Homework 3

EECS 284

Posted: January 28, 2000

Due: February 3, 2000

Learning objectives

To understand the how the instruction set architecture of a computer determines what features a programmer can access.
To understand the relationship between the datapath and the instruction cycle.
To understand the composition of memory and its relationship to the ISA.

Homework guidelines

You may discuss the homework with other students, but the work you turn in should be your own. You may not share your work with other students or use other people's work. The Engineering Honor Code governs this and all assignmments for this course.
Show all work except in obvious cases where calculations can be done mentally.
Include a cover sheet containing the following information:

EECS 284 Winter 2000

Homework #3

Your name

Your uniqname

Date handed in

Staple all pages together.
Work should be clear and neat. Typeset is preferred to handwritten.

1 10 points	Suppose we have a memory consisting of 4,096 locations, each location containing 12 bits. a) How many bits are required for an address? b) If we divide this memory into 32 pages, how many bits are required ro represent the page number? c) How many bits specify the location of a word within a page? d) What is the address of the first word on the fourth page? (Remember that page numbering starts with 0). e) What is the address of the last word on the same page?
2 15 points	a) How many times does the LC-2 use the MAR during processing of the `LD` instruction? b) How many times during processing of the `LDR` instruction? c) How many times during processing of the `LEA` instruction?
3 10 points	Calculate the maximum number of `TRAP` service routines that the LC-2 ISA allows. Show your work, clearly identifying the values on which your calculation depends.
4 20 points	Consider the following fragment of an LC-2 Assembly Language program. `LD R1, Location1 ; x3006` `NOT R2, R1 ; x3007` `ADD R2, R2, #1 ; x3008` `STI R2, Location2 ; x3009` `BRz InstrX ; x300A` `BRn InstrY ; x300B` `BRp InstrZ ; x300C` Suppose that just before this code is executed that `Location1` contains the value xFFF0, `Location2` contains x4000, address x3000 contains x56E0, and address x4000 contains x0001. a) Which of the instructions set condition codes? (Identify them by the line numbers at right). b) What will be the contents of `Location1`, `Location2`, x3000 and x4000 when the code fragment completes execution. c) What instruction will be executed next?
5 30 points	a) Write one LC-2 Assembly Language instruction that will set the condition codes based on the contents of register R1 without changing the contents of any of the general-purpose registers. b) Suppose we are adding two 16-bit two's complement integers using the instruction `ADD R3, R2, R1`, and we wish to detect whether overflow occurs. Write a sequence of Assembly Language instructions that will branch to a location labelled `OVERFLOW` if the addition operation results in overflow and to a location labelled `DONE` if the addition operation does not cause an overflow condition.
6 15 points	The LC-2 instruction `LDR DR, BaseR, Offset` can be broken down into the following constituent operations (called "micro-instructions"): `MAR <- BaseR + Offset` `MDR <- mem[MAR]` `DR <- MDR` Suppose that the designers of the LC-2 wanted to include an instruction with the Assembly Language format `MOVE DR, SR` that would copy the contents of the memory location with the address contained in `SR` and store it into the memory location whose address is in `DR`. a) Using existing LC-2 instructions (from your LC-2 manual or Appendix A of the textbook), write code to carry out a `MOVE R0, R1` instruction. If necessary, use R2 for temporary storage. b) List the constituent micro-instructions required to carry out the `MOVE` instruction.