IBM System/360 System Programmer's Guide

is entered again after the control program has checked the initial label
and positioned the tape.
You need not: reposition the tape before returning control to the
control program.
Output Trailer Label Routines
An output trailer label routine is brought into main storage when
either the EOV or CLOSE routine is executed. When your routine receives
control, the tape will have been positioned at the interrecora gap
following the last data set record that was written. After you have
written the tape mark and label, you need not reposition the tape before
returning control to the control program.
The output trailer label routine is also brought into main storage
when input data sets are closed. This allows ycu to position the tapes
if necessary.
Programming Conventions
This section describes the conventions to be followed when writing
your routines.
• Size of the routine - Nonstandard label processing routines are not
limited in size. However, if the size of such a routine exceeds
1024 bytes, you must divide the routine into load modules, each of
which is 1024 bytes or less. To pass control between load modules,
you must use the XCTL macro-instruction.
• Design of the routine - Nonstandard label processing routines must
be reenterable. Relocatable address constants cannot be used in
coding these routines or in coding any channel command words (CC~)
to be used in the routine; nor can macro-instructions be used whose
expansions contain relocatable address constants.
• Register usa(~ - The contents of registers 2 through 14 must be
saved when your routine receives control from the control progran,.
The contents of these registers must be restored before your routine
returns control.
• Entry Point of the routine - The entry point of the routine must be
the first byte of the load module, and must be on a double-word
boundary.
• Exit from the routine - The XCTL roacro-instruction (E-form) must be
used to exit from your routine and return control to a specific
cont"!:'ol program module. These modules differ depending both upon
the control program routine from which control was received, and the
type of label processing being perforrred.
Module names are shown below for each control program routine and
for each type of label processing routine.
Label Processing Routine
Input Header
Input Trailer
Output Header
output Trailer
Control Program Routine
OPEN
EOV
EOV
OPEN
EOV
EOV
CLOSE
Module Name
IGG0190B
IGG0550D
IGG0550B
IGG0190R
IGG0550H
IGGG550F
IGG0200B
Label Processing Routines 45

IBM System/360 Specifications

General

Brand	IBM
Model	System/360
Category	Desktop
Language	English