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INPUT/OUTPUT FUNCTIONS
25.3 --
Device Independent
I/O
Functions
any
aT
the
I/O
runctions
are
invoked.
IOCSBE
must be
configured to contain the address
Or
the
last
byte
Or
a
sector
buffer that is exactly large enough to accommodate an
integral number or 128-byte sectors.
An
error
will occur
ir
the
size
or
the sector buffer described by IOCSBS and lOeSDE
is not correct.
SpeciFically}
the
following
relationship
must be true:
I
OCSBE-IOCSBS+
1
--------------- =
INTEGER (Maximum
#
of Sectors)
128
IoeSBE
~ill
not
be altered by any or the IIO Tunctions.
25.30
L 21 IOeSE! --
Internal buffer pointer
This two-byte rield of the IOCB applies only to diskette
I/O.
IOeSEI
is used
to
indicate the end or valid data within
sector buffers.
Since partial buffers (an
integ~al
number
of
sectors less than or equal to the maximum sector buffer size)
may
be
read
or
writtenJ
IOCSBI is used to locate the last
valid data byte within
a
sector buffer.
rOeSB!
is initialized and changed
by
the
lID
runctions.
The
contents
Or
IOeSBI
must not be changed by the calling
program aTter
a
file has been opened when
using
the
record
IIO
functions;
however,
when using logical sector
1/0,
the
contents or IOCSBl may be changed.
The value OT lOeSBI
will
always
be
less. than
or equal to the value
oT
IOeSBE.
The
following relationship
must
always be true:
IOCSBI-IOCSBS+l
--------------- =
INTEGER (Actual
#
OT Sectors)
128
25.3.2
Reserve a device --
.RESRV
The
.RESRV
system
function
links
the
appropriate
controller
descriptor
block
(CDS) to the calling program's
IOCB.
The .RESRV function must be called before any other
or
the device independent
liD
functions can be invoked.
Section
26.2.4 should be consulted ror a description or the impact on
the .RESRV call and the IOCB when using non-standard devices.
ENTRY PARAMETERS:
x
=
The
address of an IOCB.
IaeGOW
must
contain
one
generiC device names:
DK,
or
LP.
the valid
CP,
CR,
IOCLUN
must
contain
the
logical
unit
number
Or
the device to be
reserved.
Page
25-32
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