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CSR Bit Fields

RISC-V mhartid CSR Register

Address 0xF14Privilege MachineAccess RO / XLENMachine implementation and hart identification CSRs

Machine hart ID; returns the unique identifier of the current hart.

Related Search Terms
mhartid CSRmhartid 0xF14machine hart IDhart identifierRISC-V mhartidread only machine CSR
Bit Overview
bit 3 = only bit 3; bits 12..11 = bits 12 down to 11
MSBLSB
HARTID63:0RO
Field Map

Understand mhartid By Bit Fields

1 key fields
XLEN-1:0

HARTID

RO

Current hart ID

HARTID (bits XLEN-1:0) — Current hart ID.

What This Field Controls

  • - Current hart ID

Common Values

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

Official Basis & Search Notes

mhartid is a RO CSR in machine implementation and hart identification csrs at 0xF14. Check privilege and implemented extensions before interpreting its bit fields.

mhartid address, lowest access privilege, and access class are checked against the official CSR table: 0xF14, Machine, RO.
Read it as part of machine implementation and hart identification csrs before interpreting the bit-field table on this page.
This is a read-only CSR; do not write it. Ignore reserved or WPRI field values on reads, and preserve unchanged fields when writing writable CSRs.
RISC-V Privileged Architecture ManualRISC-V Unprivileged ISA Manual

What To Check First When Reading This CSR

  • - First confirm that the current hart implements mhartid; unimplemented or insufficiently privileged accesses raise an illegal-instruction exception.
  • - Use address 0xF14 and the lowest access privilege (Machine) to decide whether software may read it directly.
  • - Do not assume fixed values for reserved, WARL, or WLRL bits; interpret the value according to the specification and implementation.

Risk Checks Before Writing

  • - mhartid is a read-only CSR; writes raise an illegal-instruction exception or are disallowed by the implementation.

Put It Back Into A Real Flow

1

Read mhartid to obtain hardware or runtime state.

2

Interpret the returned value according to the field descriptions and do not attempt to write it back.

3

If reading fails at the current privilege level, handle the illegal-instruction exception path.

FAQ

Can mhartid be accessed from any privilege level?

Do not decide from the CSR name alone. The official CSR address encoding and tables define the lowest access privilege; this entry records mhartid as Machine. Access with insufficient privilege or to an unimplemented CSR raises an illegal-instruction exception.

What is easiest to miss when using mhartid?

mhartid is read-only. Treat it as an observation point, do not try to write it, and do not depend on fixed values for reserved or WPRI fields.