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ce5fcaf172
These are used by formats like VGI since the ECC varied per machine and the 10 extra bytes of user data may contain useful information.
86 lines
2.3 KiB
C++
86 lines
2.3 KiB
C++
#include "globals.h"
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#include "fluxmap.h"
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#include "decoders/fluxmapreader.h"
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#include "decoders/decoders.h"
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#include "sector.h"
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#include "micropolis.h"
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#include "bytes.h"
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#include "fmt/format.h"
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#include "lib/decoders/decoders.pb.h"
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/* The sector has a preamble of MFM 0x00s and uses 0xFF as a sync pattern. */
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static const FluxPattern SECTOR_SYNC_PATTERN(32, 0xaaaa5555);
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/* Adds all bytes, with carry. */
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uint8_t micropolisChecksum(const Bytes& bytes) {
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ByteReader br(bytes);
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uint16_t sum = 0;
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while (!br.eof()) {
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if (sum > 0xFF) {
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sum -= 0x100 - 1;
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}
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sum += br.read_8();
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}
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/* The last carry is ignored */
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return sum & 0xFF;
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}
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class MicropolisDecoder : public AbstractDecoder
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{
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public:
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MicropolisDecoder(const DecoderProto& config):
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AbstractDecoder(config),
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_config(config.micropolis())
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{}
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RecordType advanceToNextRecord()
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{
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_fmr->seekToIndexMark();
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const FluxMatcher* matcher = nullptr;
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_sector->clock = _fmr->seekToPattern(SECTOR_SYNC_PATTERN, matcher);
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if (matcher == &SECTOR_SYNC_PATTERN) {
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readRawBits(16);
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return SECTOR_RECORD;
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}
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return UNKNOWN_RECORD;
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}
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void decodeSectorRecord()
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{
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auto rawbits = readRawBits(MICROPOLIS_ENCODED_SECTOR_SIZE*16);
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auto bytes = decodeFmMfm(rawbits).slice(0, MICROPOLIS_ENCODED_SECTOR_SIZE);
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ByteReader br(bytes);
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br.read_8(); /* sync */
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_sector->logicalTrack = br.read_8();
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_sector->logicalSide = _sector->physicalHead;
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_sector->logicalSector = br.read_8();
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if (_sector->logicalSector > 15)
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return;
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if (_sector->logicalTrack > 77)
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return;
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br.read(10); /* OS data or padding */
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auto data = br.read(256);
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uint8_t wantChecksum = br.read_8();
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uint8_t gotChecksum = micropolisChecksum(bytes.slice(1, 2+266));
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br.read(5); /* 4 byte ECC and ECC-present flag */
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if (_config.sector_output_size() == 256)
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_sector->data = data;
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else if (_config.sector_output_size() == MICROPOLIS_ENCODED_SECTOR_SIZE)
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_sector->data = bytes;
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else
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Error() << "Sector output size may only be 256 or 275";
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_sector->status = (wantChecksum == gotChecksum) ? Sector::OK : Sector::BAD_CHECKSUM;
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}
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private:
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const MicropolisDecoderProto& _config;
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};
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std::unique_ptr<AbstractDecoder> createMicropolisDecoder(const DecoderProto& config)
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{
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return std::unique_ptr<AbstractDecoder>(new MicropolisDecoder(config));
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}
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