Hi@Jeevansagar
I test this demo on myside,run it from RAM, it works on myside.
My chip is restored to the factory state through mass erase, if it fails, then you may have partitioned it before

When the Default ISR is called it means that you missed to put a handler in your project, for example, you enable a interrupt but you don't have a handler that attends this interrupt。
INT_SYS_DisableIRQ masks the specified interrupt, not all interrupts, which means that there may be other interrupts.