Merge pull request #323 from TomHarte/MSXCAS

Adds support for the MSX .CAS file format.

Storage/Tape/Formats/CAS.cpp

@@ -8,21 +8,197 @@
 
 #include "CAS.hpp"
 
+#include <cassert>
+#include <cstring>
+
 using namespace Storage::Tape;
 
-CAS::CAS(const char *file_name) :
-	file_(file_name) {
+namespace  {
+	const uint8_t header_signature[8] = {0x1f, 0xa6, 0xde, 0xba, 0xcc, 0x13, 0x7d, 0x74};
+}
+
+CAS::CAS(const char *file_name) {
+	Storage::FileHolder file(file_name);
+	uint8_t lookahead[8] = {0, 0, 0, 0, 0, 0, 0, 0};
+
+	// Get the first header.
+	get_next(file, lookahead, 8);
+	if(std::memcmp(lookahead, header_signature, sizeof(header_signature))) throw ErrorNotCAS;
+
+	File *active_file = nullptr;
+	while(!file.eof()) {
+		// Just found a header, so flush the lookahead.
+		get_next(file, lookahead, 8);
+
+		// If no file is active, create one, as this must be an identification block.
+		if(!active_file) {
+			// Determine the new file type.
+			Block type;
+			switch(lookahead[0]) {
+				case 0xd3:	type = Block::CSAVE;	break;
+				case 0xd0:	type = Block::BSAVE;	break;
+				case 0xea:	type = Block::ASCII;	break;
+
+				// This implies something has gone wrong with parsing.
+				default: throw ErrorNotCAS;
+			}
+
+			// Set the type and feed in the initial data.
+			files_.emplace_back();
+			active_file = &files_.back();
+			active_file->type = type;
+		}
+
+		// Add a new chunk for the new incoming data.
+		active_file->chunks.emplace_back();
+
+		// Keep going until another header arrives or the file ends.
+		while(std::memcmp(lookahead, header_signature, sizeof(header_signature)) && !file.eof()) {
+			active_file->chunks.back().push_back(lookahead[0]);
+			get_next(file, lookahead, 1);
+		}
+
+		// If the file ended, flush the lookahead.
+		if(file.eof()) {
+			for(int index = 0; index < 8; index++)
+				active_file->chunks.back().push_back(lookahead[index]);
+		}
+
+		switch(active_file->type) {
+			case Block::ASCII:
+				// ASCII files have as many chunks as necessary, the final one being back filled
+				// with 0x1a.
+				if(active_file->chunks.size() >= 2) {
+					std::vector<uint8_t> &last_chunk = active_file->chunks.back();
+					if(last_chunk.back() == 0x1a)
+						active_file = nullptr;
+				}
+			break;
+
+			default:
+				// CSAVE and BSAVE files have exactly two chunks, the second being the data.
+				if(active_file->chunks.size() == 2)
+					active_file = nullptr;
+			break;
+		}
+	}
+}
+
+/*!
+	Treating @c buffer as a sliding lookahead, shifts it @c quantity elements to the left and
+	populates the new empty area to the right from @c file.
+*/
+void CAS::get_next(Storage::FileHolder &file, uint8_t (&buffer)[8], std::size_t quantity) {
+	assert(quantity <= 8);
+
+	if(quantity < 8)
+		std::memmove(buffer, &buffer[quantity], 8 - quantity);
+
+	while(quantity--) {
+		buffer[7 - quantity] = file.get8();
+	}
 }
 
 bool CAS::is_at_end() {
-	return true;
+	return phase_ == Phase::EndOfFile;
 }
 
 void CAS::virtual_reset() {
-
+	phase_ = Phase::Header;
+	file_pointer_ = 0;
+	chunk_pointer_ = 0;
+	distance_into_phase_ = 0;
+	distance_into_bit_ = 0;
 }
 
 Tape::Pulse CAS::virtual_get_next_pulse() {
-	Pulse empty_pulse;
-	return empty_pulse;
+	Pulse pulse;
+	pulse.length.clock_rate = 9600;
+	// Clock rate is four times the baud rate (of 2400), because the quickest thing that might need
+	// to be communicated is a '1', which is two cycles at the baud rate, i.e. four events:
+	// high, low, high, low.
+
+	// If this is a gap, then that terminates a file. If this is already the end
+	// of the file then perpetual gaps await.
+	if(phase_ == Phase::Gap || phase_ == Phase::EndOfFile) {
+		pulse.length.length = pulse.length.clock_rate;
+		pulse.type = Pulse::Type::Zero;
+
+		if(phase_ == Phase::Gap) {
+			phase_ = Phase::Header;
+			chunk_pointer_ = 0;
+			distance_into_phase_ = 0;
+		}
+
+		return pulse;
+	}
+
+	// Determine which bit is now forthcoming.
+	int bit = 1;
+
+	switch(phase_) {
+		default: break;
+
+		case Phase::Header: {
+			// In the header, all bits are 1s, so let the default value stand. Just check whether the
+			// header is ended and, if so, move on to bytes.
+			distance_into_bit_++;
+			if(distance_into_bit_ == 2) {
+				distance_into_phase_++;
+				distance_into_bit_ = 0;
+
+				// This code always produces a 2400 baud signal; so use the appropriate Red Book-supplied
+				// constants to check whether the header has come to an end.
+				if(distance_into_phase_ == (chunk_pointer_ ? 7936 : 31744)) {
+					phase_ = Phase::Bytes;
+					distance_into_phase_ = 0;
+					distance_into_bit_ = 0;
+				}
+			}
+		} break;
+
+		case Phase::Bytes: {
+			// Provide bits with a single '0' start bit and two '1' stop bits.
+			uint8_t byte_value = files_[file_pointer_].chunks[chunk_pointer_][distance_into_phase_ / 11];
+			int bit_offset = distance_into_phase_ % 11;
+			switch(bit_offset) {
+				case 0:		bit = 0;									break;
+				default:	bit = (byte_value >> (bit_offset - 1)) & 1;	break;
+				case 9:
+				case 10:	bit = 1;									break;
+			}
+
+			// Lots of branches below, to the effect that:
+			//
+			// if bit is finished, and if all bytes in chunk have been posted then:
+			//
+			//	- if this is the final chunk in the file then, if there are further files switch to a gap.
+			//	Otherwise note end of file.
+			//
+			//	- otherwise, roll onto the next header.
+			//
+			distance_into_bit_++;
+			if(distance_into_bit_ == (bit ? 4 : 2)) {
+				distance_into_bit_ = 0;
+				distance_into_phase_++;
+				if(distance_into_phase_ == files_[file_pointer_].chunks[chunk_pointer_].size() * 11) {
+					distance_into_phase_ = 0;
+					chunk_pointer_++;
+					if(chunk_pointer_ == files_[file_pointer_].chunks.size()) {
+						chunk_pointer_ = 0;
+						file_pointer_++;
+						phase_ = (file_pointer_ == files_.size()) ? Phase::EndOfFile : Phase::Gap;
+					} else {
+						phase_ = Phase::Header;
+					}
+				}
+			}
+		} break;
+	}
+
+	// A '1' is encoded with twice the frequency of a '0'.
+	pulse.length.length = static_cast<unsigned int>(2 - bit);
+	pulse.type = (distance_into_bit_ & 1) ? Pulse::Type::High : Pulse::Type::Low;
+
+	return pulse;
 }

Storage/Tape/Formats/CAS.hpp

@@ -12,6 +12,9 @@
 #include "../Tape.hpp"
 #include "../../FileHolder.hpp"
 
+#include <cstdint>
+#include <vector>
+
 namespace Storage {
 namespace Tape {
 
@@ -35,10 +38,35 @@ class CAS: public Tape {
 		bool is_at_end();
 
 	private:
-		Storage::FileHolder file_;
-
 		void virtual_reset();
 		Pulse virtual_get_next_pulse();
+
+		// Helper for populating the file list, below.
+		void get_next(Storage::FileHolder &file, uint8_t (&buffer)[8], std::size_t quantity);
+
+		// Storage for the array of files to transcribe into audio.
+		enum class Block {
+			BSAVE,
+			CSAVE,
+			ASCII
+		};
+		struct File {
+			Block type;
+			std::vector<std::vector<std::uint8_t>> chunks;
+		};
+		std::vector<File> files_;
+
+		// Tracker for active state within the file list.
+		std::size_t file_pointer_ = 0;
+		std::size_t chunk_pointer_ = 0;
+		enum class Phase {
+			Header,
+			Bytes,
+			Gap,
+			EndOfFile
+		} phase_ = Phase::Header;
+		std::size_t distance_into_phase_ = 0;
+		std::size_t distance_into_bit_ = 0;
 };
 
 }

Storage/Tape/Tape.cpp

@@ -89,8 +89,7 @@ void TapePlayer::get_next_pulse() {
 	if(tape_) {
 		current_pulse_ = tape_->get_next_pulse();
 		if(tape_->is_at_end()) update_sleep_observer();
-	}
-	else {
+	} else {
 		current_pulse_.length.length = 1;
 		current_pulse_.length.clock_rate = 1;
 		current_pulse_.type = Tape::Pulse::Zero;