Posted: 17 days ago
KungFuFurby
He/Him
Joined: 4/19/2019
Posts: 29
I decided to personally take a look at how Binary Land did its levels because I keep hearing that it loops after 16 levels. I think it loops after 99 levels... so I decided to put that matter to rest. Data Crystal has a good start since it lists the halves accordingly: https://datacrystal.tcrf.net/wiki/Binary_Land_(NES)/Notes I came across this code at $E490: 
A5 1D 29 0F AA BD 19 E5 85 02
A5 1D 29 0F 85 03
A5 1D 20 BD EB
18 65 03 29 0F AA
BD 29 E5 85 03 60
This refers to two arrays. The array at $E519 is this (and it represents the left side)... 
0F 00 04 08 0C 01 05 09 0D 02 06 0A 0E 03 07 0B
The array at $E529 is this (and it represents the right side)... 
00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F
Now, the left side's layouts does actually loop around after 16 levels, so the loop point is half right. However, the right side's layouts don't do that. Instead, the right side is offset by the high nibble of the level ID, meaning every 16 levels, the right side actually wraps around and increments itself by one. This is the complete set that I get from level 1 to 99 as a result, combining the two by nibble (zero is excluded, and anything past 99 is excluded, as these are de-facto unused level layout combinations): 
   01 42 83 C4 15 56 97 D8 29 6A AB EC 3D 7E BF
F1 02 43 84 C5 16 57 98 D9 2A 6B AC ED 3E 7F B0
F2 03 44 85 C6 17 58 99 DA 2B 6C AD EE 3F 70 B1
F3 04 45 86 C7 18 59 9A DB 2C 6D AE EF 30 71 B2
F4 05 46 87 C8 19 5A 9B DC 2D 6E AF E0 31 72 B3
F5 06 47 88 C9 1A 5B 9C DD 2E 6F A0 E1 32 73 B4
F6 07 48 89
Quick note: the game starts at level 1, meaning index ID 0 is not used. Additionally, because the right side is influenced by the low nibble of the left side, the end result is that all of the layout combinations are unique, even though we have recycling going on. Where does the level 99 wraparound happen? That happens at $CA5B after incrementing the level ID: it checks for level 100, and if it is on level 100, it jumps back to level 1. I'll also add that level 14 appears to be the last difficulty-related change, with the addition of the flame enemies. This video does all 99 levels: Link to video So anyways, I consider this to be a similar situation to Super Off Road, except with a different way of mixing things up: namely, by using different halves on the other side. Theoretically there could have been up to 256 of these, but the hardcoded loop stops that from happening.