Lab 2 – Description

Lab 2 – MIPS instruction set

Objectives

The objective of this experiment is to research the MIPS architecture and more in-depth the instruction set . Hence the chapter 2 of Patterson and Hennesee.

Getting started

Download the components for lab 2 from the course webpage.

If you are required to change assembly source code please indicate in the source code the lines which are changed leaving the old lines intact as comment.For the experiments where you have to write a complete program please submit the source file (extension .wasm ) .

Note: the 0x12345 is the hexadecimal representation of a number.

The code snippet below is an assembly listing from a compiled C program:

21 000c 3C020001     li  $2,65536            # 0x10000
22 0010 34422345     ori $2,$2,0x2345
23 0014 AFC20008     sw  $2,8($fp)
24 0018 24020007     li  $2,7            # 0x7
25 001c AFC2000C     sw  $2,12($fp)
26 0020 8FC30008     lw  $3,8($fp)
27 0024 8FC2000C     lw  $2,12($fp)
28 0028 00000000     nop
29 002c 00621021     addu    $2,$3,$2
30 0030 AFC20010     sw  $2,16($fp)

Questions

  1. What does the the second column represent? Can you explain the content?
  2. Explain the first 2 lines of the assembly code. Use the MIPS reference (either from the book or several online pdf versions).
  3. Advanced Question – Explain the third line (sw instruction). $fp is a frame pointer, see page 103 in Patterson & Hennessy.
  4. Line 29 contains the actual addition statement. What MIPS instruction would you have expected.
  5. Give a complete description of the third column for the ORI instruction in the assembly listing. I.e. instruction format, the value of the MIPS fields.
  1. Instead of adding 7 we want to subtract 0x98 (hexadecimal!). Modify the assembly code to do this. Provide what you have changed as your answer.
  2. The last step can be done more convenient by using an immediate statement. Change your program to do this subtraction using an immediate value of 0x98.
  3. The sw instructions write values into 3 memory locations (a,b,result). What does the ALU do during this sw instruction?
  4. Explain the function of the sign extender block in the schematic
  5. Write an assembly program which mimics a walking light¬†pattern of 3 bits in a register (32 bits!!) .¬†Do this in the executer “Program Editor” window using Lab 2 singlecycle mips architecture.

For example if the pattern is 110:

Register value = 00......00000110
Register value = 00......00001100
Register value = 00......00011000
....
Register value = 11......00000000
Register value = 10......00000001
Register value = 00......00000011
....

Advanced questions

  1. Change the program to allow a change of direction depending on the contents of a register (1 = shift lift, 0 = shift right). Allow different patterns and different shift lengths (more than 32 bits)
  2. In the early days of computing Binary-coded decimal numbers where used often. Write a small program that converts a hexadecimal encoded number to a binary-coded decimal number.

A clear explanation of BCD code can be found at the wiki page

https://en.wikipedia.org/wiki/Binary-coded_decimal