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FreeDOS/kernel/kernel.asm
Bart Oldeman e67a8f5058 Changes for kernel 2028 (see history.txt) 
git-svn-id: https://svn.code.sf.net/p/freedos/svn/kernel/trunk@485 6ac86273-5f31-0410-b378-82cca8765d1b
2002-12-09 00:17:15 +00:00

957 lines
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NASM
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;
; File:
; kernel.asm
; Description:
; kernel start-up code
;
; Copyright (c) 1995, 1996
; Pasquale J. Villani
; All Rights Reserved
;
; This file is part of DOS-C.
;
; DOS-C 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, or (at your option) any later version.
;
; DOS-C 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.
;
; You should have received a copy of the GNU General Public
; License along with DOS-C; see the file COPYING. If not,
; write to the Free Software Foundation, 675 Mass Ave,
; Cambridge, MA 02139, USA.
;
; $Id$
;
%include "segs.inc"
%include "ludivmul.inc"
segment PSP
extern _ReqPktPtr:wrt LGROUP
STACK_SIZE equ 384/2 ; stack allocated in words
;************************************************************
; KERNEL BEGINS HERE, i.e. this is byte 0 of KERNEL.SYS
;************************************************************
..start:
entry:
jmp short realentry
;************************************************************
; KERNEL CONFIGURATION AREA
; this is copied up on the very beginning
; it's a good idea to keep this in sync with KConfig.h
;************************************************************
global _LowKernelConfig
_LowKernelConfig:
db 'CONFIG' ; constant
dw configend-configstart; size of config area
; to be checked !!!
configstart:
DLASortByDriveNo db 0 ; sort disks by drive order
InitDiskShowDriveAssignment db 1 ;
SkipConfigSeconds db 2 ;
ForceLBA db 0 ;
GlobalEnableLBAsupport db 1 ;
configend:
;************************************************************
; KERNEL CONFIGURATION AREA END
;************************************************************
;************************************************************
; KERNEL real entry (at ~60:20)
;
; moves the INIT part of kernel.sys to high memory (~9000:0)
; then jumps there
; to aid debugging, some '123' messages are output
; this area is discardable and used as temporary PSP for the
; init sequence
;************************************************************
realentry: ; execution continues here
push ax
push bx
pushf
mov ax, 0e31h ; '1' Tracecode - kernel entered
mov bx, 00f0h
int 010h
popf
pop bx
pop ax
jmp far kernel_start
beyond_entry: resb 256-(beyond_entry-entry)
; scratch area for data (DOS_PSP)
segment INIT_TEXT
extern _FreeDOSmain:wrt I_GROUP
;
; kernel start-up
;
kernel_start:
push ax
push bx
pushf
mov ax, 0e32h ; '2' Tracecode - kernel entered
mov bx, 00f0h
int 010h
popf
pop bx
pop ax
mov ax,I_GROUP
cli
mov ss,ax
mov sp,init_tos
int 12h ; move the init code to higher memory
mov cl,6
shl ax,cl
mov dx,init_end+15
mov cl,4
shr dx,cl
sub ax,dx
mov es,ax
mov ax,cs
mov ds,ax
xor si,si
xor di,di
mov cx,init_end+1
shr cx,1
cld
rep movsw
push es
mov ax,cont
push ax
retf
cont: ; inititalize api stacks for high water tests
mov ax,cs
mov ss,ax
mov di,seg apistk_bottom
mov es,di
mov di,apistk_bottom
mov ax,apistk_top
sub ax,di
sar ax,1
mov cx,ax
mov ax,09090h
cld
rep stosw
; Now set up call frame
mov ax,DGROUP
mov ds,ax
mov es,ax
mov bp,sp ; and set up stack frame for c
sti ; now enable them
push ax
push bx
pushf
mov ax, 0e33h ; '3' Tracecode - kernel entered
mov bx, 00f0h
int 010h
popf
pop bx
pop ax
inc bl
jns floppy
mov bl,3 ; set to C: if hard disk
floppy: mov byte [_BootDrive],bl ; tell where we came from
;!! int 11h
;!! mov cl,6
;!! shr al,cl
;!! inc al
;!! mov byte [_NumFloppies],al ; and how many
mov ax,ss
mov ds,ax
mov es,ax
jmp _FreeDOSmain
%ifdef WATCOM
global _IU4M
_IU4M:
LMULU
global _IU4D
_IU4D:
LDIVMODU
%endif
segment INIT_TEXT_END
;************************************************************
; KERNEL CODE AREA END
; the NUL device
;************************************************************
segment CONST
;
; NUL device strategy
;
global _nul_strtgy
_nul_strtgy:
mov word [cs:_ReqPktPtr],bx ;save rq headr
mov word [cs:_ReqPktPtr+2],es
retf
;
; NUL device interrupt
;
global _nul_intr
_nul_intr:
push es
push bx
les bx,[cs:_ReqPktPtr] ;es:bx--> rqheadr
or word [es:bx+3],100h ;set "done" flag
pop bx
pop es
retf
; floppy parameter table
global _int1e_table
_int1e_table: times 0eh db 0
;************************************************************
; KERNEL FIXED DATA AREA
;************************************************************
segment _FIXED_DATA
; Because of the following bytes of data, THIS MODULE MUST BE THE FIRST
; IN THE LINK SEQUENCE. THE BYTE AT DS:0004 determines the SDA format in
; use. A 0 indicates MS-DOS 3.X style, a 1 indicates MS-DOS 4.0-6.X style.
global DATASTART
DATASTART:
global _DATASTART
_DATASTART:
dos_data db 0
dw kernel_start
db 0 ; padding
dw 1 ; Hardcoded MS-DOS 4.0+ style
times (0eh - ($ - DATASTART)) db 0
global _NetBios
_NetBios dw 0 ; NetBios Number
times (26h - 0ch - ($ - DATASTART)) db 0
; Globally referenced variables - WARNING: DO NOT CHANGE ORDER
; BECAUSE THEY ARE DOCUMENTED AS UNDOCUMENTED (?) AND HAVE
; MANY MULTIPLEX PROGRAMS AND TSR'S ACCESSING THEM
global _NetRetry
_NetRetry dw 3 ;-000c network retry count
global _NetDelay
_NetDelay dw 1 ;-000a network delay count
global _DskBuffer
_DskBuffer dd -1 ;-0008 current dos disk buffer
global _inputptr
_inputptr dw 0 ;-0004 Unread con input
global _first_mcb
_first_mcb dw 0 ;-0002 Start of user memory
global _DPBp
global MARK0026H
; A reference seems to indicate that this should start at offset 26h.
MARK0026H equ $
_DPBp dd 0 ; 0000 First drive Parameter Block
global _sfthead
_sfthead dw _firstsftt ; 0004 System File Table head
dw seg _firstsftt
global _clock
_clock dd 0 ; 0008 CLOCK$ device
global _syscon
_syscon dw _con_dev,seg _con_dev ; 000c console device
global _maxbksize
_maxbksize dw 512 ; 0010 maximum bytes/sector of any block device
dw buf_info ; 0012 pointer to buffers info structure
dw seg buf_info
global _CDSp
_CDSp dd 0 ; 0016 Current Directory Structure
global _FCBp
_FCBp dd 0 ; 001a FCB table pointer
global _nprotfcb
_nprotfcb dw 0 ; 001e number of protected fcbs
global _nblkdev
_nblkdev db 0 ; 0020 number of block devices
global _lastdrive
_lastdrive db 0 ; 0021 value of last drive
global _nul_dev
_nul_dev: ; 0022 device chain root
extern _con_dev:wrt LGROUP
dw _con_dev, seg _con_dev
; next is con_dev at init time.
dw 8004h ; attributes = char device, NUL bit set
dw _nul_strtgy
dw _nul_intr
db 'NUL '
global _njoined
_njoined db 0 ; 0034 number of joined devices
dw 0 ; 0035 DOS 4 pointer to special names (always zero in DOS 5)
setverPtr dw 0,0 ; 0037 setver list
dw 0 ; 003B cs offset for fix a20
dw 0 ; 003D psp of last umb exec
global _LoL_nbuffers
_LoL_nbuffers dw 1 ; 003F number of buffers
dw 1 ; 0041 size of pre-read buffer
global _BootDrive
_BootDrive db 1 ; 0043 drive we booted from
%IFNDEF I386
db 0 ; 0044 cpu type (1 if >=386)
%ELSE
db 1 ; 0044 cpu type (1 if >=386)
%ENDIF
dw 0 ; 0045 Extended memory in KBytes
buf_info:
global _firstbuf
_firstbuf dd 0 ; 0047 disk buffer chain
dw 0 ; 004B Number of dirty buffers
dd 0 ; 004D pre-read buffer
dw 0 ; 0051 number of look-ahead buffers
db 0 ; 0053 00=conv 01=HMA
deblock_buf dd 0 ; 0054 deblock buffer
times 3 db 0 ; 0058 unknown
dw 0 ; 005B unknown
db 0, 0FFh, 0 ; 005D unknown
global _VgaSet
_VgaSet db 0 ; 0060 unknown
dw 0 ; 0061 unknown
global _uppermem_link
_uppermem_link db 0 ; 0063 upper memory link flag
_min_pars dw 0 ; 0064 minimum paragraphs of memory
; required by program being EXECed
global _uppermem_root
_uppermem_root dw 0ffffh ; 0066 dmd_upper_root (usually 9fff)
_last_para dw 0 ; 0068 para of last mem search
SysVarEnd:
;; The first 5 sft entries appear to have to be at DS:00cc
times (0cch - ($ - DATASTART)) db 0
global _firstsftt
_firstsftt:
dd -1 ; link to next
dw 5 ; count
; Some references seem to indicate that this data should start at 01fbh in
; order to maintain 100% MS-DOS compatibility.
times (01fbh - ($ - DATASTART)) db 0
global MARK01FBH
MARK01FBH equ $
global _local_buffer ; local_buffer is 256 bytes long
; so it overflows into kb_buf!!
; only when kb_buf is used, local_buffer is limited to 128 bytes.
_local_buffer: times 128 db 0
global _kb_buf
_kb_buf db 128,0 ; initialise buffer to empty
times 128+1 db 0 ; room for 128 byte readline + LF
;
; Variables that follow are documented as part of the DOS 4.0-6.X swappable
; data area in Ralf Browns Interrupt List #56
;
; this byte is used for ^P support
global _PrinterEcho
_PrinterEcho db 0 ;-34 - 0 = no printer echo, ~0 echo
global _verify_ena
_verify_ena db 0 ; ~0, write with verify
; this byte is used for TAB's
global _scr_pos
_scr_pos db 0 ; Current Cursor Column
global _switchar
_switchar db '/' ;-31 - switch char
global _mem_access_mode
_mem_access_mode db 0 ;-30 - memory allocation strategy
global sharing_flag
sharing_flag db 0 ; 00 = sharing module not loaded
; 01 = sharing module loaded, but
; open/close for block devices
; disabled
; FF = sharing module loaded,
; open/close for block devices
; enabled (not implemented)
global _net_set_count
_net_set_count db 1 ;-28 - count the name below was set
global _net_name
_net_name db ' ' ;-27 - 15 Character Network Name
db 00 ; Terminating 0 byte
;
; Variables contained the the "STATE_DATA" segment contain
; information about the STATE of the current DOS Process. These
; variables must be preserved regardless of the state of the INDOS
; flag.
;
; All variables that appear in "STATE_DATA" **MUST** be declared
; in this file as the offsets from the INTERNAL_DATA variable are
; critical to the DOS applications that modify this data area.
;
;
global _ErrorMode, _InDOS
global _CritErrLocus, _CritErrCode
global _CritErrAction, _CritErrClass
global _CritErrDev, _CritErrDrive
global _dta
global _cu_psp, _default_drive
global _break_ena
global _return_code
global _internal_data
global _CritPatch
_CritPatch dw 0d0ch ;-11 zero list of patched critical
dw 0d0ch ; section variables
dw 0d0ch
dw 0d0ch
dw 0d0ch
db 0 ;-01 - unknown
_internal_data: ; <-- Address returned by INT21/5D06
_ErrorMode db 0 ; 00 - Critical Error Flag
_InDOS db 0 ; 01 - Indos Flag
_CritErrDrive db 0 ; 02 - Drive on write protect error
_CritErrLocus db 0 ; 03 - Error Locus
_CritErrCode dw 0 ; 04 - DOS format error Code
_CritErrAction db 0 ; 06 - Error Action Code
_CritErrClass db 0 ; 07 - Error Class
_CritErrDev dd 0 ; 08 - Failing Device Address
_dta dw _sda_tmp_dm, seg _sda_tmp_dm
; 0C - current DTA, initialize to TempBuffer.
_cu_psp dw 0 ; 10 - Current PSP
break_sp dw 0 ; 12 - used in int 23
_return_code dw 0 ; 14 - return code from process
_default_drive db 0 ; 16 - Current Drive
_break_ena db 1 ; 17 - Break Flag (default TRUE)
db 0 ; 18 - flag, code page switching
db 0 ; 19 - flag, copy of 18 on int 24h abort
global _swap_always, _swap_indos
_swap_always:
global _Int21AX
_Int21AX dw 0 ; 1A - AX from last Int 21
global owning_psp, _MachineId
owning_psp dw 0 ; 1C - owning psp
_MachineId dw 0 ; 1E - remote machine ID
dw 0 ; 20 - First usable mcb
dw 0 ; 22 - Best usable mcb
dw 0 ; 24 - Last usable mcb
dw 0 ; 26 - memory size in paragraphs
dw 0 ; 28 - unknown
db 0 ; 2A - unknown
db 0 ; 2B - unknown
db 0 ; 2C - unknown
global _break_flg
_break_flg db 0 ; 2D - Program aborted by ^C
db 0 ; 2E - unknown
db 0 ; 2F - not referenced
global _DayOfMonth
_DayOfMonth db 1 ; 30 - day of month
global _Month
_Month db 1 ; 31 - month
global _YearsSince1980
_YearsSince1980 dw 0 ; 32 - year since 1980
daysSince1980 dw 0FFFFh ; 34 - number of days since epoch
; force rebuild on first clock read
global _DayOfWeek
_DayOfWeek db 2 ; 36 - day of week
_console_swap db 0 ; 37 console swapped during read from dev
global _dosidle_flag
_dosidle_flag db 1 ; 38 - safe to call int28 if nonzero
_abort_progress db 0 ; 39 - abort in progress
global _CharReqHdr
_CharReqHdr:
global _ClkReqHdr
_ClkReqHdr times 30 db 0 ; 3A - Device driver request header
dd 0 ; 58 - pointer to driver entry
global _MediaReqHdr
_MediaReqHdr times 22 db 0 ; 5C - Device driver request header
global _IoReqHdr
_IoReqHdr times 30 db 0 ; 72 - Device driver request header
times 6 db 0 ; 90 - unknown
global _ClkRecord
_ClkRecord times 6 db 0 ; 96 - CLOCK$ transfer record
dw 0 ; 9C - unknown
global __PriPathBuffer
__PriPathBuffer times 80h db 0 ; 9E - buffer for file name
global __SecPathBuffer
__SecPathBuffer times 80h db 0 ;11E - buffer for file name
global _sda_tmp_dm
_sda_tmp_dm times 21 db 0 ;19E - 21 byte srch state
global _SearchDir
_SearchDir times 32 db 0 ;1B3 - 32 byte dir entry
global _TempCDS
_TempCDS times 88 db 0 ;1D3 - TemporaryCDS buffer
global _DirEntBuffer
_DirEntBuffer times 32 db 0 ;22B - space enough for 1 dir entry
global _wAttr
_wAttr dw 0 ;24B - extended FCB file attribute
global _SAttr
_SAttr db 0 ;24D - Attribute Mask for Dir Search
global _OpenMode
_OpenMode db 0 ;24E - File Open Attribute
times 3 db 0
global _Server_Call
_Server_Call db 0 ;252 - Server call Func 5D sub 0
db 0
; Pad to 05CCh
times (25ch - ($ - _internal_data)) db 0
global _tsr ; used by break and critical error
_tsr db 0 ;25C - handlers during termination
db 0 ;25D - padding
global term_psp
term_psp dw 0 ;25E - 0??
global int24_esbp
int24_esbp times 2 dw 0 ;260 - pointer to criticalerr DPB
global _user_r, int21regs_off, int21regs_seg
_user_r:
int21regs_off dw 0 ;264 - pointer to int21h stack frame
int21regs_seg dw 0
global critical_sp
critical_sp dw 0 ;268 - critical error internal stack
global current_ddsc
current_ddsc times 2 dw 0
; Pad to 059ah
times (27ah - ($ - _internal_data)) db 0
global current_device
current_device times 2 dw 0 ;27A - 0??
global _lpCurSft
_lpCurSft times 2 dw 0 ;27e - Current SFT
global _current_ldt
_current_ldt times 2 dw 0 ;282 - Current CDS
global _lpFcb
_lpFcb times 2 dw 0 ;286 - pointer to callers FCB
global _current_sft_idx
_current_sft_idx dw 0 ;28A - SFT index for next open
; used by MS NET
; Pad to 05b2h
times (292h - ($ - _internal_data)) db 0
dw __PriPathBuffer ; 292 - "sda_WFP_START" offset in DOS DS of first filename argument
dw __SecPathBuffer ; 294 - "sda_REN_WFP" offset in DOS DS of second filename argument
; Pad to 05ceh
times (2aeh - ($ - _internal_data)) db 0
global _current_filepos
_current_filepos times 2 dw 0 ;2AE - current offset in file
; Pad to 05f0h
times (2d0h - ($ - _internal_data)) db 0
global _prev_user_r
global prev_int21regs_off
global prev_int21regs_seg
_prev_user_r:
prev_int21regs_off dw 0 ;2D0 - pointer to prev int 21 frame
prev_int21regs_seg dw 0
; Pad to 05fdh
times (2ddh - ($ - _internal_data)) db 0
global _ext_open_action
global _ext_open_attrib
global _ext_open_mode
_ext_open_action dw 0 ;2DD - extended open action
_ext_open_attrib dw 0 ;2DF - extended open attrib
_ext_open_mode dw 0 ;2E1 - extended open mode
; Pad to 0620h
times (300h - ($ - _internal_data)) db 0
global _szNames
_szNames:
;; times 11 db 0
global _FcbSearchBuffer ; during FCB search 1st/next use bottom
_FcbSearchBuffer: ; of error stack as scratch buffer
; times 43 db 0 ; - only used during int 21 call
; stacks are made to initialize to no-ops so that high-water
; testing can be performed
global apistk_bottom
apistk_bottom:
times STACK_SIZE dw 0 ;300 - Error Processing Stack
global _error_tos
_error_tos:
times STACK_SIZE dw 0 ;480 - Disk Function Stack
global _disk_api_tos
_disk_api_tos:
times STACK_SIZE dw 0 ;600 - Char Function Stack
global _char_api_tos
_char_api_tos:
apistk_top:
db 0 ; 780 ???
_VolChange db 0 ;781 - volume change
_VirtOpen db 0 ;782 - virtual open flag
; controlled variables end at offset 78Ch so pad to end
times (78ch - ($ - _internal_data)) db 0
;
; end of controlled variables
;
segment _BSS
;!! global _NumFloppies
;!!_NumFloppies resw 1
;!!intr_dos_stk resw 1
;!!intr_dos_seg resw 1
; mark front and end of bss area to clear
segment IB_B
global __ib_start
__ib_start:
segment IB_E
global __ib_end
__ib_end:
;; do not clear the other init BSS variables + STACK: too late.
; kernel startup stack
global init_tos
resw 512
init_tos:
; the last paragraph of conventional memory might become an MCB
resb 16
global __init_end
__init_end:
init_end:
segment _DATA
; blockdev private stack
global blk_stk_top
times 192 dw 0
blk_stk_top:
; clockdev private stack
global clk_stk_top
times 64 dw 0
clk_stk_top:
; have a jump to the real thing here for AARD compliance
global _CharMapSrvc ; in _DATA (see AARD)
_CharMapSrvc: jmp far CharMapSrvc2
; Dynamic data:
; member of the DOS DATA GROUP
; and marks definitive end of all used data in kernel data segment
;
segment _DATAEND
_swap_indos:
; we don't know precisely what needs to be swapped before this, so set it here.
; this is just after FIXED_DATA+BSS+DATA and before (D)CONST+BSS
; probably, the clock and block stacks and disktransferbuffer should go past
; _swap_indos but only if int2a ah=80/81 (critical section start/end)
; are called upon entry and exit of the device drivers
segment DYN_DATA
global _Dyn
_Dyn:
DynAllocated dw 0
segment ID_B
global __INIT_DATA_START
__INIT_DATA_START:
segment ID_E
global __INIT_DATA_END
__INIT_DATA_END:
segment INIT_TEXT_START
global __InitTextStart
__InitTextStart: ; and c version
;
; start end end of HMA area
segment HMA_TEXT_START
global __HMATextAvailable
__HMATextAvailable
global __HMATextStart
__HMATextStart:
;
; the HMA area is filled with 1eh+3(=sizeof VDISK) = 33 byte dummy data,
; so nothing will ever be below 0xffff:0031
;
segment _TEXT
begin_hma:
times 10h db 0 ; filler [ffff:0..ffff:10]
times 20h db 0
db 0
%ifdef WATCOM
; 32 bit multiplication + division
global __U4M
__U4M:
LMULU
global __U4D
__U4D:
LDIVMODU
%endif
;End of HMA segment
segment HMA_TEXT_END
global __HMATextEnd
__HMATextEnd: ; and c version
; The default stack (_TEXT:0) will overwrite the data area, so I create a dummy
; stack here to ease debugging. -- ror4
segment _STACK class=STACK stack
segment _LOWTEXT
; dummy interrupt return handlers
global _int22_handler
global _int28_handler
global _int2a_handler
global _empty_handler
_int22_handler:
_int28_handler:
_int2a_handler:
_empty_handler:
iret
; to minimize relocations
global _DGROUP_
_DGROUP_:
dw DGROUP
segment _LOWTEXT
global _initforceEnableA20
initforceEnableA20:
call near forceEnableA20
retf
global __HMARelocationTableStart
__HMARelocationTableStart:
global _int2f_handler
extern reloc_call_int2f_handler
_int2f_handler: jmp far reloc_call_int2f_handler
call near forceEnableA20
global _int20_handler
extern reloc_call_int20_handler
_int20_handler: jmp far reloc_call_int20_handler
call near forceEnableA20
global _int21_handler
extern reloc_call_int21_handler
_int21_handler: jmp far reloc_call_int21_handler
call near forceEnableA20
global _low_int25_handler
extern reloc_call_low_int25_handler
_low_int25_handler: jmp far reloc_call_low_int25_handler
call near forceEnableA20
global _low_int26_handler
extern reloc_call_low_int26_handler
_low_int26_handler: jmp far reloc_call_low_int26_handler
call near forceEnableA20
global _int27_handler
extern reloc_call_int27_handler
_int27_handler: jmp far reloc_call_int27_handler
call near forceEnableA20
global _int0_handler
extern reloc_call_int0_handler
_int0_handler: jmp far reloc_call_int0_handler
call near forceEnableA20
global _int6_handler
extern reloc_call_int6_handler
_int6_handler: jmp far reloc_call_int6_handler
call near forceEnableA20
global _cpm_entry
extern reloc_call_cpm_entry
_cpm_entry: jmp far reloc_call_cpm_entry
call near forceEnableA20
global _reloc_call_blk_driver
extern _blk_driver
_reloc_call_blk_driver:
jmp far _blk_driver
call near forceEnableA20
global _reloc_call_clk_driver
extern _clk_driver
_reloc_call_clk_driver:
jmp far _clk_driver
call near forceEnableA20
; global _CharMapSrvc ; in _DATA (see AARD)
extern _reloc_call_CharMapSrvc
CharMapSrvc2: jmp far _reloc_call_CharMapSrvc
call near forceEnableA20
global __HMARelocationTableEnd
__HMARelocationTableEnd:
;
; if we were lucky, we found all entries from the outside to the kernel.
; if not, BUMS
;
;
; this routine makes the HMA area available. PERIOD.
; must conserve ALL registers
; will be only ever called, if HMA (DOS=HIGH) is enabled.
; for obvious reasons it should be located at the relocation table
;
global _XMSDriverAddress
_XMSDriverAddress:
dw 0 ; XMS driver, if detected
dw 0
global __EnableA20
__EnableA20:
mov ah,3
UsingXMSdriver:
push bx
call far [cs:_XMSDriverAddress]
pop bx
retf
global __DisableA20
__DisableA20:
mov ah,4
jmp short UsingXMSdriver
dslowmem dw 0
eshighmem dw 0ffffh
global forceEnableA20
forceEnableA20:
push ds
push es
push ax
forceEnableA20retry:
mov ds, [cs:dslowmem]
mov es, [cs:eshighmem]
mov ax, [ds:00000h]
cmp ax, [es:00010h]
jne forceEnableA20success
mov ax, [ds:00002h]
cmp ax, [es:00012h]
jne forceEnableA20success
mov ax, [ds:00004h]
cmp ax, [es:00014h]
jne forceEnableA20success
mov ax, [ds:00006h]
cmp ax, [es:00016h]
jne forceEnableA20success
;
; ok, we have to enable A20 )at least seems so
;
call far __EnableA20
jmp short forceEnableA20retry
forceEnableA20success:
pop ax
pop es
pop ds
ret
;
; global f*cking compatibility issues:
;
; very old brain dead software (PKLITE, copyright 1990)
; forces us to execute with A20 disabled
;
global _ExecUserDisableA20
_ExecUserDisableA20:
cmp word [cs:_XMSDriverAddress],0
jne NeedToDisable
cmp word [cs:_XMSDriverAddress+2],0
je noNeedToDisable
NeedToDisable:
push ax
call far __DisableA20
pop ax
noNeedToDisable:
iret
segment _LOWTEXT
;
; Default Int 24h handler -- always returns fail
; so we have not to relocate it (now)
;
FAIL equ 03h
global _int24_handler
_int24_handler: mov al,FAIL
iret
;
; this makes some things easier
;
segment _LOWTEXT
global _TEXT_DGROUP
_TEXT_DGROUP dw DGROUP
segment INIT_TEXT
global _INIT_DGROUP
_INIT_DGROUP dw DGROUP
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