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120 lines
3.9 KiB
C++
120 lines
3.9 KiB
C++
//
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// G64.cpp
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// Clock Signal
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//
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// Created by Thomas Harte on 10/07/2016.
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// Copyright © 2016 Thomas Harte. All rights reserved.
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//
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#include "G64.hpp"
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#include <vector>
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#include "../PCMTrack.hpp"
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#include "../Encodings/CommodoreGCR.hpp"
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using namespace Storage::Disk;
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G64::G64(const char *file_name) :
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Storage::FileHolder(file_name) {
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// read and check the file signature
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if(!check_signature("GCR-1541", 8)) throw ErrorNotG64;
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// check the version number
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int version = fgetc(file_);
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if(version != 0) throw ErrorUnknownVersion;
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// get the number of tracks and track size
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number_of_tracks_ = (uint8_t)fgetc(file_);
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maximum_track_size_ = fgetc16le();
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}
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unsigned int G64::get_head_position_count() {
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// give at least 84 tracks, to yield the normal geometry but,
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// if there are more, shove them in
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return number_of_tracks_ > 84 ? number_of_tracks_ : 84;
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}
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std::shared_ptr<Track> G64::get_uncached_track_at_position(unsigned int head, unsigned int position) {
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std::shared_ptr<Track> resulting_track;
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// if there's definitely no track here, return the empty track
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// (TODO: should be supplying one with an index hole?)
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if(position >= number_of_tracks_) return resulting_track;
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if(head >= 1) return resulting_track;
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// seek to this track's entry in the track table
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fseek(file_, (long)((position * 4) + 0xc), SEEK_SET);
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// read the track offset
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uint32_t track_offset;
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track_offset = fgetc32le();
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// if the track offset is zero, this track doesn't exist, so...
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if(!track_offset) return resulting_track;
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// seek to the track start
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fseek(file_, (int)track_offset, SEEK_SET);
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// get the real track length
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uint16_t track_length;
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track_length = fgetc16le();
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// grab the byte contents of this track
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std::vector<uint8_t> track_contents(track_length);
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fread(&track_contents[0], 1, track_length, file_);
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// seek to this track's entry in the speed zone table
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fseek(file_, (long)((position * 4) + 0x15c), SEEK_SET);
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// read the speed zone offsrt
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uint32_t speed_zone_offset;
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speed_zone_offset = fgetc32le();
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// if the speed zone is not constant, create a track based on the whole table; otherwise create one that's constant
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if(speed_zone_offset > 3) {
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// seek to start of speed zone
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fseek(file_, (int)speed_zone_offset, SEEK_SET);
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uint16_t speed_zone_length = (track_length + 3) >> 2;
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// read the speed zone bytes
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uint8_t speed_zone_contents[speed_zone_length];
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fread(speed_zone_contents, 1, speed_zone_length, file_);
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// divide track into appropriately timed PCMSegments
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std::vector<PCMSegment> segments;
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unsigned int current_speed = speed_zone_contents[0] >> 6;
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unsigned int start_byte_in_current_speed = 0;
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for(unsigned int byte = 0; byte < track_length; byte ++) {
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unsigned int byte_speed = speed_zone_contents[byte >> 2] >> (6 - (byte&3)*2);
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if(byte_speed != current_speed || byte == (track_length-1)) {
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unsigned int number_of_bytes = byte - start_byte_in_current_speed;
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PCMSegment segment;
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segment.number_of_bits = number_of_bytes * 8;
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segment.length_of_a_bit = Encodings::CommodoreGCR::length_of_a_bit_in_time_zone(current_speed);
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segment.data.resize(number_of_bytes);
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memcpy(&segment.data[0], &track_contents[start_byte_in_current_speed], number_of_bytes);
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segments.push_back(std::move(segment));
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current_speed = byte_speed;
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start_byte_in_current_speed = byte;
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}
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}
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resulting_track.reset(new PCMTrack(std::move(segments)));
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} else {
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PCMSegment segment;
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segment.number_of_bits = track_length * 8;
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segment.length_of_a_bit = Encodings::CommodoreGCR::length_of_a_bit_in_time_zone((unsigned int)speed_zone_offset);
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segment.data = std::move(track_contents);
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resulting_track.reset(new PCMTrack(std::move(segment)));
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}
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// TODO: find out whether it's possible for a G64 to supply only a partial track. I don't think it is, which would make the
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// above correct but supposing I'm wrong, the above would produce some incorrectly clocked tracks
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return resulting_track;
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}
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