CS501 Current Midterm Paper Fall 2013 File 12

by + *!~€ûTe*Ønë~!* + on December 22, 2013 at 2:25pm

MCQs were mostly from Moaz File and below is the subjective questions with solution;

Q1: Which register is used to hold source operand and the result of the arithmetic or logical operation?

Solution:

Accumulator Register.

Q2: Briefly explain the types of branch?

Solution

Branch:

Branch instruction branches to address In Rb depending on the condition in rc.                                                                                                                                             

Branch with link:

Branch link branches to address in Rb depending on condition in rc Additionally, it copies the PC into ra before branching.

Q3: What function is performed by the reset operation of a processor and differentiate Hard reset and Soft reset.

Solution:

Two essential features of a reset instruction are clearing the control step counter and reloading the PC to a predefined value.

Hard Reset:

The SRC should perform a hard reset upon receiving a start (strt) signal. This initializes the PC and the general registers.

Soft Reset:

The SRC should perform a soft reset upon receiving a reset (rst) signal. The soft reset results in initialization of PC only.

Q4: Structural RTL for in ra, c2

Solution:

Time Step	RTL
T0 to T2	Instruction Fetch
T3	C<-IO[c2]
T4	R[ra]<-C

Q5: Write RTL and control signal notation for following add instruction:

add ra, rb, rc;

Solution:

Time Step	RTL	Control Signal
T0 to T2	Instruction Fetch	As before
T3	A<- R[rb];	RBE, R2BUS, LA
T4	C<-A+R[rc];	RCE, R2BUS, ADD, LC
T5	R[ra]<-C	Cout, RAE, BUS2R

Q6: Describe 5 examples of exception when it occur?

Solution:

Program Exceptions

These are exceptions raised during the process of decoding and executing the instruction. Examples are illegal instruction, raised in response to executing an instruction which does not belong to the instruction set. Another example would be the privileged instruction exception.

Hardware Exceptions

There are various kinds of hardware exceptions. An example would be of a timer which raises an exception when it has counted down to zero.

Trace and debugging Exceptions

Variable trace and debugging is a tricky task. An easy approach to make it possible is through the use of traps. The exception handler which would be called after each instruction execution allows examination of the program variables.

Nonmaskable Exceptions

These are high priority exceptions reserved for events with catastrophic consequences such as power loss.  These exceptions cannot be suppressed by the processor under any condition. In case of a power loss the processor might try to save the system state to the hard drive, or alert an alternate power supply.

Interrupts (External Exceptions)

Exception handlers may be written for external interrupts, thus allowing programs to respond to external events such as keyboard or mouse events.