erc-c/include/apple2.dd.h

#ifndef _APPLE2_DISK_DRIVE_H
#define _APPLE2_DISK_DRIVE_H

#include <stdbool.h>
#include <stdio.h>
#include <sys/stat.h>

#include "vm_bits.h"
#include "vm_segment.h"

/*
 * These are the possible modes a drive can be in.
 */
enum apple2_dd_mode {
    DD_READ,
    DD_WRITE,
};

/*
 * This is the length of a typical disk that is formatted in either DOS
 * 3.3 or ProDOS.
 */
#define _140K_ 143360

/*
 * And this is the length of a disk that has been formatted as a nibble
 * file (*.NIB). This is not an Apple thing, exactly; it's more of an
 * emulator thing, that emulators had used to try and get around copy
 * protection in emulation. It does complicate disk drive operation!
 */
#define _240K_ 245760

#define MAX_DRIVE_STEPS 70

/*
 * This is the last _accessible_ sector position within a track (you can
 * have 0 - 4095).
 */
#define MAX_SECTOR_POS 4095

typedef struct {
    /*
     * Disk II drives allow the stepper to move in half-tracks, so we
     * track (pun intended) the position of the head in those
     * half-tracks rather than in full tracks.
     *
     * For example, if track_pos is 4, then the effective track is 2. If
     * the track_pos is 9, then the effective track is 4, except that
     * the head is on the half-track position.
     *
     * There are, at most, 35 tracks in a conventional disk, so there
     * would be at most 70 track positions that we can iterate to.
     */
    int track_pos;

    /*
     * This is a weirder one, because while DOS cares about sectors, we
     * don't really. We just need to know how to find the right position
     * to work with in the disk image.
     *
     * Each track has 16 sectors, and each sector has 256 bytes. We can
     * then say that each track is 4k (4,096) bytes large. So while our
     * track_pos can tell us which 4k chunk we're in, the sector_pos has
     * to tell us where we are _within_ the track. Again -- we don't
     * care about the sector number, really. So the sector_pos field is
     * tracking the byte offset from the beginning of the track, such
     * that 0 ≤ sector_pos < 4096.
     */
    int sector_pos;

    /*
     * The data field is where the actual byte data for the image is
     * kept.
     */
    vm_segment *data;

    /*
     * A disk drive may be "off" or "on", regardless of whether it's
     * been selected by the peripheral interface.
     */
    bool online;

    /*
     * This is one of DD_READ or DD_WRITE (defined in the enum above).
     * The drive can only read or write at once, and the mode of
     * operation must be made explicit through this mechanism.
     */
    int mode;

    /*
     * Write protection is an attribute of the disk. Back in the day, a
     * disk would have a small segment cut out of the disk on the side;
     * this would make it writeable. A disk without that would be
     * write-protected. You could take a writeable disk and make it
     * write-protected simply by putting some solid-colored tape over
     * the cut-out.
     *
     * For our purposes, write protection is a simply boolean attribute
     * that you can enable or disable on the drive.
     */
    bool write_protect;
} apple2dd;

extern apple2dd *apple2_dd_create();
extern int apple2_dd_insert(apple2dd *, FILE *);
extern int apple2_dd_position(apple2dd *);
extern vm_8bit apple2_dd_read(apple2dd *);
extern void apple2_dd_eject(apple2dd *);
extern void apple2_dd_free(apple2dd *);
extern void apple2_dd_set_mode(apple2dd *, int);
extern void apple2_dd_shift(apple2dd *, int);
extern void apple2_dd_step(apple2dd *, int);
extern void apple2_dd_turn_on(apple2dd *, bool);
extern void apple2_dd_write(apple2dd *, vm_8bit);
extern void apple2_dd_write_protect(apple2dd *, bool);

#endif