blocks.s

：some examples of assembler level programming for the ARM（produces an ELF executable file which can

        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    ; a word from the source
        STR     r3, [r1], #4    ; store a word 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