It seems that a lot of people don't fully grasp the situation with eFuses. So, I figured I'd go ahead and write out an FAQ for them.
Edit: Made some corrections.
Q: eFuses? What?
A: The Nintendo Switch contains things called eFuses that can be blown on command. The system checks on every boot how many fuses are intact, and if too many have already been burnt, it will panic, stop the boot process, and lock up. If not enough have been burnt, it will burn more. Different firmware versions require different numbers of fuses to be blown (generally going upward every now and then from 1.0).
Q: So how is that supposed to prevent downgrading?
A: Downgrading would involve switching to a firmware that expects a lower number of fuses to be burnt than already have. There's no way around this, so the older firmware just won't boot.
Q: Can't we just unburn the eFuses?
A: eFuses are physical objects, and burning them involves physically destroying or permanently modifying part of it. There is no way to reverse this process through software.
Q: Then can't we just replace them?
A: These are microscopic objects embedded into the CPU. It would be easier and more cost effective to replace the entire CPU.
Q: Why can't we just replace the entire CPU then?
A: If you really want to disassemble your Switch and replace the CPU, be my guest. For the rest of us, it's just not practical.
Q: Is there some way to just skip the eFuse check?
A: We don't know yet.
Q: So is downgrading impossible then?
A: Not necessarily. The modding community has overcome harsh security measures in the past, so they could still overcome this one. It just so happens that this one is extremely difficult.
Q: What does this mean for emuNAND and Custom Firmware?
A: emuNAND would still check the eFuses when starting up, just like the system itself does, and act in the same way. This means that, unless sysNAND and emuNAND are on the same firmware, your system would probably end up bricked after starting emuNAND just once.
EDIT: As pointed out by multiple other users, emuNAND would have to be very poorly implemented for this to be an actual problem.
Q: Would [insert elaborate hypothetical solution here] work?
A: Maybe. Probably not, but maybe.
Q: So does this mean I shouldn't update?
A: If you care about homebrew and/or CFW, you shouldn't update anyway, for other reasons.
Q: What eFuse counts do the different firmware versions expect?
A: http://switchbrew.org/index.php?title=Fuse_registers
Edit: Made some corrections.
Q: eFuses? What?
A: The Nintendo Switch contains things called eFuses that can be blown on command. The system checks on every boot how many fuses are intact, and if too many have already been burnt, it will panic, stop the boot process, and lock up. If not enough have been burnt, it will burn more. Different firmware versions require different numbers of fuses to be blown (generally going upward every now and then from 1.0).
Q: So how is that supposed to prevent downgrading?
A: Downgrading would involve switching to a firmware that expects a lower number of fuses to be burnt than already have. There's no way around this, so the older firmware just won't boot.
Q: Can't we just unburn the eFuses?
A: eFuses are physical objects, and burning them involves physically destroying or permanently modifying part of it. There is no way to reverse this process through software.
Q: Then can't we just replace them?
A: These are microscopic objects embedded into the CPU. It would be easier and more cost effective to replace the entire CPU.
Q: Why can't we just replace the entire CPU then?
A: If you really want to disassemble your Switch and replace the CPU, be my guest. For the rest of us, it's just not practical.
Q: Is there some way to just skip the eFuse check?
A: We don't know yet.
Q: So is downgrading impossible then?
A: Not necessarily. The modding community has overcome harsh security measures in the past, so they could still overcome this one. It just so happens that this one is extremely difficult.
Q: What does this mean for emuNAND and Custom Firmware?
A: emuNAND would still check the eFuses when starting up, just like the system itself does, and act in the same way. This means that, unless sysNAND and emuNAND are on the same firmware, your system would probably end up bricked after starting emuNAND just once.
EDIT: As pointed out by multiple other users, emuNAND would have to be very poorly implemented for this to be an actual problem.
Q: Would [insert elaborate hypothetical solution here] work?
A: Maybe. Probably not, but maybe.
Q: So does this mean I shouldn't update?
A: If you care about homebrew and/or CFW, you shouldn't update anyway, for other reasons.
Q: What eFuse counts do the different firmware versions expect?
A: http://switchbrew.org/index.php?title=Fuse_registers
Last edited by The9thBit,
