3

Reading and Writing Assignments, Discussion Topics
COS/ELE 375

for class on Monday Sept. 24, 2012

Please read sections 2.1 through 2.6 of the Patterson & Hennessy text.

Please turn in written responses to these questions. Check Section 1.11 for how the text exercises work. Use "parameters" from the mustard-cover edition, which are given below in case you have the blue cover.

1. Exercise 2.6.1 for both rows of the table.

• row a: f = f + A[2];
• row b: B[8] = A[i] + A[j];

2. Exercise 2.10.1 for both rows of the table.

• row a: 0000 0010 0001 0000 1000 0000 0010 0000
• row b: 0000 0001 0100 1011 0100 1000 0010 0010

3. Exercise 2.10.4 for both rows of the table. Conventions for $s and $t registers are spelled out on the green card in the front of the book, and also on page 94. Feel free to use binary instead of hex; we don't care.

• row a: addi $t0, $t0, 0
• row b: sw $t1, 32($t2)

4. Exercise 2.15.2, both rows.

• row a: not $t1, $t2 // bit-wise invert
• row b: orn $t1, $t2, $t3 /// bit-wise OR of $t2, !$t3

5. Suppose you were contributing to the MIPS instruction set design, back in nineteen-eighty-whatever. Your idea is to make programs smaller by allowing new 16-bit instructions to be intermixed with the regular 32-bit ones. Assuming that opcode space is not an issue, propose a format for these instructions and propose three specific new instructions that use it. (We hope it is obvious that there is no "right" answer to this question; we just want you to write down your ideas.)

Then, be prepared to discuss the following in class:

6. Your 16-bit idea has been applauded by the MIPS architects, and your new format goes into the draft architecture manual. But you are having second thoughts. Why?

7. What general principles would guide you if you were designing an instruction set (back when that still made sense)? How would you decide which instructions to include and which to leave out? Feel free to elaborate, or dispute, the views of Burks, Goldstine, and von Neumann excerpted on pages 76 and 77. Would you favor a mix of instruction sizes, or stick with just one?