Hacking Why is a cIOS necessary?

[Mr. Mysterio]

I'm curious why a cIOS is necessary to run Wii game backups from the SD card. I read here that the only reason a cIOS is used is because USB1.1 is too slow to run backups from USB. Is an AHBPROT backup loader that only loads games from an SDHC possible? If not, why?

 

[GreyWolf]

An IOS slot is basically a gateway between the game that's running on the PowerPC and the rest of the system, which is walled behind the ARM core in the GPU. In order for the game to run from a USB drive or SD card the IOS the game is using to access everything has to be patched to redirect IO, etc. to the drive.

AHBPROT is also part of the hypervisor system that restricts access to the hardware along with MEMPROT for memory access. Disabling those allows you access to everything, but Wii games are written to access the hardware via the IOS mechanism so they need the patch rather than access to the hardware bus.

Even if a game happened to use IOS58, which has USB2.0, it would still be loading from the DVD because it would have been linked to the standard DVD library when it was compiled.

 

[N7Kopper]

An IOS slot is basically a gateway between the game that's running on the PowerPC and the rest of the system, which is walled behind the ARM core in the GPU. In order for the game to run from a USB drive or SD card the IOS the game is using to access everything has to be patched to redirect IO, etc. to the drive.

AHBPROT is also part of the hypervisor system that restricts access to the hardware along with MEMPROT for memory access. Disabling those allows you access to everything, but Wii games are written to access the hardware via the IOS mechanism so they need the patch rather than access to the hardware bus.

Even if a game happened to use IOS58, which has USB2.0, it would still be loading from the DVD because it would have been linked to the standard DVD library when it was compiled.

And this also explains why Gamecube loaders Devolution and Nintendont (that run in Wii mode and therefore work on the Wii U) don't need a cIOS to run, as they're coded to access the hardware bus directly by bypassing AHBPROT and MEMPROT, and only use ISO58 for tasks like USB bus access (and, by extension, Bluetooth), deciding between using the system's built-in Wi-Fi antenna and a connected Ethernet cable adapter, and other such things.

Well, maybe. I'm not an actual coder, I just know a few things and make educated guesses.