> > Adding cpu instructions is something that you can't physically do

> You can physically do it with a microcode update.

Do these ARM CPUs even have microcode? Unlike on x86 CPUs where there are some very complex instructions which have to be microcoded, on ARM all instructions are simple enough that their decoding into micro-operations can be completely hard-coded in the decoder logic.

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charcircuit 8 days ago | parent [-]

Yes, it's too risky to make CPUs without microcode. Being able to fix bugs, or at least disable things so you don't have a complete paperweight is still important even for ARM.

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cesarb 8 days ago | parent [-]

Disabling things can be done through "chicken bits" on configuration registers, no microcode necessary.

Do you know of any ARM cores used on smarphones which actually have updatable microcode? I've never heard of any. All errata fixes I've seen are of the "set this bit in a specific register" kind.

	▲	charcircuit 8 days ago \| parent [-]
		After looking further into it, you are right.