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LOGIC BLOCK EXPI,ANATIONS
1.
Your
exception
routine
instruction
issued
by
prograIP.
receives
the
OPEN
control
via
an
XCTL
macro-
or
EOV routines of the control
2.
Use the GETMAIN macro-instruction.
The
main
storage
you
obtain
must contain all your work areas, including those used to read in a
label or write a label.
3.
Use the store mUltiple instruction (STM).
4.
Figure
1 in Section I of this chapter provides the information you
need to establish addressability of the DCB address list
and
work
and
control
block
area
for
each DCB defined by the OPEN macro-
instruction.
When you receive control from the EOV routine, general
register
2
contains
the
address
of
the
DCB
for
the oata set and general
register 4 contains the address of the work and control block
area
associated with the DCB.
The
IECDSECT
macro-instruction
shown
in
chapter symbolically defines the fields of
block area (see Figqre 2 in Section I).
the
the
Appendix
work
and
of this
control
You
will also need to address the unit control block (UCB) for the
device on which the tape volume is mounted.
The address of the UCB
may be obtained from the DXDEBUCB field of the
data
extent
block
defined
by
the
IECDS£CT
macro-instruction.
The IEFUCBOB macro-
instruction (see Appendix) defines the fields of the
unit
control
block.
5.
Bit
configurations
in
the
byte addressed
by
JFCBMASK+5 incicate
whether label checks or density checks have occurred, and,
in
the
case
of
a
label
check, the condition that caused the check.
At
this point, you test bits 0 and 3.
If Eit\er
cit
is
set
to
1,
processing is required.
6.
The
field
JFCBMASK
is defined by the IECDSECT macro-instruction.
Bit settings in the byte at JFCBMASK+5 are defined as:
Bits
o
1
2
3
4-7
setting
1
1
1
1
Meaning
Label check has occurred.
Standard
label
(SL)
specified;
no
label/
nonstandard label on mounted volume.
No label (NL) or nonstandard label (NSL) speci-
fied; standard label on mounted volume.
Density check has occurred.
Reserved for future use.
If your installation
supports
a
protection
and
scheme
involving
nonstandard
labels, and/or you
retention date and protection checking on standard
incorporate code in your editor routines to
check
and retention date expiration.
retention
date
want to maintain
labels, you must
for
protEcticn
If
checking
is
desired,
you must, at this point, read the first
record and determine the label type.
To perform t:he I/O operation,
move
your
CCWs
into
the
channel
progran;
field
of
the
work and control tlock area.
The synibolic
name for the first entry in this field is
DXCCW.
Then
issue
an
EXCP
macro-instruction
specifying
trle
address
of
the
control
Label Processing Routines
61
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