CSE 820  F'00  Midterm
100 points (25% of course grade)
You are allowed to have one page of notes (8.5x11).
The exam covers Chapters 1-5 of H&P

Instructions: Read the whole question before beginning to answer
the question so you do not answer the wrong part of the question
in the wrong place.

Suggestion: This is a long test so you should read all the 
questions first and decide on the optimal order and optimal time 
to devote to each question. Point values are included to help you
plan your time.  You have 100 points and only 80 minutes so that 
is less than one minute per point.

1. Data Hazards (21 points)
  a. Define the three types of data hazards -- RAW, WAR, WAW -- 
     and indicate why each is a problem. (6 points) 
  b. Give a DLX-like code example of each hazard. (6 points)
  c. For each data hazard describe how the PowerPC 620 removes 
     the data hazard. (9 points)

2. FP (7 points)
  a. Floating Point loads and stores are handled in the integer 
     pipeline of the DLX machine. Explain why. (4 points)
  b. Why does a floating-point ADD execution unit have a 4-stage 
     pipeline, i.e. what happens in each stage? (3 points)

3. Branch Prediction (29 points)
  a. BTB
     1. Explain what a BTB is and how it works. (7 points)
     2. What problem is the BTB addressing?
        Describe how the BTB addresses that problem. (5 points)

  b. (1,2) branch-prediction buffer
     1. Diagram a (1,2) branch predictor and describe how it works.
        Include in your description how it is indexed and how the 
        prediction is updated. (9 points)
     2. What problem does this predictor address? (5 points)
        Describe how it addresses that problem.
     3. Why would one expect a (1,2) predictor be better than 
        a (0,2) predictor? (3 points)

4. PowerPC 620 (20 points)
  a. I. Define "precise exception" (2 points)
     II. Explain how the PowerPc 620 could handle precise 
         exceptions. (8 points)



  b. No forwarding is explicitly described on the PowerPC 620.
        There are two possible reasons.  Choose one and defend 
        your choice: (10 points)
          I. Forwarding provides no improvement.
          II. Forwarding cannot be done.
        (In addition to answering the question, include 
         sufficient description of forwarding so the grader 
         believes you understand how it works.)

5. Memory (18 points)
   Consider a virtually-indexed, physically-tagged cache.
     a. Describe how it works.  (4 points)
     b. What problem is it addressing?
        Describe how it addresses that problem. (6 points)
     c. Explain the limits on its size. (8 points)
        (especially explain WHY there is a limit so the grader 
         believes that you understand why)

6. What is the formula for average access time given three levels
   of cache? (5 points)
   Make sure that each term in the formula is clearly defined.