ISRO2009-78

Question

On receiving an interrupt from an I/O device,the CPU

• A. Halts for a predetermined time
• B. Branches off to the interrupt service routine after completion of the current instruction
• C. Branches off to the interrupt service routine immediately
• D. Hands over control of address bus and data bus to the interrupting device

Comments

So for TRAP ? 

Answer 1

CPU checks the status bit of interrupt at the completion of each current instruction running when there is a interrupt it service the interrupt using ISR.

so OPTION B)Branches off to the interrupt service routine after completion of the current instruction

Comments

It may not always branch to the interrupt service routine after completion of the current instruction, if interrupt is maskable.

I think answer should be

B)May branches off to the interrupt service routine after completion of the current instruction

Answer 2

ans is (b)

An interrupt service routine (ISR) is a software routine that hardware invokes in response to an interrupt. ISRs examine an interrupt and determine how to handle it. ISRs handle the interrupt, and then return a logical interrupt value.

Branches off to the interrupt service routine after completion of the current instructio

Comments

can a software invoke isr???as u have mentioned that isr is raised by h/w devices

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it is not a software or hardware it is the CPU who invokes the ISR.

better to understand.

I/O devices invokes the interrupts an CPU invokes the ISR to handles the interrupts.😐

Answer 3

1. The CPU then performs a state save, and transfers control to the interrupt handler routine at a fixed address in memory. ( The CPU catches the interrupt and dispatches the interrupt handler)
2. The interrupt handler determines the cause of the interrupt, performs the necessary processing, performs a state restore, and executes a return from interrupt instruction to return control to the CPU. ( The interrupt handler clears the interrupt by servicing the device. )