If the Reset Vector of Nios® II is set to Flash Controller, the Flash Controller is accessed at the beginning of the process after Nios® II is started.
If the simulation model in Flash ROM is not loaded at that time, Nios II will stop because it reads an undefined value.
To run simulations without the Flash ROM simulation model connected, the Nios II Boot configuration can be changed to boot and run from On Chip RAM only during simulation.
The Nios II Boot configuration can be configured to boot from On Chip RAM by setting the following.
Nios II Reset Vector: On Chip RAM
・Nios II Exception Vector: On Chip RAM
・Location of various sections of Nios II Linker Script: On Chip RAM
（Reference
Nios® II Boot Option ~ On Chip RAM (XIP) ~
https://macnicago.zendesk.com/hc/ja/articles/360029104132
[Nios® II Beginner's Guide - Nios® II Simulation]
https://www.macnica.co.jp/business/semiconductor/articles/pdf/ELS1441_Q1700_10__1.pdf
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Category: Nios® II
Tools: Nios® II EDS
Devices: -