Tengai Makyou Zero

Tengai Makyou Zero
Developers: Hudson Soft, Red Company Publisher: Hudson Soft Platform: SNES Released in JP: December 22, 1995 This game has hidden development-related text. This game has debugging material.

A late-era SNES installment of the Tengai Makyou series, perhaps most notable for being only one of three SNES games to use the SPC7110 enhancement chip (Momotarou Dentetsu Happy and Super Power League 4 being the others), in turn also making it one of the very few SNES games incompatible with the SD2SNES/FXPak Pro flash cart (as of v1.10.3).

SPC7110 Check Program

It uses the SPC7110 co-processor on the cartridge for handling data compression and accessing a RTC chip. If the internal battery dies or the SRAM gets corrupted, the game loads a test program for it on boot. A newer version of it can be found in the games mentioned above, as also them use this enhancement chip.

This happens because the first thing it ever checks on boot are the SRAM offsets 0x1FF0-0x1FFF (last 16 SRAM bytes): if they contain the string "SPC7110 CHECK OK" the game boots as normal, otherwise the game starts a SPC7110 test battery (called "mode" in-game) depending on how the string was altered:

Mode 1

The game boots into test mode 1 when it finds that the string mentioned precedently has more than two bytes altered, but not all of them are equal to 0x11.

This test battery can be started by pressing A at the prompt and it does various tests including a SRAM read/write test, so running it erases its content.

When this test battery finishes, all the SRAM bytes are set to 0xFF, except for the offsets mentioned above as they're set to 0x11 instead if the game passes all tests. The only way to exit is to reset the game and, if the game passed all the tests, now it boots into the second test mode (see below).

Mode 2

The game boots into test mode 2 if the last 16 SRAM bytes are all set to 0x11.

This test battery can be started by pressing B at the prompt. It does a second RTC test and reads back all the 0xFF bytes written on SRAM in the precedent test, then writes "SPC7110 CHECK OK" in the last 16 SRAM bytes if the game passes the whole test battery.

If all the tests pass, now resetting the game boots it as normal.

Fail

If a test in one of the two test batteries ever fails, the game writes "NG" (No Good) on-screen instead of "OK" on the right side of the failed test and, on game reset, the whole test battery repeats until all the tests pass.

Oddity

The test program doesn't check if the pressed button matches the one asked on the prompt, so pressing B at the Mode 1 prompt loads the test battery for Mode 2 and viceversa. This oddity remains in the later version of the test program. Triggering the second test battery before the first one leads to the failure of the test battery, but nothing relevant happens if the first test battery is triggered by pressing A on the Mode 2 prompt. The reason behind this choice is unknown, as it probably can be just an oversight.

(Source: jonasrosland (Discovery) - WaluigiBSOD (How it works and oddity discovery))

Build Date

Apart from checking if saved data already exists in SRAM, the game also reads a string at the SRAM offsets 0x0000-0x001F (first 32 SRAM bytes).

If more than two bytes of this string are altered, the game resets save data and its RTC clock.

The string is also relevant because it features a date preceded by the letter "V", as this letter likely stands for "Version" it can be assumed that it's the build date. So, the game was compiled on August 30, 1995 (about four months before release):

TengaiMakyo-Zero HUDSON V95-8-30

(Discovery: WaluigiBSOD)