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Several changes to phase and writes

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1. The phaser algorithm was reworked, and it should be more accurate in
choosing when to step forward or backward.
2. Writes should be committed when the latch has bit 7 high. This hasn't
actually been a problem yet, since other things are broken! But we might
as well fix it now that we've seen it.
This commit is contained in:
Peter Evans 2018-02-14 16:49:20 -06:00
parent 100621a6c6
commit 64b9cbefcb
1 changed files with 35 additions and 6 deletions
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41
src/apple2.dd.c
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@ -179,7 +179,27 @@ apple2_dd_phaser(apple2dd *drive)
{
int phase = drive->phase_state;
int last = drive->last_phase;
int step = 0;
if (phase == (last << 1)) {
step++;
} else if (phase == 0x1 && last == 0x8) {
step++;
} else if (phase == (last >> 1)) {
step--;
} else if (phase == 0x8 && last == 0x1) {
step--;
}
if (phase == 0 && last == 0) {
step = 0;
}
if (phase == 1 && last == 0) {
step = 1;
}
#if 0
// This is a bit of trickery; there is no phase state for 0x10 or
// 0x0, but we want to pretend like the phase is "next" to the bit
// we're operating with for the purpose of establishing a direction.
@ -201,7 +221,13 @@ apple2_dd_phaser(apple2dd *drive)
if (phase == 0 && last != 0x1 && last != 0x8) {
return;
}
#endif
//printf("phase:%02x last:%02x step:%d\n", phase, last, step);
apple2_dd_step(drive, step);
#if 0
// If phase > last, then we must move the head forward by a half
// track. If it's < last, then we move the head backward, again by a
// half track.
@ -210,6 +236,7 @@ apple2_dd_phaser(apple2dd *drive)
} else if (phase < last) {
apple2_dd_step(drive, -1);
}
#endif
// Recall our trickery above with the phase variable? Because of it,
// we have to save the phase_state field into last_phase, and not
@ -248,6 +275,7 @@ apple2_dd_read(apple2dd *drive)
}
vm_8bit byte = vm_segment_get(drive->data, apple2_dd_position(drive));
//printf("byte = %02x, pos = %05x\n", byte, apple2_dd_position(drive));
apple2_dd_shift(drive, 1);
return byte;
@ -320,10 +348,6 @@ apple2_dd_shift(apple2dd *drive, int pos)
while (drive->sector_pos > MAX_SECTOR_POS) {
// We need to reset the sector pos to zero, because...
drive->sector_pos -= (MAX_SECTOR_POS + 1);
// We also need to move to the next track, so let's adjust by
// two half-tracks.
apple2_dd_step(drive, 2);
}
}
@ -337,6 +361,7 @@ apple2_dd_shift(apple2dd *drive, int pos)
void
apple2_dd_step(apple2dd *drive, int steps)
{
//printf("step %d, new track_pos %d\n", steps, drive->track_pos + steps);
drive->track_pos += steps;
if (drive->track_pos > MAX_DRIVE_STEPS) {
@ -368,8 +393,10 @@ apple2_dd_write(apple2dd *drive)
return;
}
vm_segment_set(drive->data, apple2_dd_position(drive), drive->latch);
apple2_dd_shift(drive, 1);
if (drive->latch & 0x80) {
vm_segment_set(drive->data, apple2_dd_position(drive), drive->latch);
apple2_dd_shift(drive, 1);
}
}
/*
@ -401,6 +428,8 @@ apple2_dd_switch_phase(apple2dd *drive, size_t addr)
case 0x6: drive->phase_state &= ~0x8; break;
case 0x7: drive->phase_state |= 0x8; break;
}
apple2_dd_phaser(drive);
}
/*