Method of Operation
This section describes the execution of the
virtual disk initialization (IBCDASDI) Frogram and shows the processing associated
with: • Initializing virtual disks • Assigning alternate tracks.
Figure 1-2 shows the relationship of the
diagrams.
Diagram 1-2 Initializing a Virtual Disk
Diagram 1-' Overview of Virtual Disk Initialization 1-1 describes the OI the virtual
initialization program.
tiagram 1-2 shows
initialized.
hew tracks
majer
disk
are
Diagram 1-3 shows how alternate tracks
are assigned.
Diagram 1-3
Assigning Alternate Tracks
Figure 1-1. Key to Virtual Disk Initialization Method of Operation Diagrams Chapter 1. IBCD1SDI--The Virtual Disk Initializaticn program 5

Input • CP •••••• ,'",,' moch'oe 0 console
Control
Cards
Notes Module
1 The general registers are cleared and IBCDASDI the PSWs are initialized. The SEREP flags in the machine check old PSW are
set to X'FF' and the program enters
a wait state with X'FFFF' in the
address field of the PSW. An attention interrupt identifies the
virtual machine console and the input
statement is read. The control cards
may be read from a 1402, 1442, 2400, 2501, 2520, 2540, 3410, 3420, or 3505 input device.
2 Next, the CLRSCAN routine links IBCDASDI to the control statements scan routine
at RDCARD. RDCARD returns a
pointer to a field and the length of
the field in registers SCANADR and
LENGTH, respectively, and an indica-
tion of the field type in location SWITCHRD. SWITCHRD is a one-
byte switch with the following settings: Meaning
X'50' Control statement error
X'40' Bypass
X'10' First control statement
has been read
x'oa' Operator found
X'04' Keyword found
X'02' Parameter found
Processing Output IPL the device containing
the IBCDASDI module.
2 Analyze the control cards.
3 If specified, initialize
the disk. (See Diagram 1-2 for details.)
4 If specified, get an
alternate track. I}8 I Initialized virtual disk with (See Diagram 1-3 for
details.) I .... CP Label Ref Notes
START 3 The initialization routine is entered
at VOLCHK if the volume label is to
be checked and at GEN5E if the
volume label is not to be checked.
Initialization starts with the I NT AL T
routine. CKINPUl 4 Control is passed to the GETAL TYZ routine if an alternate track is to be
assigned. If volume label checking is
requested, the CKVOLLBL routine
does the checking. Assignment of alternate tracks starts with the
GETALTX routine. CLRSCAN alternate tracks assigned.
Module Label IBCDASDI VOLCHK
GEN5E IBCDASDI GETALTYZ Diagram 1-1. Overview of Virtual Disk Initialization
6 IBM VM/370 Service Routines Proqra. Logic
Ref