Nios® II Processor Reference Guide

ID 683836
Date 8/28/2023
Document Table of Contents

3.1.1. Supervisor Mode

Supervisor mode allows unrestricted operation of the processor. All code has access to all processor instructions and resources. The processor may perform any operation the Nios II architecture provides. Any instruction may be executed, any I/O operation may be initiated, and any area of memory may be accessed.

Operating systems and other system software run in supervisor mode. In systems with an MMU, application code runs in user mode, and the operating system, running in supervisor mode, controls the application’s access to memory and peripherals. In systems with an MPU, your system software controls the mode in which your application code runs. In Nios® II systems without an MMU or MPU, all application and system code runs in supervisor mode.

Code that needs direct access to and control of the processor runs in supervisor mode. For example, the processor enters supervisor mode whenever a processor exception (including processor reset or break) occurs. Software debugging tools also use supervisor mode to implement features such as breakpoints and watchpoints.

Note: For systems without an MMU or MPU, all code runs in supervisor mode.