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CSR Bit Fields

RISC-V pmpaddr26 CSR Register

Address 0x3CAPrivilege MachineAccess RW / MXLEN: RV32 encodes PA[33:2]; RV64 [53:0] encodes PA[55:2] and [63:54] is zeroMachine physical memory protection CSRs

pmpaddr26 (0x3CA) is the WARL address register for machine PMP entry 26 when 64 PMP entries are implemented; it encodes physical address bits 33:2 on RV32 and 55:2 on RV64.

Related Search Terms
pmpaddr26 CSRpmpaddr26 0x3CApmpaddr26 TORpmpaddr26 NAPOTpmpaddr26 grainpmp26cfg 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 pmpaddr26 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

pmpaddr26 is the MXLEN-bit WARL address encoding for entry 26 when 64 PMP entries are implemented. pmp26cfg.A determines its meaning; TOR uses pmpaddr25 as the lower bound.

RV32 pmpaddr encodes PA[33:2]; RV64 [53:0] encodes PA[55:2], with [63:54] zero.
TOR entry 26 uses pmpaddr25 as its lower bound and pmpaddr26 as its upper bound; NAPOT uses low pmpaddr26 bits to encode a naturally aligned power-of-two region of at least 8 bytes.
Platform grain changes low-bit readback; pmp26cfg.L or a locked TOR entry 27 can cause writes to pmpaddr26 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, pmpaddr26 exists only when 64 entries are implemented; every PMP CSR field is WARL and may be read-only zero.
  • - pmpaddr26 is accessible only to M-mode. Its readback depends on pmp26cfg.A and the platform-wide PMP grain G.
  • - With G>=2 and A=NAPOT, pmpaddr26[G-2:0] reads as ones; with G>=1 and A=OFF/TOR, pmpaddr26[G-1:0] reads as zeros, but those bits do not affect TOR matching. Changing pmp26cfg.A[1] changes readback, not the underlying stored value.
  • - Reset specifies defaults only for writable PMP A/L fields (subject to platform overrides); pmpaddr26's reset value is unspecified, but no WARL field contains an illegal value.

Risk Checks Before Writing

  • - Writes to pmpaddr26 are ignored when pmp26cfg.L=1; pmpaddr26 is also unwritable as entry 27's lower bound when that entry is locked with pmp27cfg.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.
  • - pmpaddr26 is WARL; read it back after writing and interpret the masked value using the current pmp26cfg.A and grain.
  • - With pmp26cfg.A=TOR, entry 26 matches pmpaddr25 <= y < pmpaddr26; 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 pmp26cfg.A to determine whether entry 26 uses OFF, TOR, NA4, or NAPOT.

2

Write pmpaddr26 for the selected mode; TOR also requires lower bound pmpaddr25, while NAPOT encodes range size in low bits.

3

Read back pmpaddr26 and the corresponding pmpcfg CSR to confirm the effective WARL/grain encoding; set pmp26cfg.L only after final verification.

FAQ

Where do pmpaddr26's TOR bounds come from?

With pmp26cfg.A=TOR, pmpaddr25 supplies the lower bound and pmpaddr26 the upper bound, so entry 26 matches the half-open range pmpaddr25 <= y < pmpaddr26; it matches no addresses when the lower bound is not less than the upper bound.

Why can pmpaddr26 read back differently from the written value?

pmpaddr26 is WARL, and platform grain plus pmp26cfg.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.