{$O-}
unit OvrXMS;
{ OVERXMS 1.2 - Loads overlays in XMS. }
{Assembler OBJ version written by Wilbert van Leijen }
{ This Built In Assembler version 1/03/93 }
{ adapted by Arnold Bailey [72020,1376] BIX abailey }
{ Version 1.1 Includes Bug Fix for DRDOS 6 }
{ Version 1.2 Method for determining total XMS need in AllocateXMS }
{ was different than the method used by CopyUnitToXMS. }
{ Since memory is allocate in 1k chunks there was rarely }
{ a problem unless the total size fell just below a 1k boundary}
{ Changed AllocateXMS to take into account word size }
{ moves only to and from XMS. }
{ Unofficial version }
{ Exit procedure in OvrXms was not declared as 'FAR'. This }
{ could lead to the program bombing when the exit proc chain }
{ was traversed. -- John Leier [70711,3456] }
Interface
uses Overlay;
Const
ovrNoXMSDriver = -7; { No XMS driver installed }
ovrNoXMSMemory = -8; { Insufficient XMS memory available }
Procedure OvrInitXMS;
Implementation
type
XMSMoveType=
record
BlkSize : LongInt;
SrcHandle : word;
SrcOffset : LongInt;
DestHandle : word;
DestOffset : LongInt;
end;
OvrHeader =
record
ReturnAddr : pointer;
FileOfs : LongInt;
CodeSize : word;
FixUpSize : word;
EntryPts : word;
CodeListNext : word;
LoadSeg : word;
Reprieved : word;
LoadListNext : word;
XMSOffset : LongInt;
UserData : array[0..2] of word;
end;
const
XMSDriver : pointer = NIL;
ExitSave : pointer = NIL;
OvrXMSHandle : word = $FFFF;
var
XMSMove : XMSMoveType;
procedure OvrXMSExit; FAR; { !!! Ver 1.2a bug fix [JL] }
begin
ExitProc:=ExitSave;
asm
mov dx,OvrXMSHandle
mov ah,0Ah
call [XMSDriver]
end;
end;
procedure AllocateXMS; assembler;
{Determine the size of the code block to allocate}
{Walk the CodeListNext chain}
{Store the total codesize in DX:AX}
asm
xor ax,ax
mov dx,ax
mov bx,[OvrCodeList]
@@1: add bx,[Prefixseg]
add bx,10h
mov es,bx
{** Ver 1.2 Bug Fix }
mov cx,es:[OvrHeader.CodeSize]
test cx,1 { Test for odd number of bytes}
jz @@2
inc cx { Even number of bytes only }
@@2: add ax,cx
{** Ver 1.2 Bug Fix }
adc dx,0
mov bx,es:[OvrHeader.CodeListNext]
or bx,bx
jnz @@1
{ Obtain number of kilobytes to allocate}
mov bx,1024
div bx
xchg dx,ax
inc dx
{ Allocate the block }
mov ah,9
call [XMSDriver]
or ax,ax
jz @@3
mov OvrXMSHandle,dx
@@3:
end;
function XMSReadFunc(OvrSeg : word):integer; far;
begin
asm
mov es,OvrSeg
mov ax,es:[OvrHeader.CodeSize]
mov word ptr [XMSMove.BlkSize],ax
xor ax,ax
mov word ptr [XMSMove.BlkSize+2],ax { zero high word}
mov [XMSMove.DestHandle],ax { zero dest Handle }
mov word ptr [XMSMove.DestOffset],ax { zero destination offset}
mov ax,[OvrXMSHandle]
mov [XMSMove.SrcHandle],ax
mov ax,word ptr es:[OvrHeader.XMSOffset]
mov word ptr [XMSMove.SrcOffset],ax
mov ax,word ptr es:[OvrHeader.XMSOffset+2]
mov word ptr [XMSMove.SrcOffset+2],ax
mov ax,es:[OvrHeader.LoadSeg]
mov word ptr [XMSMove.DestOffset+2],ax
mov ah,0bh
lea si,XMSMove
call [XMSDriver]
or ax,ax
jz @@1
dec ax
jmp @@2
@@1: mov ax,OvrIOError
@@2: mov @Result,ax
end;
end;
procedure CopyUnitToXMS; assembler;
asm
mov dx,es:[OvrHeader.CodeSize]
test dx,1
jz @@1
inc dx
inc es:[OvrHeader.CodeSize]
@@1: mov word ptr [XMSMove.BlkSize],dx
xor ax,ax
mov word ptr [XMSMove.BlkSize+2],ax
mov [XMSMove.SrcHandle],ax
mov word ptr [XMSMove.SrcOffset],ax
mov ax,[OvrHeapOrg]
mov word ptr [XMSMove.SrcOffset+2],ax
mov ax,[OvrXMSHandle]
mov [XMSMove.DestHandle],ax
mov word ptr [XMSMove.DestOffset],di
mov word ptr [XMSMove.DestOffset+2],bx
mov ah,0bh
lea si,XMSMove
push bx
call [XMSDriver]
pop bx
add di,dx
adc bx,0
or ax,ax
jz @@2
clc
jmp @@3
@@2: stc
@@3:
end;
procedure OvrXMSLoad;
begin
{ Walk the CodeList chain }
{ First segment is PrefixSeg+10h+OvrCodeList }
{ Push each element of overlaid unit list on the stack }
{ Keep the size of the linked list in CX }
asm
MOV AX, [OvrCodeList]
XOR CX, CX
@@1: ADD AX, [PrefixSeg]
ADD AX, 10h
MOV ES, AX
PUSH AX
INC CX
MOV AX, ES:[OvrHeader.CodeListNext]
OR AX, AX
JNZ @@1
{ Loop:}
{ Pop each element of the overlaid unit list from the stack }
XOR BX, BX
XOR DI, DI
@@2: POP ES
PUSH CX
MOV AX, [OvrHeapOrg]
MOV ES:[OvrHeader.LoadSeg], AX
MOV Word Ptr ES:[OvrHeader.XmsOffset+2], BX
MOV Word Ptr ES:[OvrHeader.XmsOffset], DI
{ Load overlay from disk }
PUSH BX
PUSH DI
PUSH ES
PUSH ES
CALL [OvrReadBuf]
POP ES
POP DI
POP BX
{ Flag unit as 'unloaded'; check return code }
MOV ES:[OvrHeader.LoadSeg], 0
NEG AX
JC @@3
CALL CopyUnitToXms
JC @@3
POP CX
LOOP @@2
@@3:
end;
end;
procedure OvrInitXMS; assembler;
{ Make sure the file's been opened}
asm
XOR AX, AX
CMP AX, [OvrDOSHandle]
JNE @@1
DEC AX { ovrError }
JMP @@5
{ Check presence of XMS driver }
@@1: MOV AX, 4300h
INT 2Fh
CMP AL, 80h
JE @@2
MOV AX, ovrNoXmsDriver
JMP @@5
{ Get XMS driver's entry point }
@@2: MOV AX, 4310h
INT 2Fh
MOV Word Ptr [XmsDriver], BX
MOV Word Ptr [XmsDriver+2], ES
CALL AllocateXms
JNZ @@3
MOV AX, ovrNoXMSMemory
JMP @@5
{ Load the overlay into XMS }
@@3: CALL OvrXmsLoad
JNC @@4
{ An error occurred. Release handle and XMS memory }
MOV DX, [OvrXmsHandle]
MOV AH, 0Ah
CALL [XmsDriver]
MOV AX, ovrIOError
JMP @@5
{ Close file }
@@4: MOV BX, [OvrDOSHandle]
MOV AH, 3Eh
INT 21h
{ OvrReadBuf := XmsReadFunc }
MOV Word Ptr [OvrReadBuf], Offset XmsReadFunc
MOV Word Ptr [OvrReadBuf+2], CS
{ ExitSave := ExitProc }
{ ExitProc := OvrXmsExit }
LES AX, [ExitProc]
MOV Word Ptr [ExitSave], AX
MOV Word Ptr [ExitSave+2], ES
MOV Word Ptr [ExitProc], Offset OvrXmsExit
MOV Word Ptr [ExitProc+2], CS
{ Return result of initialisation }
XOR AX, AX
@@5: MOV [OvrResult],AX
end;
end.