Quick question about mod chips

[Gorkensnorkel]

Since the mod chips boot directly to Hekate I have a question about the "Auto-RCM" function. If Auto-RCM is activated in Hekate and the chip fails or malfunctions at some point, will the Switch still boot into RCM?

 

[Hayato213]

Don't use AutoRCM if you got a patched unit.

 

[Gorkensnorkel]

Don't use AutoRCM if you got a patched unit.

Will it cause problems? Or brick the Switch?

 

[Hayato213]

Will it cause problems? Or brick the Switch?

You shouldn't activate autorcm on patched unit.

 

[thesjaakspoiler]

Afaik, it will brick the unit indeed.

 

[CompSciOrBust]

Whenever you install a modchip AutoRCM is enabled automatically anyway.

The Switch has something called a BCT, which basically acts as a config file for the Tegra SoC to decide which OS to load and from which storage device. The BCT has to be signed by the manufacturer (Nintendo) so that you can't just load your own OS.

When the BCT is not signed (and therefore is invalid) the Switch will assume that it is corrupt and automatically boot into RCM mode. That's how Auto RCM works. It intentionally corrupts the BCT.

Conversely the way the mod chips boot custom operating systems is by replacing the BCT with a custom one telling it to load something other than Nintendo's bootloader. Normally this would be invalid and cause the Switch to enter RCM mode, but the chips get around this by using fault injection to glitch the Tegra chip into skipping over the piece of code which checks if the BCT is an official Nintendo one.

There is some nuance as to what happens if the mod chip stops working since there are actually 3 backup BCTs that the Tegra will try to use if the first one is invalid. If the mod chip replaces all 4 BCTs then the Switch will automatically boot into RCM mode if the mod chip stops functioning. On the other hand if the mod chip only replaces the first BCT (as the original 2020 SX Core did) then the Tegra will load one of the valid backup BCTs and try to boot into the official Nintendo operating system. The problem is ALL mod chips have to replace the bootloader with a custom one and if you have a valid BCT with an invalid bootloader then you just end up getting stuck at a different section of the bootchain.

So really it doesn't matter if you enable Auto RCM or not on a mod chipped console. If you do enable it, and your mod chip is working as it is supposed to, then the mod chip will enable the console to boot just fine. If your mod chip stops working then it doesn't matter if Auto RCM is enabled or not because you're going to be bricked either way, you'll just be bricked via a different method.

Additionally if your Auto RCM implementation really fucks up the BCT then the mod chip won't be able to use it. That doesn't matter though because the chip will detect multiple failed boots in a row and rewrite its own BCT to the eMMC.

tl;dr: You probably shouldn't do it, but in reality it doesn't matter.