Under the microscope: Mobil 1 Rally Championship (PlayStation)

Advertising your website with a cheat code

In this edition, we’re examining Mobil 1 Rally Championship, the British Rally Championship-themed racing sim from Atod AB and HotGen Ltd. The PlayStation version of this game was published by EA in 2000.

Let’s use this game as a pretext for talking about the PlayStation BIOS. Something handy to know is that it provides implementations of several common C library functions. They’re easily identifiable in disassembly, because they all look alike. Here’s an example invocation of BIOS function 0x17:

800ad214 li t2,0xa0   # Load the BIOS address
800ad218 jr t2        # Jump to that address
800ad21c _li t1,0x17  # Ask for command 0x17 to be executed

The last instruction can go after the jump because the PlayStation’s MIPS CPU uses branch delay slots to try to keep its instruction pipeline full.

Function 0x17 is strcmp:

A(17h) - strcmp(str1, str2): Compares the strings up to including ending 00h byte. Returns 0 if they are identical, or otherwise [str1+N]-[str2+N], where N is the location of the first mismatch.

(excerpted from psx-spx.consoledev.net)

I always look for calls like this in games that have you enter a name or passcode, because they’re often used to process your input for cheat effects.

That brings us to Mobil 1 Rally Championship. After you enter a name on the Setup > Driver name screen, it calls the BIOS’s strcmp function with these two arguments:

• A pointer to the name you just put in.

• A pointer to the string "WWW.ATOD.SE".

Entering WWW.ATOD.SE

WWW.ATOD.SE was, of course, the development studio’s website.

A successful comparison sets the value at 800bee78 from 0x04 to 0x01. This enables a cheat menu! To access it, press Triangle to back up to the title screen. Then choose Options > Cheat mode.

The Cheats screen

The items in the menu do what you would expect:

• Access all maps makes all of the race tracks available.

• Reverse tracks reverses direction of the tracks.

• And A8 cars makes the unlockable cars available.

Left: The unlockable “Moon and Stars” track. Right: Racing on the now-unlocked track.

These are the bonus cars:

• Peugeot 206 WR

• Seat Cordoba WRC

• Subaru Impreza WRC 98

• Mitsubishi Lancer Evo V

• Proton Wira

  

  Left: An A8 car on the selection screen. Right: Racing an A8 car.

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Outro

How many people would have thought to market their website by using its URL as a cheat code? For what it’s worth, the Wayback Machine has saved what www.atod.se looked like in 2000.

In case you’re curious, the PC version of Mobil 1 Rally Championship has an entirely different cheat system. The disc stores 22 special phrases encoded with ROT13. Cheat sites like GameFAQs and IGN have a subset of them listed, but this Usenet post from 1999 has everything!

Thanks for reading. Rings of Saturn will return next week with another batch of retro game reverse engineering posts.