Re: [RISC-V] [tech-virt-mem] Help needed on physical address issues
On Tue, Aug 9, 2022 at 7:07 AM mark <markhimelstein@...> wrote:
The way to view this matter is that PA's are full 56-bit zero-extended values. It is up to PMAs to, for example, mark the top six bits of PA space as a big 'vacant' region that results in an Access Fault on all attempted accesses with PA[55:50] != 'b000000. That 'vacant' PMA region can of course be a "fixed" PMA region that only requires the address decode logic gates to implement.
The new (in development) RISC-V Unified Discovery mechanism will support low-level discovery of exactly things like this (and many other things). If you're running, for example, a Linux OS, then higher-level (post OS boot) discovery would typically be provided via Device Tree of ACPI tables.