Assembly x86 Delay loop

Question

hi i made program that will rotate two symbols - \\ and / but i dont know how to set cx counter in nested loops can someone give me advice or help me ?

here is the code of that part

program:  
      mov ah, 0fh   ; function - get video mode
      int 10h
      push ax       ; save number of columns
      push bx       ; save page number
      mov ah, 0     ; function - set video mode
      int 10h

      mov al, 0003h     ;set video mode
      int 10h

      mov cx,10d  ; Outer loop counter how many symbols rotate

      mov bx,50d  ;   this is for delay loop
      OuterLoop:
      push cx

      mov ah,02h
      mov bh, 0        ;cursor set
      mov dh, 2
      mov dl, 10
      int 10h

      mov AH,0Ah
      mov al,"/"    symbol /
      mov bh,0
      mov cx,1
      int 10h

      mov cx,bx
      call Delay       ;delay loop
      sub bx,15d

      mov ah,02h
      mov bh, 0
      mov dh, 2            cursor set
      mov dl, 10
      int 10h

      mov AH,0Ah
      mov al,"\"             ;symbol \
      mov bh,0 
      mov cx,1
      int 10h


      mov cx,bx
      call Delay  ; another delay
      sub bx,10


      pop cx       ; Restore current CX
      loop OuterLoop

      jmp START     ; and after end it should jump to start where is menu with choices

it should work like this

write / delay for example 10 sec write \\ delay 8 sec and jump to beginning and loop

thanks for advices

this is my delay procedure

Delay   PROC    NEAR                    ;

    push    ds                      ;
    push    si                      ;
    push    ax                      ;
    xor     ax, ax                  ;AX = 0
    mov     ds, ax                  ;DS = 0
    mov     si, 046Ch               ;
t1:     mov     ax, [si]                ;
t2:     cmp     ax, [si]                ;
    je      t2                      ;
    loop    t1                      ;
    pop     ax                      ;
    pop     si                      ;
    pop     ds                      ;
    ret                             ;

Delay   ENDP                            ;

i am still working on this app but it is not working all i need is this steps to be made

program : start of loop \\ delay delay 100 times / delay delay 80 times loop and after every loop to decrease delay like this 100 times 80,60,40 and so on but i dont know where to put push and pop cx because my delay procedure is working with cx. i just set cx for example to 100 and it makes delay and so on.

Answer 1

I see two problems:

First, bx is initialized here

mov bx,50d  ;   this is for delay loop

but then it gets over-written by

mov bh, 0

bh is bits 15:8 of bx

Second, in the Delay procedure, what modifies the location at [si] so that the je t2 branch falls thru? As it stands that is an infinite loop:

xor     ax, ax                  ;AX = 0
mov     ds, ax                  ;DS = 0
mov     si, 046Ch               ;
t1:     mov     ax, [si]        ;
t2:     cmp     ax, [si]        ;
        je      t2              ;
        loop    t1              ;

Update: I found that address 0x46c is a BIOS address that contains time information.

http://www.osdata.com/system/physical/lowmem.htm

So the memory you are watching in that loop is a location updated by BIOS with a counter of timer ticks (counts every 54.9 milliseconds), see

http://code.google.com/p/xtideuniversalbios/source/browse/trunk/Assembly_Library/Src/Time/TimerTicks.asm?spec=svn131&r=131

So to answer your question, before calling your Delay procedure you should load CX with the count of BIOS ticks you wish to delay (time in milliseconds divided by 54.9).

Answer 2

For to drawing my own cursor i use the timer interrupt for to become a more steady delay on different performant CPUs.

Cursor_Speed = 7
;-------------DATA--------------------------------------
          CURFLAG DB 0, 0, 0, 0
          ALTVEC  DD 0
;-------------CODE--------------------------------------
          cli
          xor      ax, ax
          mov      es, ax
          mov      ebx, DWORD PTR es:[8*4] ; Get the old Vector (Offset/Segment)
          mov     DWORD PTR[ALTVEC], ebx   ; save it
          mov     cs:DWORD PTR[OLDVEC], ebx
          mov      es:[8*4], OFFSET NEWVEC ; Set the new IRQ-Vector
          mov      es:[(8*4)+2], cs

          mov      al, 36h                    ; Set 18,2 Hertz(Standard)
          out      43h, al
          xor      al, al
          out      40h, al           ; low
          out      40h, al           ; high
          sti
;---------------------------------------------------
          ......
;---------------------------------------------------
NEWVEC:   inc     BYTE PTR[CURFLAG+1]
          cmp     BYTE PTR[CURFLAG+1], Cursor_Speed
          jb  short NOHIT
          mov     BYTE PTR[CURFLAG+1], 0
          xor     BYTE PTR[CURFLAG], 1

NOHIT:    DB 0EAh                         ; jmp far
OLDVEC    DD 0
;---------------------------------------------------

....

Alternativly we can wait of the vsinc with polling port 3DAh for to become a little bit lesser precice delay.

Dirk