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No doubt many more similar improvements are available, these are just the ones that were easy to find.
141 lines
4.5 KiB
C++
141 lines
4.5 KiB
C++
//
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// D64.cpp
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// Clock Signal
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//
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// Created by Thomas Harte on 01/08/2016.
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// Copyright 2016 Thomas Harte. All rights reserved.
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//
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#include "D64.hpp"
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#include <algorithm>
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#include <cstring>
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#include <sys/stat.h>
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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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D64::D64(const std::string &file_name) :
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file_(file_name) {
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// in D64, this is it for validation without imposing potential false-negative tests: check that
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// the file size appears to be correct. Stone-age stuff.
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if(file_.stats().st_size != 174848 && file_.stats().st_size != 196608)
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throw Error::InvalidFormat;
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number_of_tracks_ = (file_.stats().st_size == 174848) ? 35 : 40;
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// then, ostensibly, this is a valid file. Hmmm. Pick a disk ID as a function of the file_name,
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// being the most stable thing available
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disk_id_ = 0;
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for(const auto &character: file_name) {
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disk_id_ ^= character;
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disk_id_ = static_cast<uint16_t>((disk_id_ << 2) ^ (disk_id_ >> 13));
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}
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}
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HeadPosition D64::get_maximum_head_position() {
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return HeadPosition(number_of_tracks_);
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}
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std::shared_ptr<Track> D64::get_track_at_position(Track::Address address) {
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// figure out where this track starts on the disk
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int offset_to_track = 0;
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int tracks_to_traverse = address.position.as_int();
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int zone_sizes[] = {17, 7, 6, 10};
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int sectors_by_zone[] = {21, 19, 18, 17};
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int zone = 0;
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for(int current_zone = 0; current_zone < 4; current_zone++) {
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int tracks_in_this_zone = std::min(tracks_to_traverse, zone_sizes[current_zone]);
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offset_to_track += tracks_in_this_zone * sectors_by_zone[current_zone];
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tracks_to_traverse -= tracks_in_this_zone;
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if(tracks_in_this_zone == zone_sizes[current_zone]) zone++;
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}
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// seek to start of data
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file_.seek(offset_to_track * 256, SEEK_SET);
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// build up a PCM sampling of the GCR version of this track
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// format per sector:
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//
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// syncronisation: three $FFs directly in GCR
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// value $08 to announce a header
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// a checksum made of XORing the following four bytes
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// sector number (1 byte)
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// track number (1 byte)
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// disk ID (2 bytes)
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// five GCR bytes of value $55
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// = [6 bytes -> 7.5 GCR bytes] + ... = 21 GCR bytes
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//
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// syncronisation: three $FFs directly in GCR
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// value $07 to announce data
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// 256 data bytes
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// a checksum: the XOR of the previous 256 bytes
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// two bytes of vaue $00
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// = [260 bytes -> 325 GCR bytes] + 3 GCR bytes = 328 GCR bytes
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//
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// = 349 GCR bytes per sector
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std::size_t track_bytes = 349 * static_cast<std::size_t>(sectors_by_zone[zone]);
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std::vector<uint8_t> data(track_bytes);
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for(int sector = 0; sector < sectors_by_zone[zone]; sector++) {
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uint8_t *sector_data = &data[static_cast<size_t>(sector) * 349];
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sector_data[0] = sector_data[1] = sector_data[2] = 0xff;
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uint8_t sector_number = static_cast<uint8_t>(sector); // sectors count from 0
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uint8_t track_number = static_cast<uint8_t>(address.position.as_int() + 1); // tracks count from 1
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uint8_t checksum = static_cast<uint8_t>(sector_number ^ track_number ^ disk_id_ ^ (disk_id_ >> 8));
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uint8_t header_start[4] = {
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0x08, checksum, sector_number, track_number
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};
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Encodings::CommodoreGCR::encode_block(§or_data[3], header_start);
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uint8_t header_end[4] = {
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static_cast<uint8_t>(disk_id_ & 0xff), static_cast<uint8_t>(disk_id_ >> 8), 0, 0
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};
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Encodings::CommodoreGCR::encode_block(§or_data[8], header_end);
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// pad out post-header parts
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uint8_t zeros[4] = {0, 0, 0, 0};
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Encodings::CommodoreGCR::encode_block(§or_data[13], zeros);
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sector_data[18] = 0x52;
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sector_data[19] = 0x94;
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sector_data[20] = 0xaf;
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// get the actual contents
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uint8_t source_data[256];
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file_.read(source_data, sizeof(source_data));
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// compute the latest checksum
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checksum = 0;
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for(int c = 0; c < 256; c++)
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checksum ^= source_data[c];
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// put in another sync
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sector_data[21] = sector_data[22] = sector_data[23] = 0xff;
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// now start writing in the actual data
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uint8_t start_of_data[4] = {
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0x07, source_data[0], source_data[1], source_data[2]
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};
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Encodings::CommodoreGCR::encode_block(§or_data[24], start_of_data);
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int source_data_offset = 3;
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int target_data_offset = 29;
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while((source_data_offset+4) < 256) {
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Encodings::CommodoreGCR::encode_block(§or_data[target_data_offset], &source_data[source_data_offset]);
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target_data_offset += 5;
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source_data_offset += 4;
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}
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uint8_t end_of_data[4] = {
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source_data[255], checksum, 0, 0
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};
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Encodings::CommodoreGCR::encode_block(§or_data[target_data_offset], end_of_data);
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}
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return std::make_shared<PCMTrack>(PCMSegment(data));
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}
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