STAT DEV: liefert Informationen über den Disk Parameter Block.
A>stat dsk:
A: Drive Characteristics
6400: 128 Byte Record Capacity
800: Kilobyte Drive Capacity
192: 32 Byte Directory Entries
192: Checked Directory Entries
128: Records/ Extent
16: Records/ Block
40: Sectors/ Track
0: Reserved Tracks
Der zugehörige Disk Parameter Block DPB enthält die folgenden Werte. Daraus berechnet STAT die Werte für records per block und bytes per block und daraus die Ausgaben.
dpb: dw 40 ;SPT sectors per track db 4 ;BSF block shift factor db 15 ;BLM block mask db 0 ;EXM null mask dw 399 ;DSM disk size-1 dw 191 ;DRM directory max db 0E0H ;AL0 alloc 0 db 0 ;Al1 alloc 1 dw 48 ;CKS check size dw 0 ;OFS track offset rpb := 1<<BSF = 2^BSF; /* records/block */ = 2^4 = 16 bpb := 1<<BSF * 128 = 2^BSF * 128; /* bytes per block */ = 2^4*128 = 2048 Drive Characteristics := Laufwerk = A 128 Byte Record Capacity := (DSM+1) * rpb = (399+1) * 16 = 6400 Kilobyte Drive Capacity := (DSM+1) * bpb / 1024 = (399+1) * 2048 / 1024 = 800 32 Byte Directory Entries := DRM+1 = 191+1 = 192 Checked Directory Entries := CKS<<2 = CKS*4 = 48 * 4 = 192 Records/ Extent := (EXM+1) * 128 = (0+1) * 128 = 128 Records/ Block := rpb = 16 Sectors/ Track := SPT = 40 Reserved Tracks := OFS = 0
Der originale Codeauszug von STAT, geschrieben in PL/M, ist relativ leicht zu verstehen. Lediglich die Berechnung der Gesamtkapazität ist ewas komplexer gelöst; PLM arbeitet nur mit 16 Bit. Deshalb muss die Multiplikation über diesen Zahlenbereich hinaus anders gelöst werden.
/* function call 32 returns the address of the disk parameter
block for the currently selected disk, which consists of:
scptrk (2 by) number of sectors per track
blkshf (1 by) log2 of blocksize (2**blkshf=blksize)
blkmsk (1 by) 2**blkshf-1
extmsk (1 by) logical/physical extents
maxall (2 by) max alloc number
dirmax (2 by) size of directory-1
dirblk (2 by) reservation bits for directory
chksiz (2 by) size of checksum vector
offset (2 by) offset for operating system
*/
dpb based dpba structure
(spt address, bls byte, bms byte, exm byte, mxa address,
dmx address, dbl address, cks address, ofs address),
scptrk literally 'dpb.spt',
blkshf literally 'dpb.bls',
blkmsk literally 'dpb.bms',
extmsk literally 'dpb.exm',
maxall literally 'dpb.mxa',
dirmax literally 'dpb.dmx',
dirblk literally 'dpb.dbl',
chksiz literally 'dpb.cks',
offset literally 'dpb.ofs';
declare bpb address; /* bytes per block */
set$bpb: procedure;
call set$dpb; /* disk parameters set */
bpb = shl(double(1),blkshf) * sectorlen;
end set$bpb;
getalloca: procedure address;
/* get base address of alloc vector */
return mon3(27,0);
end getalloca;
add$block: procedure(ak,ab);
declare (ak, ab) address;
/* add one block to the kilobyte accumulator */
declare kaccum based ak address; /* kilobyte accum */
declare baccum based ab address; /* byte accum */
baccum = baccum + bpb;
do while baccum >= 1024;
baccum = baccum - 1024;
kaccum = kaccum + 1;
end;
end add$block;
count: procedure(mode) address;
declare mode byte; /* true if counting 0's */
/* count kb remaining, kaccum set upon exit */
declare
ka address, /* kb accumulator */
ba address, /* byte accumulator */
i address, /* local index */
bit byte; /* always 1 if mode = false */
ka, ba = 0;
bit = 0;
do i = 0 to maxall;
if mode then bit = getalloc(i);
if not bit then call add$block(.ka,.ba);
end;
return ka;
end count;
drivestatus: procedure;
declare
rpb address,
rpd address;
pv: procedure(v);
declare v address;
call crlf;
call pdecimal(v,10000);
call printchar(':');
call printb;
end pv;
/* print the characteristics of the currently selected drive */
call print(.(' ',0));
call printchar(cselect+'A');
call printchar(':');
call printx(.(' Drive Characteristics',0));
rpb = shl(double(1),blkshf); /* records/block=2**blkshf */
if (rpd := (maxall+1) * rpb) = 0 and (rpb <> 0) then
call print(.('65536: ',0)); else
call pv(rpd);
call printx(.('128 Byte Record Capacity',0));
call pv(count(false)); /* (maxall+1)*bpb/1024 */
call printx(.('Kilobyte Drive Capacity',0));
call pv(dirmax+1);
call printx(.('32 Byte Directory Entries',0));
call pv(shl(chksiz,2));
call printx(.('Checked Directory Entries',0));
call pv((extmsk+1) * 128);
call printx(.('Records/ Extent',0));
call pv(rpb);
call printx(.('Records/ Block',0));
call pv(scptrk);
call printx(.('Sectors/ Track',0));
call pv(offset);
call printx(.('Reserved Tracks',0));
call crlf;
end drivestatus;