Re: Extending the number of PMP entries

Andrew Waterman

On Fri, Oct 2, 2020 at 1:53 AM Mario Achkar <machkar@...> wrote:


Sorry about reviving an old post but I would like to verify as I do not find this clear in the privileged draft.
If a decision is taken to implement exactly 16 PMP registers, should accesses to configuration/address registers outside of these 16 cause an illegal instruction exception or simply writes are ignored and reads hardwired to 0.
Or are both of the above allowed? If so, what is the best approach for future products.

The 16-PMP scheme is the only ratified one.  It's highly unlikely, but the CSRs allocated to the 64-PMP scheme might not ultimately be so purposed.  The most conservative option is to stick to the ratified spec.


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