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160 lines
4.1 KiB
C++
160 lines
4.1 KiB
C++
//
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// AmigaADF.cpp
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// Clock Signal
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//
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// Created by Thomas Harte on 16/07/2021.
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// Copyright © 2021 Thomas Harte. All rights reserved.
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//
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#include "AmigaADF.hpp"
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#include "../../Encodings/MFM/Constants.hpp"
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#include "../../Encodings/MFM/Encoder.hpp"
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#include "../../Track/PCMTrack.hpp"
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using namespace Storage::Disk;
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namespace {
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template <typename IteratorT> void write_block(IteratorT begin, IteratorT end, std::unique_ptr<Storage::Encodings::MFM::Encoder> &encoder) {
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// Parse 1: write odd bits.
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auto cursor = begin;
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while(cursor != end) {
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uint8_t source =
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((*cursor & 0x01) >> 0) |
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((*cursor & 0x04) >> 1) |
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((*cursor & 0x10) >> 2) |
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((*cursor & 0x40) >> 3);
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++cursor;
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source |=
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((*cursor & 0x01) << 4) |
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((*cursor & 0x04) << 3) |
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((*cursor & 0x10) << 2) |
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((*cursor & 0x40) << 1);
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++cursor;
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encoder->add_byte(source);
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}
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// Parse 2: write even bits.
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cursor = begin;
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while(cursor != end) {
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uint8_t source =
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((*cursor & 0x02) >> 1) |
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((*cursor & 0x08) >> 2) |
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((*cursor & 0x20) >> 3) |
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((*cursor & 0x80) >> 4);
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++cursor;
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source |=
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((*cursor & 0x02) << 3) |
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((*cursor & 0x08) << 2) |
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((*cursor & 0x20) << 1) |
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((*cursor & 0x80) << 0);
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++cursor;
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encoder->add_byte(source);
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}
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}
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template <typename IteratorT> std::array<uint8_t, 4> checksum(IteratorT begin, IteratorT end) {
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uint64_t sum = 0;
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while(begin != end) {
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// Pull a big-endian 32-bit number.
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uint32_t next = 0;
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next |= uint64_t(*begin) << 24; ++begin;
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next |= uint64_t(*begin) << 16; ++begin;
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next |= uint64_t(*begin) << 8; ++begin;
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next |= uint64_t(*begin) << 0; ++begin;
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// Add, and then add carry too.
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sum += uint64_t(next);
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sum += (sum >> 32);
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sum &= 0xffff'ffff;
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}
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// Invert.
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sum = ~sum;
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// Pack big-endian.
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return std::array<uint8_t, 4>{
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uint8_t((sum >> 24) & 0xff),
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uint8_t((sum >> 16) & 0xff),
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uint8_t((sum >> 8) & 0xff),
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uint8_t((sum >> 0) & 0xff)
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};
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}
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}
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AmigaADF::AmigaADF(const std::string &file_name) :
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file_(file_name) {
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// Dumb validation only for now: a size check.
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if(file_.stats().st_size != 901120) throw Error::InvalidFormat;
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}
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HeadPosition AmigaADF::get_maximum_head_position() {
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return HeadPosition(80);
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}
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int AmigaADF::get_head_count() {
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return 2;
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}
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std::shared_ptr<Track> AmigaADF::get_track_at_position(Track::Address address) {
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using namespace Storage::Encodings;
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// Create an MFM encoder.
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Storage::Disk::PCMSegment encoded_segment;
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encoded_segment.data.reserve(102'400); // i.e. 0x1900 bytes.
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auto encoder = MFM::GetMFMEncoder(encoded_segment.data);
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// Each track begins with two sync words.
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encoder->output_short(MFM::MFMSync);
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encoder->output_short(MFM::MFMSync);
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// Grab the unencoded track.
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file_.seek(get_file_offset_for_position(address), SEEK_SET);
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const std::vector<uint8_t> track_data = file_.read(512 * 11);
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// Eleven sectors are then encoded.
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for(size_t s = 0; s < 11; s++) {
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// Two bytes of 0x00 act as an inter-sector gap.
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encoder->add_byte(0);
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encoder->add_byte(0);
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// Add additional sync.
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encoder->output_short(MFM::MFMSync);
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encoder->output_short(MFM::MFMSync);
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// Write the header.
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const uint8_t header[4] = {
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0xff, // Amiga v1.0 format.
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uint8_t(address.position.as_int()), // Track.
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uint8_t(s), // Sector.
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uint8_t(11 - s), // Sectors remaining.
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};
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write_block(header, &header[4], encoder);
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// Write the sector label.
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const std::array<uint8_t, 16> os_recovery{};
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write_block(os_recovery.begin(), os_recovery.end(), encoder);
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// Write checksums.
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const auto header_checksum = checksum(&header[0], &header[4]);
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write_block(header_checksum.begin(), header_checksum.end(), encoder);
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const auto data_checksum = checksum(&track_data[s * 512], &track_data[(s + 1) * 512]);
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write_block(data_checksum.begin(), data_checksum.end(), encoder);
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// Write data.
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write_block(&track_data[s * 512], &track_data[(s + 1) * 512], encoder);
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}
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return std::make_shared<Storage::Disk::PCMTrack>(std::move(encoded_segment));
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}
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long AmigaADF::get_file_offset_for_position(Track::Address address) {
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return (address.position.as_int() * 2 + address.head) * 512 * 11;
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}
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