frm

Floating-Point Dynamic Rounding Mode

Rounding modes are encoded as follows:

Table 1. Rounding mode encoding.
!Rounding Mode	Mnemonic	Meaning !000 !RNE !Round to Nearest, ties to Even !001 !RTZ !Round towards Zero !010 !RDN !Round Down (towards \(-\infty\)) !011 !RUP !Round Up (towards \(+\infty\)) !100 !RMM !Round to Nearest, ties to Max Magnitude !101 ! !Reserved for future use. !110 ! !Reserved for future use. !111 !DYN !In instruction’s rm field, selects dynamic rounding mode; In Rounding Mode register, reserved.

The behavior of floating-point instructions that depend on rounding mode when executed with a reserved rounding mode is reserved, including both static reserved rounding modes (101-110) and dynamic reserved rounding modes (101-111).

Some instructions, including widening conversions, have the rm field but are nevertheless mathematically unaffected by the rounding mode; software should set their rm field to RNE (000) but implementations must treat the rm field as usual (in particular, with regard to decoding legal vs. reserved encodings).

Attributes

Defining Extension	F, version >= F@2.2.0
CSR Address	0x2
Length	32-bit
Privilege Mode	U

Defining Extension

F, version >= F@2.2.0

CSR Address

0x2

Length

32-bit

Privilege Mode

Format

Figure 1. frm format

Field Summary

Name	Location	Type	Reset Value
frm.ROUNDINGMODE	2:0	RW-H	UNDEFINED_LEGAL

Name

Location

Type

Reset Value

frm.ROUNDINGMODE

2:0

RW-H

UNDEFINED_LEGAL

Fields

`ROUNDINGMODE`

Location: 2:0
Description: Rounding mode data.
Type: RW-H
Reset value: UNDEFINED_LEGAL

Software write

This CSR may store a value that is different from what software attempts to write.

When a software write occurs (e.g., through csrrw), the following determines the written value:

ROUNDINGMODE = CSR[fcsr].FRM = csr_value.ROUNDINGMODE;
return csr_value.ROUNDINGMODE;

Software read

This CSR may return a value that is different from what is stored in hardware.

return fcsr.FRM;