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CSR Bit Fields

RISC-V vxsat CSR Register

Address 0x009Privilege User/VectorAccess RW / XLENUser vector state CSRs

vxsat is an XLEN-bit read-write CSR whose least-significant bit indicates whether a fixed-point instruction has saturated an output to fit its destination format.

Related Search Terms
vxsat CSRvxsat 0x009vector fixed-point saturationvcsr VXSATRVV vxsat
Bit Overview
bit 3 = only bit 3; bits 12..11 = bits 12 down to 11
MSBLSB
Reserved63:1Write zeroVXSAT0RW
Field Map

Understand vxsat By Bit Fields

2 key fields
XLEN-1:1

Reserved

Write zero

Reserved bits; should be written as zeros.

Reserved (bits XLEN-1:1) — Reserved bits; should be written as zeros.

What This Field Controls

  • - Reserved bits; should be written as zeros.

Common Values

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

↗Open Official Manual
0

VXSAT

RW

Fixed-point saturation flag; mirrored in bit 0 of vcsr.

VXSAT (bit 0) — Fixed-point saturation flag; mirrored in bit 0 of vcsr.

What This Field Controls

  • - Fixed-point saturation flag; mirrored in bit 0 of vcsr.

Common Values

00

Does not indicate a fixed-point instruction saturated an output to fit its destination format.

11

Indicates at least one fixed-point instruction saturated an output to fit its destination format.

↗Open Official Manual
Official Basis & Search Notes

vxsat[0] reports saturation performed by vector fixed-point operations to fit a destination format.

vxsat has one read-write least-significant bit; its other XLEN-1 bits should be written as zero.
The vxsat bit is mirrored in vcsr.
RISC-V Unprivileged ISA ManualRISC-V Privileged Architecture Manual

What To Check First When Reading This CSR

  • - Accessing a vector CSR raises an illegal-instruction exception when mstatus.VS is Off.
  • - vxsat, vxrm, and vstart can have arbitrary values at reset; software should explicitly reset the vxrm and vxsat fields before use.

Risk Checks Before Writing

  • - vxsat[XLEN-1:1] should be written as zeros.
  • - Writing vxsat[0] is also reflected through its mirrored vcsr field.

Put It Back Into A Real Flow

1

Before using vector fixed-point state, software explicitly initializes vxsat.

2

Check vxsat[0] to determine whether destination-format saturation has occurred.

FAQ

How is vxsat related to vcsr?

vxsat is an XLEN-bit read-write CSR whose least-significant bit indicates whether a fixed-point instruction has saturated an output to fit its destination format.