;A program to compute the sum, difference,

;and absolute difference of two signed

;32-bit numbers.

;------Assembler Directives----------------

THUMB ; uses Thumb instructions

; Data Variables

AREA DATA, ALIGN=2 ; places objects in data memory (RAM)

EXPORT SUM [DATA,SIZE=4] ; export public varialbe "SUM" for use elsewhere

EXPORT DIFF [DATA,SIZE=4] ; export public varialbe "DIFF" for use elsewhere

EXPORT ABS [DATA,SIZE=4] ; export public varialbe "ABS" for use elsewhere

SUM SPACE 4 ; allocates 4 uninitialized bytes in RAM for SUM

DIFF SPACE 4 ; allocates 4 uninitialized bytes in RAM for DIFF

ABS SPACE 4 ; allocates 4 uninitialized bytes in RAM for ABS

; Code

AREA |.text|, CODE, READONLY, ALIGN=2 ; code in flash ROM

EXPORT Start ; export public function "start" for use elsewhere

NUM1 DCD -1 ; 32-bit constant data NUM1 = -1

NUM2 DCD 2 ; 32-bit constant data NUM2 = 2

;-------End of Assembler Directives----------

GET_SUM ; subroutine GET_SUM

ADD R0, R1, R2 ; R0=R1+R2

LDR R3, =SUM ; R3=&SUM, R3 points to SUM

STR R0, [R3] ; store the sum of NUM1 and NUM2 to SUM

BX LR ; subroutine return

GET_DIFF ; subroutine GET_DIFF

SUBS R0, R1, R2 ; R0=R1-R2

LDR R3, =DIFF ; R3=&DIFF, R3 points to DIFF

STR R0, [R3] ; store the different of NUM1 and NUM2 to DIFF

BMI GET_ABS ; check condition code, if N=1 (i.e. the difference is negative),

; branch to GET_ABS to calculate the absolute difference

STR_ABS ; label STR_ABS, store the absolute difference

LDR R3, =ABS ; R3=&ABS, R3 points to ABS

STR R0, [R3] ; store the absolute difference to ABS

BX LR ; subroutine return

GET_ABS ; label GET_ABS, calculate the absolute difference if the difference is negative

RSB R0, R0, #0 ; R0=0-R0;

B STR_ABS ; branch to STR_ABS to store the result

Start LDR R1, NUM1 ; R1=NUM1

LDR R2, NUM2 ; R2=NUM2

BL GET_SUM

BL GET_DIFF

ALIGN ; make sure the end of this section is aligned

END ; end of file

Questions 1. Create a table as shown below to record the values of important registers and variables when the Steps PCLRNZCV RO 2. What are the addresses of variables SUM, DIFF, and ABS? What values are stored at these addresses when the simulation is completed? 3. In this program, consider the following items including SUM, DIFF, ABS, NUM1, NUM2, and all the instructions, which are stored in RAM and which are stored in ROM? ENGR 478 4. What is the address of instructionBL GET. SUMin memory? What does this instruction do? After executing this instruction, what are the values stored in PC and LR? Why? 5. What does the instruction "BI GET_ABS" do? 6. After executing "SUBS R0, R1, R2", what are the values of the condition code flags? Why? 7. Edit sins, modify NUM1 and NUM2 to be 5 and 3 respectively and simulate the program again. What are the values stored in SUM, DIFF, and ABS after the simulation? 8. Add a new function to the sample program which compares the values of NUMI and NUM2 and stores the larger value into a new variable LARGER. You need to a. Define a new 32-bit variable LARGER b. Design a subroutine GET LARGER, draw the flowchart of the subroutine, and write assembly code to implement this subroutine