Question: When a lower-priority interrupt occur while another higher-priority interrupt is being serviced,what will the system do ? Does it halt the lower-priority interrupt until the higher-priority interrupt finish, or dismiss the lower-priority interrupt? What should I do, if I want these two interrupt to be serviced normally?

Answer: The higher priority interrupt will be serviced first. If a lower priority interrupt is being serviced and a higher priority interrupt is issued, then the lower priority interrupt will be halted and the status bit will be set. After the higher priority interrupt is serviced, then the lower priority interrupt will be serviced.