Discussion
Consider the following two statements about interrupt handling mechanisms in a CPU.
S1: In non-vectored interrupt mechanism, it usually takes more time to start the Interrupt Service Routine (ISR) when compared to that in a vectored interrupt mechanism.
S2: In daisy-chain interrupt mechanism, the CPU polls all the input devices individually to determine the source of the interrupt.
Which one of the following options is correct with respect to S1 and S2 ?
Answer: C
S1 is true and S2 is false.
S1: In a vectored interrupt scheme, the interrupting device supplies a vector that points the CPU straight at its service routine. In a non-vectored scheme, the CPU jumps to a fixed location and must then find out which device interrupted, usually by polling, before reaching the right ISR. So starting the ISR typically takes longer, and S1 is true.
S2: Daisy chaining is a hardware priority scheme. The interrupt-acknowledge signal passes from device to device along the chain, and the first requesting device stops it and places its identifying vector on the bus. The CPU does not poll each device; that describes software polling. So S2 is false.
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