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Writing ARM and Thumb Assembly Language
ARM DUI 0068B Copyright © 2000, 2001 ARM Limited. All rights reserved. 2-45
Example 2-12
AREA Block, CODE, READONLY ; name this block of code
num EQU 20 ; set number of words to be copied
ENTRY ; mark the first instruction to call
start
LDR r0, =src ; r0 = pointer to source block
LDR r1, =dst ; r1 = pointer to destination block
MOV r2, #num ; r2 = number of words to copy
MOV sp, #0x400 ; Set up stack pointer (r13)
blockcopy MOVS r3,r2, LSR #3 ; Number of eight word multiples
BEQ copywords ; Less than eight words to move?
STMFD sp!, {r4-r11} ; Save some working registers
octcopy LDMIA r0!, {r4-r11} ; Load 8 words from the source
STMIA r1!, {r4-r11} ; and put them at the destination
SUBS r3, r3, #1 ; Decrement the counter
BNE octcopy ; ... copy more
LDMFD sp!, {r4-r11} ; Don't need these now - restore
; originals
copywords ANDS r2, r2, #7 ; Number of odd words to copy
BEQ stop ; No words left to copy?
wordcopy LDR r3, [r0], #4 ; Load a word from the source and
STR r3, [r1], #4 ; store it to the destination
SUBS r2, r2, #1 ; Decrement the counter
BNE wordcopy ; ... copy more
stop MOV r0, #0x18 ; angel_SWIreason_ReportException
LDR r1, =0x20026 ; ADP_Stopped_ApplicationExit
SWI 0x123456 ; ARM semihosting SWI
AREA BlockData, DATA, READWRITE
src DCD 1,2,3,4,5,6,7,8,1,2,3,4,5,6,7,8,1,2,3,4
dst DCD 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
END