mirror of
https://github.com/TomHarte/CLK.git
synced 2024-09-08 03:54:27 +00:00
283 lines
9.8 KiB
C++
283 lines
9.8 KiB
C++
//
|
|
// SegmentParser.cpp
|
|
// Clock Signal
|
|
//
|
|
// Created by Thomas Harte on 04/05/2018.
|
|
// Copyright 2018 Thomas Harte. All rights reserved.
|
|
//
|
|
|
|
#include "SegmentParser.hpp"
|
|
|
|
#include "Encoder.hpp"
|
|
|
|
#include <array>
|
|
|
|
namespace {
|
|
|
|
const uint8_t six_and_two_unmapping[] = {
|
|
/* 0x96 */ 0x00, 0x01,
|
|
/* 0x98 */ 0xff, 0xff, 0x02, 0x03, 0xff, 0x04, 0x05, 0x06,
|
|
/* 0xa0 */ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x07, 0x08,
|
|
/* 0xa8 */ 0xff, 0xff, 0xff, 0x09, 0x0a, 0x0b, 0x0c, 0x0d,
|
|
/* 0xb0 */ 0xff, 0xff, 0x0e, 0x0f, 0x10, 0x11, 0x12, 0x13,
|
|
/* 0xb8 */ 0xff, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1a,
|
|
/* 0xc0 */ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
|
|
/* 0xc8 */ 0xff, 0xff, 0xff, 0x1b, 0xff, 0x1c, 0x1d, 0x1e,
|
|
/* 0xd0 */ 0xff, 0xff, 0xff, 0x1f, 0xff, 0xff, 0x20, 0x21,
|
|
/* 0xd8 */ 0xff, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27, 0x28,
|
|
/* 0xe0 */ 0xff, 0xff, 0xff, 0xff, 0xff, 0x29, 0x2a, 0x2b,
|
|
/* 0xe8 */ 0xff, 0x2c, 0x2d, 0x2e, 0x2f, 0x30, 0x31, 0x32,
|
|
/* 0xf0 */ 0xff, 0xff, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38,
|
|
/* 0xf8 */ 0xff, 0x39, 0x3a, 0x3b, 0x3c, 0x3d, 0x3e, 0x3f,
|
|
};
|
|
|
|
uint8_t unmap_six_and_two(uint8_t source) {
|
|
if(source < 0x96) return 0xff;
|
|
return six_and_two_unmapping[source - 0x96];
|
|
}
|
|
|
|
}
|
|
|
|
using namespace Storage::Encodings::AppleGCR;
|
|
|
|
std::map<std::size_t, Sector> Storage::Encodings::AppleGCR::sectors_from_segment(const Disk::PCMSegment &segment) {
|
|
std::map<std::size_t, Sector> result;
|
|
|
|
uint_fast8_t shift_register = 0;
|
|
|
|
const std::size_t scanning_sentinel = std::numeric_limits<std::size_t>::max();
|
|
std::unique_ptr<Sector> new_sector;
|
|
std::size_t sector_location = 0;
|
|
std::size_t pointer = scanning_sentinel;
|
|
std::array<uint_fast8_t, 8> header{{0, 0, 0, 0, 0, 0, 0, 0}};
|
|
std::array<uint_fast8_t, 3> scanner{{0, 0, 0}};
|
|
|
|
// Scan the track 1 and 1/8th times; that's long enough to make sure that any sector which straddles the
|
|
// end of the track is caught. Since they're put into a map, it doesn't matter if they're caught twice.
|
|
const size_t extended_length = segment.data.size() + (segment.data.size() >> 3);
|
|
for(size_t bit = 0; bit < extended_length; ++bit) {
|
|
shift_register = static_cast<uint_fast8_t>((shift_register << 1) | (segment.data[bit % segment.data.size()] ? 1 : 0));
|
|
|
|
// Apple GCR parsing: bytes always have the top bit set.
|
|
if(!(shift_register&0x80)) continue;
|
|
|
|
// Grab the byte.
|
|
const uint_fast8_t value = shift_register;
|
|
shift_register = 0;
|
|
|
|
scanner[0] = scanner[1];
|
|
scanner[1] = scanner[2];
|
|
scanner[2] = value;
|
|
|
|
if(pointer == scanning_sentinel) {
|
|
if(
|
|
scanner[0] == header_prologue[0] &&
|
|
scanner[1] == header_prologue[1] &&
|
|
(
|
|
scanner[2] == header_prologue[2] ||
|
|
scanner[2] == data_prologue[2]
|
|
)) {
|
|
pointer = 0;
|
|
|
|
// If this is the start of a data section, and at least
|
|
// one header has been witnessed, start a sector.
|
|
if(scanner[2] == data_prologue[2]) {
|
|
new_sector.reset(new Sector);
|
|
new_sector->data.reserve(412);
|
|
} else {
|
|
sector_location = static_cast<std::size_t>(bit % segment.data.size());
|
|
}
|
|
}
|
|
} else {
|
|
if(new_sector) {
|
|
// Check whether the value just read is a legal GCR byte, in six-and-two
|
|
// encoding (which is a strict superset of five-and-three).
|
|
if(unmap_six_and_two(value) == 0xff) {
|
|
// The second byte of the standard epilogue is illegal, so this still may
|
|
// be a valid sector. If the final byte was the first byte of an epilogue,
|
|
// chop it off and see whether the sector is otherwise intelligible.
|
|
|
|
if(new_sector->data.empty() || new_sector->data.back() != epilogue[0]) {
|
|
// No sector found; reset scanning procedure.
|
|
new_sector.reset();
|
|
pointer = scanning_sentinel;
|
|
continue;
|
|
}
|
|
|
|
// Chop off the last byte.
|
|
new_sector->data.resize(new_sector->data.size() - 1);
|
|
|
|
// Move the sector elsewhere for processing; there's definitely no way to proceed with
|
|
// the prospective sector if it doesn't parse.
|
|
std::unique_ptr<Sector> sector = std::move(new_sector);
|
|
new_sector.reset();
|
|
pointer = scanning_sentinel;
|
|
|
|
// Check for valid decoding options.
|
|
switch(sector->data.size()) {
|
|
default: // This is not a decodeable sector.
|
|
break;
|
|
|
|
// TODO: check for five-and-three / 13-sector form sectors.
|
|
|
|
case 343: { // Potentially this is an Apple II six-and-two sector.
|
|
// Check for apparent four and four encoding.
|
|
uint_fast8_t header_mask = 0xff;
|
|
for(auto c : header) header_mask &= c;
|
|
header_mask &= 0xaa;
|
|
if(header_mask != 0xaa) continue;
|
|
|
|
sector->address.volume = ((header[0] << 1) | 1) & header[1];
|
|
sector->address.track = ((header[2] << 1) | 1) & header[3];
|
|
sector->address.sector = ((header[4] << 1) | 1) & header[5];
|
|
|
|
// Check the header checksum.
|
|
uint_fast8_t checksum = ((header[6] << 1) | 1) & header[7];
|
|
if(checksum != (sector->address.volume^sector->address.track^sector->address.sector)) continue;
|
|
|
|
// Unmap the sector contents as 6 and 2 data.
|
|
bool out_of_bounds = false;
|
|
for(auto &c : sector->data) {
|
|
c = unmap_six_and_two(c);
|
|
if(c == 0xff) {
|
|
out_of_bounds = true;
|
|
break;
|
|
}
|
|
}
|
|
if(out_of_bounds) continue;
|
|
|
|
// Undo the XOR step on sector contents and check that checksum.
|
|
for(std::size_t c = 1; c < sector->data.size(); ++c) {
|
|
sector->data[c] ^= sector->data[c-1];
|
|
}
|
|
if(sector->data.back()) continue;
|
|
|
|
// Having checked the checksum, remove it.
|
|
sector->data.resize(sector->data.size() - 1);
|
|
|
|
// Undo the 6 and 2 mapping.
|
|
const uint8_t bit_reverse[] = {0, 2, 1, 3};
|
|
#define unmap(byte, nibble, shift) \
|
|
sector->data[86 + byte] = static_cast<uint8_t>(\
|
|
(sector->data[86 + byte] << 2) | bit_reverse[(sector->data[nibble] >> shift)&3]);
|
|
|
|
for(std::size_t c = 0; c < 84; ++c) {
|
|
unmap(c, c, 0);
|
|
unmap(c+86, c, 2);
|
|
unmap(c+172, c, 4);
|
|
}
|
|
|
|
unmap(84, 84, 0);
|
|
unmap(170, 84, 2);
|
|
unmap(85, 85, 0);
|
|
unmap(171, 85, 2);
|
|
|
|
#undef unmap
|
|
|
|
// Throw away the collection of two-bit chunks from the start of the sector.
|
|
sector->data.erase(sector->data.begin(), sector->data.end() - 256);
|
|
|
|
// Add this sector to the map.
|
|
sector->encoding = Sector::Encoding::SixAndTwo;
|
|
result.insert(std::make_pair(sector_location, std::move(*sector)));
|
|
} break;
|
|
|
|
case 704: { // Potentially this is a Macintosh sector.
|
|
// Attempt a six-and-two unmapping of the header.
|
|
std::array<uint_fast8_t, 5> decoded_header;
|
|
bool out_of_bounds = false;
|
|
for(size_t c = 0; c < decoded_header.size(); ++c) {
|
|
decoded_header[c] = unmap_six_and_two(header[c]);
|
|
if(decoded_header[c] == 0xff) {
|
|
out_of_bounds = true;
|
|
break;
|
|
}
|
|
}
|
|
if(out_of_bounds) continue;
|
|
|
|
// Test the checksum.
|
|
if(decoded_header[4] != (decoded_header[0] ^ decoded_header[1] ^ decoded_header[2] ^ decoded_header[3]))
|
|
sector->has_header_checksum_error = true;
|
|
|
|
// Decode the header.
|
|
sector->address.track = uint8_t(decoded_header[0] | ((decoded_header[2]&0x1f) << 6));
|
|
sector->address.sector = decoded_header[1];
|
|
sector->address.format = decoded_header[3];
|
|
sector->address.is_side_two = decoded_header[2] & 0x20;
|
|
|
|
// Reverse the GCR encoding of the sector contents to get back to 6-bit data.
|
|
for(auto &c: sector->data) {
|
|
c = unmap_six_and_two(c);
|
|
if(c == 0xff) {
|
|
out_of_bounds = true;
|
|
break;
|
|
}
|
|
}
|
|
if(out_of_bounds) continue;
|
|
|
|
// The first byte in the sector is a repeat of the sector number; test it
|
|
// for correctness.
|
|
if(sector->data[0] != sector->address.sector) continue;
|
|
|
|
// Cf. the corresponding section of Encoder.cpp for logic below.
|
|
int checksum[3] = {0, 0, 0};
|
|
for(size_t c = 0; c < 175; ++c) {
|
|
// Calculate the rolling checcksum in order to decode the bytes.
|
|
checksum[0] = (checksum[0] << 1) | (checksum[0] >> 7);
|
|
|
|
// All offsets are +1 below, to skip the initial sector number duplicate.
|
|
const uint8_t top_bits = sector->data[1 + c*4];
|
|
|
|
// Decode first byte.
|
|
sector->data[0 + c * 3] = uint8_t((sector->data[2 + c*4] + ((top_bits & 0x30) << 2)) ^ checksum[0]);
|
|
checksum[2] += sector->data[0 + c * 3] + (checksum[0] >> 8);
|
|
|
|
// Decode second byte;
|
|
sector->data[1 + c * 3] = uint8_t((sector->data[3 + c*4] + ((top_bits & 0x0c) << 4)) ^ checksum[2]);
|
|
checksum[1] += sector->data[1 + c * 3] + (checksum[2] >> 8);
|
|
|
|
// Decode third byte, if there is one.
|
|
if(c != 174) {
|
|
sector->data[2 + c * 3] = uint8_t((sector->data[4 + c*4] + ((top_bits & 0x03) << 6)) ^ checksum[1]);
|
|
checksum[0] += sector->data[2 + c * 3] + (checksum[1] >> 8);
|
|
}
|
|
|
|
// Reset carries.
|
|
checksum[0] &= 0xff;
|
|
checksum[1] &= 0xff;
|
|
checksum[2] &= 0xff;
|
|
}
|
|
|
|
// Test the checksum.
|
|
if(
|
|
checksum[0] != uint8_t(sector->data[703] + ((sector->data[700] & 0x03) << 6)) ||
|
|
checksum[1] != uint8_t(sector->data[702] + ((sector->data[700] & 0x0c) << 4)) ||
|
|
checksum[2] != uint8_t(sector->data[701] + ((sector->data[700] & 0x30) << 2))
|
|
) sector->has_data_checksum_error = true;
|
|
|
|
// Chop to size, and that's that.
|
|
sector->data.resize(524);
|
|
|
|
// Add this sector to the map.
|
|
sector->encoding = Sector::Encoding::Macintosh;
|
|
result.insert(std::make_pair(sector_location, std::move(*sector)));
|
|
} break;
|
|
}
|
|
} else {
|
|
new_sector->data.push_back(value);
|
|
}
|
|
} else {
|
|
// Just capture the header in place; it'll be decoded
|
|
// once a whole sector has been read.
|
|
header[pointer] = value;
|
|
++pointer;
|
|
if(pointer == 8) {
|
|
pointer = scanning_sentinel;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
return result;
|
|
}
|