CS 2731 Recitation 11

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CS 2733/2731
Computer Organization II
Fall 2004
Recitation 11
Pipelining: Stalls with lw
    Week 11: Nov 1-5
Due (on time): 2004-11-10  23:59:59
Due (late):        2004-11-14  23:59:59

Note: Submit on actual sheets of paper at the time given at the bottom of this recitation.
Recitation 11 must be submitted following directions at: submissions on or before

2004-11-10 23:59:59 (that's Wednesday, 10 November 2004, 11:59:59 pm) for full credit.
2004-11-14 23:59:59 (that's Sunday, 14 November 2004, 11:59:59 pm) for 75% credit.

Outline: This recitation studies how a stall is used to handle the lw instruction using the pipelined implementation of MIPS. Stalls are also needed by branches and by exceptions. You are to turn in four annotated diagrams showing cycles 3 through 6 as described in Exercise 6.24 starting on page FMP 6.14-13 on the CD. (Chapter 6, For More Practice.)

The location of the exercise is confusing, since it starts on page FMP 6.14-13. Then the next two pages: FMP 6.14-14 and 6.14-15, contain diagrams related to the previous exercise. The diagram on the top of page FMP 6.14-16 is supposed to be a blank for the previous exercise, but by mistake it is the same as the blank for this exercise. Finally, Exercise 6.24 continues on the second half of page FMP 6.14-16. Pages FMP 6.14-17 through FMP 6.14-19 contain diagrams related to this exercise. You are to use 4 copies of the blank diagram on page FMP 6.14-16 or page FMP 6.14-20 to finish this recitation. (Your answers should be similar to the diagrams on pages FMP 6.14-17 through FMP 6.14-19.) (Wheh!)

Here is a GIF image of Figure 6.14.17 on page FMP 6.14-20, the blank page that you need for this recitation: Figure 6.14.17

In Exercise 6.24, the authors illustrate a stall and the use of the Hazard Detection Unit with the following sequence of instructions:


lw     $2,   20($1)
and    $4,   $2,    $5
or     $4,   $4,    $2
add    $9,   $4,    $2

The work of Exercise 6.24 is to do the same thing with the following very similar sequence of instructions:


lw     $2,   20($1)
add    $4,   $5,    $2
sub    $4,   $4,    $2

The Forwarding Unit: Notice that the Forwarding Unit is also necessary for correct execution here, as is illustrated in the book's diagrams and as will be explained in class. You must also show the actions of the Forwarding Unit in your diagrams.

What you should submit: The pages that you submit should first have Your Name, the Course Number, and the Recitation Number. The rest of the pages should have the following in it, in the order below, and clearly labeled, including at the beginning the appropriate number 1-2.

Contents of hand submission for Recitation 11:
Last Name, First Name; Course Number; Recitation Number (11).

You must submit four diagrams on actual sheets of paper. Note change of due date: These must be turned in during class on Monday, 15 November 2004 for full credit.

Revision date: 2004-11-02. (Please use ISO 8601, the International Standard.)