How the Nintendo Switch prevents downgrades by irreparably blowing its own fuses

Re:How the Nintendo Switch prevents downgrades by irreparabl... by ThePowerOfFuet on Tuesday June 16, 2020 @04:08AM (#23536926)

> I'm unclear on how these hardware fuses actually work. Are they actual fuses that can be burnt on will by excessive power?

No, they're not like the fuses in your house. These can be blown by software to irrevocably change something which can then be verified later, or in other cases to prevent reprogramming of a microcontroller (which can be programmed only if the programming fuse is still intact.

>Does this mean FUSE_RESERVED_ODM7 actually contains multiple fuses?

No, that's the name of one fuse. Once you upgrade the device next time, the upgrade tool would, for example, blow FUSE_RESERVED_ODM8; older software would verify that this fuse (and the higher-numbered ones) are NOT blown, and refuse to boot otherwise.

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Re:How the Nintendo Switch prevents downgrades by irreparabl... by arghwhat on Tuesday June 16, 2020 @04:17AM (#23536966)

> No, that's the name of one fuse.

No, it's a 32-bit segment belonging to the 256-bit odm_reserved segment. FUSE_RESERVED_ODM7 is specifically the last 32-bit segment.

Some fuse information can be read here: https://docs.nvidia.com/jetson/archives/l4t-archived/l4t-323....

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Re:How the Nintendo Switch prevents downgrades by irreparabl... by outadoc on Tuesday June 16, 2020 @04:12AM (#23536940)

Thanks! Definitely more clear.

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