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5e34c1b6b8
I've now seemingly verified that the values read back by the CPU are those I'm intending to produce, so I'm at a loss.
103 lines
2.9 KiB
C++
103 lines
2.9 KiB
C++
//
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// NIB.cpp
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// Clock Signal
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//
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// Created by Thomas Harte on 21/04/2018.
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// Copyright © 2018 Thomas Harte. All rights reserved.
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//
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#include "NIB.hpp"
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#include "../../Track/PCMTrack.hpp"
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#include "../../Encodings/AppleGCR.hpp"
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#include <vector>
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using namespace Storage::Disk;
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namespace {
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const long track_length = 6656;
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const std::size_t number_of_tracks = 35;
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}
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NIB::NIB(const std::string &file_name) :
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file_(file_name) {
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// A NIB should be 35 tracks, each 6656 bytes long.
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if(file_.stats().st_size != track_length*number_of_tracks) {
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throw Error::InvalidFormat;
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}
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// TODO: all other validation. I.e. does this look like a GCR disk?
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}
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int NIB::get_head_position_count() {
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return number_of_tracks * 4;
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}
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std::shared_ptr<::Storage::Disk::Track> NIB::get_track_at_position(::Storage::Disk::Track::Address address) {
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// NIBs contain data for even-numbered tracks underneath a single head only.
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if(address.head) return nullptr;
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const long file_track = static_cast<long>(address.position >> 2);
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file_.seek(file_track * track_length, SEEK_SET);
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std::vector<uint8_t> track_data = file_.read(track_length);
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// NIB files leave sync bytes implicit and make no guarantees
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// about overall track positioning. So the approach taken here
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// is to look for the epilogue sequence (which concludes all Apple
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// tracks and headers), then treat all following FFs as a sync
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// region, then switch back to ordinary behaviour as soon as a
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// non-FF appears.
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PCMSegment segment;
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std::size_t start_index = 0;
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std::set<size_t> sync_starts;
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// Establish where syncs start by finding instances of 0xd5 0xaa and then regressing
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// from each along all preceding FFs.
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for(size_t index = 0; index < track_data.size(); ++index) {
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if(track_data[index] == 0xd5 && track_data[(index+1)%track_data.size()] == 0xaa) {
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size_t start = index - 1;
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size_t length = 0;
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while(track_data[start] == 0xff) {
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start = (start + track_data.size() - 1) % track_data.size();
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++length;
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}
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if(length >= 5) {
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sync_starts.insert((start + 1) % track_data.size());
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if(start > index)
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start_index = start;
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}
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}
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}
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if(start_index) {
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segment += Encodings::AppleGCR::six_and_two_sync(static_cast<int>(start_index));
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}
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std::size_t index = start_index;
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for(const auto &location: sync_starts) {
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// Write from index to sync_start.
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PCMSegment data_segment;
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data_segment.data.insert(
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data_segment.data.end(),
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track_data.begin() + static_cast<off_t>(index),
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track_data.begin() + static_cast<off_t>(location));
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data_segment.number_of_bits = static_cast<unsigned int>(data_segment.data.size() * 8);
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segment += data_segment;
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// Add a sync from sync_start to end of 0xffs.
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if(location == track_length-1) break;
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index = location;
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while(index < track_length && track_data[index] == 0xff)
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++index;
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segment += Encodings::AppleGCR::six_and_two_sync(static_cast<int>(index - location));
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}
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return std::make_shared<PCMTrack>(segment);
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}
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