2030
Computer ECE Engineering
Final Exam Problem
Problem 1 (6 parts, 25 points)
Assembly Language Programming
This problem deals with a program to do chromakeying. The attached sheet lists the instruction set it uses. Chromakeying is used to superpose a figure, such as a weatherman, on a background image, such as a weathermap.
+
=
Blue screen image
Background image
Combined image
The chromakey program is given 2 images, stored in memory: a) a blue-screen image which consists of a figure (e.g., windsurfer) in front of a blue screen this is stored in contiguous memory locations starting at address 1000; and b) a background image (e.g., a globe) on which the figure should be superposed this is stored in contiguous memory locations starting at address 3000. The program creates the combined image and stores it in memory starting at address 6000. Each of these words in memory contains a set of packed pixels. The code consists of a main program labeled chromakey (shown below) and two subroutines create_mask and mask_b (shown on pages 8 and 9).
address 100 104 108 112 116 120 124 128 132 136 140 144 148 152 156 160 label chromakey: instruction addi $12,$0,1000 addi $13,$0,3000 addi $14,$0,6000 addi $15,$0,1512 lw $1, ($12) lw $2, ($13) jal create_mask jal mask_B and $6,$2,$3 and $7,$1,$4 or $8,$6,$7 sw $8, ($14) addi $12,$12,4 addi $13,$13,4 addi $14,$14,4 bne $12,$15,loop
loop:
1
ECE 2030
Computer Engineering
Final Exam Problem
Part A (4 points) Suppose that when line 132 is reached while executing chromakey, registers $1 through $4 have the values shown in the table below. What value is in register $8 when line 144 is reached 3 cycles later? Note that all the values are given in hexadecimal notation except $2s value which is given in decimal notation. Give your answer in hexadecimal. Register $1 $2 $3 $4 $8 Value 0x35F3C339 39510 0xF00F0FF0 0x0FF0F00F
Part B (4 points) How many words are read in from memory (using lw) by the chromakey program?
total number of data words read:
2
ECE 2030
Computer Engineering
Final Exam Problem
address 250 254 258 262 266 270 274 278 282 286 290 294
label create_mask:
loop:
skip:
instruction sub $3,$3,$3 addi $30,$0,3 addi $21,$0,8 add $22,$1,$0 and $20,$22,0xF bne $30,$20,skip or $3,$3,0xF0000000 srl $3,$3,4 srl $22,$22,4 subi $21,$21,1 bne $21,$0,loop jr $31
Part C (4 points) When the create_mask subroutine (above) is called from chromakey, what the are values in the following registers at line 262? Register $3 $30 $21 $31 Part D (4 points) The create_mask subroutine assumes that a word of packed pixels from the blue screen image is in register $1. It copies the value in $1 to register $22 (line 262). Then it unpacks the pixels (i.e., extracts each pixel from $22 in turn) and checks whether each pixel is blue (pixel value = 3) or not. How many pixels are packed in each word and how many bits are used to encode each pixel? Assume each word is 32 bits long. Value
total number of pixels/word: number of bits/pixel:
3
ECE 2030
Computer Engineering
Final Exam Problem
address 500 504 508
label mask_B:
instruction sub $4,$0,$3 subi $4,$4,1 jr $31
Part E (5 points) If register $3 has value 0xF0FF00F0 when the subroutine mask_B is called, what value does $4 have when the subroutine returns (i.e., at line 508)? Register $3 $4 Value 0xF0FF00F0
Part F (4 points) Assume twos complement arithmetic is being used. If $3 is treated as a boolean variable A, what boolean function does mask_B compute? In other words, give a Boolean expression in terms of A for what mask_B computes.
4
ECE 2030
Computer Engineering MIPS Instruction Set (subset)
add subtract add immediate multiply divide and or and immediate or immediate xor xor immediate shift left logical shift right logical shift left arithmetic shift right arithmetic load word store word load upper immediate branch if equal branch if not ...