;==============================================================


stack	segment stack		; keep MS link happy by providing null stack
stack	ends

CODE	SEGMENT PARA		; start off in code.

;==============================================================

data	segment byte		; provide a separate DATA segment
				; actually all come after the code
;==============================================================
;  V A R I A B L E S

BannerMsg	DB 13d,10d
		db '$'

UsageMsg	DB 'Insert the diskette you used for CMOSSave.',13,10
		DB 'then try:',13,10
		DB 'CMOSRest A:\CMOS.Sav',13,10
		DB 'or if the file is on hard disk try:',13,10
		DB 'CMOSRest C:\CMOS.Sav',13,10
		DB 'Read CMOS.TXT to find how to use it properly.',13,10
		db '$'

FileTroubleMsg	DB 'Error',7,13,10
		DB 'Cannot find/read the disk file.',13,10
		db '$'

WorkedMsg	DB 'CMOS successfully restored',13,10
		db '$'


FilenamePtr	DW	0
			; pointer to filename in command line

CMOSSize	DB	0
			; size of cmos in bytes

CMOSBuff	db 0	; dynamic buffer will grow to 128
			; it hangs out past the end of the program

data		ends

com	group	code,data	; force data segment to go at the end

	ASSUME	CS:com,DS:com,ES:com,SS:com
				; seg regs cover everything
	ORG	100H		; in Code segment

;==========================

Main	proc	far

;	M A I N L I N E   R O U T I N E
Start:
	lea	dx,BannerMsg	; display the banner
	Call	Say
	Call	Parse		; get filename from command line

	call	ReadCMOS	; read CMOS contents from file
	call	CalcCMOSSize	; it is 64 or 128 bytes long?
	call	PutCMOS 	; store buffer to CMOS

	lea	dx,WorkedMsg	; crow about success
	Call	Say
Done:
	mov	ax,4c00h
	int	21h		;normal termination

Main	EndP

;===============================================================

Trouble proc	near

FileTrouble:
	Lea	dx,FileTroubleMsg	; display file trouble
	Call	Say
	Jmp	Abort

abort:
				; error exit
	mov	ax, 4c04h	; ERRORLEVEL = 4
	int	21h		; DIE

Trouble endp

;===============================================================

MLeading	PROC	Near

;	Remove leading blanks
;	on entry BX is addr of string, CX its length
;	trims off any leading blanks, leaving result in BX CX
;	length may also be 0 or 1, but not -ve
;	If the entire string is blank the result is the null string
	mov	di,bx
	mov	al,20H		; AL = blank  -- the search char
	jcxz	mleading2	; jump if null string
	repe	scasb		; scan ES:DI forwards till hit non blank
				; DI points just after it (wrap ok)
				; cx IS ONE TOO SMALL, OR 0 IF NONE FOUND
	je	mleading1	; jump if entire string was blank
	inc	cx		; CX is length of remainder of string
mleading1:
	dec	di		; DI points to non-blank
mleading2:
	mov	bx,di		; put address back
	ret

MLeading	ENDP

;========================================

MTrailing	PROC	Near

;	Remove trailing blanks.
;	on entry BX is addr of string, CX its length
;	trims off any trailing blanks, leaving result in BX CX
;	length may also be 0 or 1, but not -ve
;	If the entire string is blank the result is the null string
	mov	di,bx
	add	di,cx		; calc addr last char in string
	dec	di
	mov	al,20H		; AL = blank  -- the search char
	jcxz	mtrailing1	; jump if null string
	std
	repe	scasb		; scan ES:DI backwards till hit non blank
				; DI points just ahead of it (wrap ok)
				; CX is one too small, or 0 if none found
	cld
	je	mtrailing1	; jump if whole string was blank
	inc	cx
mtrailing1:
	ret

MTrailing	ENDP

;========================================

Parse		PROC	NEAR
;	Parse the command line to remove lead/trail blanks from
;	the single drive parameter and terminate it by 2 nulls.
;	sample inputs
;	CMOSRest A:\CMOS.SAV
;	CMOSRest	B:\MySub\MyCMOS.SAV
;
;	When Done DS:BX points to start of string.
;	String will be terminated by 2 nulls
;	CX counts bytes in string exclusive of nulls
				; counted string at HEX 80 PSP
				; contains command line.
				; Preceeded by unwanted spaces.
				; possibly followed by unwanted spaces.
				; currently missing a trailing null.
	xor	ch,ch
	mov	cl,ds:80H
	mov	bx,81H
	call	Mleading	; get rid of leading blanks
	call	MTrailing	; get rid of trailing blanks
	mov	di,bx		; calc addr of byte just past end
	add	di,cx
	mov	word ptr [di],0 ; plop in pair of nulls after string
	mov	FileNamePtr,bx	; remember where filename was
	jcxz	SyntaxTrouble	; missing parm.
	ret

SyntaxTrouble:
	lea	dx,UsageMsg		; display usage message
	Call	Say
	Jmp	Abort

Parse		ENDP

;======================================

Say	Proc

;	on entry DX points to a string to display
	push	ax
	MOV	AH,9
	Int	21h
	pop	ax
	ret

Say	EndP

;======================================

GetCMOS Proc	Near

;	Get 128 byte contents of CMOS into a buffer.

	mov	cx,128		; count of times through loop
	lea	bx,CMOSBuff	; where to put the contents
	sub	al,al		; start offset in CMOS
GetLoop:
	Call	PeekCmos	; al=offset ah=contents
	mov	byte ptr[bx],ah
	inc	al
	inc	bx
	loop	GetLoop
	ret

GetCMOS EndP

;===============================================================


PutCMOS Proc	Near

;	Put 128-byte contents of buffer into CMOS.
;	do not touch the volatile bytes

	mov	cx,128		; count of times through loop
	lea	bx,CMOSBuff	; where to put the contents
	sub	al,al		; start offset in CMOS
PutLoop:
	call	Volatile	; test if this is a volatile byte
				; test offset in al
	jc	LeaveItAlone
	mov	ah,byte ptr[bx]
	Call	PokeCMOS	; al=offset ah=contents

LeaveItAlone:
	inc	bx
	inc	al
	loop	PutLoop
	ret

PutCMOS EndP



;===============================================================




;	Add to this list if you need more volatile bytes.
;	Remember the trailing h.

VolatileList	db	0ch,032h

VolatileCount	equ	$-VolatileList


Volatile	Proc	near

;	Is cmos offset in AL volatile?	If so set carry.
;	These bytes will be undisturbed.
;	Preserves all registers.
;	00..09, 0C and 32 are volatile, rest are not.
;	0A 0B 0D 0E 0F used to be considered volatile, now are not.
;	if cmos is small, all bytes past end are considered volatile

	cmp	al,CMOSSize		; bytes past end are volatile
	jae	IsVolatile
	cmp	al,09h
	jbe	IsVolatile		; early bytes are for timing
	push	cx
	push	di
	mov	cx,VolatileCount
	lea	di,VolatileList
	repne	scasb			; search till find a match
	pop	di
	pop	cx
	je	IsVolatile

IsNotVolatile:
	clc				; clear carry
	ret

IsVolatile:
	stc
	ret

Volatile	EndP


;===============================================================


CalcCMOSSize	Proc	near

;	Is CMOS 64 or 128 bytes long?
;	It is 64 if bytes at 10..2F match those at 50..6F.
;	Otherwise it is 128 bytes.
;	Preserves all registers.

	push	si
	push	di
	push	cx
	lea	si,CMOSBuff+10h
	lea	di,CMOSBuff+50h
	mov	cx,02fh+1-10h
	repe	cmpsb
	je	IsCMOS64

IsCMOS128:
	mov	CMOSSize,128	; differ, must be a big CMOS
	jmp	CalcCMOSSizeDone

IsCMOS64:
	mov	CMOSSize,128	; all same, small CMOS

CalcCMOSSizeDone:
	pop	cx
	pop	di
	pop	si

	ret

CalcCMOSSize	EndP


;===============================================================


PeekCMOS	proc	near

;	Reads one byte from cmos.
;	on entry al has offset desired
;	on exit ah has the contents of that byte.
;	preserves all registers

;	See page 5-81 IBM AT Tech ref BIOS listing for how to read CMOS
;	We always enable the NMI with bit 7 on.

	push	bx
	push	ax
	cli				; disable interrupts
	or	al,80h			; disable NMI
	out	70h,al			; output the byte address to CMOS
	jmp	$+2			; delay, safer than nop
	in	al,71h			; read the CMOS byte
	jmp	$+2			; delay, safer than nop
	mov	bl,al
					; re-enable the NMI
	mov	al,0dh			; point to battery status register
	out	70h,al			; leave pointing at a safe r/o register
	sti				; restore interrupts
	pop	ax
	mov	ah,bl
	pop	bx
	ret

PeekCMOS	EndP


;===============================================================


PokeCMOS	proc	near

;	Stuffs one byte into cmos.
;	on entry al has offset desired, ah has the value to stuff.
;	Preserves all registers.

;	See page 5-81 IBM AT Tech ref BIOS listing for how to write CMOS
;	We always enable the NMI with bit 7 on.

	push	ax
	cli				; disable interrupts
	or	al,80h			; disable NMI
	out	70h,al			; output the byte address to CMOS
	jmp	$+2			; delay, safer than nop

	mov	al,ah			; get contents
	out	71h,al			; poke the CMOS byte
	jmp	$+2			; delay, safer than nop
					; re-enable the NMI
	mov	al,0dh			; point to battery status register
	out	70h,al			; leave pointing at a safe r/o register
	sti				; restore interrupts
	pop	ax
	ret

PokeCMOS	EndP

;===============================================================


ReadCMOS	Proc	Near

;	Open a file read the CMOS into a buffer

	mov	dx,FileNamePtr	; DS:DX point to file
	xor	al,al		; AL=0 is attribute read/only
	mov	ah,03Dh 	; DOS open function
	int	21h
	jc	FileTrouble
	mov	bx,ax		; save handle
	mov	cx,128		; read 128 bytes
	lea	dx,CMOSBuff	; buffer address
	mov	ah,3fH		; DOS read
	int	21h
	jc	FileTrouble
	cmp	ax,128
	jne	FileTrouble
	mov	ah,3eh		; DOS close
	int	21h
	jc	FileTrouble
	ret

ReadCMOS	EndP



;===============================================================

CODE	ends			; end of code segment
	end	Start