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

Re:How the Nintendo Switch prevents downgrades by irreparabl... by wolfgke on Tuesday June 16, 2020 @04:09AM (#23536933)

> There are 256 bits in the set of ODM_RESERVED fuses, and there are 8 ODM_RESERVED. This allows for 32 fuses, or 32 future FW versions (provided they burn a fuse on every major release).

Can someone explain how the author gets from the numbers 256 and 8 to the count of 32 fuses?

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Re:How the Nintendo Switch prevents downgrades by irreparabl... by marcan_42 on Tuesday June 16, 2020 @08:17AM (#23538217)

Fuses are in 32 bit words. There are 8 such words available for ODM usage, giving a total of 256 fuse bits. However, of those only one word is used for the anti-downgrade stuff. So that's just 32 firmware levels.

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Re:How the Nintendo Switch prevents downgrades by irreparabl... by nitrogen on Tuesday June 16, 2020 @04:21AM (#23536977)

Maybe that's 256 bits divided into eight chunks of 32?

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Re:How the Nintendo Switch prevents downgrades by irreparabl... by indigo945 on Tuesday June 16, 2020 @04:47AM (#23537116)

I think it's the other way around, there's 32 fuse-bytes of 8 fuse-bits each, adding up to 256 bits of PROM.

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