fluxengine/arch/amiga/encoder.cc

#include "lib/globals.h"
#include "lib/decoders/decoders.h"
#include "lib/encoders/encoders.h"
#include "amiga.h"
#include "lib/crc.h"
#include "lib/readerwriter.h"
#include "lib/image.h"
#include "arch/amiga/amiga.pb.h"
#include "lib/encoders/encoders.pb.h"

static bool lastBit;

static int charToInt(char c)
{
    if (isdigit(c))
        return c - '0';
    return 10 + tolower(c) - 'a';
}

static void write_bits(
    std::vector<bool>& bits, unsigned& cursor, const std::vector<bool>& src)
{
    for (bool bit : src)
    {
        if (cursor < bits.size())
            lastBit = bits[cursor++] = bit;
    }
}

static void write_bits(
    std::vector<bool>& bits, unsigned& cursor, uint64_t data, int width)
{
    cursor += width;
    lastBit = data & 1;
    for (int i = 0; i < width; i++)
    {
        unsigned pos = cursor - i - 1;
        if (pos < bits.size())
            bits[pos] = data & 1;
        data >>= 1;
    }
}

static void write_bits(
    std::vector<bool>& bits, unsigned& cursor, const Bytes& bytes)
{
    ByteReader br(bytes);
    BitReader bitr(br);

    while (!bitr.eof())
    {
        if (cursor < bits.size())
            bits[cursor++] = bitr.get();
    }
}

static void write_sector(std::vector<bool>& bits,
    unsigned& cursor,
    const std::shared_ptr<const Sector>& sector)
{
    if ((sector->data.size() != 512) && (sector->data.size() != 528))
        error("unsupported sector size --- you must pick 512 or 528");

    uint32_t checksum = 0;

    auto write_interleaved_bytes = [&](const Bytes& bytes)
    {
        Bytes interleaved = amigaInterleave(bytes);
        Bytes mfm = encodeMfm(interleaved, lastBit);
        checksum ^= amigaChecksum(mfm);
        checksum &= 0x55555555;
        write_bits(bits, cursor, mfm);
    };

    auto write_interleaved_word = [&](uint32_t word)
    {
        Bytes b(4);
        b.writer().write_be32(word);
        write_interleaved_bytes(b);
    };

    write_bits(bits, cursor, 0xaaaa, 2 * 8);
    write_bits(bits, cursor, AMIGA_SECTOR_RECORD, 6 * 8);

    checksum = 0;
    Bytes header = {0xff, /* Amiga 1.0 format byte */
        (uint8_t)((sector->logicalTrack << 1) | sector->logicalSide),
        (uint8_t)sector->logicalSector,
        (uint8_t)(AMIGA_SECTORS_PER_TRACK - sector->logicalSector)};
    write_interleaved_bytes(header);
    Bytes recoveryInfo(16);
    if (sector->data.size() == 528)
        recoveryInfo = sector->data.slice(512, 16);
    write_interleaved_bytes(recoveryInfo);
    write_interleaved_word(checksum);

    Bytes data = sector->data.slice(0, 512);
    write_interleaved_word(
        amigaChecksum(encodeMfm(amigaInterleave(data), lastBit)));
    write_interleaved_bytes(data);
}

class AmigaEncoder : public Encoder
{
public:
    AmigaEncoder(const EncoderProto& config):
        Encoder(config),
        _config(config.amiga())
    {
    }

public:
    std::unique_ptr<Fluxmap> encode(std::shared_ptr<const TrackInfo>& trackInfo,
        const std::vector<std::shared_ptr<const Sector>>& sectors,
        const Image& image) override
    {
        /* Number of bits for one nominal revolution of a real 200ms Amiga disk.
         */
        int bitsPerRevolution = 200e3 / _config.clock_rate_us();
        std::vector<bool> bits(bitsPerRevolution);
        unsigned cursor = 0;

        fillBitmapTo(bits,
            cursor,
            _config.post_index_gap_ms() * 1000 / _config.clock_rate_us(),
            {true, false});
        lastBit = false;

        for (const auto& sector : sectors)
            write_sector(bits, cursor, sector);

        if (cursor >= bits.size())
            error("track data overrun");
        fillBitmapTo(bits, cursor, bits.size(), {true, false});

        auto fluxmap = std::make_unique<Fluxmap>();
        fluxmap->appendBits(bits,
            calculatePhysicalClockPeriod(_config.clock_rate_us() * 1e3, 200e6));
        return fluxmap;
    }

private:
    const AmigaEncoderProto& _config;
};

std::unique_ptr<Encoder> createAmigaEncoder(const EncoderProto& config)
{
    return std::unique_ptr<Encoder>(new AmigaEncoder(config));
}