TITLE Turbo Pascal XMS support for loading overlays - By Wilbert van Leijen
PAGE 65, 132
LOCALS @@
Data SEGMENT Word Public
ASSUME DS:Data
; XMS block move record
XmsMoveType STRUC
BlkSize DD ?
SrcHandle DW ?
SrcOffset DD ?
DestHandle DW ?
DestOffset DD ?
XmsMoveType ENDS
; TP overlay manager record
OvrHeader STRUC
ReturnAddr DD ? ; Virtual return address
FileOfs DD ? ; Offset into overlay file
CodeSize DW ? ; Size of overlay
FixupSize DW ? ; Size of fixup table
EntryPts DW ? ; Number of procedures
CodeListNext DW ? ; Segment of next overlay
LoadSeg DW ? ; Start segment in memory
Reprieved DW ? ; Loaded in memory flag
LoadListNext DW ? ; Segment of next in load list
XmsOffset DD ? ; Offset into allocated XMS block
UserData DW 3 DUP(?)
OvrHeader ENDS
XmsDriver DD ? ; Entry point of XMS driver
ExitSave DD ? ; Pointer to previous exit proc
XmsMove XmsMoveType <>
OvrXmsHandle DW ? ; Returned by XMS driver
Extrn PrefixSeg : Word
Extrn ExitProc : DWord
Extrn OvrResult : Word
Extrn OvrCodeList : Word
Extrn OvrDosHandle : Word
Extrn OvrHeapOrg : Word
Extrn OvrReadBuf : DWord
Data ENDS
Code SEGMENT Byte Public
ASSUME CS:Code
Public OvrInitXMS
ovrIOError EQU -4
ovrNoXMSDriver EQU -7
ovrNoXMSMemory EQU -8
OvrXmsExit PROC
; Release handle and XMS memory
MOV DX, [OvrXmsHandle]
MOV AH, 10
CALL [XmsDriver]
; Restore pointer to previous exit procedure
LES AX, [ExitSave]
MOV Word Ptr [ExitProc], AX
MOV Word Ptr [ExitProc+2], ES
RETF
OvrXmsExit ENDP
AllocateXms PROC
; Determine the size of the XMS block to allocate:
; Walk the CodeListNext chain
; Store the total codesize in DX:AX
XOR AX, AX
XOR DX, DX
MOV BX, [OvrCodeList]
@@1: ADD BX, [PrefixSeg]
ADD BX, 10h
MOV ES, BX
ADD AX, ES:[OvrHeader.CodeSize]
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 @@2
MOV [OvrXmsHandle], DX
@@2: RETN
AllocateXms ENDP
; Function XmsReadFunc(OvrSeg : Word) : Integer; Far;
XmsReadFunc PROC
; Swap the code from XMS to the heap
PUSH BP
MOV BP, SP
MOV ES, [BP+6]
MOV AX, ES:[OvrHeader.CodeSize]
MOV Word Ptr [XmsMove.BlkSize], AX
XOR AX, AX
MOV Word Ptr [XmsMove.BlkSize+2], AX
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
XOR AX, AX
MOV [XmsMove.DestHandle], AX
MOV Word Ptr [XmsMove.DestOffset], AX
MOV AX, ES:[OvrHeader.LoadSeg]
MOV Word Ptr [XmsMove.DestOffset+2], AX
MOV AH, 11
LEA SI, XmsMove
CALL [XmsDriver]
OR AX, AX
JZ @@1
DEC AX
JMP @@2
@@1: MOV AX, ovrIOError
@@2: POP BP
RETF 2
XmsReadFunc ENDP
; Copy an overlaid unit from the heap to XMS
; If successful, carry flag is cleared
; In/Out:
; BX:DI = offset into XMS memory block
CopyUnitToXms PROC
; XMS requires that an even number of bytes is moved
MOV DX, ES:[OvrHeader.CodeSize]
TEST DX, 1
JZ @@1
INC DX
INC ES:[OvrHeader.CodeSize]
; Get the fields of the XMS block move structure
@@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, 11
LEA SI, XmsMove
CALL [XmsDriver]
; Bump code size
ADD DI, DX
ADC BX, 0
; Check return code from XMS driver
OR AX, AX
JZ @@2
CLC
RETN
@@2: STC
RETN
CopyUnitToXms ENDP
OvrXmsLoad PROC
PUSH BP
MOV BP, SP
; 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
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: MOV SP, BP
POP BP
RETN
OvrXMSLoad ENDP
OvrInitXMS PROC
; Make sure the file's been opened
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, 10
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
RETF
OvrInitXMS ENDP
Code ENDS
END
