bin/DISKDEF.LIB

;	CP/M 2.0 disk re-definition library
;
;	Copyright (c) 1979
;	Digital Research
;	Box 579
;	Pacific Grove, CA
;	93950
;
;	CP/M logical disk drives are defined using the
;	macros given below, where the sequence of calls
;	is:
;
;	disks	n
;	diskdef	parameter-list-0
;	diskdef	parameter-list-1
;	...
;	diskdef	parameter-list-n
;	endef
;
;	where n is the number of logical disk drives attached
;	to the CP/M system, and parameter-list-i defines the
;	characteristics of the ith drive (i=0,1,...,n-1)
;
;	each parameter-list-i takes the form
;		dn,fsc,lsc,[skf],bls,dks,dir,cks,ofs,[0]
;	where
;	dn	is the disk number 0,1,...,n-1
;	fsc	is the first sector number (usually 0 or 1)
;	lsc	is the last sector number on a track
;	skf	is optional "skew factor" for sector translate
;	bls	is the data block size (1024,2048,...,16384)
;	dks	is the disk size in bls increments (word)
;	dir	is the number of directory elements (word)
;	cks	is the number of dir elements to checksum
;	ofs	is the number of tracks to skip (word)
;	[0]	is an optional 0 which forces 16K/directory entry
;
;	for convenience, the form
;		dn,dm
;	defines disk dn as having the same characteristics as
;	a previously defined disk dm.
;
;	a standard four drive CP/M system is defined by
;		disks	4
;		diskdef	0,1,26,6,1024,243,64,64,2
;	dsk	set	0
;		rept	3
;	dsk	set	dsk+1
;		diskdef	%dsk,0
;		endm
;		endef
;
;	the value of "begdat" at the end of assembly defines the
;	beginning of the uninitialize ram area above the bios,
;	while the value of "enddat" defines the next location
;	following the end of the data area.  the size of this
;	area is given by the value of "datsiz" at the end of the
;	assembly.  note that the allocation vector will be quite
;	large if a large disk size is defined with a small block
;	size.
;
dskhdr	macro	dn
;;	define a single disk header list
dpe&dn:	dw	xlt&dn,0000h	;translate table
	dw	0000h,0000h	;scratch area
	dw	dirbuf,dpb&dn	;dir buff,parm block
	dw	csv&dn,alv&dn	;check, alloc vectors
	endm
;
disks	macro	nd
;;	define nd disks
ndisks	set	nd	;;for later reference
dpbase	equ	$	;base of disk parameter blocks
;;	generate the nd elements
dsknxt	set	0
	rept	nd
	dskhdr	%dsknxt
dsknxt	set	dsknxt+1
	endm
	endm
;
dpbhdr	macro	dn
dpb&dn	equ	$		;disk parm block
	endm
;
ddb	macro	data,comment
;;	define a db statement
	db	data		comment
	endm
;
ddw	macro	data,comment
;;	define a dw statement
	dw	data		comment
	endm
;
gcd	macro	m,n
;;	greatest common divisor of m,n
;;	produces value gcdn as result
;;	(used in sector translate table generation)
gcdm	set	m	;;variable for m
gcdn	set	n	;;variable for n
gcdr	set	0	;;variable for r
	rept	65535
gcdx	set	gcdm/gcdn
gcdr	set	gcdm - gcdx*gcdn
	if	gcdr = 0
	exitm
	endif
gcdm	set	gcdn
gcdn	set	gcdr
	endm
	endm
;
diskdef	macro	dn,fsc,lsc,skf,bls,dks,dir,cks,ofs,k16
;;	generate the set statements for later tables
	if	nul lsc
;;	current disk dn same as previous fsc
dpb&dn	equ	dpb&fsc	;equivalent parameters
als&dn	equ	als&fsc	;same allocation vector size
css&dn	equ	css&fsc	;same checksum vector size
xlt&dn	equ	xlt&fsc	;same translate table
	else
secmax	set	lsc-(fsc)	;;sectors 0...secmax
sectors	set	secmax+1;;number of sectors
als&dn	set	(dks)/8	;;size of allocation vector
	if	((dks) mod 8) ne 0
als&dn	set	als&dn+1
	endif
css&dn	set	(cks)/4	;;number of checksum elements
;;	generate the block shift value
blkval	set	bls/128	;;number of sectors/block
blkshf	set	0	;;counts right 0's in blkval
blkmsk	set	0	;;fills with 1's from right
	rept	16	;;once for each bit position
	if	blkval=1
	exitm
	endif
;;	otherwise, high order 1 not found yet
blkshf	set	blkshf+1
blkmsk	set	(blkmsk shl 1) or 1
blkval	set	blkval/2
	endm
;;	generate the extent mask byte
blkval	set	bls/1024	;;number of kilobytes/block
extmsk	set	0	;;fill from right with 1's
	rept	16
	if	blkval=1
	exitm
	endif
;;	otherwise more to shift
extmsk	set	(extmsk shl 1) or 1
blkval	set	blkval/2
	endm
;;	may be double byte allocation
	if	(dks) > 256
extmsk	set	(extmsk shr 1)
	endif
;;	may be optional [0] in last position
	if	not nul k16
extmsk	set	k16
	endif
;;	now generate directory reservation bit vector
dirrem	set	dir	;;# remaining to process
dirbks	set	bls/32	;;number of entries per block
dirblk	set	0	;;fill with 1's on each loop
	rept	16
	if	dirrem=0
	exitm
	endif
;;	not complete, iterate once again
;;	shift right and add 1 high order bit
dirblk	set	(dirblk shr 1) or 8000h
	if	dirrem > dirbks
dirrem	set	dirrem-dirbks
	else
dirrem	set	0
	endif
	endm
	dpbhdr	dn	;;generate equ $
	ddw	%sectors,<;sec per track>
	ddb	%blkshf,<;block shift>
	ddb	%blkmsk,<;block mask>
	ddb	%extmsk,<;extnt mask>
	ddw	%(dks)-1,<;disk size-1>
	ddw	%(dir)-1,<;directory max>
	ddb	%dirblk shr 8,<;alloc0>
	ddb	%dirblk and 0ffh,<;alloc1>
	ddw	%(cks)/4,<;check size>
	ddw	%ofs,<;offset>
;;	generate the translate table, if requested
	if	nul skf
xlt&dn	equ	0		;no xlate table
	else
	if	skf = 0
xlt&dn	equ	0		;no xlate table
	else
;;	generate the translate table
nxtsec	set	0	;;next sector to fill
nxtbas	set	0	;;moves by one on overflow
	gcd	%sectors,skf
;;	gcdn = gcd(sectors,skew)
neltst	set	sectors/gcdn
;;	neltst is number of elements to generate
;;	before we overlap previous elements
nelts	set	neltst	;;counter
xlt&dn	equ	$		;translate table
	rept	sectors	;;once for each sector
	if	sectors < 256
	ddb	%nxtsec+(fsc)
	else
	ddw	%nxtsec+(fsc)
	endif
nxtsec	set	nxtsec+(skf)
	if	nxtsec >= sectors
nxtsec	set	nxtsec-sectors
	endif
nelts	set	nelts-1
	if	nelts = 0
nxtbas	set	nxtbas+1
nxtsec	set	nxtbas
nelts	set	neltst
	endif
	endm
	endif	;;end of nul fac test
	endif	;;end of nul bls test
	endm
;
defds	macro	lab,space
lab:	ds	space
	endm
;
lds	macro	lb,dn,val
	defds	lb&dn,%val&dn
	endm
;
endef	macro
;;	generate the necessary ram data areas
begdat	equ	$
dirbuf:	ds	128	;directory access buffer
dsknxt	set	0
	rept	ndisks	;;once for each disk
	lds	alv,%dsknxt,als
	lds	csv,%dsknxt,css
dsknxt	set	dsknxt+1
	endm
enddat	equ	$
datsiz	equ	$-begdat
;;	db 0 at this point forces hex record
	endm
;