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A comment on How the Nintendo Switch prevents downgrades by irreparably blowing its own fuses. Parent comment

Re:How the Nintendo Switch prevents downgrades by irreparabl... by arghwhat on Tuesday June 16, 2020 @04:15AM (#23536958)
"Fuses" in this context are just non-volatile memory that cannot be reset. Once a bit is set to 1, it stays there. They're often used for configuration and for things like sealing off programming/readout on microcontrollers.

FUSE_RESERVED_ODM7 is 32 bits wide, hence contains "32 fuses". The system has many fuses, but 256 bits (RESERVED_ODM0-RESERVED_ODM7) are for the device manufacturers to use for their own purpose, which is what Nintendo is doing here.

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Re:How the Nintendo Switch prevents downgrades by irreparabl... by londons_explore on Tuesday June 16, 2020 @06:31AM (#23537553)
On some chips they are literally bits of polysilicon that burn. On most devices they're flash memory that doesn't have any circuitry to do erases.
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Re:How the Nintendo Switch prevents downgrades by irreparabl... by marcan_42 on Tuesday June 16, 2020 @08:20AM (#23538247)
You're thinking microcontrollers with flash. This is not one of those.

Modern high performance CPUs/SoCs do not contain flash, ever (the processes are incompatible). When we talk about SoC fuses, we mean real fuses (or antifuses), not the Flash "fuses" of some microcontrollers (which can be erased with UV light).

Actual technologies vary. It could be fuses (metal, polysilicon, or other) or antifuses (e.g. gate oxide breakdown, "blown" means it conducts), but they're all irreversible.

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