; Hard disk I/O for MS-DOS 2.0

	PAGE	60,132

	INCLUDE  IODEF.ASM

IO	GROUP	CODE

CODE	SEGMENT BYTE PUBLIC 'IOSYS'
	ASSUME	CS:IO, DS:IO

;----------------------------------------

	IF	INSTALL

HDSKDEV:	;Header for hard disk
	DD	-1
	DW	2000H
	DW	STRATEGY
	DW	HDSK$IN
	DB	?

	ELSE

	PUBLIC	HDSKTBL

	EXTRN	EXIT:NEAR, CMDERR:NEAR, BUS$EXIT:NEAR, PTRSAV:DWORD
	ENDIF

;-----------------------------------------

HDSKTBL:
	DW	HDSK$INIT
	DW	HARDCHG
	DW	GET$HBPB
	DW	CMDERR
	DW	HARDREAD
	DW	BUS$EXIT
	DW	EXIT
	DW	EXIT
	DW	HARDWRITE
	DW	HARDWRITE

;*************************************************************

DIRENT		EQU	96
ALLOCSIZ	EQU	4
FATSIZ		EQU	6


		IF	IMI
NHEADS		EQU	6	; Number of heads
NSECT		EQU	8	; Number of sectors per track
NTRACKS		EQU	306	; Number of cylinders
LOWCURTRK	EQU	0	; First track of low write current
PRECOMTRK	EQU	256	; First track to set precomp bit
		ENDIF


		IF	SCRIBE
NHEADS		EQU	4	; Number of heads
NSECT		EQU	8	; Number of sectors per track
NTRACKS		EQU	480	; Number of cylinders
LOWCURTRK	EQU	0	; First track of low write current
PRECOMTRK	EQU	0	; First track to set precomp bit
		ENDIF


RESETHDC	EQU	54H
STARTHDC	EQU	55H
HARDRDOP	EQU	0
HARDWROP	EQU	1
RETRY		EQU	3	; # of times to try disk command
TIMEOUT		EQU	10	; 0.2 sec/loop--set 2 seconds for 10 MHZ CPU

HDCPARAM:
HDIR		DB	0	; Direction
HSTEP		DW	1	; Amount to step
HDRIVE		DB	0DCH	; Drive/head select
DMAAD		DW	0	; DMA address
DMAHI		DB	0
ARG1:
HCYL		DW	-1	; Current cylinder
HHEAD		DB	0	; Current head
HSECT		DB	0	; Current sector
OPCODE		DB	0	; Read/write code
HSTAT		DB	0	; Return status

		IF	INSTALL
NEXTAD		DW	HDCPARAM
		ELSE
NEXTAD		DW	HDCPARAM+10H*BIOSSEG
		ENDIF

NEXTADHI	DB	0
;---------------------------------------------
	IF	INSTALL

PTRSAV  	DD	0

STRATP  PROC	 FAR
STRATEGY:
	MOV	WORD PTR CS:[PTRSAV],BX
	MOV	WORD PTR CS:[PTRSAV+2],ES
	RET
STRATP  ENDP


HDSK$IN:
	PUSH	SI
	MOV	SI,OFFSET IO:HDSKTBL

DISPATCH PROC	FAR
ENTRY:
	PUSH	AX
	PUSH	CX
	PUSH	DX
	PUSH	DI
	PUSH	BP
	PUSH	DS
	PUSH	ES
	PUSH	BX

	LDS	BX,CS:[PTRSAV]	;GET POINTER TO I/O PACKET

	MOV	AL,[BX.UNIT]	;AL = UNIT CODE
	MOV	AH,[BX.MEDIA]	;AH = MEDIA DESCRIP
	MOV	CX,[BX.COUNT]	;CX = COUNT
	MOV	DX,[BX.START]	;DX = START SECTOR

	XCHG	DI,AX
	MOV	AL,[BX.CMD]
	XOR	AH,AH
	ADD	SI,AX
	ADD	SI,AX
	CMP	AL,11
	JA	CMDERR
	XCHG	AX,DI
	LES	DI,[BX.TRANS]
	PUSH	CS
	POP	DS

	CALL	[SI]			;GO DO COMMAND

	LDS	BX,CS:[PTRSAV]
	MOV	[BX.STATUS],AX		;MARK OPERATION COMPLETE
	SUB	[BX.COUNT],CX		;Subtract amount transfered
	POP	BX
	POP	ES
	POP	DS
	POP	BP
	POP	DI
	POP	DX
	POP	CX
	POP	AX
	POP	SI
	RET				;RESTORE REGS AND RETURN
DISPATCH ENDP

; Standard return types

EXIT:
	XOR	CX,CX			;Transfer complete
	MOV	AH,00000001B		;All done
	RET

BUS$EXIT:				;DEVICE BUSY EXIT
	MOV	AH,00000011B
	RET

CMDERR:
	MOV	AL,3			;UNKNOWN COMMAND ERROR
	MOV	AH,10000001B		;MARK ERROR RETURN
	RET

	ENDIF

;---------------------------------------

HARDCHG:
	LDS	BX,[PTRSAV]
	MOV	BYTE PTR [BX.TRANS],1	;Disk not changed
	JMP	EXIT

HARDREAD:
	MOV	OPCODE,HARDRDOP
	JMP 	SHORT HARDIO

HARDWRITE:
	MOV	OPCODE,HARDWROP

HARDIO:
	PUSH	DS
	XOR	SI,SI
	MOV	BP,[NEXTAD]
	MOV	AL,[NEXTADHI]
	MOV	DS,SI
 	MOV	WORD PTR [SI+50H],BP
	MOV	BYTE PTR [SI+52H],AL

	OUT	RESETHDC,AL	; Reset hard disk controller
	POP	DS
	MOV	AX,ES
	SHL	AX,1
	RCL	SI,1
	SHL	AX,1
	RCL	SI,1
	SHL	AX,1
	RCL	SI,1
	SHL	AX,1
	RCL	SI,1
	ADD	AX,DI
	MOV	DMAAD,AX
	XCHG	AX,SI
	ADC	AL,0
	MOV	DMAHI,AL
	CMP	HCYL,-1		; Is current track invalid?
	JNZ	COMPPOS
	CALL	RESTORE		; Home disk head
COMPPOS:
	PUSH	DX
	MOV	SI,NSECT	; Sector/track on hard disk
	XCHG	AX,DX
	XOR	DX,DX
	DIV	SI		; AX=track, DX=sector
	INC	DX		; Sector numbers start with 1
	MOV	HSECT,DL
	MOV	SI,NHEADS
	XOR	DX,DX
	DIV	SI		; AX=cylinder, DX=head
	MOV	HHEAD,DL
	SHL	DL,1
	SHL	DL,1
	NOT	DL
	AND	DL,9CH
	CMP	AX,PRECOMTRK
	JB	SAVHEAD1
	OR	DL,80H		; Turn on precomp
SAVHEAD1:
	CMP	AX,LOWCURTRK	; Need low write current?
	JAE	SAVHEAD
	OR	DL,40H		; Turn off low write current
SAVHEAD:
	MOV	HDRIVE,DL	; Drive/head select byte
	MOV	DX,AX
	XCHG	HCYL,AX		; Set current cyl, get previous
	SUB	DX,AX		; Amount to move
	MOV	AL,0		; Assume movement IN
	JAE	HAVSTEP
	NEG	DX		; Get absolute value
	MOV	AL,10H		; Set movement OUT
HAVSTEP:
	MOV	HDIR,AL
	MOV	HSTEP,DX
	POP	DX		; BX,CX,DX have orignal command parameters

; All set for hard disk operation!

HARDREADWRITE:
	MOV	AH,RETRY	; Retry count
HCOM:
	CALL	HDCCOM
	JNZ	NOTNEXT		; If not successful, don't bump to next sector
	ADD	DMAAD,1024
	ADC	DMAHI,0
	INC	DX
	MOV	AL,HSECT
	INC	AL
	CMP	AL,NSECT+1	; Stay on this track?
	MOV	HSECT,AL
	LOOPNZ	HARDREADWRITE
	JCXZ	OKRET
	JMP	COMPPOS		; Re-compute everything

OKRET:
	MOV	AH,1		;No error
	RET

NOTNEXT:
	CMP	AL,1		; Is drive not ready?
	JBE	HARDERR		; Don't retry if not ready or time out
	DEC	AH
	JNZ	HCOM

; Hard disk error on hard disk. AL has the error code. Convert disk 
; error code to MSDOS 2.0 error code

HARDERR:
	MOV	HCYL,-1		; Force restore next time
	CMP 	AL,10		; Is it a reasonable error code?
	JB	NEXT1
	MOV	AL,0		; General disk failure
NEXT1:
	MOV	BX,OFFSET IO:ERRTAB	; Set DOS error table
	XLAT
	MOV	AH,81H		; ERROR
	RET			; CX = number of sectors to go

ERRTAB:
	DB	12		; General failure
	DB	2		; Drive not ready
	DB	12		
	DB	12
	DB	8		; Sector not found
	DB	8		; Data not found
	DB	12		; Data overrun
	DB	4		; Data CRC error
	DB	10		; Write fault
	DB	4		; Header CRC error

;Restore head on hard disk. 
RESTORE:
	MOV	ARG1+1,30	; 3 ms step time, no head settle delay
	MOV	AX,7+100H*4	; 1024 byte sector, LOAD CONSTANTS command
	XCHG	AX,ARG1+3	; Previous opcode in AH
	MOV	BL,1
	CALL	QUICKCOM	; Execute command
	JNZ	EXITREST	; Abort if controller failure
	MOV	ARG1+1,0	; Set to fast step (after restore)
	MOV	HSTEP,0FFFH	; Maximum number of steps
	MOV	HDIR,10H	; Step out
	CALL	HDCCOM		; Restore and set fast seek
	MOV	HCYL,0		; Now on track zero
EXITREST:
	MOV	OPCODE,AH
	RET

HDCCOM:
	MOV	BL,TIMEOUT
QUICKCOM:
	PUSH	CX
	XOR	CX,CX
	MOV	HSTAT,0
	OUT	STARTHDC,AL
HWAIT:
	MOV	AL,HSTAT
	OR	AL,AL
	LOOPZ	HWAIT		; Try for 2 seconds
	JNZ	HRET
	DEC	BL
	JNZ	HWAIT
HRET:
	POP	CX
	MOV	HSTEP,0
	CMP	AL,-1
	RET
	
GET$HBPB:
;  Set up BPB for Hard disk controller. Real simple isn't it?
	MOV	SI,OFFSET IO:HARDDRIVE	; Hard disk Parm table
SETBPB:
	LDS	BX,[PTRSAV]
	MOV	[BX.MEDIA],1		;One hard disk
	MOV	[BX.COUNT],SI
	MOV	[BX.COUNT+2],CS
	JMP	EXIT


; ***************************************************************************

HINITTAB:
	DW	HARDDRIVE

HARDDRIVE:
	DW	1024		; Sector size
	DB	ALLOCSIZ	; Allocation unit
	DW	1		; Reserved sectors
	DB	2
	DW	DIRENT		; Directory entries
	DW	NSECT*NHEADS*NTRACKS
	DB	1		; Media descriptor
	DW	FATSIZ		; Number of sectors for 1 Fat

BREAK	LABEL	BYTE		; Break address

;**************************************************************
; Code below this point is thrown away for installable versions

HDSK$INIT:

	IF	INSTALL
	MOV	AX,CS
	MOV	BX,AX
	MOV	CL,4
	SHL	AX,CL
	ROL	BX,CL
	AND	BL,0FH
	ADD	[NEXTAD],AX
	ADC	[NEXTADHI],BL
	LDS	BX,[PTRSAV]
	MOV	WORD PTR [BX.TRANS],OFFSET IO:BREAK
	MOV	WORD PTR [BX.TRANS+2],CS
	PUSH	CS
	POP	DS
	ENDIF

	MOV	SI,OFFSET IO:HINITTAB
	JMP	SETBPB

CODE	ENDS
	END