Nios® II Processor Reference Guide

ID 683836
Date 10/22/2020
Public
Document Table of Contents

3.4.2. Control Registers

Control registers report the status and change the behavior of the processor. Control registers are accessed differently than the general-purpose registers. The special instructions rdctl and wrctl provide the only means to read and write to the control registers and are only available in supervisor mode.

Note: When writing to control registers, all undefined bits must be written as zero.

The Nios® II architecture supports up to 32 control registers. All non-reserved control registers have names recognized by the assembler.

Table 10.  Control Register Names and Bits
Register Name Register Contents
0 status Refer to The status Register
1 estatus Refer to The estatus Register
2 bstatus Refer to The bstatus Register
3 ienable Internal interrupt-enable bits

The ienable Register

Available only when the external interrupt controller interface is not present. Otherwise reserved.

4 ipending Pending internal interrupt bits

The ipending Register

Available only when the external interrupt controller interface is not present. Otherwise reserved.

5 cpuid Unique processor identifier
6 Reserved Reserved
7 exception Refer to The exception Register
8 pteaddr Refer to The pteaddr Register

Available only when the MMU is present. Otherwise reserved.

9 tlbacc Refer to The tlbacc Register

Available only when the MMU is present. Otherwise reserved.

10 tlbmisc Refer to The tlbmisc Register

Available only when the MMU is present. Otherwise reserved.

11 eccinj Refer to The eccinj Register

Available only when ECC is present.

12 badaddr Refer to The badaddr Register
13 config Refer to The config Register

Available only when the MPU or ECC is present. Otherwise reserved.

14 mpubase Refer to The mpubase Register

Available only when the MPU is present. Otherwise reserved.

15 mpuacc Refer to The mpuacc Register for MASK variations table.

Available only when the MPU is present. Otherwise reserved.

16–31 Reserved Reserved

The following sections describe the non-reserved control registers.

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