> Before I reinvent the wheel, can anybody comment on the feasibility of
> producing a non-repeated playfield by writing PF0, PF1 and PF2 chasing the
> scanning beam before data required for the repeated section? Of course,
> there would be two lots of writes required per scan line, but I'm interested
> to know if its been done. What I'm asking, I guess, is when it comes to
> drawing the right half of the PF, does the hardware re-read the PF
> registers, or is it buffered internally somehow?
As I'm sure you know by now this is possible and used by many games.
Recently, I ran a few tests to see when changes to the PF registers
really occur and here are the results I got. I'm pretty sure these
were for an unreflected playfield.
Have Fun!
Brad
P.S. You're 4 color playfield doesn't look very good using
Stella (the emulator) running under X windows. Since
changing the colors of the playfield every frame makes
the emulator redraw most of the window every frame. I'd
suggest limiting the 4 colors to a small part of the
screen if you want it playable on the emulators.
Changing CTRLPF PF Bits
-----------------------
* Change the reflect bit at or before cycle 48 and the display
will correspond to the reflect value you specify
* Change the reflect bit after cycle 48 and the display will
correspond to the old reflect value
* Changes to the score bit and the priority bit take effect
at the end of the cycle they are changed (even in the middle
of a 4 pixel wide playfield block)
Hitting PF Registers
--------------------
Here are the results of hitting PF0, PF1, and PF2 at various cycles.
The end result of this table is that the display of changes to the
playfield registers are delayed by some number of pixels. The delay
is either 2, 3, 4 or 5 pixels depending on when the register is hit.
Looks like the delay can be calculated as delay[cycle mod 4], where
the delay array is given as delay[4] = {4, 5, 2, 3}.
Cycle Pixel Effect
----- ----- ------
22 -2 No display problems (cy * 3 - 68) + d = ?
23 1 First 4 pixels of PF0 not changed (23 * 3 - 68) + 3 = 4
24 4 First 8 pixels of PF0 not changed (24 * 3 - 68) + 4 = 8
25 7 First 12 pixels of PF0 not changed (25 * 3 - 68) + 5 = 12
26 10 First 12 pixels of PF0 not changed * (26 * 3 - 68) + 2 = 12
27 13 First 16 pixels of PF0 not changed (27 * 3 - 68) + 4 = 16
28 16 First 4 pixels of PF1 not changed (28 * 3 - 68) + 4 = 20
29 19 First 8 pixels of PF1 not changed .
30 22 First 8 pixels of PF1 not changed * .
31 25 First 12 pixels of PF1 not changed .
32 28 First 16 pixels of PF1 not changed
33 31 First 20 pixels of PF1 not changed
34 34 First 20 pixels of PF1 not changed *
35 37 First 24 pixels of PF1 not changed
36 40 First 28 pixels of PF1 not changed
37 43 First 32 pixels of PF1 not changed
38 46 First 32 pixels of PF1 not changed *
39 49 First 4 pixels of PF2 not changed
40 52 First 8 pixels of PF2 not changed
41 55 First 12 pixels of PF2 not changed
42 58 First 12 pixels of PF2 not changed *
43 61 First 16 pixels of PF2 not changed
44 64 First 20 pixels of PF2 not changed
45 67 First 24 pixels of PF2 not changed
46 70 First 24 pixels of PF2 not changed *
47 73 First 28 pixels of PF2 not changed
48 76 First 32 pixels of PF2 not changed
49 79 First 4 pixels of PF0 not changed
50 82 First 4 pixels of PF0 not changed *
51 85 First 8 pixels of PF0 not changed
52 88 First 12 pixels of PF0 not changed
53 91 First 16 pixels of PF0 not changed
54 94 First 16 pixels of PF0 not changed *
55 97 First 4 pixels of PF1 not changed
56 100 First 8 pixels of PF1 not changed
57 103 First 12 pixels of PF1 not changed
58 106 First 12 pixels of PF1 not changed *
59 109 First 16 pixels of PF1 not changed
60 112 First 20 pixels of PF1 not changed
61 115 First 24 pixels of PF1 not changed
62 118 First 24 pixels of PF1 not changed *
63 121 First 28 pixels of PF1 not changed
64 124 First 32 pixels of PF1 not changed
65 127 First 4 pixels of PF2 not changed
66 130 First 4 pixels of PF2 not changed *
67 133 First 8 pixels of PF2 not changed
68 136 First 12 pixels of PF2 not changed
69 139 First 16 pixels of PF2 not changed
70 142 First 16 pixels of PF2 not changed *
71 145 First 20 pixels of PF2 not changed
72 148 First 24 pixels of PF2 not changed
73 151 First 28 pixels of PF2 not changed
74 154 First 28 pixels of PF2 not changed *
75 157 First 32 pixels of PF2 not changed
--------------------------------------------------------------------------
Bradford W. Mott (bwmott@xxxxxxx) Computer Science Department
http://www4.ncsu.edu/~bwmott/www North Carolina State University
--------------------------------------------------------------------------
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