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https://github.com/davidgiven/fluxengine.git
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127 lines
3.4 KiB
C++
127 lines
3.4 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 "protocol.h"
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#include "decoders/decoders.h"
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#include "sector.h"
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#include "apple2.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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const FluxPattern SECTOR_RECORD_PATTERN(24, APPLE2_SECTOR_RECORD);
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const FluxPattern DATA_RECORD_PATTERN(24, APPLE2_DATA_RECORD);
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const FluxMatchers ANY_RECORD_PATTERN({ &SECTOR_RECORD_PATTERN, &DATA_RECORD_PATTERN });
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static int decode_data_gcr(uint8_t gcr)
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{
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switch (gcr)
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{
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#define GCR_ENTRY(gcr, data) \
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case gcr: return data;
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#include "data_gcr.h"
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#undef GCR_ENTRY
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}
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return -1;
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}
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/* This is extremely inspired by the MESS implementation, written by Nathan Woods
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* and R. Belmont: https://github.com/mamedev/mame/blob/7914a6083a3b3a8c243ae6c3b8cb50b023f21e0e/src/lib/formats/ap2_dsk.cpp
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*/
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static Bytes decode_crazy_data(const uint8_t* inp, Sector::Status& status)
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{
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Bytes output(APPLE2_SECTOR_LENGTH);
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uint8_t checksum = 0;
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for (unsigned i = 0; i < APPLE2_ENCODED_SECTOR_LENGTH; i++)
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{
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checksum ^= decode_data_gcr(*inp++);
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if (i >= 86)
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{
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/* 6 bit */
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output[i - 86] |= (checksum << 2);
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}
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else
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{
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/* 3 * 2 bit */
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output[i + 0] = ((checksum >> 1) & 0x01) | ((checksum << 1) & 0x02);
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output[i + 86] = ((checksum >> 3) & 0x01) | ((checksum >> 1) & 0x02);
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if ((i + 172) < APPLE2_SECTOR_LENGTH)
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output[i + 172] = ((checksum >> 5) & 0x01) | ((checksum >> 3) & 0x02);
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}
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}
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checksum &= 0x3f;
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uint8_t wantedchecksum = decode_data_gcr(*inp);
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status = (checksum == wantedchecksum) ? Sector::OK : Sector::BAD_CHECKSUM;
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return output;
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}
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static uint8_t combine(uint16_t word)
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{
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return word & (word >> 7);
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}
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class Apple2Decoder : public AbstractDecoder
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{
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public:
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Apple2Decoder(const DecoderProto& config):
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AbstractDecoder(config)
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{}
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RecordType advanceToNextRecord()
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{
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const FluxMatcher* matcher = nullptr;
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_sector->clock = _sector->bitcell = _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 decodeSectorRecord()
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{
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/* Skip ID (as we know it's a APPLE2_SECTOR_RECORD). */
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readRawBits(24);
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/* Read header. */
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auto header = toBytes(readRawBits(8*8)).slice(0, 8);
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ByteReader br(header);
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uint8_t volume = combine(br.read_be16());
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_sector->logicalTrack = combine(br.read_be16());
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_sector->logicalSector = combine(br.read_be16());
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uint8_t checksum = combine(br.read_be16());
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if (checksum == (volume ^ _sector->logicalTrack ^ _sector->logicalSector))
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_sector->status = Sector::DATA_MISSING; /* unintuitive but correct */
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}
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void decodeDataRecord()
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{
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/* Check ID. */
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Bytes bytes = toBytes(readRawBits(3*8)).slice(0, 3);
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if (bytes.reader().read_be24() != APPLE2_DATA_RECORD)
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return;
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/* Read and decode data. */
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unsigned recordLength = APPLE2_ENCODED_SECTOR_LENGTH + 2;
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bytes = toBytes(readRawBits(recordLength*8)).slice(0, recordLength);
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_sector->status = Sector::BAD_CHECKSUM;
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_sector->data = decode_crazy_data(&bytes[0], _sector->status);
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}
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};
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std::unique_ptr<AbstractDecoder> createApple2Decoder(const DecoderProto& config)
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{
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return std::unique_ptr<AbstractDecoder>(new Apple2Decoder(config));
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}
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