.MH "Appendix C -- Requirements for Subsystem Programs"
This appendix gives the technical specifications of requirements
for programs that run under the Subsystem.  It is included to
allow non-Ratfor programs to run under the Subsystem.
.sp
.tc \
.ta 4
.in +7
.ti -7
.ul
32S and 16S addressing modes
.sp
.ti -3
-\There is no support for the execution of these addressing
modes.
.sp 2
.ti -7
.ul
64R & 32R addressing modes
.sp
.ti -3
-\The 64R mode library routines cannot access the Subsystem common
areas, so 32R and 64R mode programs cannot execute under the
[cc]mc |
Subsystem.
[cc]mc
.sp 2
.ti -7
.ul
64V addressing mode
.sp
.ti -3
-\Segments '4040 and '4041 may not be disturbed.
.sp
.ti -3
-\When a Subsystem program is executed, the stack is already
constructed in segment '4041.  However, the executing program
may rebuild it if desired.
.sp
.ti -3
-\Programs that use native i/o routines must inform their native
i/o routines of the Subsystem (if they wish to take advantage
of Subsystem i/o) by calling the proper initialization routines,
i.e. 'init$f' for Fortran 66 and Fortran 77, 'init$p' for Pascal
and 'init$plg' for PL/I G.
.sp
.ti -3
-\The program must terminate with a call to the Subsystem
routine 'swt' at the end of its execution
or its main program must return to its caller.
A
[bf stop]
statement in Ratfor will be transformed into a call to
'swt'.
.sp
.ti -3
-\The program must not tamper with any file units already open
by the Subsystem.  It should always use a Subsystem or Primos
call to obtain an unused file unit.
.sp
.ti -3
-\The program must be in a P300 format runfile or a SEG-compatible
segment directory.
.sp
.ti -3
-\If the program is in a P300 format runfile,
it must have been loaded by the modified version
of the segmented loader, 'swtseg', or the entry control block
for the main program must be at location '1000 in segment '4000.
.sp
.ti -3
-\The runfile must not expect any segment other than '4000
to be initialized before execution, unless it is loaded from
a SEG-compatible segment directory.
.sp
.ti -3
-\The default load sequence produced by 'ld' will correctly
link programs requiring up to 64K words of procedure (code)
and linkage (initialized local data) frames.  Up to 27 64K
word segments may be used for uninitialized common blocks.
Up to 64K words of local data may be allocated on the
stack.  Programs loaded from SEG-compatible segment directories
may be as large as the operating system permits, as long as they
do not modify segments '4040 and '4041.
.sp 2
.ul
.ti -7
32I addressing mode
.sp
.ti -3
-\Programs in 32I mode may be executed under the Subsystem
subject to the same constraints as
64V mode programs.
.in -7