Ace Test Series: CO & Architecture - Instruction Execution

Question

CPU can leave current instruction execution, without completing it for :

• A. Service of interrupt
• B. DMA
• C. Both
• D. Neither

Comments

The answer should be clearly DMA , because we know that in say cycle stealing mode DMA steals the bus from cpu just before its about use the bus for transfer.

Is it correct explanation.

Answer is correct though

Answer 1

the correct reason for the answer DMA :- is difference between DMA request and Interrupt request. in case of interrupt request c.p.u has to store current status of programme and complete the current instruction to be free to execute interrupt service routine but in case of DMA request c.p.u just have to halt for a time period in the situation it is in ..there is no need to save its current status and to be free so a DMA request can arrive at any machine cycle(i.e. fetch ,decode)

source:- NPTEL  sir raman lecture

Answer 2

Answer should be only DMA because processor can give bus mastership to DMA during the execution of an instruction.

A can not be the option because processor only checks for interrupt after it completes its instruction execution.

Note - If during an instruction execution an exception occur then also processor can leave current instruction execution and run exception handler. But exceptions and interrupts are two different things.

Answer 3

Option B) DMA is the answer , because CPU can provide bus to DMA during the execution of an instruction.

Whereas, In case of Interrupt , CPU only checks for interrupt after current instruction is executed.