IBM System/360 System Programmer's Guide

information for the label identifier (VOLIABI), the label sequence
number (VOLNO), and the volume serial number (VOLSERNO) fields, and
record the balance of the label as blanks.
You enter VOL in the label identifier field, a 1 in the label
sequence number field, and a six character serial number in the
volume serial number field. Note: To ensure that two or more tape
volumes carrying the same serial number are not produced, write to
the operator at this point for assignment of a serial number.
Data set header labels 1 and 2 are constructed by the OPEN or EOV
routines after control is returned to them.
Note: If you desire, at this point, you may change the control
block settings to conform to the characteristics of the tape volume
mounted, i.e., reset the label type field in the JFCB to conform
with the type of label on the volume mounted, and change the
density field in the DCB to the density of the tape mounted.
17. The syrrbolic name for the volume serial number field in the unit
control block is SRTEVOLI. The "mount switch" is the high order
bit of the field named SRTEDMCT in the unit control block. These
fields are defined by the IEFUCBOB macro-instruction. Exclusive
OR(XC) the SRTEVOLI field with itself. OR(OI) the SRTEDMCT field
with X'80'.
18. When receiving control from the OPEN routine, you must process the
entire DCB list. The last entry in the list can be recognized by a
"1" in bit 0 of the first byte in the entry.
19. You increment the pointer to the DCB address list by four bytes.
You must also increment the pointer to the work and control block
area for each DCB. You increment this pointer by 8 bytes.
20. Use the load multiple instruction (LM). Note: When preparing to
return to EOV you must insert a hexadecimal 03 in Register 8.
21. Use the FREEMAIN macro-instruction.
22. Return control to the OPEN or EOV routines via an XCTL macro-
instruction, specifying the module to be given control as follows:
Return From
OMODVOL1
EMODVOLl
To Module
IGG0190A (OPEN)
IGG0550P (EOV)
Note: OPEN and EOV will rewind the volume upon receiving control from
OMODVOL1 or EMODVOL1.
Return is via the XCTL macro-instruction (E-form). See Section 1
Explanation of Logic Blocks -- item 22.
INSERTING YOUR LABEL EDITOR ROUTINES INTO THE CONTROL PROGRAM
You insert your editor routines into the control program after system
generation by making a linkage editor run against the system library
named SYS1.SVCLIB. You will be replacing the IBM supplied editor
routines OMODVOLl and/or EMODVOLl with your routines.
Label Processing Routines 63

IBM System/360 Specifications

General

Brand	IBM
Model	System/360
Category	Desktop
Language	English