Pokewalker

Cloning a Snickers. {Credit: Etchy, YouTube)

The Pokéwalker is a gadget that was sold alongside the Pokémon HeartGold and SoulSilver games for the Nintendo DS, using which you could take a Pokémon of your choice with you on a walk. Not only would you earn points while walking, but you’d be able to find items, battle wild Pokémon, etc. The Pokémon inside the device is however linked to the game cartridge. This fact turned into tragedy when [Etchy] found his old Pokéwalker with a treasured Pokémon still on it, but was forced to erase the device as he had lost the cartridge over the years.

Although he had been told repeatedly by then that it was impossible to transfer such a digital pet to a new save file, this never felt right. Although it made some sense that a specific critter would be linked to a specific save file as a level of security, there’s also the question of whether all data of the Pokémon in question would be erased from said save file.

Fortunately, [Dmitry] has reverse-engineered the Pokéwalker already, including the infrared protocol that uses the IR transceiver in the cartridge itself. As it turns out, only some basic information is sent over to the device, while the Pokémon is simply hidden in the save file, including the data that isn’t sent to the device. Case closed, right?

Continue reading “Rescuing A Pokémon Off A Pokéwalker After Losing The Game Cartridge” →

The PokeWalker is part of Nintendo’s long quest to get children (and likely some adults) walking and exercising. There’s the PokeWalker, Pokemon Pikachu, PokeBall Plus, Pokemon Pikachu 2, Pokemon mini, and of course Pokemon Go. Despite being out a decade, there wasn’t a ROM dump for the device and there was minimal documentation on the communication protocol. [Dmitry Grinberg] took it upon himself to change all that and crack the PokeWalker open.

At its heart, the PokeWalker is just a pedometer with an IR port and a 96×64 grayscale screen. It came out in 2009 to accompany the new Pokemon release for the Nintendo DS. Cracking open the device revealed a 64KB EEPROM, a Renesas H8/38606R CPU, a Bosch BMA150 accelerometer, and a generic IR transceiver. The CPU is particularly interesting as in addition to being quite rare, it has a mix of 8, 16, and 32 bits with 24-bit pointers. This gives it a 64K address space. While the CPU is programmable, any attempt to do so erases the onboard flash. The communication protocol packets have an 8-bit header that precedes each packet. The header has a checksum, a command byte, and four bytes of session id, and an unused byte. Curiously enough, every byte is XOR’d with 0xAA before being broadcast.

One command is an EEPROM write, which uses back-referencing compression. Each chunk of data to be written is packaged into 128-byte chunks, though 128 bytes likely won’t be sent thanks to the compression. The command can theoretically reference 4k bytes back, but in practice, it can only reference 256 bytes back. It was this command that laid the foundation for the exploit. By carefully crafting the command to send, the command can overflow the decompression buffer and into executable code. Only a few bytes can be overflowed so the payload needs to be carefully crafted. This allowed for an exploit that reads the system ROM and broadcasts it out the IR port. Only 22k bytes can be dumped before the watchdog reboots the device. By changing the starting address, it was easy to do multiple passes.

After the ROM was stitched together from the different passes, the different IR commands were analyzed. In particular, a command was found that allows direct writes into RAM. This makes for a much easier exploit as you can write your exploit, then override a pointer in the event table, then have the exploit revert the event table once the system naturally jumps to your exploit.

[Dmitry] finishes off this amazing exploit by writing a PalmOS app to dump the ROM from a PokeWalker as well as modify the system state. PalmOS was chosen as it is an easy and cheap way to have a programmable IR transciever. All in all, a gorgeous hack with a meticulous writeup. This isn’t the first video game accessory that’s been reverse engineered with a scrupulous writeup, and we’re sure it won’t be the last.

Continue reading “Reverse Engineering A PokeWalker” →