Nios II Classic Processor Reference Guide

ID 683620
Date 10/28/2016
Document Table of Contents

8.5.76. rdprs

Instruction read from previous register set

rB ←  prs.rA + σ(IMM16)

Assembler Syntax

rdprs rB, rA, IMM16


rdprs r6, r7, 0


Sign-extends the 16-bit immediate value IMM16 to 32 bits, and adds it to the value of rA from the previous register set. Places the result in rB in the current register set.


The previous register set is specified by status.PRS. By default, status.PRS indicates the register set in use before an exception, such as an external interrupt, caused a register set change.

To read from an arbitrary register set, software can insert the desired register set number in status.PRS prior to executing rdprs.

If shadow register sets are not implemented on the Nios II core, rdprs is an illegal instruction.


Supervisor-only instruction

Illegal instruction

Instruction Type


Instruction Fields

A = Register index of operand rA

B = Register index of operand rB

IMM16 = 16-bit signed immediate value

Bit Fields
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
IMM16 0x38