我有一個68k大會程序,計算3x3陣列的對角線的值的平均值並將其存儲。
ORG $1000
START: ; first instruction of program
* Put program code here
move.w n,d6 ; d6 = 0000 0003
clr.l d7 ; sum = 0
move.w #2,d4 ; size of element 0000 0002
mulu.w d6,d4 ; n times size of element
; d4 0000 0006
movea.l #A,a0 ; address of the array
loop tst.w d6 ; if (n == 0)
beq done ; go to done else go to next instruction
subq.w #1,d6 ; 3 - 1, 2 - 1, 1 - 1, done
add.w (a0)+,d7 ; a0 address is incremented 2 bytes since its word length
; content of address a0 is stored in d7
; d7 = 0000 0001, 0000 0005, 0000 0009
add.l d4,a0 ; increment for diagonals which in 3x3 = 3 position = 6 bytes
; a0 = 02 + 06 = 08, 08 + 06 = 10 hex = 16 decimal
bra loop ; restart loop until condition is met
done divu.w n,d7 ; now d7 has the sume of diagonals
; d7 = 1 + 5 + 9 = 15
; 15/3 = 5
; result is stored in d7 = 5
move.l d7,store ; d7 is stored in
SIMHALT ; halt simulator
* Put variables and constants here
A dc.w 1,2,3,4,5,6,7,8,9
n dc.w 3
org $2000 ; what does this do?
store ds.l 1 ; notice its long word
END START ; last line of source
我什麼都明白了這個代碼怎麼回事除了行:
org $2000 ; what does this do?
store ds.l 1 ; notice its long word
有人能在簡單的話給我解釋一下,什麼組織「$ 2000」在做什麼,「ds.l 1」 。什麼是DS命令,它後面的數字1代表什麼?
我檢查內存塊d7的值是否存儲在地址0000 2000中,但這又與DS.L前面的數字1有什麼關係,ORG通常做什麼?