;    File              : $BDOSLDR.A86$
;
;    Description       :
;
;    Original Author   : DIGITAL RESEARCH
;
;    Last Edited By    : $CALDERA$
;
;-----------------------------------------------------------------------;
;    Copyright Work of Caldera, Inc. All Rights Reserved.
;      
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;
;    ENDLOG

	include i:reqhdr.equ
	include i:driver.equ
	include	config.equ

;	MISC constants
CR		equ	0dh			;the usual
LF		equ	0ah


DATTS		equ	byte ptr 11
 DA_VOLUME	equ	08h
 DA_DIR		equ	10h
DBLOCK1		equ	word ptr 26


eject
CGROUP		group	INITCODE, INITDATA

INITCODE	cseg	'INITCODE'

eject
if DOS5
VER_MUSTBE	equ	1072h
else
VER_MUSTBE	equ	1071h
endif

	Public	dos_version_check

	Public	read_dos		; read BDOS from disk

;--------
read_dos:	; read in the BDOS
;--------
	call	login_drive		; build BPB for the boot drive
	mov	si,offset dos_name	; get name of file to open
	call	open_file		; open the BDOS file
	call	read_file		; read in the system file
	ret

login_drive:
;-----------
	les	di,boot_device		; get device driver address
	mov	dl,boot_drv		; get the boot drive sub unit
	mov	ax,es
	or	ax,di			; make sure boot device is initialised
	 jnz	login_drive10
	jmp	dev_fail
login_drive10:
	mov	ax,es:6[di]		; get strategy offset
	mov	strat_off,ax
	mov	strat_seg,es		; get strategy segment
	mov	ax,es:8[di]		; get interrupt offset
	mov	intrpt_off,ax
	mov	intrpt_seg,es		; get interrupt segment

	mov	bx,offset req_hdr
	mov	ds:RH_UNIT,dl		; save logical unit to use
	mov	ds:RH_CMD,CMD_BUILD_BPB
	call	device_request		; tell it to build a BPB
	 jc	dev_fail		; return if can't determine BPB
	push	ds ! push si
	push	ds ! pop es
	mov	di,offset local_bpb	; ES:DI -> local BPB copy
	mov	cx,BPB_LENGTH
	lds	si,ds:RH2_BPB		; copy BPB to local memory
	rep	movsb
	pop	si ! pop ds

;	Now we have to figure out whether the media uses 12 or 16 bit FATs.
;	To that end, we need to compute the # of clusters on the drive:

	mov	fat16,0			; assume 12 bit FAT

	mov	al,BT_nfats		; compute FAT size
	mov	ah,0			; AX = # of FAT copies (usually 2)
	mul	BT_fat_size		; AX/DX = size of FAT in sectors

	add	ax,BT_reserved_sectors	; add in bootstrap sectors
	adc	dx,0
	mov	cx,ax			; CX/BP = sector address of root dir
	mov	bp,dx

	mov	ax,32			; compute root directory size
	mul	BT_dirsize		; AX/DX = bytes in directory
	mov	bx,BT_bytes_per_sector
	dec	bx			; BX = sector size - 1 for rounding
	add	ax,bx			; round up to next sector size
	adc	dx,0
	inc	bx			; BX = sector size in bytes
	div	bx			; AX = # of root directory sectors
	add	cx,ax			; CX/BP = sectors before data area
	adc	bp,0

	mov	ax,BT_total_sectors	; AX/DX = total disk size in sectors
	sub	dx,dx
	test	ax,ax			; is it actually larger than 65535?
	 jnz	dev_small		; no, AX/DX is correct
	mov	ax,BT_total_long	; else get real size from extension
	mov	dx,BT_total_long+2
dev_small:				; AX/DX = disk size in sectors
	sub	ax,cx			; AX/DX = data sectors
	sbb	dx,bp
					; now convert this to clusters
	mov	bl,BT_sctr_per_cluster
	mov	bh,0			; BX = sectors per clusters
	div	bx			; AX = # of data clusters
	inc	ax
	inc	ax			; cluster 0,1 are reserved
	cmp	ax,0FF6h		; is this too large for 12 bits?
	 jbe	dev_12bit		; skip if 12 bits will do
	mov	fat16,-1		; else we use 16 bits
dev_12bit:
	ret


dos_version_check:
;-----------------
	mov	ax,4452h
	int	21h			; try and get DRDOS version number
	 jc	dev_fail		;  it's not DRDOS !
	cmp	ax,VER_MUSTBE		; version check the DRDOS BDOS
	 jne	dev_fail		;  reject all but the one we want
	ret				; return now I'm happy

dev_fail:	; any error has occurred loading the BDOS
;--------
; Print '$' terminated message at offset DX to console without using the BDOS
;
	mov	dx,offset dos_msg
	les	di,resdev_chain		; get first device driver address
fail_scan:
	test	es:DH_ATTRIB[di],DA_CHARDEV
	 jz	fail_next		; skip if not a character device
	test	es:DH_ATTRIB[di],DA_ISCOT
	 jnz	fail_found		; skip if console device found
fail_next:
	les	di,es:[di]		; get next device
	jmps	fail_scan
fail_found:
	mov	ax,es:6[di]		; get strategy offset
	mov	strat_off,ax
	mov	strat_seg,es		; get strategy segment
	mov	ax,es:8[di]		; get interrupt offset
	mov	intrpt_off,ax
	mov	intrpt_seg,es		; get interrupt segment

	mov	bx,offset req_hdr
	mov	ds:RH_CMD,CMD_OUTPUT	; write to console
	mov	ds:RH_LEN,RH4_LEN	; set request header length
	mov	ds:RH4_BUFOFF,dx	; set address of string
	mov	ds:RH4_BUFSEG,ds
	mov	ds:RH4_COUNT,-1
	mov	si,dx			; now find the end of the string
fail_count_chars:
	inc	ds:RH4_COUNT		; print another char
	lodsb				; examine the next one
	cmp	al,'$'			; terminating char ?
	 jnz	fail_count_chars
	call	device_request		; call the console driver

	sti
	jmps	$			; wait for reboot


device_request:		; general device driver interface
;--------------
;	entry:	BX -> request header
;	exit:	CY = 1 if error

	push	ds ! push es
	push	ds ! pop es
	mov	ds,strat_seg
	callf	cs:strat_ptr
	callf	cs:intrpt_ptr
	pop	es ! pop ds
	test	ds:RH_STATUS,RHS_ERROR
	 jnz	devreq_err
	clc
	ret
devreq_err:
	jmp	dev_fail		; print error message


	ret
	
open_file:	; open BDOS system file
;---------
;	entry:	SI -> 11 byte file name

	mov	al,BT_nfats
	cbw
	mul	BT_fat_size		; DX:AX = # FAT sectors

	mov	cx,ax			; CX = rel_sctr dir start
	mov	dx,BT_dirsize		; dx = # entries to scan

open_f1: 				; CX = current dir sector
					; DX = current dir count
					; SI -> file name
	push	cx ! push dx ! push si
	push	ds ! pop es		; ES:BX -> sector buffer
	mov	bx,offset sector_buffer
	mov	dx,1			; read one directory sector
	call	rd_sector_rel		;     via disk driver
	pop	si ! pop dx ! pop cx
	inc	cx			; increment sector for next time

	sub	bx,bx			; start at beginning of sector
open_f2:
	lea	di,sector_buffer[bx]	; ES:DI -> directory entry
	push	si ! push di ! push cx	; save name ptr and count
	push	ds ! pop es
	mov	cx,11
	repe	cmpsb			; check if name matches
	pop	cx ! pop di ! pop si
	 jne	open_f3			; skip if name doesn't match
	test	DATTS[di],DA_DIR+DA_VOLUME
	 jz	open_foundit		; skip if matches
open_f3:
	dec	dx			; count down root directory entries
	 jz	open_fail		; skip if root directory done
	add	bx,32			; next entry in directory sector
	cmp	bx,BT_bytes_per_sector	; sector complete?
	 jb	open_f2			; loop back while more
	jmps	open_f1			; read next directory sector

open_fail:				; file not found
	jmp	dev_fail

open_foundit:				; found the open file handle
	mov	ax,DBLOCK1[di]		; get first disk block
	mov	start_cluster,ax	; save starting cluster
	xor	ax,ax
	ret				; return success


read_file:	; read BDOS files into memory at MEM_CURRENT:0000
;---------
	mov	ax,current_dos		; Get the Segment address to
	mov	dta_seg,ax		; load the BDOS at
	sub	ax,ax
	mov	dta_off,ax
rd_file1:
	mov	cluster_count,1		; we can read at least one cluster
	mov	cx,start_cluster
rd_file2:				; check if next cluster contiguous
	push	cx			; save current cluster number
	call	next_cluster		; get link to next cluster
	pop	dx			; get previous cluster #
	inc	dx			; is current cluster contiguous?
	cmp	cx,dx			; contiguos if CX == DX
	 jne	rd_file3		; no, need a separate read
	inc	cluster_count		; else read one more cluster
	jmps	rd_file2		; try again with next cluster
rd_file3:				; CX = next chain, multi cluster read
	push	cx			; save start of next chain
	les	bx,dta_ptr		; ES:BX -> transfer address
	mov	cx,start_cluster	; previous contiguous chain starts here
	mov	dx,cluster_count	; length of chain in clusters
	call	rd_cluster		; read DX clusters
	mov	al,BT_sctr_per_cluster
	mov	ah,0			; AX = sectors per cluster
	mul	cluster_count		; AX = sectors in chain to read
	mul	BT_bytes_per_sector	; AX = bytes in chain to read
	add	dta_off,ax
	pop	cx			; CX = next (noncontiguous) cluster
	mov	start_cluster,cx	; start of new chain
	inc	cx			; was it end of file cluster number?
	 jnz	rd_file1		; go back for more if not
					; else all clusters done
	ret


get_FAT_byte:
;------------
;	entry:	BX = offset into FAT

	mov	ax,bx			; BX = offset into FAT
	sub	dx,dx			; AX/DX = 32 bit offset
	div	BT_bytes_per_sector	; AX = sector, DX = offset in sector
	push	dx			; save offset in sector
	call	locate_FAT		; read FAT sector AX
	pop	bx			; BX = offset in FAT sector
	mov	al,sector_buffer[bx]	; get byte from FAT buffer
	ret


locate_FAT:
;----------
;	entry:	AX = FAT sector to locate

	cmp	ax,current_fatsec	; AX = sector offset into FAT
	 je	locate_FAT_match	; O.K. if same as last time

	mov	current_fatsec,ax	; set new sector for next time
	push	cx ! push si		; preserve FAT index
	mov	cx,ax			; CX = sector number
	mov	bx,offset sector_buffer
	push	ds ! pop es		; ES:BX -> sector buffer
	mov	dx,1			; DX = single sector
	call	rd_sector_rel		; read FAT sector
	pop	si ! pop cx		; restore FAT index

locate_FAT_match:			; return with right sector in buffer
	ret


eject
;	reads sectors relative to start of DOS area on disk (start=0)
;	same parameters as rd_sector
rd_sector_rel:
;-------------
;	entry:	CX = sector address relative to first FAT sector
;		DX = sector count

	sub	bp,bp				;overflow word = 0
	add	cx,BT_reserved_sectors
	adc	bp,0
;	jmps	rd_sector
	

;	reads absolute sectors from hard disk using rom bios
rd_sector:
;---------
;	entry:	DX = number of sectors
;		ES:BX -> data transfer buffer
;		DS -> program global data segment
;		CX/BP = absolute sector # (32 bit) (low/high)

	push	cx ! push dx		; save parameters
	mov	req3_bufoff,bx		; save transfer offset
	mov	req3_bufseg,es		; save transfer segment
	mov	req3_count,dx		; set sector count
	mov	bx,offset req_hdr	; BX -> request header
	mov	ds:RH_CMD,CMD_INPUT	; read from disk device
	mov	req3_sector,cx		; set requested sector address
if DOS5
	mov	req_hdr,RH4_LEN
	mov	req3_sector32,cx	;  with 32 sector number
	mov	req3_sector32+2,bp
	test	bp,bp			; large sector number?
	 jz	rd_sec1			; no, normal request header
	mov	req3_sector,0FFFFh	; mark as a large request
rd_sec1:
else
	mov	req3_sector+2,bp	; (support large DOS drives)
	mov	req_hdr,24		; indicate large request
endif
	call	device_request		; tell it to read sectors
	pop	cx ! pop dx
	ret				; if CY, AH=error code


rd_cluster:
;----------
;	entry:	CX = DOS cluster number.
;		DX = cluster count
;		ES:BX -> transfer buffer

	push	bx ! push es

	mov	al,BT_sctr_per_cluster
	mov	ah,0			; AX = sectors per cluster
	mul	dx			; AX = sectors in all clusters
	push	ax			; save the sector count

	sub	cx,2			; cluster 2 is data area start
	mov	al,BT_sctr_per_cluster
	cbw
	mul	cx			; AX,DX = relative sector #
	mov	cx,ax
	mov	bp,dx			; CX,BP = data area sector #

	mov	al,BT_nfats		; compute FAT size
	mov	ah,0			; AX = # of FAT copies (usually 2)
	mul	BT_fat_size		; AX/DX = size of FAT in sectors
	add	cx,ax
	adc	bp,dx			; CX,BP = end of FAT sectors

	mov	ax,32
	mul	BT_dirsize		; AX,DX = bytes in root directory
	mov	bx,BT_bytes_per_sector
	dec	bx
	add	ax,bx			; round up directory size
	adc	dx,0
	inc	bx
	div	bx			; AX = root directory sectors
	add	cx,ax
	adc	bp,0			; add root directory size

	add	cx,BT_reserved_sectors	; add in boot sector(s)
	adc	bp,0

	pop	dx ! pop es ! pop bx	; sector count, disk address

	jmp	rd_sector		; DX secs from CX/BP to ES:BX


;	Finds the NEXT cluster after the one passed in CX in an allocation
;	chain by using the FAT.  Returns the carry set if the end of chain
;	mark is found, otherwise returns the NEW cluster # in CX.
next_cluster:
;------------
	push	dx ! push bx		; save some registers
	cmp	fat16,0			; check if this is 12 bit media
	 je	next_cluster12		; skip if old fashioned 12 bit
	mov	ax,2
	mul	cx			; AX/DX = byte offset in FAT (max. 128K)
	div	BT_bytes_per_sector	; AX = FAT sector #, DX = byte offset
	push	dx			; save byte offset within sector
	call	locate_FAT		; get FAT sector AX
	pop	bx			; BX = offset within sector
	mov	cx,word ptr sector_buffer[bx]
					; get 16 bit from FAT

	cmp	cx,0FFF7h		; check if too large for #
	 jae	next_cluster_eof	; set carry, EOF
	clc
	jmps	next_cluster_ret	; good link

next_cluster12:				; DOS 2.x disk
	push	cx			; save cluster number
	mov	bx,cx
	add	bx,bx			; BX = cluster# * 2
	add	bx,cx			; BX = cluster# * 3
	shr	bx,1			; BX = cluster# * 1.5
	push	bx			; save offset in the FAT
	inc	bx			; BX = offset of high byte
	call	get_FAT_byte		; get the high byte in AL
	pop	bx			; BX = offset of low byte
	push	ax			; save high byte on stack
	call	get_FAT_byte		; get the low byte in AL
	pop	bx			; pop off high byte into BL
	mov	ah,bl			; set high byte, AX = word
	pop	cx			; restore cluster number
	shr	cx,1			; test if even or odd
	 jnc	even_fat		; if even entry, done
	mov	cl,4			; odd entry, shift down one nibble
	shr	ax,cl			; else need to justify
even_fat:				; even entry, strip off top bits
	and	ax,0fffh		; bx[0..11] are cluster
	mov	cx,ax			; CX = cluster number
	cmp	cx,0ff7h		; compare with largest legal 12 bit #
	 jae	next_cluster_eof	; check for end mark
	clc
	jmps	next_cluster_ret	; return value in CX, CY = 0
next_cluster_eof:
	mov	cx,-1			; indicate end of chain
	stc				; end of chain
next_cluster_ret:
	pop	bx ! pop dx
	ret


eject
;
;	INITIALIZED DATA SEGMENT
;	========================
INITDATA	dseg	'INITDATA'

		extrn	resdev_chain:dword	; resident device driver root
		extrn	current_dos:word	; current BDOS segment
		extrn	boot_device:dword	; device driver we boot from
		extrn	boot_drv:byte		; boot drive
		extrn	dos_name:byte		; name of BDOS file

strat_ptr	rd	0
strat_off	rw	1
strat_seg	rw	1

intrpt_ptr	rd	0
intrpt_off	rw	1
intrpt_seg	rw	1

dta_ptr		rd	0
dta_off		rw	1
dta_seg		rw	1

start_cluster	rw	1
cluster_count	rw	1

current_fatsec	dw	-1			; no FAT sector read yet
fat16		dw	0			; defaults to 12 bit FAT

;	single error message if BDOS can't be loaded:


include	initmsgs.def				; Include TFT Header File


;dos_msg	db	CR,LF,'Can''t load DOS file.$'


;	static request header for DOS device driver I/O

req_hdr		db	22
req_unit	rb	1
req_cmd		rb	1
req_status	rw	1
		rd	2
req_media	rb	1
		rb	16

req1_return	equ	byte ptr req_media+1
req1_volid	equ	word ptr req_media+2

req2_bufoff	equ	word ptr req_media+1
req2_bufseg	equ	word ptr req_media+3
req2_bpb	equ	word ptr req_media+5

req3_buffer	equ	dword ptr req_media+1
req3_bufoff	equ	word ptr req_media+1
req3_bufseg	equ	word ptr req_media+3
req3_count	equ	word ptr req_media+5
req3_sector	equ	word ptr req_media+7
req3_volid	equ	word ptr req_media+9
req3_sector32	equ	word ptr req_media+13

;	local copy of the BPB for the boot device

local_bpb		rb	0
BT_bytes_per_sector	rw	1
BT_sctr_per_cluster	rb	1
BT_reserved_sectors	rw	1
BT_nfats		rb	1
BT_dirsize		rw	1
BT_total_sectors	rw	1
BT_fatid		rb	1
BT_fat_size		rw	1
BT_sectors_per_track 	rw	1
BT_nheads		rw	1
BT_hidden_sectors	rw	2
BT_total_long		rw	2
BPB_LENGTH		equ	(offset $-offset local_bpb)

	extrn	sector_buffer:byte

	end