Question

What happens when an exception is completed?

(a) TRAP instruction executes

(b) SWI instruction executes

(c) RFI instruction executes

(d) terminal count increases

The question was posed to me during an internship interview.

I need to ask this question from RISC Exceptions topic in chapter Interrupts and Exceptions of Embedded Systems

Answer 1

The correct answer is (c) RFI instruction executes

For explanation I would say: When an exception is recognised, the address of the instruction and the MSR are stored in the supervisor registers and the processor moves to the supervisor mode and starts to execute the handler which is associated with the vector table. The handler examines the DSISR and FPSCR registers and carries out the required function. When it gets completed the RFI or return-from-interrupt instruction is executed.