Metal Gear — saves on the Yamanooto

Metal Gear saves to tape. The patch redirects the game's 20 calls to the tape BIOS to a virtual tape in the cartridge's flash: the file name, SKIP/FOUND, VERIFY and the retries are still the game's own. It holds 3 saves.

109 bytes changed in 34 stretches · 8 KB driver · one 64 KB sector · no ROM distributed

How to play

As with the tape: pause (F1), F5 saves and F4 loads; you can also load from the Game Over. The name you type (up to 6 letters) is the slot: an existing name overwrites that save; a new one goes to the first free slot, and if there is none the game says SAVE ERROR.

Note that this is the game, not the patch: what gets saved is the snapshot the game takes at its checkpoints (the elevators). Whatever you picked up after the last elevator is not in the save, just like with a real tape.

What you need

• The game ROM, which this repository does not distribute: Metal Gear (Konami, 1987, RC-750), 131,072 bytes, sha256 999b5a97488d0dd479aab8c467be14233eb7437cbd1d37cf348765dfeed8429d. It is the dump it was tested with; the patcher checks every site, so with another dump it refuses instead of breaking it.
• Python 3.
• A Yamanooto, 2 MB or 8 MB.

Building the image

python tools/imagen.py metalgear.rom

You get metalgear_yamanooto.rom (256 KB), ready to flash from the start of the flash: it boots the game on its own, with no menu. Flashing it replaces the menu and games on the cartridge. In openMSX:

openmsx -cart metalgear_yamanooto.rom -romtype Yamanooto

make test runs the 4 tests: the .bin files come from their .asm, the patcher refuses another ROM and, with the ROM in the root, outside the stretches the patcher declares the game is the original byte for byte and the image is the reference one.

How it works

• The game's 13 bank switches (ld (6000h/8000h/0A000h),a, all in bank 0) move to the Konami SCC registers of the same window (7000h/9000h/B000h): that is the mode a Yamanooto starts in, so the game boots on its own from the start of the flash.
• The 20 tape BIOS calls (TAPION, TAPIN, TAPIOF, TAPOON, TAPOUT and TAPOOF) live in bank 0x0F, the save/load bank. Each one is repointed to one of six entry points written into that bank's filler: 56 bytes at 0xBFA7.
• Those entry points put the driver (launcher/mg1_driver.asm, 8 KB appended as bank 0x10) in the 0x8000 window with interrupts off, because the game's interrupt switches banks for the sound.
• The driver acts as the tape: it serves the blocks of the saved games and collects the ones the game writes. Each slot is [0xA5][6-byte name][2-byte length][0x301 bytes of data], every 0x400 bytes of a 64 KB flash sector (relative bank 0x18). When the data block is closed, the start of the sector is copied to RAM (0xD800), the sector is erased and reprogrammed from an engine in RAM (0xF100). The game's VERIFY then reads the real flash.
• The addresses come from Manuel Pazos' annotated disassembly (GuillianSeed/MetalGear), checked byte for byte on the dump above.

Where it comes from

It comes from nPackR, which uses it to put the game in a collection. Here it comes on its own: the image boots the game directly, with no menu. GPL v3 licence (LICENSE) and a non-commercial note (NOTICE.md).

Tested

In openMSX on 2026-07-05: save at an elevator, switch off and load.