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88 lines
3.0 KiB
C++
88 lines
3.0 KiB
C++
#include "globals.h"
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#include "decoders/decoders.h"
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#include "encoders/encoders.h"
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#include "tids990/tids990.h"
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#include "crc.h"
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#include "fluxmap.h"
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#include "decoders/fluxmapreader.h"
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#include "sector.h"
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#include "record.h"
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#include "track.h"
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#include <string.h>
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#include <fmt/format.h>
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/* The Texas Instruments DS990 uses MFM with a scheme similar to a simplified
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* version of the IBM record scheme (it's actually easier to parse than IBM).
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* There are 26 sectors per track, each holding a rather weird 288 bytes.
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*/
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/*
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* Sector record:
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* data: 0 1 0 1 0 1 0 1 .0 0 0 0 1 0 1 0 = 0x550a
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* mfm: 00 01 00 01 00 01 00 01.00 10 10 10 01 00 01 00 = 0x11112a44
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* special: 00 01 00 01 00 01 00 01.00 10 00 10 01 00 01 00 = 0x11112244
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* ^^
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* When shifted out of phase, the special 0xa1 byte becomes an illegal
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* encoding (you can't do 10 00). So this can't be spoofed by user data.
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*/
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const FluxPattern SECTOR_RECORD_PATTERN(32, 0x11112244);
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/*
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* Data record:
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* data: 0 1 0 1 0 1 0 1 .0 0 0 0 1 0 1 1 = 0x550c
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* mfm: 00 01 00 01 00 01 00 01.00 10 10 10 01 00 01 01 = 0x11112a45
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* special: 00 01 00 01 00 01 00 01.00 10 00 10 01 00 01 01 = 0x11112245
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* ^^
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* When shifted out of phase, the special 0xa1 byte becomes an illegal
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* encoding (you can't do 10 00). So this can't be spoofed by user data.
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*/
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const FluxPattern DATA_RECORD_PATTERN(32, 0x11112245);
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const FluxMatchers ANY_RECORD_PATTERN({ &SECTOR_RECORD_PATTERN, &DATA_RECORD_PATTERN });
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AbstractDecoder::RecordType Tids990Decoder::advanceToNextRecord()
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{
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const FluxMatcher* matcher = nullptr;
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_sector->clock = _fmr->seekToPattern(ANY_RECORD_PATTERN, matcher);
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if (matcher == &SECTOR_RECORD_PATTERN)
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return RecordType::SECTOR_RECORD;
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if (matcher == &DATA_RECORD_PATTERN)
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return RecordType::DATA_RECORD;
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return RecordType::UNKNOWN_RECORD;
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}
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void Tids990Decoder::decodeSectorRecord()
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{
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auto bits = readRawBits(TIDS990_SECTOR_RECORD_SIZE*16);
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auto bytes = decodeFmMfm(bits).slice(0, TIDS990_SECTOR_RECORD_SIZE);
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ByteReader br(bytes);
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uint16_t gotChecksum = crc16(CCITT_POLY, bytes.slice(1, TIDS990_SECTOR_RECORD_SIZE-3));
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br.seek(2);
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_sector->logicalSide = br.read_8() >> 3;
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_sector->logicalTrack = br.read_8();
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br.read_8(); /* number of sectors per track */
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_sector->logicalSector = br.read_8();
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br.read_be16(); /* sector size */
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uint16_t wantChecksum = br.read_be16();
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if (wantChecksum == gotChecksum)
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_sector->status = Sector::DATA_MISSING; /* correct but unintuitive */
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}
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void Tids990Decoder::decodeDataRecord()
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{
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auto bits = readRawBits(TIDS990_DATA_RECORD_SIZE*16);
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auto bytes = decodeFmMfm(bits).slice(0, TIDS990_DATA_RECORD_SIZE);
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ByteReader br(bytes);
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uint16_t gotChecksum = crc16(CCITT_POLY, bytes.slice(1, TIDS990_DATA_RECORD_SIZE-3));
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br.seek(2);
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_sector->data = br.read(TIDS990_PAYLOAD_SIZE);
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uint16_t wantChecksum = br.read_be16();
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_sector->status = (wantChecksum == gotChecksum) ? Sector::OK : Sector::BAD_CHECKSUM;
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}
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