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SYSTEM
DESCRIPTION
24.8 -- System Function Calls
Chapte~s
2S and 27 contain the detailed
ent~y
parameters
and
exit conditions
TO~
all MDOS system functions.
Some
system
runctions may not be able to
pe~fo~m
their
expected action.
These functions will
~etu~n
an
indication
oT
whether
a
normal
return or an abnormal return is being
made.
This condition is
alwa~s
passed back in the
processor
status (condition code) register.
In addition, a status byte
may be returned in on@ of the parameter tables or registers.
Some of the
more
complex
system
functions
involving
input
or output can encounter ratal error conditions as well
as non-fatal error conditions.
Fatal errors suggest that the
program
is
hopelessly
confused.
In these cases, the only
logical action is to display what the problem
app~ars
to
be
and
to
re-enter
the
MDOS
command interpreter.
Non-fatal
errors can include such things
as
illegal
record
Tormats,
checksum
er'T'OT'S, rile protection violation,
lack
oT
space on
the diskette: etc.
Such conditions are noted and returned to
the
calling
program.
In
these
instances,
it
is
the
responsibility of the calling program to identify the
source
of the error and decide what the course or action should be.
24.9 MDOS Equate File
With
each
MDOS
system
diskette comes a file,
EGU.SAj
known as the MOOS equate file.
The MDOS equate file contains
the
deTinitions
of
all
symbols
that
are required
b~
the
resident MDOS and all of the MOOS commands.
Not all
or
these
symbols
will
be
required
by
the useri however,
the .pile is
left as is to make it as useful as possible.
The MDOS equate file contains the Tollowing definitions.
The
sequence
of
the
d'escT'iptions more or less rollows the
sequence of the file
from
beginning
to
end.
Four
mac~o
definitions
aT'e
found
at
the beginning of the MOOS equate
file that are useful to the user.
Macro Name
Function
SKIP2
To be used as
an
i
nstruc ti on.
Th
e
SKIPl
effect
or
the
instT'uction
is
to
execute a
bT'anch
to
location
*+3.
The
"*11
rereT's to the address oT the
branch
instruction.
The
condition
codes
are
changed
as
in
a
GFX
instruction;
however,
this
branch
instruction requires only one byte OT
memory.
To be used as
an
inst~uction.
The
effect
oT
the
instruction
is
to
Page
24-25
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