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85 lines
2.7 KiB
C
85 lines
2.7 KiB
C
#ifndef _APPLE2_DISK_DRIVE_H
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#define _APPLE2_DISK_DRIVE_H
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/*
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* These are the possible modes a drive can be in.
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*/
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enum apple2dd_mode {
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DD_READ,
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DD_WRITE,
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};
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#define MAX_DRIVE_STEPS 70
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typedef struct {
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/*
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* Disk II drives allow the stepper to move in half-tracks, so we
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* track (pun intended) the position of the head in those
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* half-tracks rather than in full tracks.
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*
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* For example, if track_pos is 4, then the effective track is 2. If
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* the track_pos is 9, then the effective track is 4, except that
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* the head is on the half-track position.
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*
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* There are, at most, 35 tracks in a conventional disk, so there
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* would be at most 70 track positions that we can iterate to.
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*/
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int track_pos;
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/*
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* This is a weirder one, because while DOS cares about sectors, we
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* don't really. We just need to know how to find the right position
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* to work with in the disk image.
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*
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* Each track has 16 sectors, and each sector has 256 bytes. We can
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* then say that each track is 4k (4,096) bytes large. So while our
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* track_pos can tell us which 4k chunk we're in, the sector_pos has
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* to tell us where we are _within_ the track. Again -- we don't
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* care about the sector number, really. So the sector_pos field is
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* tracking the byte offset from the beginning of the track, such
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* that 0 ≤ sector_pos < 4096.
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*/
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int sector_pos;
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/*
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* The data field is where the actual byte data for the image is
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* kept.
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*/
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vm_segment *data;
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/*
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* A disk drive may be "off" or "on", regardless of whether it's
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* been selected by the peripheral interface.
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*/
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bool online;
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/*
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* This is one of DD_READ or DD_WRITE (defined in the enum above).
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* The drive can only read or write at once, and the mode of
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* operation must be made explicit through this mechanism.
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*/
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int mode;
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/*
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* Write protection is an attribute of the disk. Back in the day, a
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* disk would have a small segment cut out of the disk on the side;
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* this would make it writeable. A disk without that would be
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* write-protected. You could take a writeable disk and make it
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* write-protected simply by putting some solid-colored tape over
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* the cut-out.
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*
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* For our purposes, write protection is a simply boolean attribute
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* that you can enable or disable on the drive.
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*/
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bool write_protect;
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} apple2dd;
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extern apple2dd *apple2dd_create();
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extern void apple2dd_free(apple2dd *);
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extern void apple2dd_step(apple2dd *, int);
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extern void apple2dd_set_mode(apple2dd *, int);
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extern void apple2dd_turn_on(apple2dd *, bool);
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extern void apple2dd_write_protect(apple2dd *, bool);
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#endif
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