By Bill Bolton
Software Tools,
P.O. Box 80,
Newport Beach,
NSW, 2106,
AUSTRALIA
Introduction
------------
This program is an improved disk dump utility for CP/M. Any
CP/M file may be dumped to the console. In addition any sector
or group of sectors may be dumped in the same format. The
utility can be made to handle any CP/M 2.X disk system as
outlined later.
The program is referred to as DD6 when refering to the
latest implementation or DDX when refering to all
implementations including the latest one.
--- OPERATION ---
The program may be run either by typing DD6, or DD6 followed
by the file name or track and sector. If DD6 is typed the
program responds with a heading, followed by a '*' and waits for
more user input. Operation in this mode is similar to other
utilities such as PIP or DDT.
The operation desired may then be typed in as follows:
DD6 file.nam
DD6 A:file.nam
DD6 C:file.nam
or may be typed separately as:
DD6
*file.nam (the * is the program prompt)
*B:file.nam
The file is dumped by examining its directory entry to
obtain block allocation, number of records and extent
information. The file is then dumped on a block by block basis,
this allows display of the track and sector numbers as a file is
dumped. The last block of a file is only dumped up to the last
sector actually used by the file.
All sector dumps display hex addresses in the range 00 to
7F as a 2 digit hex number, except in the case of a COM file
dump. When a COM file is being dumped, the first sector is
assumed to start at 0100H and all subsequent addresses are
incremented from this base address and displayed as a 4 digit
hex number.
A sector dump heading is displayed at the top of each sector
dumped and indicates the drive selected, whether 1 or 2
sided, its physical sector size, the track number, logical
sector number and a dump count:
The dump count displays the running total of sectors dumped
from a single command line. This is useful for locating a
particular sector of a file or block. A modified version of the
CP/M User's Group binary COMPARE utility, which indicates file
differences with decimal sector numbers that are directly
equivalent to DDX Dump Count numbers, is available from
Software Tools.
The program may also be used to dump disk sectors directly
and dump any CP/M sector block (or group) - block size
information is obtained from the CP/M 2.X DPB (Disk Parameter
Block) of the drive concerned. The sectors containing the
directory may dumped with a simple single command and a map of
the block allocations may be likewise displayed.
DD6 TRACK 3 SECTOR 7
DD6 TRACK 5 SECTOR 3 - 9
DD6 TRACK 6 (dumps all sectors on the track)
DD6 GROUP 19
DD6 DIR
DD6 MAP
The words TRACK, SECTOR and GROUP may be abbreviated as
follows:
DD6 T 7 S 3-4
DD6 G 4
*TRACK 5 S 6
*SECTOR 2-9 T 14
DD6 B: TRACK 3
DD6 A: T 9 S 4-6
DD6 B: G 5
DD6 B:MAP
Note that the format is quite free. Spaces are usually
ignored. They are only required after the words TRACK, SECTOR
and GROUP or T, S and G and after the word DD6.
In previous versions of DDX the block or cluster was
refered to as a "group" as this term is still used as a command
to maintain compatibility with previous versions. Digital
Research now use the term "block" instead of "group" and this
file and most of the comments in the source file use the term
"block".
-- EDITING ---
A limited editing feature is included in the dump utility to
allow changing of data on disk. The edit works as follows - any
single logical sector of any drive may be edited by requesting
display of the sector followed by the word EDIT.
DD6 D:TRACK 4 SECTOR 2 EDIT
The requested sector will be displayed followed by an
edit prompt:
EDIT -
Enter the address of the first byte to be changed. The
program will respond by typing back the address entered and the
present contents of that address. To change the contents, enter
the new byte followed by a carriage return. The program will
display the next address and its contents. To stop entering data
type a period, the sector will then be redisplayed showing the
changes. The edit feature works almost exactly like the 'S'
command in DDT, typing only a carriage return omits entry.
The change is not made permanent until it is written back
onto the disk, you exit the edit mode by typing;
WRITE (write the changed sector back onto disk)
STOP (stop the edit without writing to disk)
All edit entries must be made in hex. Entering non hex
characters results in an error message. The permissable address
range is from 00 to 7F, larger addresses give an error message.
When entering a block of bytes the addresses are computed modulo
128, the next address after 7F is 00.
The edit feature should be used with caution as it is
possible to edit CP/M to "death" by changing a single byte. One
occasionally valuable use is to restore files which have been
accidentally erased. Erasing a file using the ERA command does
not erase the data from the disk, but only writes an E5 into the
first byte of its directory entry. To restore the file, display
the directory using the DD6 DIR command. Find the sector
containing the entry in question and display it using the EDIT
feature. Change the byte preceeding the file name from E5 to 00
and write the sector back on disk. This will restore the file
provided that you have not used any programs which write data to
disk since erasing the file. *** BE WARNED *** If you have run a
program that writes data to disk since erasing the file you may
find that the erased file's allocated blocks have been used for
another file and the integrity of the erased file therefore
destroyed.
--- CP/M 2.X ---
This latest version of DDX benefits from running under CP/M
2.X. As the DPB location is now accessable via BIOS calls it is
possible to extract nearly all the information needed to allow
dynamic determination of a drives characteristics.
There are only two hardware dependent subroutines, one is
optional and simply sets up the sector display header to suit
your requirements. As it is not possible to determine the actual
density or number of sides directly from the DPB, as CP/M
doesn't care about that information, you must write the code.
The 1791 controller chip has this available as status inform
ation and most other controller chips seem to have something
similar.
The other hardware dependent routine concerns the handling
of Track 0. In all IBM compatible formats Track 0 is always
single density 3740 format. You must be able to overide all
dynamically set parameters of DD6 and force your disk
controller to read Track 0 as single density, 26 x 128 byte
sectors. The Morrow Disk Jockey 2D and Godbout Disk 1 do this
automatically so it was simply a matter of feeding the correct
sector numbers to the controller. Fortunately Track 0 is not
involved in file or block dumps so it is easy to treat it as
an exception and only one subroutine needs to be altered.
SECTOR NUMBERING - Single density CP/M maintains a skew
factor of 6 on 8" IBM 3741 compatible disks (i.e the standard
implementation). This means that logical sector 1 on a track is
physical sector 1 while logical sector 2 is physical sector 7 on
that track etc. This is done to provide greatest internal
efficency of operation for CP/M in accessing disks.
CP/M sees each 128 byte sector on a single density disk as
one logical record so there is a direct relationship between
sector size and data block size. With double density disk
recording systems there are several possible sizes for sectors.
The IBM 2D standard allows for sector sizes of 256, 512 or 1024
bytes. Double density and Hard disk implementations which use
physical sectors sizes that are multiples of 128 bytes have to
DEBLOCK the physical sector into 128 byte logical sectors.
The BIOS handles all blocking and deblocking, so that legal
sector numbers for BIOS set sector calls are 1 to the maximum
number of 128 byte sectors for the track size, the BIOS then
does the deblocking and translation to physical sectors on the
disk. The BIOS accesses all data bytes of a physical sector by
reading them into a buffer in memory and then accessing the
required 128 byte section of the buffer to give 128 byte logical
sectors.
BLOCK SIZE - Standard CP/M 1.4 is set up to recognise 243
blocks per disk. The block is the smallest amount of disk space
which can be allocated and disk space is allows allocated in
blocks. In a standard single density system on IBM 3741
compatible 8" disk the block size is 1K bytes or 8 sectors of
128 bytes each.
Block sizes for double density and hard disks vary but are
always a multiple of 1K bytes. The actual size is determined
form the DPB.
When using the DD6 GROUP N command a calculation of the
sector numbers covered by any particular block is made and a
look up of the XLT (sector translation tables) in the BIOS is
used to take into account the skew factor in use on the specific
CP/M implementation.
The current source listing is for a Godbout "Disk 1" based
CP/M 2.X system and a 24 x 80 video display. If you have a 16 x
64 video display you will need to remove some of the spaces
inserted in the dump display by the PRTSEC routine.
DD6 should be readily adaptable to other CP/M 2.X systems,
including hard disk systems. As far as possible all values which
might reasonably be expected to exceed 256 in any realisable
disk system are manipulated as 16 bit values. Therefore the
large sectors sizes, sector numbers and track numbers likely
to be found on a hard disks should present no problem. The
program does make a few assumptions about the way CP/M 2.X
handles the disk parameter block allocation, it assumes that
it is all done dynamically in the BIOS. As all the multiple
density CP/M 2.X systems that I have come across manage to
do this (some more elegently than others !) I think that it is
a safe assumption.
--- OTHER DETAILS ---
As with other CP/M utilities a ^S 'freezes' the display and
^C returns to CP/M. Hitting the 'space bar' will abort the dump
currently in progress and either exit or return to command
level, depending on how you entered the utility. Dump cont
ains many error and consistancy checks. The resulting
messages are generally self explanatory.
DD6 was assembled using the CP/M MAC assembler and uses a
large library of macros called MACRO3.LIB which is available
from Software Tools. (N.B. MACRO3.LIB is an revision of
MACRO.LIB, as used by Sam Singer's single density version, with
extensions to the CALLBIOS and DISKIO macros to handle CP/M
2.2, and several new macros added).
This disk dumper is in a continuing state of development and
refinement. There is now a version for the Morrow Designs Hard
Disk controller with a DJ2D or a Godbout Disk 1 controller,
called DDH. Many new features are planned and will be added in
the towards the end of 1981.
