Cromemco Multi-User BASIC User manual

Five Dollars
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Part No. 023-0061
CROMEMCO
Multi-User BASIC
Instruction Manual
CROMEMCO, Inc.
280 Bernardo Avenue
Mountain View, CA 94043
ｃｯｰｹｲｾｧｨｴ © 1979
CROMEMCO, INC.
ALL RIGHTS RESERVED
November 1979

Table of Contents
1. Introduction ••••••
Overview ••••••••
Getting Started ••
Backup •••••••••
· ..
•••• 1
• • 2
.4
• •• 4
....
.........
2. User Protection ••••••••••••••••
Directory Protection •••••••••
Protection of File Integrity ••
Protection from Deadlock ••••••
• ••••• 5
.6
• • • • • • • • • • • 6
.7
3.
Description
of
the Operating
System.
.10
· ..
4. Attributes of the Operating System ••••
Type Ahead ••••••••••••••• ' •••••••••••••
CDOS Call to Display Job Information.
.12
• •••• 13
• ••• 14
.............·
..
·....
.
..
.15
· ....•.. •• 16
• •••••• 17
. ..••....•....• • 18
• .19
.21
• .22
• .23
• •••• 24
• .25
• • • • .27
• ••••• . 28
· ••••••.• • 30
.31
Commands.
. ..
. ...
..
. ..
·....
·...
·...
·.
...
.
..
· ...
. ..
.....
Multi-User CDOS Intrinsic
BACKG.
BAS.
CHA.
DETACH ••
ATTACH.
KI
LL ••••
LOGOFF ••
MORE.
PRT: •••
RESCUE •••••••••••••••••••
SET •••••••••••
SYS.
TIME •••••••••••••••
5.
·.
6.
Multi-User BASIC
Variable Names.
Line Names.
Variable
· ..
and Line Names. .32
• ••• 33
•••• 34
7. Multi-User
BASIC
Commands ••
· ...
· ..
..35
CLEAR ••• .....·
...
·.... ..... ·.... •
36
COMMON.
· ...
·......
..37
DELREM. .
... •••• 39
EXPAND. ......·
...
..·.·
..
• •• 41
IF ••• THEN
DO • • • ELSE. •• ENDDO.
• .42
LVAR •••
. ...
...... ·
...
•• ,.44
NOLIST.
·. .
.. • ••• 46
OPEN •••
· ..
.48
PROTECT. .....·
...
·.... ...·...
•• 50

8. Cromemco In-Line BASIC Editor ••••••••••••••••• 51
EDIT ••••••••••••••••••••••••••••••••••••••••• 54
FIND ••••••••••••••••••••••••••••••••••••••••• 55
CHANGE ••••••••••••••••••••••••••••••••••••••• 56
9. Multi-User BASIC Error Messages •••••• ••••• 57
10. Modification of Multi-User BASIC •••••••••••••• 59
Customizing the Command Line ••••••••••••••••• 60
Access to CDOS Programs & Commands ••••••••••• 63
Restricting Use of the CHA Command ••••••••••• 63
Restricting Use of the MORE Command •••••••••• 64
Restricting Use of the KILL Command •••••••••• 64
Machine Level BASIC Instructions ••••••••••••• 64
Disk Drive Configuration ••••••••••••••••••••• 65
11. Hardware Configuration •••••••••••••••••••••••• 66
System RAM Cards ••••••••••••••••••••••••••••• 67
User RAM Cards ••••••••••••••••••••••••••••••• 68
Disk Controller Card ••••••••••••••••••••••••• 69
Serial Interface Card •••••••••••••••••••••••• 69
Interrupt Priority Cable ••••••••••••••••••••• 70
Special Configuration •••••••••••••••••••••••• 70
Index

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Multi-User BASIC Instruction Manual
Introduction
Introduction
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Multi-User BASIC Instruction Manual
Introduction
An Overview
C romemco' s new Mul ti-User BASIC Operating System
includes features which are usually found only on
large computers. It is composed of a ｴｩｭ･ｾｳｨ｡ｲｩｮｧ
operating system, Multi-User COOS, and an enhanced
version of Cromemco 16K Extended BASIC. The
hardware configuration requi red for the operation
of the Multi-User BASIC Software System is shown in
chapter 11 of this manual.
The current version includes many new features.
Users are no longer restricted to running BASIC.
One user can run the assembler, for example, while
another is running the FORTRAN compiler, and a
third is running BASIC.
The new version allows users to start several jobs
from the same terminal by using the Multi-User COOS
command, DETACH. Other new COOS commands are:
- ATTACH retrieves aDETACHed job.
- BACKG allows a job to be run in the background.
- BAS loads and runs BASIC.
- CHA is the command.entered in order to change
diskettes.
-KILL
allows jobs to be terminated from
selected terminals.
- LOGOFF allows users to terminate their sessions.
- MORE
allows users to obtain larger memory
allocations.
-PRT:
allows the use r s to
dot .... matrix or fully
printer with CTRL-P.
access either a
formed character
- RESCUE allows users to initialize disabled
terminals.
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Multi-User BASIC Instruction Manual
Introduction
-SET
-SYS
-TIME
allows the user of terminal-l to set the
time, date, and adj ust the clock rate.
Each user may set the number of nulls
after each RETURN, an automatic line feed
after each RETURN, and a user-selected
ERASE character.
dis pI a y s for a 11 use r s : job n urn b e r ,
status (busy or wai t), whether BAS IC is
loaded, which CDOS program is running,
how much memory is allocated, terminal
number and user name, and the time that
user logged on.
displays the current time and date.
Since Multi-User COOS buffers input from the
terminal keyboards, users can enter characters
before the executing program requests them. This
feature, commonly known as "type-ahead", is often
very convenient to use.
Multi-User BASIC includes the following attributes
in addition to those of 16K Extended BASIC:
-
an in line BASIC text editor
- upper and lower case program text
- variable names up to 31 characters long
- line and subroutine names up to 31 characters
long
- many new statements and commands such as
- PROTECT which insures that a file cannot be
read from, written to, or erased
- IF ••• THEN OO ••• ELSE ••• ENOOO
ｾ COMMON for linking BASIC programs
- LVAR which lists the variables, functions,
and label names of the program together with
their current values
NOLIST and OELREM which can be used to
protect proprietary SAVEd BASIC programs
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Multi-User BASIC Instruction Manual
Introduction
Getting Started
Turn on the terminals, disk drives, and computer.
Set each of the terminals to 9600, 481313, 2400,
1200, 300, 150, or 110 baud. The terminals need
not all be set the same. Place the Multi-User
system diskette in Disk Drive A. Depress the
RETURN key on terminal-l several times.
prompts will be issued for the name of the user,
the date, and the time.
After the time is set, the following prompt is
issued:
place diskette in Drive A and press any key
This provides the option of exchanging the disk in
Drive A before going on.
Prompts are then issued to determine whether or not
diskettes are loaded into the remaining drives in
the system. All files left open on the diskettes
in any of the drives will be closed. This provides
a way to rectify the situation when the computer is
inadvertently reset with files open.
Additional users may then log on the other
terminals.
Log-on for each of these users is accompl ished by
pushing RETURN several times so that the operating
system can detect the baud rate of the terminal. A
prompt will then be issued for the user's name.
Wr i te-protecting di skettes is not necessary wi th
Multi-User BASIC. Write-protected diskettes are
those 8" di sks wi th a notch exposed and those 5"
disks with the notch covered. There is a facility
for write-protecting files instead. See the
PROTECT command.
Backup
It is strongly recommended that a backup disk be
made immediately upon receiving your FDM software
package.
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Multi-User BASIC Instruction Manual
User Protection
User Protection
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Multi-User BASIC Instruction Manual
User Protection
Multi-User BASIC provides several different kinds
of protection for users.
Directory Protection
The operating system maintains directories which
contain information about the files stored on the
disks. In order to protect this information, locks
are provided in the operating system to insure that
a user can complete cer.tain kinds of directory
accesses, once begun, before another user can begin
one.
For example, suppose that after BASIC has begun to
execute aCLOSE file statement for a user, the
operating system interrupts and switches to a
second user. If the second user then attempts to
execute a RENAME file statement, the operating
system will cancel the turn and not allow further
execution time until the CLOSE statement has been
completed ·for the first user.
Protection of File Integrity
There are two different senses in which files can
be safeguarded. Multi-User BASIC has the PROTECT
command
which can be used to specify that'a file
cannot be erased, written to, or read from. This
helps to preserve files from inadvertant miSuse.
There is another way in which files
protected in mul ti-user systems which
than one user to write to the same file.
need to be
allow more
Suppose that two users access a file storing charge
account information for a retail store in the
following sequence.
User-l reads the reco rd fo r accoun t no. 300
and use r-2 al so reads the same! reco rd.
User-l adds a new charge. to the account and
writes the record back to the file.
User-2 makes a correction to the address field
of the account and updates the file.
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Multi-User BASIC Instruction Manual
User Protection
The result is that the charge data that user-l
added to the record is lost because it has been
over-written by user-2. This is called the mutual
exclusion problem.
What is needed is a way to restrict access to
files. This is provided by the OPEN statement. A
file can be opened by a user in several ways:
(W) exclusive permission to write to the
file, but non..-exclusive permission to
read from it, .
(X)
exclusive permission to read and write,
(N) a guarantee that no user will wri te to
the file, and non-exclusive permission
to read, or
(R) non-exclusive permission to read the
file.
The solution to
example above is
for two people to
open for writing.
the problem illustrated by the
automatic since there is no way
simultaneously have the same file
This, however, can present another problem. One
user can have a file open for wri ting for a long
time, locking all others out. A way to minimize
this problem is to write ,the BASIC program so that
the file is opened only for reading (R) while the
user is searching through it. When the user is
actually ready to update the file, the BASIC
program should open it for reading and writing (W
or X) just long enough to re-read the record that
is to be altered (to insure that current data is
being acted upon) and to write the corrected record
back to the file.
In cases where records refer to each other so that
updating one record requires updating the other,
the file must be'open for reading and writing long
enough to re-reao and update both records.
Protection from Deadlock
When a data base includes more than one file,
records iq one file may refer to records in another
file in ｴｨｾ data base.
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Multi-User BASIC Instruction Manual
User Protection
In this case, updating a record in one file may
require updating records in other files also.
Therefore, when a user is ready to update a record,
the BASIC program should open all the files in the
data base for reading and writing (W or X) just
long enough to re-read the record and relevant
cross-referenced records and to update them.
This introduces the potential for a new problem,
however. Suppose that user-l has file-l open for
writing and user-2 has file-2 open for writing, but
both users need both files open for writing to
complete the current operation. This is a
deadlock. Neither user can proceed.
Multi-User BASIC has a feature which can be used to
avoid this dilemma. If a BASIC program
concatenates a series of statements from the
following list, then the directory will be "locked
from the time the first statement in the series
begins execution until a statement which is not in
the list occurs.
OPEN
CLOSE
CREATE
PROTECT
ERASE
This means that after a user has opened the first
file in a list of consecutive files, no other user
can open a file further down in the list even if
the operating system interrupts and switches to
another user.
Deadlock will not occur
includes code such as the
opening of the data base.
base incl udes files named
"file-3".
8
if the BASIC program
following to handle the
We assume that the data
"file-I", "file-2", and

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Multi-User BASIC Instruction Manual
User Protection
10 Integer False, True, Try'again, Error'number
20 Fa1se=0
30 True=Not False
1000 *Open'data'base
1010 On Error Goto Data'base'in'use
1020 Open \1\ "file-I", OW"
1030 Open \2\ "fi1e-2", OW"
1040 Open \3\ ＢｦｩＱ･ＭＳｾＬ OW"
1045 Rem DO NOT INTERSPERSE ANY STATEMENT
1050 Rem AMONG THE THREE LINES ABOVE.
1060 Rem IF WE HAVE REACHED THIS POINT, THEN WE HAVE
1070 Rem SUCCEEDED IN OPENING ALL THE FILES
1080 Rem IN THE DATA BASE.
1090 Rem RESTORE THE NORMAL ERROR HANDLER.
1100 On Error Goto Norma1'error'hand1er
.
1200 *Data'base'in'use
1205 Rem IT IS IMPERATIVE THAT WE TRY TO CLOSE
1210 Rem ALL FILES IN THE DATA BASE, EVEN THOUGH
1220 Rem SOME MAY NOT HAVE BEEN OPENED
1230 Rem AT THE TIME THE ERROR ｏｃｃｕｒｒｅｄｾ
1235 Rem TEMPORARILY MAKE DO'NOTHING, WHICH DOES
1240 Rem NOTHING AT ALL, THE ERROR HANDLER.
1250 Error'number = Sys(3)
1260 On Error Gosub Do'nothing
1270 Close \1\
1280 Close \2\
1290 Close \3\
1300 Rem RESTORE THE ERROR HANDLER
1310 On Error Goto Norma1'error'hand1er
1320 Rem UNLESS THE ERROR WAS 224
1330 Rem (FILE BUSY), DO NOT TRY AGAIN.
1340 Try'again = False
1350 If Error'number = 224 Then Do
1350 Input"Data Base busy. Try again? ",Rep1y$
1360 If Rep1y$(0,0)="y"Then Try'again=True
1365 If Rep1y$(0,0)="Y"Then Try'again=True
1370 Enddo
1380 If Try'again=True Then Goto Open'data'base
1500 *Do'nothing
1510 Return
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Multi-User BASIC Instruction Manual
Operating System Description
Description of the Operating System
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Multi-User BASIC Instruction Manual
operating System Description
Description of the Operating System
The operating system has control of the computer.
When a user logs on, the operating system finds an
empty bank of memory and then enters the user into
the active queue. The users in this queue take
turns executing their programs. Each turn is on
the order of tens of milliseconds duration.
However, if a user requests input or output which
is not ready, the operating system terminates the
user's current turn and does_ not grant another turn
until the input or output is ready.
Terminal input and output are serviced by means of
interrupts. When a key is pushed on the user's
keyboard, the current process in execution is
interrupted long enough for the operating system to
get the character and put it into the user's
terminal buffer. If blocked awaiting this input,
the user would take a place in the active queue.
When a turn comes around again, the user's program
can then fetch the character from the buffer.
Terminal output is handled in a similar manner.
Another function of the operating system is to
coordinate requests for input from and output to
the disks. When a user makes such a request, it is
placed into the disk I/O queue, and the user is
blocked until the request has been serviced.
The requests in the disk queue are ordered by disk
and by track. This minimi zes the motion of the
disk heads required to service the users.
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Multi-User BASIC Instruction Manual
Attributes of Multi-User CDOS
Attributes of Multi-User CD OS
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Multi-User BASIC Instruction Manual
Attributes of Multi-User CDOS
Type-ahead
Since Multi-User CDOS buffers input from the
terminal keyboards, users can enter characters
before the executing program requests them. This
feature, commonly known as II type-ahead II , is often
helpful. When using the Screen Editor, for
example, one can insert a string of characters and
then begin to delete some characters following the
string without having to first wait for the screen
to be upda ted.
In case of error, typing CTRL-U will discard all
the characters which have not already been utilized
by the executing program.
There is a second way of entering characters at the
keyboard before the executing program requires
them. CDOS and many programs which run under CD OS
accept keyboard input one line at a time. The user
types the characters of the line and then
terminates the line with a carriage return. In
Mul t i-Use rCDOS, the 1 i nefeed key may be used
instead of the carriage return key to separate
d i ffe rent input 1 ines sent to the prog ram. The
linefeed is transformed into a carriage return when
it is sent to the executing program. However, none
of the characters are sent to the program until an
actual carriage return is typed. For example, one
could enter the following line followed by a
carriage return.
ERA *.BAKIBATCHISTATIASMB TESTFILE.ABZI
Note that each linefeed is echoed to the terminal
screen as a vertical bar "1". After the carriage
return is typed, each string of characters followed
by a carriage return is sent to CDOS or the
executing program as a separate line. When the
program receives the line, the line is echoed
again. In the current example, the user would then
see (assuming we are using disk drive A):
A.ERA *.BAK
A.BATCH
Batch version 00.05
-STAT
-ASMB
TESTFILE.ABZ
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Multi-User BASIC Instruction Manual
Attributes of Multi-User CDOS
CDOS
Call To Display Job Information
The new CDOS system call 0DFH will return the job
number, terminal number and name of the current
user. To use it call 0005 with 0DFH in the C-
register. The current job number will be returned
in the C-register and the terminal number in the B-
reg ister. These wi 11 be encoded in ASCI Ie If the
job is detached, there will be no terminal number
and an asterisk will be returned in the B-register.
The DE-register containing the address of the user
name in memory. The last ·character of the name is
marked by having its parity bit set.
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Multi-User BASIC Instruction Manual
Multi-User CDOS Commands
Multi-User CDOS Commands
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Multi-User BASIC Instruction Manual
Multi-User CDOS Commands
command: BACKG
This command can be used to place a job in the
background. A background job will only run when
all jobs not in the background are waiting for
input or output.
BATCH is a CD as program which is, for all practical
purposes, the same as the @ command described in
the CDOS instruction manual. A job can be placed
in the background by executing a BATCH file which
includes the BACKG command.as one of its lines. If
this is done, then all of the commands which follow
the BACKG command in the BATCH file will run in the
background. If the command on the last line in the
BATCH file completes execution and return is made
to CDOS, the foreground mode of operation resumes.
For example, entering the following three lines
will cause BASIC to run in the background in the
current job until return is made to CD as by means
of the BASIC command BYE.
A.BATCH
!BACKG
!BAS SORT.SAV
In the above, "A." is the CDOS prompt and "I" is
the BATCH prompt.
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