;
; FLASH.A86 - Version 0.0
; Flashes The LEDs On An AT Keyboard Until A Key Is Pressed
; Freeware from Kirk Lawrence
;  (Disassembled from the DOS program LEDS.COM; author unknown)
;
;   Improvements over original DOS version:
;    Routine added to check for AT-class machine.
;    Timing routine changed to make the flash rate independent of CPU speed.
;
        cseg
        org     100h
        jmp     okay
;
num     dw      0
error   db      13,10,'  This program requires an AT-class computer.'
        db      13,10,07,'$'
;
start:
;-------------------------------------------------------------------
; This routine checks the processor type to insure that we've got an
; AT-class machine.
;
        pushf                   ;push flags
        pop     ax              ;get flags
        mov     cx,ax           ;save flags
        and     ax,0FFFh        ;clear flag bits 12-15
        push    ax              ;save flag value on stack
        popf                    ;replace current flags value
        pushf                   ;get new flags
        pop     ax              ;store new flags in AX
        and     ax,0F000h       ;if bits 12-15 are set, then CPU
        cmp     ax,0F000h       ;  is an 8086/8088
        jne     okay            ;we've got an AT, so go do the deed
        mov     cl,9            ;function 9 - print string
        mov     dx,offset error ;point to error message
        int     224             ;call BDOS
        xor     cx,cx           ;function 0 - reset system
        int     224             ;exit to CP/M-86
;---------------------------------
; This is the start of the program.
;
okay:
        mov     ax,0040h
        mov     es,ax
        mov     bx,0017h
        mov     es: al,[bx]
        and     al,70h
        mov     bx,01A4h
        mov     [bx],al
sub3:
        mov     al,01
        call    sub1
        call    sub2
        mov     al,02
        call    sub1
        call    sub2
        mov     al,04
        call    sub1
        call    sub2
        mov     ah,01
        int     16h
        jz      sub3
        mov     ah,00
        int     16h
        mov     bx,0017h
        and     es: byte ptr [bx],08Fh
        mov     bx,01A4h
        mov     al,[bx]
        mov     bx,0017h
        or      es: [bx],al
        mov     cl,04
        shr     al,cl
        call    sub1
        xor     cx,cx
        xor     ax,ax
        xor     dx,dx
        int     224
sub1:
        mov     ah,al
sub4:
        in      al,064h
        test    al,02
        jnz     sub4
        mov     bx,0097h
        and     es: byte ptr [bx],0EFh
        mov     al,0EDh
        out     60h,al
sub5:
        mov     bx,0097h
        test    es: byte ptr [bx],010h
        jz      sub5
        mov     al,ah
        out     60h,al
        ret
;-------------------------------------------------------------------------
; Here's the improved timing routine.  It uses the BIOS timer interrupt,
; thereby making the LED flash rate independent of the processor's speed,
; and allowing the program to perform consistently on all computers.
; Originally, a LOOP was used -- with the number of loops set to an
; arbitrary value.
;
sub2:
        push    ax              ;preserve register AX
        mov     ah,00           ;function 0 - read system timer
        int     1Ah             ;call BIOS timer services
        add     dx,1            ;add our delay factor
        mov     num,dx          ;move total into variable
count:
        mov     ah,00h          ;function 0 - read system timer
        int     1Ah             ;call BIOS timer services
        cmp     dx,num          ;has time period elapsed?
        je      thatsall        ;yes, go return
        jmp     count           ;no, go count some more
thatsall:
        pop     ax              ;restore register AX
        ret                     ;return
end