Problem Set Number 3
Computer Science 471

Due by 5 PM, Monday Oct. 7, 1996

The first two problems ask you to explore adding the MIPS instruction jal to the single-cycle implementation of Chapter 5; the next two ask the same for the addiu instruction. Problem Set 4 will include exercises 5.3, 5.4, 5.5, 5.13, 5.14, and 5.15, which are related to the ones below. You might want to save a copy of your answers.

1. (5 points) Exercise 5.1 from the Patterson & Hennessy text. Make your additions with reference to Figure 5.29, but be sure to use the corrected version of the figure contained in the handout. The format of the jal instruction appears in Figure 3.11.

2. (5 points) Exercise 5.2 from the text. Show how all the control lines are set for jal, not just the new ones you add. Hardware designers really like don't-care values in logical specifications, since these often allow smaller, more efficient implementations. Therefore, please use don't-care (``X'') as much as possible in your answer.

3. (5 points) Exercise 5.11 from the text. MIPS doesn't have a subiu instruction (recall problem number 2 from Problem Set 2). This may explain why the addiu instruction sign-extends the immediate value, just like addi. Sections 4.2 and 4.3 of the text discuss related matters at length.

4. (5 points) Exercise 5.12 from the text. As in problem 2, above, show how all the control lines are set, and use as many don't-cares as possible.

5. (10 points) Can you simplify or clean up the PC logic in (the corrected version of) Figure 5.29? If the PC is always a multiple of 4, why do we need the little ``shift left 2'' blobs, and why do we need to add 4 instead of 1? Please re-draw all the PC logic (PC, PC+4 adder, Instruction Memory, the paths that originate in the instruction itself, the PC displacement adder, and the muxes) to take advantage of the fact that PC is always a multiple of 4. Assume the Instruction Memory does not need the 2 low-order bits of PC. In your drawing, be absolutely scrupulous about labelling the widths of the data paths and showing exactly which bits go where. If this idea won't work, please say why.

6. (20 points) Problem number 7 (the buggy Pentium problem) from Problem Set 2 (postponed from last week due to hardware illness).

7. (5 points) Another chapter questionnaire to help improve the book before the hardcover printing. The chapter 4 questionnaire may be found at Please fill it out and e-mail the result to the publisher as directed. As usual, please do not ``cc your instructor on this email,'' as the form directs. To get the 5 points for this question, just write down the time you sent your message to the publisher.

8. (1 point) How long did this take you, not counting the reading, and with whom did you work?