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CSR Bit Fields

RISC-V sireg CSR Register

Address 0x151Privilege SupervisorAccess RW / XLENSupervisor AIA, timer, and indirect interrupt CSRs

sireg (0x151) is an Sscsrind Supervisor indirect-register alias that accesses extension state selected by siselect.

Related Search Terms
sireg CSRsireg 0x151sireg aliassiselect CSRSscsrindindirect CSR
Bit Overview
bit 3 = only bit 3; bits 12..11 = bits 12 down to 11
MSBLSB
ALIAS_DATA63:0Depends on select
Field Map

Understand sireg By Bit Fields

1 key fields
XLEN-1:0

ALIAS_DATA

Depends on select

Alias data window; exact read/write semantics are defined by the extension selected by siselect, and cannot be inferred from this CSR name for unimplemented select values.

ALIAS_DATA (bits XLEN-1:0) — Alias data window; exact read/write semantics are defined by the extension selected by siselect, and cannot be inferred from this CSR name for unimplemented select values.

What This Field Controls

  • - Alias data window; exact read/write semantics are defined by the extension selected by siselect, and cannot be inferred from this CSR name for unimplemented select values.

Common Values

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

↗Open Official Manual
Official Basis & Search Notes

sireg is not an independent fixed-meaning register; it is an alias window selected by siselect.

Sscsrind defines sireg* behavior through the siselect/sireg* combination and the selected extension.
CTR uses siselect 0x200..0x2FF for CTR entries; AIA IMSIC uses 0x70..0xFF for interrupt-file state.
Do not assume zero reads, writability, or fixed side effects for unimplemented select values.
RISC-V Privileged Architecture Manual - CSR tableRISC-V Privileged Architecture Manual - Smcsrind/SscsrindRISC-V Advanced Interrupt Architecture - IMSIC CSRsRISC-V Privileged Architecture Manual - SmctrRISC-V Privileged Architecture Manual

What To Check First When Reading This CSR

  • - First confirm that the hart implements the extension containing sireg; unimplemented or insufficiently privileged CSR accesses raise an illegal-instruction exception.
  • - Use address 0x151, the lowest access privilege, and the official access class to decide whether software may access it directly.
  • - Do not assume fixed values for reserved, WPRI, WARL, or WLRL fields; interpret them according to the specification and implementation.

Risk Checks Before Writing

  • - When writing sireg, modify only the officially defined target fields and preserve unchanged bits.
  • - Handle WARL, WLRL, WPRI, and reserved fields according to the official specification; do not overwrite the whole CSR as an ordinary integer.

Put It Back Into A Real Flow

1

First write siselect to choose the indirect-register number.

2

Then access the corresponding alias window through sireg.

3

If the selected extension or window is not implemented, handle illegal-instruction exceptions or the officially specified UNSPECIFIED behavior.

FAQ

Why are sireg bit fields unlike ordinary CSRs?

Because it is an alias window; bit fields depend on the current siselect value and selected extension.