86Box/src/floppy/fdd_mfm.c

/*
 * 86Box    A hypervisor and IBM PC system emulator that specializes in
 *          running old operating systems and software designed for IBM
 *          PC systems and compatibles from 1981 through fairly recent
 *          system designs based on the PCI bus.
 *
 *          This file is part of the 86Box distribution.
 *
 *          Implementation of the HxC MFM image format.
 *
 *
 *
 * Authors: Miran Grca, <mgrca8@gmail.com>
 *
 *          Copyright 2018-2019 Miran Grca.
 */
#include <math.h>
#include <stdarg.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <wchar.h>
#define HAVE_STDARG_H
#include <86box/86box.h>
#include <86box/timer.h>
#include <86box/plat.h>
#include <86box/fdd.h>
#include <86box/fdd_86f.h>
#include <86box/fdd_img.h>
#include <86box/fdd_mfm.h>
#include <86box/fdc.h>

#pragma pack(push, 1)
typedef struct {
    uint8_t hdr_name[7];

    uint16_t tracks_no;
    uint8_t  sides_no;

    uint16_t rpm;
    uint16_t bit_rate;
    uint8_t  if_type;

    uint32_t track_list_offset;
} mfm_header_t;

typedef struct {
    uint16_t track_no;
    uint8_t  side_no;
    uint32_t track_size;
    uint32_t track_offset;
} mfm_track_t;

typedef struct {
    uint16_t track_no;
    uint8_t  side_no;
    uint16_t rpm;
    uint16_t bit_rate;
    uint32_t track_size;
    uint32_t track_offset;
} mfm_adv_track_t;
#pragma pack(pop)

typedef struct {
    FILE *f;

    mfm_header_t     hdr;
    mfm_track_t     *tracks;
    mfm_adv_track_t *adv_tracks;

    uint16_t disk_flags, pad;
    uint16_t side_flags[2];

    int br_rounded, rpm_rounded,
        total_tracks, cur_track;

    uint8_t track_data[2][256 * 1024];
} mfm_t;

static mfm_t *mfm[FDD_NUM];
static fdc_t *mfm_fdc;

#ifdef ENABLE_MFM_LOG
int mfm_do_log = ENABLE_MFM_LOG;

static void
mfm_log(const char *fmt, ...)
{
    va_list ap;

    if (mfm_do_log) {
        va_start(ap, fmt);
        pclog_ex(fmt, ap);
        va_end(ap);
    }
}
#else
#    define mfm_log(fmt, ...)
#endif

static int
get_track_index(int drive, int side, int track)
{
    mfm_t *dev = mfm[drive];
    int    i, ret = -1;

    for (i = 0; i < dev->total_tracks; i++) {
        if ((dev->tracks[i].track_no == track) && (dev->tracks[i].side_no == side)) {
            ret = i;
            break;
        }
    }

    return ret;
}

static int
get_adv_track_index(int drive, int side, int track)
{
    mfm_t *dev = mfm[drive];
    int    i, ret = -1;

    for (i = 0; i < dev->total_tracks; i++) {
        if ((dev->adv_tracks[i].track_no == track) && (dev->adv_tracks[i].side_no == side)) {
            ret = i;
            break;
        }
    }

    return ret;
}

static void
get_adv_track_bitrate(int drive, int side, int track, int *br, int *rpm)
{
    mfm_t *dev = mfm[drive];
    int    track_index;
    double dbr;

    track_index = get_adv_track_index(drive, side, track);

    if (track_index == -1) {
        *br  = 250;
        *rpm = 300;
    } else {
        dbr  = round(((double) dev->adv_tracks[track_index].bit_rate) / 50.0) * 50.0;
        *br  = ((int) dbr);
        dbr  = round(((double) dev->adv_tracks[track_index].rpm) / 60.0) * 60.0;
        *rpm = ((int) dbr);
    }
}

static void
set_disk_flags(int drive)
{
    int      br = 250, rpm = 300;
    mfm_t   *dev             = mfm[drive];
    uint16_t temp_disk_flags = 0x1080; /* We ALWAYS claim to have extra bit cells, even if the actual amount is 0;
                                          Bit 12 = 1, bits 6, 5 = 0 - extra bit cells field specifies the entire
                                          amount of bit cells per track. */

    /* If this is the modified MFM format, get bit rate (and RPM) from track 0 instead. */
    if (dev->hdr.if_type & 0x80)
        get_adv_track_bitrate(drive, 0, 0, &br, &rpm);
    else {
        br  = dev->br_rounded;
        rpm = dev->rpm_rounded;
    }

    switch (br) {
        case 500:
            temp_disk_flags |= 2;
            break;

        case 300:
        case 250:
        default:
            temp_disk_flags |= 0;
            break;

        case 1000:
            temp_disk_flags |= 4;
            break;
    }

    if (dev->hdr.sides_no == 2)
        temp_disk_flags |= 8;

    dev->disk_flags = temp_disk_flags;
}

static uint16_t
disk_flags(int drive)
{
    mfm_t *dev = mfm[drive];

    return dev->disk_flags;
}

static void
set_side_flags(int drive, int side)
{
    mfm_t   *dev             = mfm[drive];
    uint16_t temp_side_flags = 0;
    int      br = 250, rpm = 300;

    if (dev->hdr.if_type & 0x80)
        get_adv_track_bitrate(drive, side, dev->cur_track, &br, &rpm);
    else {
        br  = dev->br_rounded;
        rpm = dev->rpm_rounded;
    }

    /* 300 kbps @ 360 rpm = 250 kbps @ 200 rpm */
    if ((br == 300) && (rpm == 360)) {
        br  = 250;
        rpm = 300;
    }

    switch (br) {
        case 500:
            temp_side_flags = 0;
            break;

        case 300:
            temp_side_flags = 1;
            break;

        case 250:
        default:
            temp_side_flags = 2;
            break;

        case 1000:
            temp_side_flags = 3;
            break;
    }

    if (rpm == 360)
        temp_side_flags |= 0x20;

    /*
     * Set the encoding value to match that provided by the FDC.
     * Then if it's wrong, it will sector not found anyway.
     */
    temp_side_flags |= 0x08;

    dev->side_flags[side] = temp_side_flags;
}

static uint16_t
side_flags(int drive)
{
    mfm_t *dev = mfm[drive];
    int    side;

    side = fdd_get_head(drive);

    return dev->side_flags[side];
}

static uint32_t
get_raw_size(int drive, int side)
{
    mfm_t *dev = mfm[drive];
    int    track_index, is_300_rpm;
    int    br = 250, rpm = 300;

    if (dev->hdr.if_type & 0x80) {
        track_index = get_adv_track_index(drive, side, dev->cur_track);
        get_adv_track_bitrate(drive, 0, 0, &br, &rpm);
    } else {
        track_index = get_track_index(drive, side, dev->cur_track);
        br          = dev->br_rounded;
        rpm         = dev->rpm_rounded;
    }

    is_300_rpm = (rpm == 300);

    if (track_index == -1) {
        mfm_log("MFM: Unable to find track (%i, %i)\n", dev->cur_track, side);
        switch (br) {
            case 250:
            default:
                return is_300_rpm ? 100000 : 83333;
            case 300:
                return is_300_rpm ? 120000 : 100000;
            case 500:
                return is_300_rpm ? 200000 : 166666;
            case 1000:
                return is_300_rpm ? 400000 : 333333;
        }
    }

    /* Bit 7 on - my extension of the HxC MFM format to output exact bitcell counts
       for each track instead of rounded byte counts. */
    if (dev->hdr.if_type & 0x80)
        return dev->adv_tracks[track_index].track_size;
    else
        return dev->tracks[track_index].track_size * 8;
}

static int32_t
extra_bit_cells(int drive, int side)
{
    return (int32_t) get_raw_size(drive, side);
}

static uint16_t *
encoded_data(int drive, int side)
{
    mfm_t *dev = mfm[drive];

    return ((uint16_t *) dev->track_data[side]);
}

void
mfm_read_side(int drive, int side)
{
    mfm_t *dev = mfm[drive];
    int    track_index, track_size;
    int    track_bytes, ret;

    if (dev->hdr.if_type & 0x80)
        track_index = get_adv_track_index(drive, side, dev->cur_track);
    else
        track_index = get_track_index(drive, side, dev->cur_track);

    track_size  = get_raw_size(drive, side);
    track_bytes = track_size >> 3;
    if (track_size & 0x07)
        track_bytes++;

    if (track_index == -1)
        memset(dev->track_data[side], 0x00, track_bytes);
    else {
        if (dev->hdr.if_type & 0x80)
            ret = fseek(dev->f, dev->adv_tracks[track_index].track_offset, SEEK_SET);
        else
            ret = fseek(dev->f, dev->tracks[track_index].track_offset, SEEK_SET);
        if (ret == -1)
            fatal("mfm_read_side(): Error seeking to the beginning of the file\n");
        if (fread(dev->track_data[side], 1, track_bytes, dev->f) != track_bytes)
            fatal("mfm_read_side(): Error reading track bytes\n");
    }

    mfm_log("drive = %i, side = %i, dev->cur_track = %i, track_index = %i, track_size = %i\n",
            drive, side, dev->cur_track, track_index, track_size);
}

void
mfm_seek(int drive, int track)
{
    mfm_t *dev = mfm[drive];

    mfm_log("mfm_seek(%i, %i)\n", drive, track);

    if (fdd_doublestep_40(drive)) {
        if (dev->hdr.tracks_no <= 43)
            track /= 2;
    }

    dev->cur_track = track;
    d86f_set_cur_track(drive, track);

    if (dev->f == NULL)
        return;

    if (track < 0)
        track = 0;

    mfm_read_side(drive, 0);
    mfm_read_side(drive, 1);

    set_side_flags(drive, 0);
    set_side_flags(drive, 1);
}

void
mfm_load(int drive, char *fn)
{
    mfm_t *dev;
    double dbr;
    int    i, size;

    writeprot[drive] = fwriteprot[drive] = 1;

    /* Allocate a drive block. */
    dev = (mfm_t *) malloc(sizeof(mfm_t));
    memset(dev, 0x00, sizeof(mfm_t));

    dev->f = plat_fopen(fn, "rb");
    if (dev->f == NULL) {
        free(dev);
        memset(floppyfns[drive], 0, sizeof(floppyfns[drive]));
        return;
    }

    d86f_unregister(drive);

    /* Read the header. */
    size = sizeof(mfm_header_t);
    if (fread(&dev->hdr, 1, size, dev->f) != size)
        fatal("mfm_load(): Error reading header\n");

    /* Calculate tracks * sides, allocate the tracks array, and read it. */
    dev->total_tracks = dev->hdr.tracks_no * dev->hdr.sides_no;
    if (dev->hdr.if_type & 0x80) {
        dev->adv_tracks = (mfm_adv_track_t *) malloc(dev->total_tracks * sizeof(mfm_adv_track_t));
        size            = dev->total_tracks * sizeof(mfm_adv_track_t);
        if (fread(dev->adv_tracks, 1, size, dev->f) != size)
            fatal("mfm_load(): Error reading advanced tracks\n");
    } else {
        dev->tracks = (mfm_track_t *) malloc(dev->total_tracks * sizeof(mfm_track_t));
        size        = dev->total_tracks * sizeof(mfm_track_t);
        if (fread(dev->tracks, 1, size, dev->f) != size)
            fatal("mfm_load(): Error reading tracks\n");
    }

    /* The chances of finding a HxC MFM image of a single-sided thin track
       disk are much smaller than the chances of finding a HxC MFM image
       incorrectly converted from a SCP image, erroneously indicating 1
       side and 80+ tracks instead of 2 sides and <= 43 tracks, so if we
       have detected such an image, convert the track numbers. */
    if ((dev->hdr.tracks_no > 43) && (dev->hdr.sides_no == 1)) {
        dev->hdr.tracks_no >>= 1;
        dev->hdr.sides_no <<= 1;

        for (i = 0; i < dev->total_tracks; i++) {
            if (dev->hdr.if_type & 0x80) {
                dev->adv_tracks[i].side_no <<= 1;
                dev->adv_tracks[i].side_no |= (dev->adv_tracks[i].track_no & 1);
                dev->adv_tracks[i].track_no >>= 1;
            } else {
                dev->tracks[i].side_no <<= 1;
                dev->tracks[i].side_no |= (dev->tracks[i].track_no & 1);
                dev->tracks[i].track_no >>= 1;
            }
        }
    }

    if (!(dev->hdr.if_type & 0x80)) {
        dbr             = round(((double) dev->hdr.bit_rate) / 50.0) * 50.0;
        dev->br_rounded = (int) dbr;
        mfm_log("Rounded bit rate: %i kbps\n", dev->br_rounded);

        dbr              = round(((double) dev->hdr.rpm) / 60.0) * 60.0;
        dev->rpm_rounded = (int) dbr;
        mfm_log("Rounded RPM: %i kbps\n", dev->rpm_rounded);
    }

    /* Set up the drive unit. */
    mfm[drive] = dev;

    set_disk_flags(drive);

    /* Attach this format to the D86F engine. */
    d86f_handler[drive].disk_flags        = disk_flags;
    d86f_handler[drive].side_flags        = side_flags;
    d86f_handler[drive].writeback         = null_writeback;
    d86f_handler[drive].set_sector        = null_set_sector;
    d86f_handler[drive].write_data        = null_write_data;
    d86f_handler[drive].format_conditions = null_format_conditions;
    d86f_handler[drive].extra_bit_cells   = extra_bit_cells;
    d86f_handler[drive].encoded_data      = encoded_data;
    d86f_handler[drive].read_revolution   = common_read_revolution;
    d86f_handler[drive].index_hole_pos    = null_index_hole_pos;
    d86f_handler[drive].get_raw_size      = get_raw_size;
    d86f_handler[drive].check_crc         = 1;
    d86f_set_version(drive, D86FVER);

    d86f_common_handlers(drive);

    drives[drive].seek = mfm_seek;

    mfm_log("Loaded as MFM\n");
}

void
mfm_close(int drive)
{
    mfm_t *dev = mfm[drive];

    if (dev == NULL)
        return;

    d86f_unregister(drive);

    drives[drive].seek = NULL;

    if (dev->tracks)
        free(dev->tracks);

    if (dev->adv_tracks)
        free(dev->adv_tracks);

    if (dev->f)
        fclose(dev->f);

    /* Release the memory. */
    free(dev);
    mfm[drive] = NULL;
}

void
mfm_set_fdc(void *fdc)
{
    mfm_fdc = (fdc_t *) fdc;
}