Question

Part 2 (22 pts)

.ORIG x3000
LEA R1, STRZ
AND R2, R2, #0
LD R4, CHAR
REPEAT LDR R3, R1, #0
BRz FINISH   ;Branch to FINISH if the value of R3 is zero
ADD R3, R3, R4
BRnp PASS   ;Branch to PASS if the value of R3 is positive or negative
ADD R2, R2, #1
PASS ADD R1, R1, #1
BR REPEAT   ;Branch always to REPEAT
FINISH ST R2, COUNT
HALT
CHAR .FILL xFF91
COUNT .FILL x0000
STRZ .STRINGZ "Hello world!"
.END

Attached you will find the code for this part in the file q2.asm.

Step 1: Download q2.asm and add it to the PennSim folder.

Step 2: Open the simulator and type the following instructions in the command line:

as lc3os.asm

load lc3os.obj

as q2.asm

load q2.obj

Step 3: Set PC to x3000.

Step 4: Run code and observe results.

Now answer the following questions:

Question 1: The ADDRESS and VALUE columns of the following table are snapshots of the assembler’s memory after you load the object file q2.obj. Fill in the CHARACTER column with the character each value represents. (6.5 pts)

ADDRESS	VALUE	CHARACTER
x300E	x0048
x300F	x0065
x3010	x006C
x3011	x006C
x3012	x006F
x3013	x0020
x3014	x0077
x3015	x006F
x3016	x0072
x3017	x006C
x3018	x0064
x3019	x0021
x301A	x0000

Question 2: Fill in the symbol table created by the assembler after you load the object file q2.obj. (3 pts)

SYMBOL NAME	MEMORY ADDRESS
REPEAT
PASS
FINISH
CHAR
COUNT
STRZ

Question 3: How many times is the instruction at label “REPEAT” executed? (2 pts)

Question 4: How many times is the instruction at label “PASS” executed? (2 pts)

Question 5: What is the value of register R3 at the END of the 5^th iteration? (2 pts)

Question 6: What is the value of register R3 at the END of the 8^th iteration? (2 pts)

Question 7: Why did we set the value at label “CHAR” to xFF91? (Answer in one sentence only.) (2 pts)

Question 8: What is the final value of register R2 at the end of the execution? (0.5 pts)

Questions 9: Describe what this program does in one sentence only. (2 pts)

Answer 1

Question 1:

ADDRESS	VALUE	CHARACTER
x300E	x0048
x300F	x0065
x3010	x006C
x3011	x006C
x3012	x006F
x3013	x0020
x3014	x0077
x3015	x006F
x3016	x0072
x3017	x006C
x3018	x0064
x3019	x0021
x301A	x0000

Question 2:

SYMBOL NAME	MEMORY ADDRESS
REPEAT	3003
PASS	3008
FINISH	300A
CHAR	300C
COUNT	300D
STRZ	300E

Question 3: Instruction at label "REPEAT" is executed 13 times

Question 4: Instruction at label “PASS” is executed 12 times

Question 5: The value of register R3 at the END of the 5^th iteration is x0020

Question 6: The value of register R3 at the END of the 8^th iteration is x0072

Question 7: To count the number of 'o' present in the string. (ASCII value of 'o' is decimal 111 and FF91 is decimal -111)

Question 8: The final value of register R2 at the end of the execution is 2

Questions 9: The program is iterating through the string "Hello world!"