An MSP430-based system interfaces 4 external devices (ED0, ED1, ED2, ED3), each capable of generating an interrupt request. The external devices place a request by setting the request line (a transition from a logic one to a logic zero). The request lines are connected on port 1 pins P2.7 (ED0), P2.6, P1.1, and P1.0 (ED3), respectively. A request line is kept active as long as the interrupt request is pending, until the request is serviced. Answer the following questions.

A) Specify the registers that need to be initialized at the beginning to configure the system for accepting the interrupts from the devices ED0-ED3. Fill in the table below. Note: to specify interrupts active on the falling edge the edge-selection bits should be set to 1.

B) How many ISRs is needed to handle events from ED0-ED3? If requests from ED0 and ED1 occur at the same time, ED0 should be serviced first; if requests from ED2 and ED3 occur at the same time, ED2 should be serviced first. Once in a service routine, multiple requests can be serviced if pending. Outline the main steps taken in the interrupt service routine associated with Port 1

C) Assume that processing request from each peripheral takes ~4 ms (e.g., if two requests are active at the same time, an ISR will take 8 ms to execute). The processor is in a low-power mode when not executing code in an ISR. The following table describes a sequence of events in time. Fill in the table by answering what happens with the MSP430 on each relevant event if we know the following: ED0 raises an interrupt request at 35 ms, ED2 at 37 ms, and ED1 at 40 ms.

Time	Event	MSP430 status
0 ms	SW initialization	Active (run initialization software)
10 ms	Go to a low-power mode	Sleep
35 ms	Request from ED0 is received