Computer Science 2500 Computer Organization Rensselaer Polytechnic Institute Spring 2009

Agenda

• Announcements
  • Extended office hours today: 1:30-4:30, to help accomodate those who may have a 2-4 PM class. I will stay a bit beyond 4:30 to continue helping anyone who arrives by then.
• Exam in 1 week
  • All topics up to MIPS Programming
    • Bits and numbers, computer arithmetic
    • Basics of C programming
    • Instruction set architectures
    • MIPS ISA: registers, instruction formats, basic instruction set
    • MIPS assembly language programming
  • Exam will be designed to take 90 minutes, you will have the full 110
  • We will spend as much time as you wish reviewing on Friday - bring questions
  • You may use a single double-sided 8.5x11" page of handwritten notes (which you will submit with your exam), but no other resources during the exam
• Lab 4 recap
• Lab 5 out
• Lecture assignment recap
• Sequential circuits
  • edge detection
  • clocks
  • latches and flip-flops
  • counters

Bigger Lecture Assignment

Due at the start of class, Friday, February 27.

Turn in short answers to these questions. Please turn in a hard copy (typeset or handwritten are OK). We will discuss these questions during class, so no late submissions are accepted.

1. Draw a much simpler circuit that is equivalent to the following:

   

2. Occasionally it is necessary to add 1 to a number, for example, a program counter. Construct a device that is less expensive than a ripple-carry adder, that adds one to a value that is provided (D0..D3) and provides the result on the output (Q0..Q3). (Hint: you may consider a modular approach.)
3. Here is a review question about the MIPS ISA, along the lines of the things I could ask on the exam. Recall that the designers of the MIPS instruction set architecture chose to disallow memory access during all but the lw and sw instructions.
   a. Describe briefly in your own words why they made this decision.
   b. Suppose you wanted to provide MIPS assembly pseudoinstructions to hide this restriction from assembly language programmers. Recall that the register $at is reserved for use by the assembler in the implementation of pseudoinstructions.
   For each of the following potential pseudoinstructions, either give the appropriate MIPS instructions that could be generated, or indicate why it cannot be done.
   

   (i)	add $t0, $t1, 0($t2) # t0 = t1 + value at address t2
   (ii)	add 0($t0), $t1, 0($t2)
   (iii)	add $t0, 0($t1), 0($t2)
   (iv)	add 0($t0), 0($t1), 0($t2)

   c. Would you recommend the inclusion of such pseudoinstructions into the MIPS assembly language? Why or why not?
   d. Perhaps such an extension would be better suited to be an extension to the MIPS ISA itself. Describe how this might be accomplished. Consider the MIPS instruction format and the goals of the MIPS ISA design. Which MIPS ISA design principles does your design compromise?
4. Bring other questions to class to review for the first exam.