[GBC] Metal Gear Solid

[liber-m]

The hash matches with the No-Intro dump

Describe the issue
On stage 3, the game freeze with white screen after you enter the elevator.

Rom Information

game
  sha256: 56a69d19ba26941a25adad8bdf17c7baba12245097e901999f4c897eec877ddb
  name:   Metal Gear Solid (USA)
  title:  Metal Gear Solid (USA)
  label:  METALGEARGB
  serial: BMGE
  board:  MBC5
    memory
      type: ROM
      size: 0x200000
      content: Program
    memory
      type: RAM
      size: 0x2000
      content: Save

[CasualPokePlayer]

This is just one of the examples of some games relying on cartridge open bus behavior. This typically just uses the last value on the cartridge bus (what regions comprise the cartridge bus vary depending on DMG vs CGB, though it would just be the same as with OAM DMA), although that typically pulls back up to 0xFF within a single speed m-cycle. Exact behavior could vary from cart to cart and be instance specific (time it takes to pullup could vary slightly, or potentially you have bits randomly set rather than a straight 0xFF immediately due to the nature of pullups; though that would be limited to very short amount of time) since fun non-deterministic behavior. Returning 0xFF (which ares and various less accurate emulators do) is also theoretically possible also resulting in a crash/freeze on console for these kinds of games.