Code Examples from Class

• Copy to RAM

   AREA Exaddress, CODE, READONLY
   EXPORT Reset_Handler
Reset_Handler
   LDR R9, =list
   mov R7, #4 ; number in list
   ldr r6, =datastart

loop
   ldr r8,[r9],#4
   str r8,[r6],#4
   subs r7,r7,#1
   bne loop

stop b stop
   ALIGN
list DCW 0x1111, 0x2222, 0x3333, 0x4444, 0x5555
   ALIGN
string DCB "This is a test.",0
string2 DCB 'T','h','i'
   ALIGN
   AREA Thedata, DATA, NOINIT, READWRITE
datastart SPACE 20

   END

• Subroutine Example1

; First Subroutine Example
; This program demonstrates using a subroutine,
; saving registers on the stack, etc.

; Rob Frohne, 1/3/2013

stack_start EQU 0x40001000
   AREA Subroutine_Example, CODE

   ENTRY

Start
   ldr sp, =stack_start ; Tell where we will place the stack.
                        ; (It goes down (lower addresses from here.)

   mov r1, #1 ; Store some numebers in some registers
   mov r2, #2
   mov r3, #3

   bl subroutine

stop b stop

; This subroutine saves the registers,
; messes up the registers locally,
; then restores the registers and returns.

subroutine
   stmfd sp!, {r1-r2,lr} ; save used registers and the link register (r14)
   mov r1,#0xffffffff ; mess up the registers
   mov r2, r1
   ldmfd sp!, {r1,r2,pc} ; pop the stack and return

   END