Until someone (
@d0k3 ,
@Plailect ?) lands here and explains it deeper (if possible!): CTRNAND is just a partition of the
nand, the bigger one, responsible of containing system titles. The direct difference between a CTRNAND backup and a full NAND backup is you don't touch FIRM0/FIRM1 or TWL,AGB or key storage partitions. So what you are really doing is a backup of the system titles.
They might found a way to trick N3DS in properly booting a 3DS CTRNAND since 2.1 system software version is only available to 3DS, perhpahs with a dedicated franken-ctrnand modified enough to grab the otp but not agressively changed to provide universal support.
From my point of view we are not directly changing FIRM partitions by the CTRNAND restore, but then again the process is called CTRNAND transfer for a reason so modification of FIRM0 might be done manually afterwards because afaik the "bug" responsible for the OTP register to be left open is located in the 2.1.0 FIRM.
It really gets me the point of being "universal". That might mean nand backup sharing between hacked systems.
EDIT: From d0k3's release notes:
- CTRNAND Transfer...: This menu contains various options to enable transfer of CTRNAND partitions between consoles.
- Auto CTRNAND Transfer: Automatically transfer a transferable CTRNAND image to this consoles NAND. Without A9LH installed, this will overwrite the FIRM0, FIRM1, CTRNAND. With A9LH installed, this will only overwrite CTRNAND. O3DS images can be transferred into N3DS consoles, but the NCSD header of the NAND may be overwritten.
- Dump transferable CTRNAND: Dump a CTRNAND image for later use in the feature above. Transferables images can be shared between consoles.
- Autofix CTRNAND: Use this to automatically fixes the CMACs for movable.sed, *.db and system saves inside the CTRNAND. It will also fix the inside the data folder. This is useful f.e. when a CTRNAND from another console was previously injected the regular way.SO
So this means we might not need to downgrade anymore. Just make a 9.2 CTRNAND transfer (even o3ds to n3ds). I wonder if this might bypass the N's 11.0 hardcoded min system title version list as I don't think the transfer is using the direct installing/removal of titles into the system. Then again, running d9 requires arm9 and I highly doubt the CTRNAND transfer functionality uses arm11k services only so I think it doesn't make any changes to the 11.0 people.