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Section A:
System interface
A.7.2. Program header
If
a program contains function modules,
it is preceded by
a
256-byte
header
describing
where the modules are located within the
file.
The
header may additionally bear information on system variables to be chan-
ged;
the
loader does the appropriate assignments after loading is
fi-
nished.
But the header may as well be empty,
in which case the
loader
is
11
tricked
out
11
and does not remove itself from memory.
It
it
then
possible
to call the loader from the program using system function
59.
On
the
other hand,
a program may consist mer.ely of a header
and
the
associated
function modules.
When such a program file is
loaded,
the
command
interpreter
suppresses the search for inactive modules on
its
next
invocation.
It becomes thus possible to keep modules
with
their
termination
flag set.
The subsequent program may use these
functions,
they are removed only after the program run being terminated.
System call 60 has been defined to communicate with modules.
This
call
has
several
parameters which can be tested by all modules
loaded.
If
none of them shows any reaction, the EOS system kernel returns 0FFH in A
and
00H
in
H.
Let
us do a view on the header.
It begins with a 16-byte
organization
area:
DB
0C9H
Header designation
ow
CODESIZE
length of program code
DB
0C9H,0,0
jump to a parameter setting routine
DS
9
-
reserved
-
DB
NFUNC
number of function modules (0-15)
The organization area is followed by up to 15 entries,
one per function
module linked:
ow
OFFSET
offset of module
in
file
ow
CODESIZE
Module length
ow
EXTRA
RAM required additionally
DB
'NAME
B
bytes module name
ow
0
-
reserved
-
Non-existing entries are filled with zeros.
EOS System manual
Daeumling & Zimmermann
Page 15
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