Super Xevious: GAMP no Nazo

Super Xevious: GAMP no Nazo
Developer: TOSE Publisher: Namco Platform: NES Released internationally: June 18, 2020 (Namco Museum Archives Vol. 2) Released in JP: September 19, 1986 This game has hidden developer credits. This game has debugging material. This game has a hidden level select.

Not to be confused with Super Xevious from the Arcades, this Famicom exclusive sequel involves solving riddles to move onto the next stage. If one fails to solve the riddle, the stage repeats until it's solved. There's also a fan-translation in English. It's the Riddle of GAMP!

Secret Password Screen

Start a new game. Before destroying any enemy on the level, press Start to pause the game. Then press Up, Down, Left, Right, A, B. The Secret Password Screen will appear. Press Left / Right to select a digit, press A / B to select a number. Press Start to play. Levels passwords:

6974 - Level 2 1797 - Level 3 5328 - Level 4 3580 - Level 5 6541 - Level 6 3024 - Level 7

Developer Credits

The game contains a hidden copyright text encoded with the regular ASCII charset, but shifted down by 128 characters, at 0x19F90:

*Copyright 1986 namco ltd. all rights reserved 
*program checker Haruhisa.udagawa &  Kumi.Hanaoka
watashiwa kumichan ga daisukida!

And also at 0x1FE50:

Haruhisa.udagawa &  Kumi.Hanaoka

The last sentence in the first string means "I love Kumi-chan so much!".

CRC Test

There are a series of Namco games, made by the programmers Haruhisa Udagawa and Kumi Hanaoka, that contain the same self-test for data integrity and they are (Babel no Tou, Dragon Buster, Family Jockey, Lupin Sansei: Pandora no Isan, Mappy-Land, Pro Yakyuu: Family Stadium, Sanma no Meitantei, Sky Kid, and Valkyrie no Bouken: Toki no Kagi Densetsu, respectively).

To enable any of these tests you need a special device that should be plugged into the expansion port. The operation of that device is very simple. It should accept the data bit from the data input port and return it back inverted to the output data port. The device consists of a 4-bit shift register, working as some sort of FIFO buffer. The input bits are shifted to the output after 4 cycles.

At the game's boot, it tries to send some special data to the device. If the data output doesn't match the data input inverted, then the game continues the normal operation. But if all data (usually 32, rarely 64 bytes) matches, self-tests will be performed. The program calculates 24-bit partial checksums for the PRG (excluding the last 8K) and the CHR data, summing only every 15th byte, and comparing it against the etalon.

Before testing of the PRG data, the background color turns red, before testing the CHR data, it turns green. If any of these tests have failed, the program will jump directly to the reset routine. It means, one of these tests will be performed infinitely, but until the special device is unplugged, or until the test has passed.

Normally, you'll see the red to green flash just before the game's boot. Or the static red screen if the PRG data is bad, or the flashing red to green screen if CHR data isn't good.

Using the Game Genie code GEOYNTEI, you can skip tests for the special device presense and jump straight to the integrity tests.