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编 写 ARM 和 Thumb 汇 编 语 言
示 例 2-13
AREA Tblock, CODE, READONLY ; Name this block of code
num EQU 20 ; Set number of words to be copied
ENTRY
; Mark first instruction to execute
header
; The first instruction to call
MOV sp, #0x400 ; Set up stack pointer (r13)
ADR r0, start + 1 ; Processor starts in ARM state,
BX r0 ; so small ARM code header used
; to call Thumb main program
CODE16
; Subsequent instructions are Thumb
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
blockcopy
LSR r3,r2, #2 ; Number of four word multiples
BEQ copywords ; Less than four words to move?
PUSH {r4-r7} ; Save some working registers
quadcopy
LDMIA r0!, {r4-r7} ; Load 4 words from the source
STMIA r1!, {r4-r7} ; and put them at the destination
SUB r3, #1 ; Decrement the counter
BNE quadcopy ; ... copy more
POP {r4-r7} ; Don't need these now-restore originals
copywords
MOV r3, #3 ; Bottom two bits represent number
AND r2, r3 ; ...of odd words left to copy
BEQ stop ; No words left to copy?
wordcopy
LDMIA r0!, {r3} ; load a word from the source and
STMIA r1!, {r3} ; store it to the destination
SUB r2, #1 ; Decrement the counter
BNE wordcopy ; ... copy more
stop MOV r0, #0x18 ; angel_SWIreason_ReportException
LDR r1, =0x20026 ; ADP_Stopped_ApplicationExit
SWI 0xAB ; Thumb 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
ARM DUI 0204BSC © 2002、 2003 ARM Limited 版 权 所 有 。 保 留 所 有 权 利 。 2-49