colin
/
Hazard3
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Describe new pmpcfgm0 register

This commit is contained in:
Luke Wren 2022-08-08 23:08:31 +01:00
parent 5819f8eb7e
commit 259a402e28
1 changed files with 21 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

21
doc/sections/csr.adoc
View File

@ -647,6 +647,27 @@ no_more_irqs:
mret
----
=== Custom Memory Protection CSRs
==== mpmpcfgm0
Address: 0xbd0
PMP M-mode configuration. One bit per PMP region. Setting a bit makes the corresponding region apply to M-mode (like the `pmpcfg.L` bit) but does not lock the region.
PMP is useful for non-security-related purposes, such as stack guarding and peripheral emulation. This extension allows M-mode to freely use any currently unlocked regions for its own purposes, without the inconvenience of having to lock them.
Note that this does not grant any new capabilities to M-mode, since in the base standard it is already possible to apply unlocked regions to M-mode by locking them. In general, PMP regions should be locked in ascending region number order so they can't be subsequently overridden by currently unlocked regions.
Note also that this is not the same as the "rule locking bypass" bit in the ePMP extension, which does not permit locked and unlocked M-mode regions to coexist.
[cols="10h,20h,~", options="header"]
|===
| Bits | Name | Description
| 31:16 | - | RES0
| 15:0 | `m` | Regions apply to M-mode if this bit _or_ the corresponding `pmpcfg.L` bit is set. Regions are locked if and only if the corresponding `pmpcfg.L` bit is set.
|===
=== Custom Power Control CSRs
==== msleep