ftp.barnyard.co.uk/2015.02.ftp.barnyard.co.uk.tar/ftp.barnyard.co.uk/cpm/walnut-creek-CDROM/SIMTEL/CPMUG/CPMUG049.ARK/CDOS.DOC

Text File | 1984-04-29 | 10KB | 193 lines

          GENERAL NOTES ON CDOS' UNDOCUMENTED FEATURES

When  CDOSGEN asks you whether the drive is large [L] or  small
[S] try answering 'X'.  You will then get a menu for  Shugarts,
etc.

You  can  use  the  'SYS.DIR'  FCB  create call of CDOS 1.07 or
higher to access  the  directory  regardless  of  its  size  or
position  on the disk.  Although the FCB created with this call
is write protected, you can reset that  attribute  bit and  can
then write to the directory as well as read it.

Disk Labels.
A directory label is written to the disk by STAT and is used to
ascertain  the  storage capacity of the disk and the number  of
directory entries (64 to 512).
The last 8 bytes of the first boot loader sector (usually  side
0  track 0 sector 1) are always recorded in single density  and
contain eight bytes indicating the type of disk to the BIOS, eg
     LGSSSD
for Large (8"), Single Sided, Single Density
or   LGDSDD
for 8" Double Sided, Double Density diskettes (1.2 MBytes)

STAT  2.15  was written for a WD1797 FDC chip (it  records  the
side  numbers  into the address fields) although a  WD1793  was
eventually used.  CDOS 2.36 does not support the 1797, however,
and this chip will not work instead of the 1793 on the 16FDC.

Double Density Recording Format:
16 sectors of 512 bytes are used per track.(MFM)
A 12 interleave is used (1,C,7,2,D,8,3,E,9,4,F,A,5,10,B,6)
Although  a 4 interleave can be read as COM files in my 4MHz no
wait state system a 6 interleave speeds throughput by a  factor
of  two.  (use 1,2,3,4,5,6,C,D,E,F,10,7,8,9,A,B).  INIT can  be
modified  to  do  this..  if  interested write me  and  I  will
disclose all....

Finally,  if  someone has deciphered how to call the 2.36  BIOS
directly without getting error returns I am all ears...

Trevor Marshall,
26 Mirrelia Way, Ferndale, Western Australia 6155
phone International (619)4576049   or national [phone]
14 December 1980

Notes added by:    Chuck Weingart        February 1, 1981
        2152 W. Iowa
        Chicago, Ill 60622

On the "X" feature of CDOSGEN, described above, you must respond
to  several  questions,  such  as  "Fast  or  Slow",  "Single or
Double".  All Shugart type drives are "slow".   "Double"  drives
are  those like the Persci, that have one seek mechanism for two
different disks, or when you are  using  a  Shugart  851  double
sided  drive as two "drives" (one "drive" on each side, requires
rewiring the cable).

In CDOSGEN 2.36, when you respond "S" to  the  drive  type,  you
again  get  a "Fast or Slow?"  question.  MPI drives are "fast",
and Shugart 400 and Wangco drives are "slow" in my experience.

It is easy to attach one of the new Shugart  801/851  drives  to
the 4FDC, just use the "TS" data separator (install the jumper).
If  you  are  trying  to use an old 800-1 or 801 drive, the data
separator adjustments probably have to be changed to  work  with
the 4FDC.

To attach the MPI model 52 double-sided 5" drive to a 4FDC, just
add  a jumper on the 4FDC from J4 pin 21 to J2 pin 32, if one is
not already there.  Then gen a 5"  double-sided  drive  at  that
position  with 2.17 or greater, initialize some disks with INIT,
and write a double-sided label with STAT, and you are  ready  to
go. I converted to double-sided in one hour, and it's great!

To  attach  a  Shugart 851 to the 4FDC, install the TS jumper as
noted above.  Disconnect the wires 2, 12, 18, and  32  from  the
cable (at the drive end is easiest).  Connect the Shugart pin 12
to  the 4FDC pin 2 (for side select), Shugart pin 30 to 4FDC pin
4 (for Drive select 3), and Shugart pin 32 to 4FDC pin  18  (for
Drive select 4).  Connect a jumper from J4 pin 21 to J3 pin 2 if
one  is  not  already  there.   Use  the "X" feature and 2.17 or
greater, initialize disks with INIT, and label  the  disks  with
STAT for double-sided operation.

CDOS  1.07  can  be  used  unchanged  on the California Computer
Systems 2422 disk controller if there is a  Cromemco  compatible
console  port  at  0,  such  as a 3P + S, Cromemco TUART, or the
console on the Cromemco SCC.  The latter will have to  have  two
modifications  made:  the  prom (U25) must be altered to put the
parallel port at address 04 somewhere else  (such  as  0E),  and
there  must  be  a 220 ohm resistor in series with U52 pin 6 (to
delay PWR) and a 400pf capacitor from U52 pin 6 to  ground  (pin
8).

CDOS 2.17 can be used on  the  CCS  2422  controller  in  single
density  if  one  uses  the  1.07  bootstrap  loader.   The 2.17
bootstrap will not work without a hardware change  on  the  2422
board,  and  it is somewhat lengthy.  There will be a persistent
problem of read errors on track 2 sector 1, but this is  due  to
the  WD1793 chip.  Just Retry the operation and it will clear up
every time.

CDOS 2.17 has a command, VERIFY, with  one  of  three  operands.
VERIFY ON will enable read-after-write verification on the disk.
VERIFY  OFF will disable that, and just VERIFY will indicate the
status of the feature.  VERIFY is not present in CDOS 2.36.

CDOS 2.17 and up has  several  undocumented  commands:  REM  and
ATTR.   ATTR  is  the  same  as  ATRIB, and REM is for inserting
remarks into your batch file, because the REM line is ignored.

Although  it  isnt  currently  stated  in  any   Cromemco   doc-
umentation  that  I have seen (and I have written Cromemco twice
about it with no answer),  all  versions  of  Cromemco  software
shipped  since  about  February 1980 come with the system genned
for 64K.  If you have a copy of CDOS 1.07, you can run the  2.17
or  2.36  versions  of CDOSGEN under 1.07 in order to generate a
smaller system.  The new versions of CDOSGEN will not run  in  a
32K system, tho, they are quite a bit bigger.

For users of non-Cromemco memory boards that want to get a "full
house"  (64K),  here is how to add a Phantom signal to the 4FDC.
Add a jumper from IC46(74367) pin 15 to IC31(2708) pin 20.   Add
a  jumper from IC46 pin 12 to pin 8 (ground).  Add a jumper from
IC46 pin 11 to S100 pin 67 (Phantom output).  The  memory  board
addressed  at  C000H  must  respond  to  the  Phantom signal, of
course.  The RES switch (SW2) must be set on.  This way, you can
use the 4FDC RDOS program until CDOS is booted, then  the  EPROM
will  be turned off and the memory board "behind" it can then be
used.  This method must be used even in  many  boards  that  are
advertised  as  "Cromemco banking compatible" because the boards
do not have the feature of being bank-disabled upon power-up.

CDOS 2.17 now takes about 11K minimum for itself.  CDOS 2.36 now
takes 14K minimum.

STAT for 2.36 has several undocumented switches: /M, /N, /E, and
/EZ.   STAT/M  allows  you to change the "master" drive (the one
that CDOS looks at if it cant find  a  program  on  the  current
drive).   STAT/N  gives  a  5-up directory display.  STAT/E is a
directory erase, with prompting.  STAT/EZ erases, and no prompts
as I recall.

Jordan Siedband tells me that 2.36  will  not  read  CP/M  disks
correctly,  cause  unknown.   Keep  a copy of 2.17 around if you
want to continue to use CPMUG stuff.  There is one thing that is
obvious to anyone who has looked: CP/M and CDOS directories  are
compatable  only in  "1.4 mode", that is, no system flags of any
kind set in the directories,  either  CP/M  2.2  flags  or  CDOS
flags. When they  are  not  compatable, the one operating system
will usually clobber directory entries in the  other  format  or
refuse to work.

CDOS 1.07 and up have an  undocumented  error  message:  LOGICAL
DISK ERROR n.  This message is produced if you do something like
request  a  track that does not exist, or a sector that does not
exist, or try an operation that is impossible for the  drive  to
perform.   You will generally get these messages only if you are
trying to do disk I/O thru the "BIOS" directly.

There is a small bug in the Divide Integers CDOS call  (8AH)  in
2.17  -  the BC register will be altered.  No problem in 1.07 or
2.36 as far as I can tell.

All  versions  of  CDOS have the CP/M "BIOS" jump table in them,
but none of them use it.  That is, you can jump to  the  entries
in this table, but cannot modify the jump addresses in the table
and  expect it to work.  The first entry in the table, the "cold
start" jump, is a jump to itself, because CDOS never  uses  this
entry,  and  the  user  is not supposed to use it, either.  This
makes routines like FAST rather difficult  to  use  under  CDOS.
Some CPMUG programs set themselves below the operating system by
changing the address at location 6, but that will not work under
CDOS.   You  can use the CDOS call 97H to do the same thing, see
the manual for details.

All  versions of CDOS I have used  try  to initialize all  TUART
ports in the system.  That is, they will output to ports 12, 13,
22,  23,  52,  53,  62, ...  F2, and F3.  If you have some other
hardware at those addresses, good luck.  CDOS will also zero out
the Dazzler port at 0E every time it starts disk I/O.

CDOS 2.17 and up will disable all interrupts when doing disk I/O
and never  re-enable.   This  means  you  can't  use  the  timer
interrupts available in the TMS5501.

If anyone figures out what attributes S and U are, I would like
to know.  They can be set, reset, and listed,  but dont seem to
make any difference to the operating system. Could they be used
for Hard disk files?