NES Platoon 0s Speedrun from a bad cartridge connection

You can talk about almost anything that you want to on this board.

Moderator: Moderators

Post Reply
User avatar
Dwedit
Posts: 4924
Joined: Fri Nov 19, 2004 7:35 pm
Contact:

NES Platoon 0s Speedrun from a bad cartridge connection

Post by Dwedit »

Video: https://www.speedrun.com/platoon/run/ylr59r3y

In this video, NESCardinality was beginning speedrun attempts for Platoon, and the game happened to boot to a glitched version of the ending. He considered that to be a 0s "new world record" for a "glitched" category.

So what happened? Why did the game boot straight to a glitched ending?

---

Platoon happens to be programmed in such a way that each bank acts like a independent program. PRG bank switches happen infrequently, only when you move on to the next level. 0x8000 is an entry point for each bank.

When you run 0x8000 of each bank you get these results:
Bank 0: Ending
Bank 1: Game Over Screen (this bank is also used for other text prompts)
Bank 2: Last Level, "The Jungle Confrontation"
Bank 3: Point and aim level "Night has fallen"
Bank 4: Maze level "The Tunnel System"
Bank 5: First level "Entering the Combat Zone"
Bank 6: Title Screen
Bank 7: Fixed Bank, If you run 0x8000 of this bank, it jumps to the Title Screen.

In this case, the MMC1 was unable to see any writes, and it remained in its initial state. This MMC1 happened to default to 16K PRG Bank Mode, 8K CHR bank mode, Fixed PRG bank at end, PRG Bank 0 selected, CHR Bank 0 selected, Single Screen mirroring selected.

The game tries to switch to PRG Bank 6 at bootup to select the title screen, then it jumps to 0x8000. If this fails, and it jumps to Bank 0 instead, it runs the ending.

My hypothesis was that Cartridge Pin 14 (CPU R/W) was not connected when the cartridge was inserted, and that would cause the MMC1 to not see any writes at all. Later on in the video, the connection got better, then mapper writes started taking effect, so the graphics cleared up, and the game was able to boot to the Title again. Am I correct about a disconnected Pin 14 being the cause?
Here come the fortune cookies! Here come the fortune cookies! They're wearing paper hats!
Post Reply