Question

Q3. Demonstrate the process of executing a nested subroutine, where you will have three subroutines. Subroutine number 2 will be called from subroutine number 1, while subroutine number 3 will be called from subroutine number 2. In Keil uVision, screenshot your result, by showing the value of PC and LR. Discuss your results by relating the values in PC, LR and stack for each subroutine call.

Answer 1

Example:Example:

AREA subrout, CODE, READONLY     ; Name this block of code

ENTRY                     ; Mark first instruction to execute

start   MOV     r0, #10 ; Set up parameters
           MOV     r1, #3

           BL      doadd   ;

Call subroutine

stop    MOV     r0, #0x18         ; angel_SWIreason_ReportException

LDR     r1, =0x20026      ; ADP_Stopped_ApplicationExit

SVC     #0x123456         ; ARM semihosting (formerly SWI)

doadd   ADD     r0, r0, r1        ; Subroutine code
        BX      lr                ; Return from subroutine
        END                       ; Mark end of file