_speed(uint8_t speed) {
+	// This may not be exactly right; I wish there were more science here but
+	// instead it's empirical based on tape speed versus value stored plus
+	// a guess as to where the CPC puts the dividing line.
+	set_cpc_one_zero_boundary(float(speed) * 14.35f);
+}
+
+void Parser::set_cpc_one_zero_boundary(float boundary) {
+	is_one_ = boundary;
+	too_long_ = is_one_ * 16.0f / 9.0f;
+	too_short_ = is_one_ * 0.5f;
+	is_pilot_ = too_long_;
+}
+
 void Parser::inspect_waves(const std::vector<Storage::Tape::ZXSpectrum::WaveType> &waves) {
 	switch(waves[0]) {
 		// Gap and Pilot map directly.
diff --git a/Storage/Tape/Parsers/Spectrum.hpp b/Storage/Tape/Parsers/Spectrum.hpp
index e8a2d5b32..2b99fcbfb 100644
--- a/Storage/Tape/Parsers/Spectrum.hpp
+++ b/Storage/Tape/Parsers/Spectrum.hpp
@@ -63,6 +63,11 @@ class Parser: public Storage::Tape::PulseClassificationParser<WaveType, SymbolTy
 		};
 		Parser(MachineType);
 
+		/*!
+			Calibrates the expected data speed using a value in the CPC's native tape-speed measurement scale.
+		*/
+		void set_cpc_read_speed(uint8_t);
+
 		/*!
 			Finds the next block from the tape, if any.
 
@@ -117,6 +122,8 @@ class Parser: public Storage::Tape::PulseClassificationParser<WaveType, SymbolTy
 
 		std::array<float, 8> calibration_pulses_;
 		size_t calibration_pulse_pointer_ = 0;
+
+		void set_cpc_one_zero_boundary(float);
 };
 
 }