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112 lines
3.5 KiB
C++
112 lines
3.5 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 <cstring>
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#include <vector>
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#include "../../Track/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 std::string &file_name) :
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file_(file_name) {
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// read and check the file signature
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if(!file_.check_signature("GCR-1541")) throw Error::InvalidFormat;
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// check the version number
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int version = file_.get8();
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if(version != 0) throw Error::UnknownVersion;
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// get the number of tracks and track size
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number_of_tracks_ = file_.get8();
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maximum_track_size_ = file_.get16le();
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}
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HeadPosition G64::get_maximum_head_position() {
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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 HeadPosition(number_of_tracks_ > 84 ? number_of_tracks_ : 84, 2);
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}
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std::shared_ptr<Track> G64::get_track_at_position(Track::Address address) {
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std::shared_ptr<Track> resulting_track;
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// seek to this track's entry in the track table
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file_.seek(long((address.position.as_half() * 4) + 0xc), SEEK_SET);
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// read the track offset
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const uint32_t track_offset = file_.get32le();
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// if the track offset is zero, this track doesn't exist, so...
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if(!track_offset) return nullptr;
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// seek to the track start
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file_.seek(long(track_offset), SEEK_SET);
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// get the real track length
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const uint16_t track_length = file_.get16le();
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// grab the byte contents of this track
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const std::vector<uint8_t> track_contents = file_.read(track_length);
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// seek to this track's entry in the speed zone table
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file_.seek(long((address.position.as_half() * 4) + 0x15c), SEEK_SET);
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// read the speed zone offsrt
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const uint32_t speed_zone_offset = file_.get32le();
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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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file_.seek(long(speed_zone_offset), SEEK_SET);
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// read the speed zone bytes
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const uint16_t speed_zone_length = (track_length + 3) >> 2;
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uint8_t speed_zone_contents[speed_zone_length];
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file_.read(speed_zone_contents, speed_zone_length);
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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 == uint16_t(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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Encodings::CommodoreGCR::length_of_a_bit_in_time_zone(current_speed),
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number_of_bytes * 8,
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&track_contents[start_byte_in_current_speed]);
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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 = std::make_shared<PCMTrack>(std::move(segments));
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} else {
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PCMSegment segment(
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Encodings::CommodoreGCR::length_of_a_bit_in_time_zone(unsigned(speed_zone_offset)),
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track_length * 8,
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track_contents
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);
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resulting_track = std::make_shared<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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