PAGE
;	S E L E C T   D I S K   D R I V E
;
;	Select the disk drive for subsequent disk transfers and
;	return the appropriate DPB address.   This routine
;	diverges from the normal CP/M implementation of just
;	saving the disk selection value until the transfer is
;	performed.  This divergence is required because floppy
;	disks are a removable media and come in more than on
;	format.  This routine determines the correct format and
;	initializes the DPH with the appropriate values for the
;	format type.
;
;	ENTRY	C = disk delection value.
;		DE and 1 = 0, must determine disk type.
;		         = 1, drive type has been determined.
;
;	EXIT	HL = 0, if drive not selectable.
;		HL = DPH address if drive is selectable.
;
;		DPH is intialized for the appropriate floppy
;		disk format.

SELDSK:	proc
	CMP	CL,#NDSK
	JL	SELD2		;If valid drive
SELD1:	LD	BX,#0		;Flag invalid drive selection
	RET

SELD2:	PUSH	DX		;Save drive selection mask
	LD	CH,#0

	MOV	BX,CX
	ADD	BX,#DSKMSK
	LD	AL,[BX]
	STO	AL,SEKDSK	;Save selection code

	MOV	BX,CX		;Compute DPH address
	SHL	BX		;*2
	SHL	BX		;*4
	SHL	BX		;*8
	SHL	BX		;*16
	ADD	BX,#DPBASE

	MOV	DX,BX		;Save DPH address
	LD	BX,[BX+5*2]	;DPH DPB address
	DEC	BX
	LD	AL,[BX]		;Get disk type from DPB
	STO	AL,SEKTYP	;Save disk type
	MOV	BX,DX		;BX = DPH address
	POP	DX		;Restore Drive selction mask
	CMP	AL,#MAXFTP
	JG	SELD3		;If hard disk
	AND	DL,#1		;Mask selected bit
	JNZ	SELD3		;If drive previously selected

	PUSH	BX		;Save DPH address
	PUSH	CX		;Save drive selection
	CALL	TREAD		;Determine disk type
	POP	CX		;Restore drive selection
	POP	DX		;Restore DPH address
	JNZ	SELD1		;If disk type not determined

	STO	AL,SEKTYP	;Save disk type
	LD	AH,#0
	PUSH	AX
	SHL	AX		;*2
	SHL	AX		;*4
	SHL	AX		;*8
	SHL	AX		;*16
	ADD	AX,#DPBS1+1	;AX = DPB address
	MOV	BX,DX		;BX = DPH address
	STO	AX,[BX+5*2]	;Set DPB address into DPH
	POP	BX		;Restore disk type
	AND	BL,#0FEh	;Remove sided bit
	ADD	BX,#XTABLE	;Compute translation table address
	LD	AX,[BX]		;Get translation table address
	MOV	BX,DX
	STO	AX,[BX]		;address into DPH
SELD3:	RET
	PAGE
;	H O M E
;
;	Return disk to home.  This routine sets the track number
;	to zero.  The current host disk buffer is flushed to the
;	disk.

HOME:
	CALL	FLUSH		;Flush host buffer
	XOR	AX,AX
	STO	AL,HSTACT	;Clear host active flag
	STO	AL,UNACNT	;Clear sector count
	STO	AX,SEKTRK
	RET
	SPACE	4,10
;	S E T   T R A C K.
;
;	Set track number.  The track number is saved for later
;	use during a disk transfer operation.
;
;	ENTRY	BC = track number.

SETTRK:
	STO	CX,SEKTRK	;Set track
	LD	AX,UNATRK
	CMP	AX,CX
	JNE	CUNACT		;If not same track
	RET
	SPACE	4,10
;	Clear Unallocated block count (force pre-reads).

CUNACT:	LD	AL,#0		;A = 0
	STO	AL,UNACNT	;Clear unallocated block count
	RET
	SPACE	4,10
;	Set the sector for later use in the disk transfer.  No
;	actual disk operations are perfomed.
;
;	Entry	BC = sector number.

SETSEC:
	STO	CL,SAVSEC	;sector to seek
	RET
	SPACE	4,10
;	Set Disk memory address for subsequent disk read or
;	write routines.  This address is saved in DMAADR until
;	the disk transfer is performed.
;
;	ENTRY	BC = Disk memory address.
;
;	EXIT	DMAADR = BC.

SETDMA:
	STO	CX,DMAADR
	RET
	SPACE	4,10
;	Translate sector number from logical to physical.
;
;	ENTRY	DE = 0, no translation required.
;		DE = translation table address.
;		BC = sector number to translate.
;
;	EXIT	HL = translated sector.

SECTRN:
	LD	AL,UNASEC
	CMP	AL,CL
	JZ	:7		;If sectors match
	CALL	CUNACT
:7:	STO	CL,LOGSEC
	MOV	BX,CX
	ADD	BX,DX		;Sector + translation table address
	OR	DH,DL
	JZ	:8		;If no translation
	LD	BL,[BX]
	LD	BH,#0
:8:	RET
	SPACE	4,10
;	S E T   E X T E N D E D   B A N K
;
;	Set the extended bank data tranfer address.
;
;	ENTRY	C = Extended address bank.
;
;	EXIT	DMAADE = C.

SETXAD:
	STO	CX,DMASEG
	RET