Source code of Windows XP (NT5)
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PAGE ,132 TITLE DXEMM2.ASM -- Dos Extender MEMM Enable Code
; Copyright (c) Microsoft Corporation 1989-1991. All Rights Reserved.
;***********************************************************************;; DXEMM2.ASM -- Dos Extender MEMM Enable Code;;-----------------------------------------------------------------------;; This module provides routines that attempt to enable MEMM/CEMM/EMM386; drivers. DOSX tries to disable MEMM when starting up, and enables MEMM; when terminating.;; NOTE: This code is in a seperate file from the disable logic because; the disable code is discarded after initialization.;;-----------------------------------------------------------------------;; 12/08/89 jimmat Finally got around to implementing this.;;***********************************************************************
.286p
; -------------------------------------------------------; INCLUDE FILE DEFINITIONS; -------------------------------------------------------
.xlist .sallinclude segdefs.incinclude gendefs.inc .list
if NOT VCPI
; -------------------------------------------------------; GENERAL SYMBOL DEFINITIONS; -------------------------------------------------------
; -------------------------------------------------------; EXTERNAL SYMBOL DEFINITIONS; -------------------------------------------------------
; -------------------------------------------------------; DATA SEGMENT DEFINITIONS; -------------------------------------------------------
DXDATA segment
public fMEMM_Disabled, MEMM_State, MEMM_Call
fMEMM_Disabled db 0 ; NZ if MEMM disabledMEMM_state db 0 ; Initial MEMM state
MEMM_Call dd 0 ; far call address into EMM driver
DXDATA ends
; -------------------------------------------------------; CODE SEGMENT VARIABLES; -------------------------------------------------------
DXCODE segment
DXCODE ends
DXPMCODE segment
DXPMCODE ends
; ------------------------------------------------------- subttl MEMM/CEMM/EMM386 Enable Routines page; -------------------------------------------------------; MEMM/CEMM/EMM386 ENABLE ROUTINES; -------------------------------------------------------
DXCODE segment assume cs:DXCODE
; -------------------------------------------------------; EMMEnable -- This routine attempts to re-enable any installed; MEMM/CEMM/EMM386 driver.;; Input: none; Output: CY off - EMM driver enabled (or never disabled); CY set - EMM installed, and can't disable; Errors:; Uses: All registers preserved
assume ds:DGROUP,es:NOTHING,ss:NOTHING public EMMEnable
EMMEnable proc near
push ax
cmp fMEMM_Disabled,0 ; Did we disable MEMM before? jz enable_exit ; no, don't need to enable then
mov ah,01 ; Set state command mov al,MEMM_state ; Get initial state cmp al,2 ; They return 0 (on), 1 (off), jbe @f ; 2 (auto on), 3 (auto off) -- but mov al,2 ; we can only set 1 - 2@@: call [MEMM_Call] ; and restore it jc not_enabled
mov fMEMM_Disabled,0 ; no longer disabled
clc jmp short enable_exit
not_enabled: stc
enable_exit: pop ax
ret
EMMEnable endp
; -------------------------------------------------------
DXCODE ends
;****************************************************************
endif ; NOT VCPI
end
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