Very cool. Concerning the RNG differences between console revisions, I know Gyre and Feasel talked about how RNG is affected in their run of Final Fantasy at AGDQ, which you can watch here: . What's weird is they found that the memory was consistent at boot with the top loaders, while you found that resetting the top loader changes the RNG every time. Nice find!

I've been playing around with the RNG routines. It looks like the routine itself is at $8151, and its calculation depends on the values of $8A, $8B, and $3D0-$407. It looks like $8B is always offset from $8A by 0x17 mod 0x36 in normal gameplay, so its effect on RNG calculation can be effectively ignored. $8C appears to be where the result is saved, but doesn't actually influence the generation itself. I haven't seen anything with $8F - not sure why. The RNG reset routine is at $813E. Here's some Python code I threw together that computes the RNG values:

It looks like this routine is called at least twice per enemy spawn. Some spawns will call it more, such as the tricycle kid, which I think does a third call to figure out how far to move.

As for the top and front loader differences, I think it has to do with the PPU state. The NES dev wiki goes into detail; in particular, [quote]The Reset button on the Control Deck resets the PPU only on the front-loading NES (NES-001). On top-loaders (Famicom, NES-101), the Reset button resets only the CPU.[/quote] The wiki also gives some sample code to make sure that 29658 cycles have passed since power on; Paperboy does this at $8057:

[quote] 00:8057:20 3E 81 JSR initialize_RNG 00:805A:20 51 81 JSR get_RNG 00:805D:AD 02 20 LDA PPU_STATUS = #$00 00:8060:10 F8 BPL $805A 00:8062:AD 02 20 LDA PPU_STATUS = #$00 00:8065:10 FB BPL $8062 [/quote]

On BizHawk, the RNG routine is called 317 times as the game first starts. My guess would be that because the top loader doesn't reset the PPU, the get_RNG routine gets called a randomish number of times compared to the front loader? But I would expect that the routines should end up synced eventually anyway. I don't have any NES hardware so I can't test anything.

I've been working on a Lua script for FCEUX that can play through days and count the number of frames and lag frames to see if I can find some better RNG starting states. I've made some simplifications: rather than try to dodge obstacles, I just periodically save a state, and if I ever crash, I load the last state and just change the player's x position randomly to see if I can bypass the obstacle. It's not perfect, but it's easy. I'm also not throwing any newspapers; instead I just manually mark all houses as delivered at the end. It seems like it's necessary to finish each day with a dog, and right now I'm not sure where the enemy type is stored, so that will need more work. I'm also ignoring the orbs. But if this all works, hopefully I can just have it grind through different RNG states until it finds a good one.