Valkyrie no Bouken: Toki no Kagi Densetsu

Developer Credits
The game contains hidden copyright text: COPYRIGHT 1986 NAMCO LTD. ALL RIGHTS RESERVED A.WACHI

CRC Test
There are a series of Namco games, all written by the same programmers, Haruhisa Udagawa and Kumi Hanaoka, that contain the same self-test for data integrity (Babel no Tou, Dragon Buster, Family Jockey, Lupin Sansei: Pandora no Isan, Mappy-Land, Pro Yakyuu: Family Stadium, Sanma no Meitantei, Sky Kid, Super Xevious: Gump no Nazo).

To enable any of these tests, you need a special device that should be plugged into the expansion port. The operation of the 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 go to the data input port and then are shifted to the data output port after a 4 cycles.

During the game's startup, 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 operating normally. But if all data (usually 32 or rarely 64 bytes) match, 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 the PRG data, the background color turns red. Before testing the CHR data, it turns green. If any of these tests fail, the program will jump directly to the reset routine. That means one of these tests will be performed infinitely 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. If the PRG data is bad, you'll see a static red screen or a flashing red to green screen if the CHR data is bad.

Using this Game Genie code you can skip tests for the special device detection and jump straight to the integrity tests.