Solution

The correct answer is C, D, B, E, A

Key Points

To arrange the steps of handling subroutines in the correct order, let's understand the logical sequence:

• Save the contents of processor registers (C)
  • The first step is to save the current state of the processor registers to ensure that the current process can be resumed correctly after the interrupt is serviced.
• Check which flag is set (D)
  • Next, identify which device or event has triggered the interrupt by checking the flags.
• Service the device whose flag is set (B)
  • Then, perform the necessary actions to service the device or handle the event that triggered the interrupt.
• Restore the contents of processor registers (E)
  • After the device has been serviced, restore the processor registers to their previous state so that the interrupted process can continue correctly.
• Turn on the interrupt facility on (A)
  • Finally, re-enable the interrupt facility to allow the system to handle future interrupts.

So, the correct order is: C, D, B, E, A