Lab 2 : Pseudo Instructions and Memory Access Name: Sign the following statement: On my honor, as an Aggie, I have neither given nor received unauthorized aid on this academic work 1 Objective The objective of this lab is to make you more familiar with MIPS pseudo instructions as well as using memory. 2 Pre-requisite Before starting with this lab, you are required to know what pseudo-instructions are, as well as how MIPS accesses memory. 3 Basic Memory Access 1. Type the following program into MARS (save it as lab2a.s) and use it to answer the questions below 1 Computer Architecture and Design, Lab 2 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 2 . data msg1 : . a s c i i z ”A 17 byte message \n” msg2 : . a s c i i z ” Another message o f 27 b y t e s \n” num1 : . byte 45 num2 : . h a l f 654 num3 : . word 0 x c a f e b a b e num4 : . word 0 x f e e d f a c e . text . globl main main : l i $v0 , 4 #s y s t e m c a l l f o r p r i n t s t r l a $a0 , msg1 #a d d r e s s o f s t r i n g t o p r i n t syscall l a $a0 , msg2 #a d d r e s s o f s t r i n g t o p r i n t syscall lb $t0 , num1 #l o a d num1 i n t o $ t 0 l h $t1 , num2 #l o a d num2 i n t o $ t 1 lw $t2 , num3 #l o a d num3 i n t o $ t 2 lw $t3 , num4 #l o a d num4 i n t o $ t 3 li $v0 , 10 # system c a l l f o r e x i t syscall # we a r e o u t o f h e r e . (a) What are the assembly instructions for the pseudo instruction la $a0, msg2? (b) What is the address for each of the following items? Object Address Data Segment Text Segment msg1 msg2 num1 num2 num3 num4 (c) Why does msg2 start 18 bytes after msg1 when msg1 is only 17 bytes long? Computer Architecture and Design, Lab 2 3 (d) Why are there unused bytes between num1, num2, and num3, but num4 start immediately after num3? 2. Go to the Settings on menu bar and make sure the item Popup dialog for input syscalls (5,6,7,8,12) is checked. Type the following program into MARS (save as lab2b.s): 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 . data msg1 : . word 0 : 2 4 . text . globl main main : l i $v0 , 8 #s y s c a l l f o r r e a d s t r l a $a0 , msg1 #l o a d a d d r e s s o f msg1 t o s t o r e s t r i n g l i $a1 , 100 #msg1 i s 100 b y t e s syscall lb $t0 , 5 ( $a0 ) #l o a d t h e c h a r a c t e r i n t o $ t 0 l i $t1 , ’ a ’ #g e t v a l u e o f ’ a ’ b l t $t0 , $t1 , nomodify #do n o t h i n g i f l e t t e r i s l e s s than ’ a ’ l i $t1 , ’ z ’ #g e t v a l u e o f ’ z ’ bgt $t0 , $t1 , nomodify #do n o t h i n g i f l e t t e r i s g r e a t e r than ’ z ’ addi $t0 , $t0 , −0x20 #encap t h e l e t t e r sb $t0 , 5 ( $a0 ) #s t o r e t h e new l e t t e r nomodify : l i $v0 , 4 #s y s c a l l f o r p r i n t s t r syscall li $v0 , 10 # system c a l l f o r e x i t syscall # we a r e o u t o f h e r e . Specify the operation performed by the program: Computer Architecture and Design, Lab 2 4 3. Write a program that reads a string from the user and outputs the number of lowercase letters in the string. Save your program as lab2c.s, and run it to make sure it works correctly. Demonstrate your progress to the TA. . 4. Type the following program into MARS (save your program as lab2d.s): 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 . data hextable : . a s c i i ” 0123456789 a b c d e f ” msg1 : . a s c i i z ”Your number i n Hex i s : ” . text . globl main main : l i $v0 , 5 #s y s c a l l f o r r e a d i n t syscall add $s1 , $v0 , $0 l i $v0 , 4 #s y s c a l l f o r p r i n t s t r l a $a0 , msg1 syscall l a $a1 , h e x t a b l e srl $t0 , $s1 , 4 #g e t upper 4 b i t s add $a2 , $a1 , $ t 0 #g e t a d d r e s s i n h e x t a b l e lb $a0 , 0 ( $a2 ) #g e t c h a r a c t e r l i $v0 , 11 #s y s c a l l f o r p r i n t c h a r syscall andi $t0 , $s1 , 0 x f #g e t l o w e r 4 b i t s add $a2 , $a1 , $ t 0 #g e t a d d r e s s i n h e x t a b l e lb $a0 , 0 ( $a2 ) #g e t c h a r a c t e r l i $v0 , 11 #s y s c a l l f o r p r i n t s t r syscall li $v0 , 10 # system c a l l f o r e x i t syscall # we a r e o u t o f h e r e . Specify the operation performed by the program: 5. Write a program that reads a number x from the user, and prints the first x letters of the alphabet (in lower case). You do not need to check whether the number is positive. Save your program as lab2f.s, and run it to make sure it works correctly. Demonstrate your progress to the TA. . Computer Architecture and Design, Lab 2 4 Deliverables • Submit completed copy of this lab manual. • Include the following in a compressed file (.zip format) to your TA: – The source code for all .s files. – All log files. 5
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