fluxengine/arch/northstar/encoder.cc

#include "lib/core/globals.h"
#include "arch/northstar/northstar.h"
#include "lib/data/sector.h"
#include "lib/core/bytes.h"
#include "lib/decoders/decoders.h"
#include "lib/encoders/encoders.h"
#include "lib/data/image.h"
#include "lib/encoders/encoders.pb.h"

#define GAP_FILL_SIZE_SD 30
#define PRE_HEADER_GAP_FILL_SIZE_SD 9
#define GAP_FILL_SIZE_DD 62
#define PRE_HEADER_GAP_FILL_SIZE_DD 16

#define GAP1_FILL_BYTE (0x4F)
#define GAP2_FILL_BYTE (0x4F)

#define TOTAL_SECTOR_BYTES ()

static void write_sector(std::vector<bool>& bits,
    unsigned& cursor,
    const std::shared_ptr<const Sector>& sector)
{
    int preambleSize = 0;
    int encodedSectorSize = 0;
    int gapFillSize = 0;
    int preHeaderGapFillSize = 0;

    bool doubleDensity;

    switch (sector->data.size())
    {
        case NORTHSTAR_PAYLOAD_SIZE_SD:
            preambleSize = NORTHSTAR_PREAMBLE_SIZE_SD;
            encodedSectorSize = PRE_HEADER_GAP_FILL_SIZE_SD +
                                NORTHSTAR_ENCODED_SECTOR_SIZE_SD +
                                GAP_FILL_SIZE_SD;
            gapFillSize = GAP_FILL_SIZE_SD;
            preHeaderGapFillSize = PRE_HEADER_GAP_FILL_SIZE_SD;
            doubleDensity = false;
            break;
        case NORTHSTAR_PAYLOAD_SIZE_DD:
            preambleSize = NORTHSTAR_PREAMBLE_SIZE_DD;
            encodedSectorSize = PRE_HEADER_GAP_FILL_SIZE_DD +
                                NORTHSTAR_ENCODED_SECTOR_SIZE_DD +
                                GAP_FILL_SIZE_DD;
            gapFillSize = GAP_FILL_SIZE_DD;
            preHeaderGapFillSize = PRE_HEADER_GAP_FILL_SIZE_DD;
            doubleDensity = true;
            break;
        default:
            error("unsupported sector size --- you must pick 256 or 512");
            break;
    }

    int fullSectorSize = preambleSize + encodedSectorSize;
    auto fullSector = std::make_shared<std::vector<uint8_t>>();
    fullSector->reserve(fullSectorSize);

    /* sector gap after index pulse */
    for (int i = 0; i < preHeaderGapFillSize; i++)
        fullSector->push_back(GAP1_FILL_BYTE);

    /* sector preamble */
    for (int i = 0; i < preambleSize; i++)
        fullSector->push_back(0);

    Bytes sectorData;
    if (sector->data.size() == encodedSectorSize)
        sectorData = sector->data;
    else
    {
        ByteWriter writer(sectorData);
        writer.write_8(0xFB); /* sync character */
        if (doubleDensity == true)
        {
            writer.write_8(0xFB); /* Double-density has two sync characters */
        }
        writer += sector->data;
        if (doubleDensity == true)
        {
            writer.write_8(northstarChecksum(sectorData.slice(2)));
        }
        else
        {
            writer.write_8(northstarChecksum(sectorData.slice(1)));
        }
    }
    for (uint8_t b : sectorData)
        fullSector->push_back(b);

    if (sector->logicalSector != 9)
    {
        /* sector postamble */
        for (int i = 0; i < gapFillSize; i++)
            fullSector->push_back(GAP2_FILL_BYTE);

        if (fullSector->size() != fullSectorSize)
            error("sector mismatched length ({}); expected {}, got {}",
                sector->data.size(),
                fullSector->size(),
                fullSectorSize);
    }
    else
    {
        /* sector postamble */
        for (int i = 0; i < gapFillSize; i++)
            fullSector->push_back(GAP2_FILL_BYTE);
    }

    bool lastBit = false;

    if (doubleDensity == true)
    {
        encodeMfm(bits, cursor, fullSector, lastBit);
    }
    else
    {
        encodeFm(bits, cursor, fullSector);
    }
}

class NorthstarEncoder : public Encoder
{
public:
    NorthstarEncoder(const EncoderProto& config):
        Encoder(config),
        _config(config.northstar())
    {
    }

    std::unique_ptr<Fluxmap> encode(std::shared_ptr<const TrackInfo>& trackInfo,
        const std::vector<std::shared_ptr<const Sector>>& sectors,
        const Image& image) override
    {
        int bitsPerRevolution = 100000;
        double clockRateUs = _config.clock_period_us();

        const auto& sector = *sectors.begin();
        if (sector->data.size() == NORTHSTAR_PAYLOAD_SIZE_SD)
            bitsPerRevolution /= 2; // FM
        else
            clockRateUs /= 2.00;

        std::vector<bool> bits(bitsPerRevolution);
        unsigned cursor = 0;

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

        if (cursor > bits.size())
            error("track data overrun");

        std::unique_ptr<Fluxmap> fluxmap(new Fluxmap);
        fluxmap->appendBits(bits,
            calculatePhysicalClockPeriod(
                clockRateUs * 1e3, _config.rotational_period_ms() * 1e6));
        return fluxmap;
    }

private:
    const NorthstarEncoderProto& _config;
};

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