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CSR Bit Fields

RISC-V pmpaddr46 CSR Register

Address 0x3DEPrivilege MachineAccess RW / MXLEN: RV32 encodes PA[33:2]; RV64 [53:0] encodes PA[55:2] and [63:54] is zeroMachine physical memory protection CSRs

pmpaddr46 (0x3DE) is the WARL address register for machine PMP entry 46 when 64 PMP entries are implemented; it encodes physical address bits 33:2 on RV32 and 55:2 on RV64.

Related Search Terms
pmpaddr46 CSRpmpaddr46 0x3DEpmpaddr46 TORpmpaddr46 NAPOTpmpaddr46 grainpmp46cfg A
Bit Overview
bit 3 = only bit 3; bits 12..11 = bits 12 down to 11
MSBLSB
063:54WARL/reads zeroaddress[55:2]53:0WARL/may be RO0
Field Map

Understand pmpaddr46 By Bit Fields

2 key fields
63:54

0

WARL/reads zero

RV64: the upper ten bits are zero in the standard pmpaddr format; this segment is part of the WARL format.

0 (bits 63:54) — RV64: the upper ten bits are zero in the standard pmpaddr format; this segment is part of the WARL format.

What This Field Controls

  • - RV64: the upper ten bits are zero in the standard pmpaddr format; this segment is part of the WARL format.

Common Values

This field is better understood together with surrounding context than as a fixed memorized enumeration.

↗Open Official Manual
53:0

address[55:2]

WARL/may be RO0

RV64: encodes bits 55:2 of a 56-bit physical address. Unimplemented physical-address bits make the field WARL; every PMP CSR field may be implemented as read-only zero.

address[55:2] (bits 53:0) — RV64: encodes bits 55:2 of a 56-bit physical address. Unimplemented physical-address bits make the field WARL; every PMP CSR field may be implemented as read-only zero.

What This Field Controls

  • - RV64: encodes bits 55:2 of a 56-bit physical address. Unimplemented physical-address bits make the field WARL; every PMP CSR field may be implemented as read-only zero.

Common Values

This field is better understood together with surrounding context than as a fixed memorized enumeration.

↗Open Official Manual
Official Basis & Search Notes

pmpaddr46 is the MXLEN-bit WARL address encoding for entry 46 when 64 PMP entries are implemented. pmp46cfg.A determines its meaning; TOR uses pmpaddr45 as the lower bound.

RV32 pmpaddr encodes PA[33:2]; RV64 [53:0] encodes PA[55:2], with [63:54] zero.
TOR entry 46 uses pmpaddr45 as its lower bound and pmpaddr46 as its upper bound; NAPOT uses low pmpaddr46 bits to encode a naturally aligned power-of-two region of at least 8 bytes.
Platform grain changes low-bit readback; pmp46cfg.L or a locked TOR entry 47 can cause writes to pmpaddr46 to be ignored. Smepmp MML=1 changes L's permission meaning, but the relevant L=1 rules remain locked unless RLB=1 temporarily bypasses locking.
RISC-V ISA Manual 2026-07-09 release - Machine ISA PMPRISC-V Privileged Architecture - Physical Memory ProtectionRISC-V Privileged Architecture - Smepmp Physical Memory Protection Rules

What To Check First When Reading This CSR

  • - PMP is optional; implementations may provide 0, 16, or 64 entries, with the lowest-numbered entries implemented first. Therefore, pmpaddr46 exists only when 64 entries are implemented; every PMP CSR field is WARL and may be read-only zero.
  • - pmpaddr46 is accessible only to M-mode. Its readback depends on pmp46cfg.A and the platform-wide PMP grain G.
  • - With G>=2 and A=NAPOT, pmpaddr46[G-2:0] reads as ones; with G>=1 and A=OFF/TOR, pmpaddr46[G-1:0] reads as zeros, but those bits do not affect TOR matching. Changing pmp46cfg.A[1] changes readback, not the underlying stored value.
  • - Reset specifies defaults only for writable PMP A/L fields (subject to platform overrides); pmpaddr46's reset value is unspecified, but no WARL field contains an illegal value.

Risk Checks Before Writing

  • - Writes to pmpaddr46 are ignored when pmp46cfg.L=1; pmpaddr46 is also unwritable as entry 47's lower bound when that entry is locked with pmp47cfg.A=TOR. Without Smepmp, locking persists until hart reset. With Smepmp MML=1, L changes permission meaning, but the L=1 M-mode-only or locked Shared-Region rules it defines remain locked unless mseccfg.RLB=1 temporarily bypasses locking.
  • - pmpaddr46 is WARL; read it back after writing and interpret the masked value using the current pmp46cfg.A and grain.
  • - With pmp46cfg.A=TOR, entry 46 matches pmpaddr45 <= y < pmpaddr46; if the lower bound is not less than the upper bound, it matches no addresses. NA4 is not selectable when G>=1.

Put It Back Into A Real Flow

1

Read pmp46cfg.A to determine whether entry 46 uses OFF, TOR, NA4, or NAPOT.

2

Write pmpaddr46 for the selected mode; TOR also requires lower bound pmpaddr45, while NAPOT encodes range size in low bits.

3

Read back pmpaddr46 and the corresponding pmpcfg CSR to confirm the effective WARL/grain encoding; set pmp46cfg.L only after final verification.

FAQ

Where do pmpaddr46's TOR bounds come from?

With pmp46cfg.A=TOR, pmpaddr45 supplies the lower bound and pmpaddr46 the upper bound, so entry 46 matches the half-open range pmpaddr45 <= y < pmpaddr46; it matches no addresses when the lower bound is not less than the upper bound.

Why can pmpaddr46 read back differently from the written value?

pmpaddr46 is WARL, and platform grain plus pmp46cfg.A[1] masks low-bit readback: NAPOT can read ones while OFF/TOR reads zeros. Changing A[1] does not alter the underlying stored value.