Title Force an MsDos Disk Foreign Drive B: (16_Oct_84)
;
;	Copyright 1982,1983,1984
;	Morrow Designs, Inc.
;	San Leandro, Ca
;	John Zalabak
;
	.z80
	aseg
	org	100h

;----------------------------------------------------------------------
; Index: Foreign (16_Oct_84)
;---------------------------
;
;	Begin_Foreign	Main Line of Foreign Drive Routine
;
;	Install_Xlt	Install the translate table for this drive
;	Enter_Xlt	Enter a new translation table into the free space
;	Install_Dph	Install the Xlt pointer in the Dph
;	Install_Dpb	OverLay the current drive's Dpb
;	Get_Pointer	Get a Pointer into the current data structure
;	Install_Mtab	Update the drive's MTAB
;
;	Get_Buffer	Move system memory into the local buffer
;	Put_Buffer	Put the Local Buffer into System Memory
;	Extended_Bios	Call the Bios Cold Boot Entry Point
;
;	Message Strings
;	Data Areas
	page		60

;----------------------------------------------------------------------
; Local Equates (15_Oct_84)
;--------------------------
;
		;Bdos Functions
Bdos_Entry	equ	5		;Bdos Entry Location
Bdos_PString	equ	9		;Print a String

		;Bios Entry Definitions
Bios_Entry	equ	0		;Bios Entry Location
EB_Write_Sys	equ	1		;Write to System Memory
EB_Get_Mtabs	equ	3		;Get the System Mtabs
EB_Get_DPHs	equ	4		;Get the System's Dphs
EB_Get_DPBs	equ	5		;Get the System's Dpbs
EB_Get_Char_Tbl	equ	6		;Get the Character Table
EB_Get_Free	equ	8		;Get the Free Space Pool
EB_Execute	equ	14		;Execute in the System Bank

		;Length Definitions
Dpb_Length	equ	15		;Define the length of a DPB

		;Offset Definitions
SelDsk_Offset	equ	9 * 3		;"  SelDsk "   "   "    "     "
MftOff		equ	14		;format type in MTAB from dskdef1

		;MTAB's Dskdef0 Mask Bytes
$DEF0		equ	11111111b xor ($FRGN or $SECZRO or $DBLMED)
$FRGN		equ	01000000b	;Drive is Foreign (Not Morrow)
$SECZRO		equ	00100000b	;Sectors Start w/Sector 0 not 1
$DBLMED		equ	00000100b	;Double Sided Media
$HRDDSK		equ	00000010b	;Hard Disk (used in drive selection)

		;MTAB's Dskdef1 Mask Bytes
$DEF1		equ	11111111b xor ($DRVDEN or $128 or $256 or $512 or $1024)
$DRVDEN		equ	00100000b	;Double Density Media
$128		equ	00000000b	;128 Bytes per Sector
$256		equ	00000001b	;256 Bytes per Sector
$512		equ	00000010b	;512 Bytes per Sector
$1024		equ	00000011b	;1024 Bytes per Sector

		;Translation Table Code
ib2cod		equ	9		;MsDos Ibm Code

		;Ascii Character Equates
Control_C	equ	3		;Control C (Cp/m warm boot)
BackSpace	equ	8		;Back Space one Character
Tab		equ	9		;Tab
Cr		equ	0Dh		;Carriage Return
Lf		equ	0Ah		;Line Feed
Esc		equ	1Bh		;Escape
Bright		equ	'('		;Set High Lighting Mode
Dim		equ	')'		;Set Low Lighting Mode
		page

;----------------------------------------------------------------------
; Main Line of Foreign Drive Routine (15_Oct_84)
;-----------------------------------------------
;
Begin_Foreign:
	ld	sp,Local_Stack		;(local stack's at end of local buffer)
	call	Install_Xlt		;Get the translate table for this drive
	or	a			;If (Translate Table was Installed)
	jr	nz,Quit

	call	Install_Dph		;	Install xlt pointer in the dph
	call	Install_Dpb		;	Overlay the Dpb
	call	Install_Mtab		;	Update the drive's MTAB
	ld	a,0
Quit:	jp	Bios_Entry		;Warm Boot
	page

;----------------------------------------------------------------------
; Install the translate table for this drive (4_Jan_84)
;------------------------------------------------------
;	1) Drives with no translation tables return Immediately (with accm=0).
;	2) If the table was found or successfully installed then the accm is
;	   returned equal to zero.
;	3) If there was insufficient room in the table for the new translate
;	   table or the program failed to find a native drive then the accm
;	   is returned non-zero.
;	4) Register Usage:
;		A  -> General Purpose
;		BC -> Length for moves
;		DE -> Pointer to Xtl - 1
;		HL -> Pointer into free space
;
Install_Xlt:
	ld	de,(xltlen)		;If (the drive has NO translate table)
	ld	a,d
	or	e
	ret	z			;	Return (status 0 = ok)

	ld	a,EB_Get_Free		;	A:= Function_8 (get free space)
	call	Get_Buffer		;	HL:= Pointer to Start Free Space

	;Search for a matching xlt or the end of the free space
nomtch:	ld	a,(xlt)			;Loop	A:= xlt code in template
	cp	(hl)			;	If (table header MATCHES xlt code)
	jp	nz,skip1

	ex	de,hl			;		DE:= Start of Xtl
	inc	de
	inc	de			;		(use matching xlt table)
	jr	SXout			;			Goto get xtl address

skip1:	ld	a,0FFh			;	A:= End of Table code
	cp	(hl)			;	If (entry type eq EOT)
	jr	nz,skip3

	ld	a,(dsk0)		;		If (drive eq foreign)
	and	$FRGN
	jr	nz,skip2

	ld	de,MisTbl		;			DE:= error message
	ld	c,Bdos_PString		;			(bdos print string function)
	call	Bdos_Entry		;			BDOS Print String Function
Fatalº	jð	Fataì			»			Hang: Fataì Error

	;Enter the Translate table into the free space pool
skip2:	call	Enter_Xlt		;		enter the new xlt table
	or	a			;		If (entry could not be made)
	ret	nz			;			Return (error)

	;Generate the System's address for the new translate table
SXout:	inc	de
	ex	de,hl			;		HL:= Start of Xtl in loc buf
	ld	de,Local_Buffer		;		DE:= Start of Local Buffer
	or	a			;		(clear the carry)
	sbc	hl,de			;		HL:= Offset from start Loc Buf
	ld	de,(Save_DE)		;		DE:= Start of system free space
	add	hl,de			;		HL:= Pointer to xtl in free space
	ld	(Save_DPH),hl		;		Save Xlt Pointer

	call	Put_Buffer		;		ReWrite free space to sys mem
	ld	a,0
	ret				;		Return (no error)

	;Move the pointer to the start of the next entry
skip3:	inc	hl			;	get length of this xlt table
	ld	e,(hl)			;	and add it to the pointer.
	inc	hl
	ld	d,(hl)
	inc	hl
	add	hl,de
	jp	nomtch			;	(look at next xlt)
	page

;----------------------------------------------------------------------
; Enter a new translation table into the free space (7_Nov_83)
;-------------------------------------------------------------
;	1) This routine is only used by the getxlt routine.
;	2) If the table was successfully installed then the DE register
;	   pair is returned pointing to the start of the table - 1 and the
;	   accm is returned zero.
;	3) If there wasn't enough room in the table then the DE register
;	   pair is returned pointing to the start of the error message and
;	   accm is returned non-zero.
;	4) Register Usage:
;		A  -> General Purpose, returned non-zero for error
;		BC -> Used to hold offsets
;		DE -> Temp data storage, returned with pointer to xlt or error
;		HL -> Data pointer, enter with HL pointing at type byte
;
Enter_Xlt:
	inc	hl
	ld	e,(hl)
	inc	hl
	ld	d,(hl)
	ex	de,hl			;HL:= Space Remaining
	push	de			;DE:= Start of Xtl Pointer - 1

	;Check if the xlt will fit
	ld	bc,(xltlen)		;BC:= length of table
	inc	bc
	inc	bc
	inc	bc			;(include type byte and length word)
	xor	a			;(clear carry)
	sbc	hl,bc			;If (space insufficient)
	jr	nc,NewSkp

	ld	c,Bdos_PString		;	(bdos print string function)
	ld	de,Nosp			;	DE:= out of space message
	call	Bdos_Entry		;	BDOS Print String Function
	ld	a,0FFh			;	A:=  error return status
	jr	NewErr			;	GOTO error return

	;Copy the new xlt into the free space (type, leng-lo, leng-hi, table..)
NewSkp:	push	hl			;(save space remaining)
	ld	hl,xlt			;HL:= new xlt table pntr.
	dec	de			;(DE overlays current end of table entry)
	dec	de			;DE:= Pointer to Xtl in free space
	ldir				;move xlt
	pop	hl			;(hl=space remaining)

	;Setup new EOT entry (type, space_remaining-lo, space_remaining-hi)
	ex	de,hl			;DE:= remaining space
	ld	(hl),0FFh		;put eot code at end of table
	inc	hl
	ld	(hl),e			;put space left at end of table
	inc	hl
	ld	(hl),d
	ld	a,0			;A:= Successful Completion

NewErr:	pop	de			;DE:= xlt-1 pointer
	ret				;Return
	page

;----------------------------------------------------------------------
; Install the Xlt pointer in the Dph (5_Jan_84)
;----------------------------------------------
;
Install_Dph:
	ld	a,EB_Get_DPHs		;A:= Get the System's Dphs Function (4)
	call	Get_Pointer		;HL:= Pointer to start of Dph

	ld	de,(xltlen)		;If (the drive has a translate table)
	ld	a,e
	or	e
	jr	z,setsk1

	ld	de,(Save_DPH)		;DE:= Xtl Pointer

SetSk1:	ld	(hl),e
	inc	hl
	ld	(hl),d

	call	Put_Buffer		;Restore the Dph Buffer
	ret

;----------------------------------------------------------------------
; OverLay the current drive's Dpb (5_Jan_84)
;-------------------------------------------
;
Install_Dpb:
	ld	a,EB_Get_DPBs		;A:= Get the System's Dpbs Function (5)
	call	Get_Pointer		;HL:= Pointer to start of Dpb

	ex	de,hl			;DE:= Start of Current Dph
	ld	hl,dpb			;HL:= pointer to new Dpb
	ld	bc,Dpb_Length		;BC:= length of Dpb
	ldir				;replace Dpb
	call	Put_Buffer		;ReWrite the Dpb Buffer
	ret

;----------------------------------------------------------------------
; Get a Pointer into the current data structure (5_Jan_84)
;---------------------------------------------------------
;	1) This routine (used only by GetDph and GetDpb) returns the
;	   HL register pair pointing to the start of the current Dpb/Dph
;	   in the local buffer
;	2) Notice that a function number is passed in the accm:
;		4 - Get System Dphs
;		5 - Get System Dpbs
;
Get_Pointer:
	call	Get_Buffer		;Fill Local Buffer (function 4 or 5)
	ld	hl,Local_Buffer
	ld	de,(Save_Drive)		;DE:= Drive Number (0-15)
	rlc	e
	ld	d,0			;multiply drive number by 2
	add	hl,de			;HL:= Pointer to pointer to Dpb/Dph

	ld	e,(hl)
	inc	hl
	ld	d,(hl)
	ex	de,hl			;HL:= Pointer to Dpb/Dph in sys mem

	ld	de,(Save_DE)		;DE:= Start of system buffer
	xor	a			;(Clear the carry)
	sbc	hl,de			;HL:= Offset to start of Dpb/Dph

	ld	de,Local_Buffer
	add	hl,de			;HL:= Pointer to Dpb/Dph in loc buf
	ret
	page

;----------------------------------------------------------------------
; Update the drive's MTAB (4_Jan_83)
;-----------------------------------
;	1) This routine updates the disk definition bytes in the current
;	   drive's MTAB.
;	2) The first byte of the MTAB is dskdef0. It contains flags for
;		1) Foreign Drive ($FRGN bit 6)
;		2) Sector Numbering Starting with Sector 0 (SECZRO bit 5)
;		3) Double Sided Media (DBLMED bit 2)
;	3) The second byte of the MTAB is dskdef1. It contains flags for
;		1) Double Density Media (DRVDEN bit 5)
;		2) Sector Size Code ($128, $256, $512 and $1024 in bits 0 & 1)
;	4) Register Usage:
;		A  -> General Purpose
;		BC -> General Purpose
;		HL -> Pointer
;
Install_Mtab:
	ld	a,EB_Get_Mtabs		;A:= Function_3 (get mtabs)
	call	Get_Buffer		;HL:= Start of Mtabs

	ld	bc,(Save_Drive)		;BC:= Drive Number (0-15)
	call	Set_HL_to_Mtab		;HL:= Pointer to Drive's Mtab

	;Update dskdef0
	ld	a,(hl)			;A:= dskdef0 for this drive
	and	$DEF0			;Remove bits that're (potentially) set
	ld	b,a
	ld	a,(dsk0)		;B:= dskdef0 for this media
	or	b
	ld	(hl),a			;set dskdef0

	;Update dskdef1
	inc	hl			;HL:= dskdef1 for this drive
	ld	a,(hl)			;A:= dskdef1 for this drive
	and	$DEF1			;Remove bits that're (potentially) set
	ld	b,a
	ld	a,(dsk1)		;B:= dskdef1 for this media
	or	b
	ld	(hl),a			;set dskdef1

	;Update the format type byte
	ld	bc,mftoff		;BC:= Offset to format type (dskdef1)
	add	hl,bc			;HL:= Pointer to format byte in MTAB
	ld	a,(xlt)
	ld	(hl),a			;Format type:= current media's format code
	call	Put_Buffer		;Write the Mtabs back into system memory
	ret				;Return

;----------------------------------------------------------------------
; Set the HL Pair Pointing to the Current Mtab (15_Oct_84)
;---------------------------------------------------------
;	1) This routine Sets the HL pair as a pointer to the current drive's
;	   Mtab. This routine assmume that the Mtabs have been read into
;	   the local buffer (Local_Buffer).
;	2) The BC register pair contains the drive number (0 to max drives)
;
Set_HL_to_Mtab:
	push	bc
	rlc	c			;Drive_Number * 16 (length of 1 mtab)
	rlc	c
	rlc	c
	rlc	c
 	ld	b,0			;BC:= drive number * single mtab length
	ld	hl,Local_Buffer		;HL:= Start of Local Buffer
	add	hl,bc			;HL:= pointer to start of current mtab
	pop	bc
	ret				;Return
	page

;----------------------------------------------------------------------
; Move system memory into the local buffer (4_Jan_84)
;----------------------------------------------------
;	1) This routine forces the destination to be the local buffer, calls
;	   the cold start (extended bios functions) entry point, and then saves
;	   the registers after swapping hl and de.
;
Get_Buffer:
	ld	de,Local_Buffer		;DE:= Pointer to Local Buffer
	call	Extended_Bios		;Move System Memory into local buffer

	ld	(Save_BC),bc		;Save the returned registers
	ex	de,hl			;HL:= Pointer to first xlt
	ld	(Save_DE),de
	ld	(Save_HL),hl
	ret				;Return

;----------------------------------------------------------------------
; Put the Local Buffer into System Memory (4_Jan_84)
;---------------------------------------------------
;	1) This is the inverse of Get_Buffer; It replaces the system's memory
;	   with the contents of the local buffer.
;	2) Get_Buffer MUST be called before entering this routine.
;
Put_Buffer:
	ld	a,EB_Write_Sys		;Function_1:= Write to system memory
	ld	bc,(Save_BC)
	ld	de,(Save_DE)
	ld	hl,(Save_HL)		;Restore the Returned Registers
	call	Extended_Bios		;Write Mtabs back into system memory
	ret

;----------------------------------------------------------------------
; Call the Bios Cold Boot Entry Point (4_Jan_84)
;-----------------------------------------------
;	1) The Cold Boot Entry point to the bios (1st entry in the bios
;	   jump table) is located by looking at locations 1 & 2 which
;	   point to the warm boot address (the desired address + 3).
;
Extended_Bios:
	push	hl			;Save the HL Register Pair
	ld	hl,(Bios_Entry+1)	;HL:= Warm Boot Address
	ld	l,0			;HL:= Cold Boot Address
	ex	(sp),hl			;Restore the HL Register Pair
	ret				;Goto The Cold Boot entry
	page

;----------------------------------------------------------------------
; Error Messages (15_Oct_84)
;---------------------------
;
mistbl:	db	Esc,Bright,Cr,Lf,Tab
	db	'Portions of CP/M are missing from memory.'
	db	Cr,Lf
	db	'Push reset to re-boot CP/M.$'

nosp:	db	Esc,Bright,Cr,Lf,Tab
	db	'Too many foreign drives are defined.'
	db	Cr,Lf
	db	'Push reset to clear all foreign drives. $'
	page

;----------------------------------------------------------------------------
; IBM: D.S. - D.D. Media Characteristics - 9 sectors/track (11_Oct_84)
;----------------------------------------------------------------------
;	Physical Media Characteristics:
;		Double Sided
;		Sector numbering starts with sector 1
;		Double Density
;		512 bytes per sector
;		9 sectors per track
;
dsk0:	db	$FRGN or $DBLMED	;(dsk0) value to be ored into dskdef0
dsk1:	db	$DRVDEN or $512		;(dsk1) value to be ored into dskdef1

	;DPB Definiton
dpb:	dw	36		;secs per track
	db	3		;block shift
	db	7		;block mask
	db 	1		;extnt mask
	dw	359		;disk size-1
	dw	111		;directory max
	db	0f0h		;alloc0
	db	0		;alloc1
	dw	16		;check size
	dw	1		;offset

	;XLT Table Definition
xlt:	db	ib2cod		;format code for IBM Drives
xltlen:	dw	0		;Translation table length

;----------------------------------------------------------------------
; General Data Area (15_Oct_84)
;------------------------------
;
		;Save Location for Max_Drives, Current_Drive and Dph Values
Save_Drive:	dw	1		;Save Location for the drive number
Save_DPH:	dw	0		;Save Location for replacement Dph Xlt pointer

		;Save Locations for Get/Put Buffer
Save_BC:	dw	0		;Save of the BC registers after bios_0 call
Save_DE:	dw	0		;Save of the DE registers after bios_0 call
Save_HL:	dw	0		;Save of the HL registers after bios_0 call

		;Local Buffers
		ds	40h
Local_Stack:	dw	0		;Local Stack Area builds down
Local_Buffer:	dw	0		;Local Buffer for system data
		end