mirror of
https://github.com/davidgiven/fluxengine.git
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95 lines
2.9 KiB
C++
95 lines
2.9 KiB
C++
#include "globals.h"
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#include "fluxmap.h"
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#include "fluxmapreader.h"
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#include "protocol.h"
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#include "record.h"
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#include "decoders.h"
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#include "sector.h"
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#include "amiga.h"
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#include "bytes.h"
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#include "fmt/format.h"
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#include <string.h>
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#include <algorithm>
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/*
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* Amiga disks use MFM but it's not quite the same as IBM MFM. They only use
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* a single type of record with a different marker byte.
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*
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* See the big comment in the IBM MFM decoder for the gruesome details of how
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* MFM works.
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*/
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static const FluxPattern SECTOR_PATTERN(48, AMIGA_SECTOR_RECORD);
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static Bytes deinterleave(const uint8_t*& input, size_t len)
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{
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assert(!(len & 1));
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const uint8_t* odds = &input[0];
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const uint8_t* evens = &input[len/2];
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Bytes output;
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ByteWriter bw(output);
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for (size_t i=0; i<len/2; i++)
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{
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uint8_t o = *odds++;
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uint8_t e = *evens++;
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/* This is the 'Interleave bits with 64-bit multiply' technique from
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* http://graphics.stanford.edu/~seander/bithacks.html#InterleaveBMN
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*/
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uint16_t result =
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(((e * 0x0101010101010101ULL & 0x8040201008040201ULL)
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* 0x0102040810204081ULL >> 49) & 0x5555) |
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(((o * 0x0101010101010101ULL & 0x8040201008040201ULL)
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* 0x0102040810204081ULL >> 48) & 0xAAAA);
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bw.write_be16(result);
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}
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input += len;
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return output;
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}
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static uint32_t checksum(const Bytes& bytes)
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{
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ByteReader br(bytes);
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uint32_t checksum = 0;
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assert((bytes.size() & 3) == 0);
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while (!br.eof())
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checksum ^= br.read_be32();
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return checksum & 0x55555555;
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}
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nanoseconds_t AmigaDecoder::findSector(FluxmapReader& fmr, Track& track)
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{
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return fmr.seekToPattern(SECTOR_PATTERN);
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}
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void AmigaDecoder::decodeSingleSector(FluxmapReader& fmr, Track& track, Sector& sector)
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{
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const auto& rawbits = fmr.readRawBits(AMIGA_RECORD_SIZE*16, sector.clock);
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const auto& rawbytes = toBytes(rawbits).slice(0, AMIGA_RECORD_SIZE*2);
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const auto& bytes = decodeFmMfm(rawbits).slice(0, AMIGA_RECORD_SIZE);
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const uint8_t* ptr = bytes.begin() + 3;
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Bytes header = deinterleave(ptr, 4);
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Bytes recoveryinfo = deinterleave(ptr, 16);
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sector.logicalTrack = header[1] >> 1;
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sector.logicalSide = header[1] & 1;
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sector.logicalSector = header[2];
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uint32_t wantedheaderchecksum = deinterleave(ptr, 4).reader().read_be32();
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uint32_t gotheaderchecksum = checksum(rawbytes.slice(6, 40));
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if (gotheaderchecksum != wantedheaderchecksum)
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return;
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uint32_t wanteddatachecksum = deinterleave(ptr, 4).reader().read_be32();
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uint32_t gotdatachecksum = checksum(rawbytes.slice(62, 1024));
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sector.data = deinterleave(ptr, 512);
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sector.status = (gotdatachecksum == wanteddatachecksum) ? Sector::OK : Sector::BAD_CHECKSUM;
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}
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