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CLK/Storage/Disk/DiskImage/Formats/DMK.cpp

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//
// DMK.cpp
// Clock Signal
//
// Created by Thomas Harte on 08/01/2018.
// Copyright 2018 Thomas Harte. All rights reserved.
//
#include "DMK.hpp"
#include "../../Encodings/MFM/Constants.hpp"
#include "../../Encodings/MFM/Encoder.hpp"
#include "../../Track/PCMTrack.hpp"
using namespace Storage::Disk;
2023-05-16 20:40:09 +00:00
namespace {
std::unique_ptr<Storage::Encodings::MFM::Encoder> new_encoder(Storage::Disk::PCMSegment &segment, bool is_double_density) {
std::unique_ptr<Storage::Encodings::MFM::Encoder> encoder;
if(is_double_density) {
encoder = Storage::Encodings::MFM::GetMFMEncoder(segment.data);
segment.length_of_a_bit = Storage::Encodings::MFM::MFMBitLength;
} else {
encoder = Storage::Encodings::MFM::GetFMEncoder(segment.data);
segment.length_of_a_bit = Storage::Encodings::MFM::FMBitLength;
}
return encoder;
}
}
DMK::DMK(const std::string &file_name) :
file_(file_name) {
// Determine whether this DMK represents a read-only disk (whether intentionally,
// or by virtue of filesystem placement).
uint8_t read_only_byte = file_.get8();
if(read_only_byte != 0x00 && read_only_byte != 0xff) throw Error::InvalidFormat;
is_read_only_ = (read_only_byte == 0xff) || file_.get_is_known_read_only();
// Read track count and size.
head_position_count_ = int(file_.get8());
track_length_ = long(file_.get16le());
// Track length must be at least 0x80, as that's the size of the IDAM
// table before track contents.
if(track_length_ < 0x80) throw Error::InvalidFormat;
// Read the file flags and apply them.
uint8_t flags = file_.get8();
head_count_ = 2 - ((flags & 0x10) >> 4);
head_position_count_ /= head_count_;
is_purely_single_density_ = !!(flags & 0x40);
// Skip to the end of the header and check that this is
// "in the emulator's native format".
file_.seek(0xc, SEEK_SET);
uint32_t format = file_.get32le();
if(format) throw Error::InvalidFormat;
}
HeadPosition DMK::get_maximum_head_position() {
return HeadPosition(head_position_count_);
}
int DMK::get_head_count() {
return head_count_;
}
bool DMK::get_is_read_only() {
return true;
// Given that track serialisation is not yet implemented, treat all DMKs as read-only.
// return is_read_only_;
}
long DMK::get_file_offset_for_position(Track::Address address) {
return (address.head*head_count_ + address.position.as_int()) * track_length_ + 16;
}
std::shared_ptr<::Storage::Disk::Track> DMK::get_track_at_position(::Storage::Disk::Track::Address address) {
file_.seek(get_file_offset_for_position(address), SEEK_SET);
// Read the IDAM table.
uint16_t idam_locations[64];
std::size_t idam_count = 0;
for(std::size_t c = 0; c < sizeof(idam_locations) / sizeof(*idam_locations); ++c) {
idam_locations[idam_count] = file_.get16le();
if((idam_locations[idam_count] & 0x7fff) >= 128) {
idam_count++;
}
}
// Grab the rest of the track.
std::vector<uint8_t> track = file_.read(size_t(track_length_ - 0x80));
// Default to outputting double density unless the disk doesn't support it.
bool is_double_density = !is_purely_single_density_;
std::vector<PCMSegment> segments;
std::unique_ptr<Encodings::MFM::Encoder> encoder;
segments.emplace_back();
encoder = new_encoder(segments.back(), is_double_density);
std::size_t idam_pointer = 0;
const std::size_t track_length = size_t(track_length_) - 0x80;
std::size_t track_pointer = 0;
while(track_pointer < track_length) {
// Determine bytes left until next IDAM.
std::size_t destination;
if(idam_pointer != idam_count) {
destination = (idam_locations[idam_pointer] & 0x7fff) - 0x80;
} else {
destination = track_length;
}
// Output every intermediate byte.
if(!is_double_density && !is_purely_single_density_) {
is_double_density = true;
segments.emplace_back();
encoder = new_encoder(segments.back(), is_double_density);
}
while(track_pointer < destination) {
encoder->add_byte(track[track_pointer]);
track_pointer++;
}
// Exit now if that's it.
if(destination == track_length) break;
// Being now located at the IDAM, check for a change of encoding.
bool next_is_double_density = !!(idam_locations[idam_pointer] & 0x8000);
if(next_is_double_density != is_double_density) {
is_double_density = next_is_double_density;
segments.emplace_back();
encoder = new_encoder(segments.back(), is_double_density);
}
// Now at the IDAM, which will always be an FE regardless of FM/MFM encoding,
// presumably through misunderstanding of the designer? Write out a real IDAM
// for the current density, then the rest of the ID: four bytes for the address
// plus two for the CRC. Keep a copy of the header while we're here, so that the
// size of the sector is known momentarily.
std::size_t step_rate = (!is_double_density && !is_purely_single_density_) ? 2 : 1;
encoder->add_ID_address_mark();
uint8_t header[6];
for(int c = 0; c < 6; ++c) {
track_pointer += step_rate;
encoder->add_byte(track[track_pointer]);
header[c] = track[track_pointer];
}
track_pointer += step_rate;
// Now write out as many bytes as are found prior to an FB or F8 (same comment as
// above: those are the FM-esque marks, but it seems as though transcription to MFM
// is implicit).
while(true) {
uint8_t next_byte = track[track_pointer];
track_pointer += step_rate;
if(next_byte == 0xfb || next_byte == 0xf8) {
// Write a data or deleted data address mark.
if(next_byte == 0xfb) encoder->add_data_address_mark();
else encoder->add_deleted_data_address_mark();
break;
}
encoder->add_byte(next_byte);
}
// Now write out a data mark (the file format appears to leave these implicit?),
// then the sector contents plus the CRC.
encoder->add_data_address_mark();
int sector_size = 2 + (128 << header[3]);
while(sector_size--) {
encoder->add_byte(track[track_pointer]);
track_pointer += step_rate;
}
idam_pointer++;
}
return std::make_shared<PCMTrack>(segments);
}