Makes a first attempt at NIB support.

Components/DiskII/DiskII.cpp

@@ -78,7 +78,7 @@ void DiskII::set_data_register(uint8_t value) {
 }
 
 uint8_t DiskII::get_shift_register() {
-//	printf("[%02x] ", shift_register_);
+//	if(shift_register_ & 0x80) printf("[%02x] ", shift_register_);
 	inputs_ &= ~input_command;
 	return shift_register_;
 }

Storage/Disk/DiskImage/Formats/NIB.cpp

@@ -8,11 +8,16 @@
 
 #include "NIB.hpp"
 
+#include "../../Track/PCMTrack.hpp"
+#include "../../Encodings/AppleGCR.hpp"
+
+#include <vector>
+
 using namespace Storage::Disk;
 
 namespace {
 
-const std::size_t track_length = 6656;
+const long track_length = 6656;
 const std::size_t number_of_tracks = 35;
 
 }
@@ -24,7 +29,7 @@ NIB::NIB(const std::string &file_name) :
 		throw ErrorNotNIB;
 	}
 
-	// TODO: all other validation.
+	// TODO: all other validation. I.e. does this look like a GCR disk?
 }
 
 int NIB::get_head_position_count() {
@@ -33,13 +38,59 @@ int NIB::get_head_position_count() {
 
 std::shared_ptr<::Storage::Disk::Track> NIB::get_track_at_position(::Storage::Disk::Track::Address address) {
 	// NIBs contain data for even-numbered tracks underneath a single head only.
-	if(address.head || (address.position&1)) return nullptr;
+	if(address.head) return nullptr;
 
-//	const int file_track = address.position >> 1;
-//	file_.seek(static_cast<long>(file_track * track_length), SEEK_SET);
-//	std::vector<uint8_t> track_data = file_.read(track_length);
+	const long file_track = static_cast<long>(address.position >> 2);
+	file_.seek(file_track * track_length, SEEK_SET);
+	std::vector<uint8_t> track_data = file_.read(track_length);
 
-	// TODO: determine which FFs are syncs, and produce track.
+	// NIB files leave sync bytes implicit and make no guarantees
+	// about overall track positioning. So the approach taken here
+	// is to look for the epilogue sequence (which concludes all Apple
+	// tracks and headers), then treat all following FFs as a sync
+	// region, then switch back to ordinary behaviour as soon as a
+	// non-FF appears.
+	std::vector<Storage::Disk::PCMSegment> segments;
 
-	return nullptr;
+	std::size_t start_index = 0;
+	std::set<size_t> sync_starts;
+
+	// Establish where syncs start by finding instances of 0xd5 0xaa and then regressing
+	// from each along all preceding FFs.
+	for(size_t index = 0; index < track_data.size(); ++index) {
+		if(track_data[index] == 0xd5 && track_data[(index+1)%track_data.size()] == 0xaa) {
+			size_t start = index - 1;
+			while(track_data[start] == 0xff)
+				start = (start + track_data.size() - 1) % track_data.size();
+
+			sync_starts.insert((start + 1) % track_data.size());
+			if(start > index)
+				start_index = start;
+		}
+	}
+
+	if(start_index)
+		segments.push_back(Encodings::AppleGCR::six_and_two_sync(static_cast<int>(start_index)));
+
+	std::size_t index = start_index;
+	for(const auto &location: sync_starts) {
+		// Write from index to sync_start.
+		PCMSegment data_segment;
+		data_segment.data.insert(
+			data_segment.data.end(),
+			track_data.begin() + static_cast<off_t>(index),
+			track_data.begin() + static_cast<off_t>(location));
+		data_segment.number_of_bits = static_cast<unsigned int>(data_segment.data.size() * 8);
+		segments.push_back(std::move(data_segment));
+
+		// Add a sync from sync_start to end of 0xffs.
+		if(location == track_length-1) break;
+
+		index = location;
+		while(index < track_length && track_data[index] == 0xff)
+			++index;
+		segments.push_back(Encodings::AppleGCR::six_and_two_sync(static_cast<int>(index - location)));
+	}
+
+	return std::shared_ptr<PCMTrack>(new PCMTrack(segments));
 }

Storage/Disk/Track/PCMSegment.hpp

@@ -25,7 +25,7 @@ namespace Disk {
 	Bits from each byte are taken MSB to LSB.
 */
 struct PCMSegment {
-	Time length_of_a_bit;
+	Time length_of_a_bit = Time(1);
 	unsigned int number_of_bits = 0;
 	std::vector<uint8_t> data;