Sonic Eraser Notes

WHAT DO WE HAVE
FFD00C FFD04C FFD08C FFD0CC (all 4-bytes)
stores the current piece
FFD10C FFD14C FFD18C FFD1CC (all 4-bytes)
stores the next piece

The last byte of the value in the previous addresses can tell you the tile type
52 White Square
5A Red Triangle
62 Gold Triangle
6A Green Square
72 Blue Circle
7A Orange Diamond
82 Pink Cross

To tell which slot corresponds to what tile of a piece, use the following tables
The way to read this is as follows: a piece can contain tiles in any of 2 rows and 4 columns
If an O piece is the current piece, then FFD00F will refer to the tile at the bottom left (row 2, column 1),
FFD04F to the tile at the bottom right (row 2, column 2), FFD08F to the tile at the top right (row 1, column 2),
and FFD0CF to the tile at the top left (row 1, column 1)

(Inverted L piece)
    Row     Column
0F   2       3
4F   1       3
8F   1       2
CF   1       1

(O piece)
0F   2       1
4F   2       2
8F   1       2
CF   1       1

(I piece)
0F   1       3
4F   1       2
8F   1       1
CF   1       4

(T piece)
0F   2       2
4F   1       3
8F   1       2
CF   1       1

(L piece)
0F   2       1
4F   1       3
8F   1       2
CF   1       1

LINE FF:283A
Sets D00C to contain A66A based on value D1
LINE FF:2836
Sets D1 to contain A66A based on $(A1+D0+2)

-WORRYING ABOUT A1 FIRST
LINE FF:280A
Sets A1 to contain 81E8 based on D1
LINE FF:2806
Sets D1 to contain 81E8 based on $(A1+D0) constant?)

--WORRYING ABOUT A1
LINE FF:2802
Sets A1 to value of long $D008, which is 28154 (CONSTANT?)

--WORRYING ABOUT D0
Line FF:27FE
Sets D0 to value of word $D006
(3870) Line 02:BA34
Sets $D006 to $D106
(3700) Line 02:DB908 sets $D106 to D0
(3699) Line 02:B906 multiplies D0 by 2
(3693) Line 02:B8FA ands D0 and D2 together
(3692) D0 obtains its value from an RNG function
WORRYING ABOUT D0 LATER

02:B220 is the start of an RNG routine code
The game starts the RNG routine the frame the arrow of mode select appears on screen, and stops as soon as you select Round mode (not when you select Round 0). The RNG seed is always reset even if you go back to the title screen in between rounds, so waiting the same amount of time will always yield the same results.

-- From the moment the arrow appears
Wait 1 frame 6115E4FA
P O W
G

Wait 2 frames 388BAC0A
B P O
    W

Address FFC714 holds RNG Seed