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ISRO | ISRO CS 2009 | Question 22

Last Updated : 04 Jun, 2018
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A certain microprocessor requires 4.5 microseconds to respond to an interrupt. Assuming that the three interrupts I1, I2 and I3 require the following execution time after the interrupt is recognized:
i. I1 requires 25 microseconds
ii. I2 requires 35 microseconds
iii. I3 requires 20 microseconds

I1 has the highest priority and I3 has the lowest. What is the possible range of time for I3 to be executed assuming that it may or may not occur simultaneously with other interrupts?

(A) 24.5 microseconds to 39.5 microseconds
(B) 24.5 microseconds to 93.5 microseconds
(C) 4.5 microseconds to 24.5 microseconds
(D) 29.5 microseconds 93.5 microseconds


Answer: (B)

Explanation: If I3 is executed assuming without other interrupts:
Time interval = Interrupt processing time + Execution time = 4.5 + 20 microseconds = 24.5 microseconds
If I3 is executed simultaneously with other interrupts:
Time interval = Interrupt processing time + Execution time for I1, I2, I3 = 4.5 + 25 + 4.5 + 35 + 4.5 + 20 = 93.5 microseconds

So, option (B) is correct.

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