Bill Huffman wrote:
Chipmakers sometimes wish to include code in a memory region which isConcerning PMP, that's what I was suggesting, yes.
I wonder if there is a way it can be done for code executable in S/UI believe the answer can be physical memory attributes (PMAs), which
apply in addition to the software-programmable PMP mechanism. If this
is a ROM at known addresses, then just say the region is execute-only
according to the machine's PMAs. PMP can't override that.
If the address range is unknown at chip fabrication time or starts as
writable, you can still invent a custom mechanism to manipulate the
chip's PMAs underneath the standard PMP facility, without violating
any RISC-V rules as I understand them. Obviously, a custom mechanism
wouldn't be portable beyond your own line of chips, but it doesn't need
to be for this purpose, does it?
- John Hauser