Ans: (b)

1

• Given the importance of registers, what is the
  rate of increase in the number of registers in a
  chip over time?
• Very fast They increase as fast as Moores law
• Very slow They only increase as the instruction
  set changes

• Ans (b)
• Moores law projects the doubling of transistors
  every couple of years and has nothing to do with
  registers.
• The number of registers will change only if
  instruction set architecture is changed. Because
  machine code has only 5 bits to represent each
  register, so it would require a substantial
  change (a new ISA)

2

• 2. Define the R-format instruction
• What are the various fields?
• What is the basic lay-out?
• What does each field represent?
• Are all of the bits used / needed for each field?
• Given an example of an R-format instruction in
  MIPS assembler and the corresponding machine code

• Fields
• Op-code operation code
• Rs, Rt source registers
• Rd destination register
• SA shift amount
• Funct-code function specifier

Example add r1, r2, r0 000000 00010
00000 00001 00000 100000
3

• 3. Define the I-format instruction
• What are the various fields?
• What is the basic lay-out?
• What does each field represent?
• Why this instruction format needed as opposed to
  the R-format?
• Give an example of an I-format instruction in
  MIPS assembler and the corresponding machine code

• Fields
• Op-code operation code
• Rs source register
• Rt destination register
• Immediate 2s complement constant

Example addi r1, r2, 1 001000 00010
00001 0000000000000001
4
4. What is the range of addresses for conditional
branches in the MIPS ISA?
5

• 5. Answer the following questions as true or
  false
• The beq instruction always modifies the program
  counter register
• The add instruction does not modify the PC
• The jal instruction always modifies the PC
• The instruction beq r1,r2,1 will advance the PC
  by one byte if r1r2
• The instruction beq r1,r2,1 will advance the PC
  by one word if r1r2

• Ans
• T. PC PC4 even if r1 ltgt r2
• F. PC PC4
• T. Unconditional branch
• F. PC PC4 4 x 1
• F. PC PC4 4 x 1

6
6. Find the shortest sequence of core MIPS
instruction to determine the absolute value of a
twos complement integer. Please the result into
r3.

• There are several possible answers to this
  question.
• However, in general, all involve the following
  two steps
• Convert the number to a positive value if it is
  negative, which can be done by multiplication,
  xor, nor, etc
• Move the value to r3

7
7. Write out the truth table, the logic equation
and draw the gates for the Sum bit of a 1-bit
adder
Sum bit is 1 if an odd number of the three inputs
1 ?XOR the three inputs