Hacking Question eFuse burning - updating firmware

[vMasked]

Hi guys,

Just a quick question. I loaded the SX OS CFW. (I didn't create an EmuNAND) I then installed choidujournx and booted back to the SX OS CFW from the boot options. I ran the firmware update, it then rebooted back with AutoRCM.

Now my question is, because it rebooted in AutoRCM, does that mean I didn't burn an eFuse?

My other question is, if I did burn an eFuse, does that mean the efuses will keep getting burnt every single time I boot up the Switch without RCM?! OR do efuses only get burnt after an firmware update that didn't reboot after the update via RCM?

Just to avoid confusion, if it didn't boot back up in AutoRCM after the update does it burn the efuse to match the firmware version (i.e 2) and then that's a 2 count? Or will it just keep burning more and more if I boot up the OFW without RCM or a bootloader etc.

Hope this makes sense! One last thing... does it only matter if you ever wanted to downgrade? Because if so I'll never downgrade and therefore I wouldn't really care.

If you could answer this, I'd be very appreciative! This is the last piece of the puzzle for me!

 

[bad361]

Hi guys,

Just a quick question. I loaded the SX OS CFW. (I didn't create an EmuNAND) I then installed choidujournx and booted back to the SX OS CFW from the boot options. I ran the firmware update, it then rebooted back with AutoRCM.

Now my question is, because it rebooted in AutoRCM, does that mean I didn't burn an eFuse?

My other question is, if I did burn an eFuse, does that mean the efuses will keep getting burnt every single time I boot up the Switch without RCM?! OR do efuses only get burnt after an firmware update that didn't reboot after the update via RCM?

Just to avoid confusion, if it didn't boot back up in AutoRCM after the update does it burn the efuse to match the firmware version (i.e 2) and then that's a 2 count? Or will it just keep burning more and more if I boot up the OFW without RCM or a bootloader etc.

Hope this makes sense! One last thing... does it only matter if you ever wanted to downgrade? Because if so I'll never downgrade and therefore I wouldn't really care.

If you could answer this, I'd be very appreciative! This is the last piece of the puzzle for me!

RCM prevents burning fuses and iirc it just skips fuse check completely, so if you don't want to burn em accidentally, always use autoRCM and don't update officially cause it disables autoRCM. The amount of fuses burnt corresponds to the firmware version, you can check it here - https://gist.github.com/jonluca/0d7ce7da7c84de5163be0b49b3e319cc

You don't lose fuses on every official boot indefinitely, you just burn the needed amount for your current OFW once, that's all. And yes, all that fuse hassle only matters if you want the possibility to downgrade in the future.

Actually you can downgrade with burnt fuses, but you will need to use RCM every time you want to launch anything (including OFW) to skip fuse check, otherwise your switch won't launch due to fuse mismatch.

 

[vMasked]

RCM prevents burning fuses and iirc it just skips fuse check completely, so if you don't want to burn em accidentally, always use autoRCM and don't update officially cause it disables autoRCM. The amount of fuses burnt corresponds to the firmware version, you can check it here - https://gist.github.com/jonluca/0d7ce7da7c84de5163be0b49b3e319cc

You don't lose fuses on every official boot indefinitely, you just burn the needed amount for your current OFW once, that's all. And yes, all that fuse hassle only matters if you want the possibility to downgrade in the future.

Actually you can downgrade with burnt fuses, but you will need to use RCM every time you want to launch anything (including OFW) to skip fuse check, otherwise your switch won't launch due to fuse mismatch.

Thanks so much for your reply.

I think I finally understand it now.

When I upgraded my firmware, it rebooted back with AutoRCM, so I skipped the efuse check. Now lets say I turn it off and turn off AutoRCM a few days later and boot up my switch normally without RCM will this burn efuses every single time I boot up the OFW? Or does it only burn once if it don't reboot with autoRCM after updating?

That's the only thing I'm slightly confused about lol. If I keep booting up my switch without RCM is it burning an efuse lol..

Many thanks again!

 

[bad361]

Thanks so much for your reply.

I think I finally understand it now.

When I upgraded my firmware, it rebooted back with AutoRCM, so I skipped the efuse check. Now lets say I turn it off and turn off AutoRCM a few days later and boot up my switch normally without RCM will this burn efuses every single time I boot up the OFW? Or does it only burn once if it don't reboot with autoRCM after updating?

That's the only thing I'm slightly confused about lol. If I keep booting up my switch without RCM is it burning an efuse lol..

Many thanks again!

Yes, if you will boot your switch without RCM even once, you will burn fuses to match OFW fuse count. E.g if you were on fw 4.1 and had fuse count of 5 (that is the fuses burnt count for that FW) and then updated with choi to 9.1 with autoRCM, you would still have had 5 fuses burnt. But as soon as you would turn your switch on without RCM even once, you'd have instantly burnt 6 more fuses (cause OFW 9.1 expects 11 fuses burnt).

 

[vMasked]

Yes, if you will boot your switch without RCM even once, you will burn fuses to match OFW fuse count. E.g if you were on fw 4.1 and had fuse count of 5 (that is the fuses burnt count for that FW) and then updated with choi to 9.1 with autoRCM, you would still have had 5 fuses burnt. But as soon as you would turn your switch on without RCM even once, you'd have instantly burnt 6 more fuses (cause OFW 9.1 expects 11 fuses burnt).

Oh wow, thanks for clearing that up!

Tbh I don't care about downgrading I'll never do that. Will it affect anything else? If the efuse count exceeds?

So once it matches up and burns the 11 fuses, will that then be it? I can carry on booting normally and it won't keep burning fuses, because it's already matched the count?

Thanks again btw

 

[bad361]

Oh wow, thanks for clearing that up!

Tbh I don't care about downgrading I'll never do that. Will it affect anything else? If the efuse count exceeds?

So once it matches up and burns the 11 fuses, will that then be it? I can carry on booting normally and it won't keep burning fuses, because it's already matched the count?

Thanks again btw

1. No, it doesn't affect anything else.
2. Yes, that will be it, you will have 11 fuses burnt for the rest of your staying on 9.1. Later FW updates may require more fuses burnt, so...i think you get it.

 

[vMasked]

1. No, it doesn't affect anything else.
2. Yes, that will be it, you will have 11 fuses burnt for the rest of your staying on 9.1. Later FW updates may require more fuses burnt, so...i think you get it.

Thanks so much mate. Mind is at ease now, I've searched for ages for an easy explanation of this and could find it no where. You simplified it perfectly!