Several changes to phase and writes

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.

src/apple2.dd.c

@@ -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);
+	if (drive->latch & 0x80) {
-    apple2_dd_shift(drive, 1);
+		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);
 }
 
 /*