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0 pointskazinator10y ago0 comments

If I have no access to the firmware, but neither does anyone else, then it's just a part of the hardware. That is okay.

I don't care whether a given processor is microcoded via a tiny ROM, or whether it is all hard-wired gates; the difference is just in the instruction execution timings.

We are not "hosed" in any way by this.

As soon as the microcode is writable, then we have questions: can anyone write any arbitrary microcode and put it in place? Or is there some tamper-proof layer containing that only accepts signed microcode, and who has the keys?

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ksk10y ago

>If [...] but neither does anyone else, then it's just a part of the hardware

That has never been the case, for practical manufacturing reasons.

>As soon as the microcode is writable, then we have questions:

It has been writable for more than a decade I think.

kazinatorOP10y ago

Uh, microcode has been around since the 1960's!

Any aspect of the machine which is data-driven is de facto hardware if that data is fixed in read-only memory.

Consider than an AND gate can just be memory. The two inputs can be treated as a two bit address: 00, 01, 10, or 11. If we stuff in the values 0, 0, 0, 1 into the 1-bit content cells at these addresses, we have an AND gate.

If this memory is ROM, then the overall circuit is not distinguishable from a conventional AND gate where a few transistors do the signaling directly.

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