In Nios II Software Developer’s Handbook (January 2014) P8-11, I found following information. When the SBT selects the interrupt API, it defines one of the following symbols in system.h, to identify which interrupt API is available: ■ ALT_ENHANCED_INTERRUPT_API_PRESENT —Defined if the enhanced API is implemented ■ ALT_LEGACY_INTERRUPT_API_PRESENT —Defined if the legacy API is implemented Does it mean to edit system.h directory? I confirmed that edited system.h works correctly. But in this method, I need edit every time after generating BSP. Is there more smart way such as setting GUI switch or other permanent FLAG. Thank you.