source: xtideuniversalbios/trunk/Assembly_Library/Src/Time/Delay.asm @ 376

; Project name  :   Assembly Library
; Description   :   Delay functions.

;
; XTIDE Universal BIOS and Associated Tools 
; Copyright (C) 2009-2010 by Tomi Tilli, 2011-2012 by XTIDE Universal BIOS Team.
;
; This program is free software; you can redistribute it and/or modify
; it under the terms of the GNU General Public License as published by
; the Free Software Foundation; either version 2 of the License, or
; (at your option) any later version.
; 
; This program is distributed in the hope that it will be useful,
; but WITHOUT ANY WARRANTY; without even the implied warranty of
; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
; GNU General Public License for more details.      
; Visit http://www.gnu.org/licenses/old-licenses/gpl-2.0.html
;       

; Section containing code
SECTION .text

;--------------------------------------------------------------------
; Delay is always at least one millisecond since
; RTC resolution is 977 microsecs.
;
; Delay_MicrosecondsFromAX
;   Parameters:
;       AX:     Number of microsecs to wait
;   Returns:
;       Nothing
;   Corrupts registers:
;       AX
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
Delay_MicrosecondsFromAX:
    push    dx
    push    cx

    xor     cx, cx
    xchg    dx, ax                          ; Microsecs now in CX:DX
    mov     ah, EVENT_WAIT                  ; Event Wait
    int     BIOS_SYSTEM_INTERRUPT_15h
    sti                                     ; XT BIOSes return with interrupt disabled

    pop     cx
    pop     dx
    mov     ax, 1                           ; Prepare to wait 1 timer tick
    jc      SHORT Delay_TimerTicksFromAX    ; Event Wait was unsupported or busy
    ret


;--------------------------------------------------------------------
; First tick might take 0...54.9 ms and remaining ticks
; will occur at 54.9 ms intervals.
;
; Delay_TimerTicksFromAX
;   Parameters:
;       AX:     Number of timer ticks to wait
;   Returns:
;       Nothing
;   Corrupts registers:
;       AX
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
Delay_TimerTicksFromAX:
    push    dx

    sti                         ; Make sure that interrupts are enabled
    xchg    dx, ax
    call    TimerTicks_ReadFromBdaToAX
    add     dx, ax              ; DX = end time
.WaitLoop:
    call    TimerTicks_ReadFromBdaToAX
    cmp     ax, dx
    jb      SHORT .WaitLoop     ; Loop until end time is reached

    pop     dx
    ret