source: xtideuniversalbios/trunk/XTIDE_Universal_BIOS/Src/Device/Timer.asm@ 465

; Project name  :   XTIDE Universal BIOS
; Description   :   Timeout and delay functions for INT 13h services.

;
; 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

;--------------------------------------------------------------------
; Timer_InitializeTimeoutWithTicksInCL
;   Parameters:
;       CL:     Timeout value in system timer ticks
;       DS:     Segment to RAMVARS
;   Returns:
;       Nothing
;   Corrupts registers:
;       CX
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
Timer_InitializeTimeoutWithTicksInCL:
    mov     [RAMVARS.bTimeoutTicksLeft], cl     ; Ticks until timeout
    call    ReadTimeFromBdaToCX
    mov     [RAMVARS.bLastTimeoutUpdate], cl    ; Start time
    ret


;--------------------------------------------------------------------
; Timer_SetCFifTimeout
;   Parameters:
;       DS:     Segment to RAMVARS
;   Returns:
;       CF:     Set if timeout
;               Cleared if time left
;   Corrupts registers:
;       CX
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
Timer_SetCFifTimeout:
    call    ReadTimeFromBdaToCX
    cmp     cl, [RAMVARS.bLastTimeoutUpdate]
    je      SHORT .StillPollingTheSameTick
    mov     [RAMVARS.bLastTimeoutUpdate], cl
    sub     BYTE [RAMVARS.bTimeoutTicksLeft], 1 ; DEC does not update CF
.StillPollingTheSameTick:
    ret


;--------------------------------------------------------------------
; Delay is always at least one millisecond since
; RTC resolution is 977 microsecs.
;
; Timer_DelayMicrosecondsFromAX
;   Parameters:
;       AX:     Number of microsecs to wait
;   Returns:
;       Nothing
;   Corrupts registers:
;       AX
;--------------------------------------------------------------------
Timer_DelayMicrosecondsFromAX:
%ifndef USE_AT
    mov     ax, 2
    ; Fall to Timer_DelayTimerTicksFromAX
%else
    push    dx
    push    cx

    xor     cx, cx
    xchg    dx, ax                      ; Microsecs now in CX:DX
    mov     ah, EVENT_WAIT
    int     BIOS_SYSTEM_INTERRUPT_15h
    sti                                 ; XT BIOSes return with interrupts disabled. TODO: Maybe we can remove this since it's in an AT-only block?

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


;--------------------------------------------------------------------
; First tick might take 0...54.9 ms and remaining ticks
; will occur at 54.9 ms intervals.
;
; Timer_DelayTimerTicksFromAX
;   Parameters:
;       AX:     Number of timer ticks to wait
;   Returns:
;       Nothing
;   Corrupts registers:
;       AX
;--------------------------------------------------------------------
Timer_DelayTimerTicksFromAX:
    sti                             ; Make sure that interrupts are enabled
    call    ReadTimeFromBdaToCX
    add     ax, cx                  ; AX = end time
.WaitLoop:
    call    ReadTimeFromBdaToCX
    cmp     cx, ax
    jne     SHORT .WaitLoop         ; Loop until end time is reached
    ret


;--------------------------------------------------------------------
; ReadTimeFromBdaToCX
;   Parameters
;       Nothing
;   Returns:
;       CX:     System time in 54.9 ms ticks
;   Corrupts registers:
;       Nothing
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
ReadTimeFromBdaToCX:
    push    ds
    LOAD_BDA_SEGMENT_TO ds, cx
    mov     cx, [BDA.dwTimerTicks]  ; Read low WORD only
    pop     ds
    ret