Appendix F

CP/M Disk Definition Library


This file is intended to be included with your CBIOS to provide disk definitions. A version of the file without the HTML codes is available here.

;       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
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
dpbhdr  macro   dn
dpb&dn  equ     $               ;disk parm block
ddb     macro   data,comment
;;      define a db statement
        db      data            comment
ddw     macro   data,comment
;;      define a dw statement
        dw      data            comment
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
gcdm    set     gcdn
gcdn    set     gcdr
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
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
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
;;      otherwise, high order 1 not found yet
blkshf  set     blkshf+1
blkmsk  set     (blkmsk shl 1) or 1
blkval  set     blkval/2
;;      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
;;      otherwise more to shift
extmsk  set     (extmsk shl 1) or 1
blkval  set     blkval/2
;;      may be double byte allocation
        if      (dks) > 256
extmsk  set     (extmsk shr 1)
;;      may be optional [0] in last position
        if      not nul k16
extmsk  set     k16
;;      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
;;      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
dirrem  set     0
        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
        if      skf = 0
xlt&dn  equ     0               ;no xlate table
;;        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)
        ddw     %nxtsec+(fsc)
nxtsec  set     nxtsec+(skf)
        if      nxtsec >= sectors
nxtsec  set     nxtsec-sectors
nelts   set     nelts-1
        if      nelts = 0
nxtbas  set     nxtbas+1
nxtsec  set     nxtbas
nelts   set     neltst
        endif   ;;end of nul fac test
        endif   ;;end of nul bls test
defds   macro   lab,space
lab:    ds      space
lds     macro   lb,dn,val
        defds   lb&dn,%val&dn
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
enddat  equ     $
datsiz  equ     $-begdat
;;      db 0 at this point forces hex record

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