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INPUT/OUTPUT
FUNCTIONS
25.3 -- Device Independent IIO Functions
"
---....
Th e norma 1
seq,uenc e'
fo,..
call
i
ng
th e
I/O
func t ions.
.J
regardless of the device being used, ·is:
· RESRV
· OPEN
· QETRC
.PUTRC
· CLOSE
· RELES'
Reserve a device
Open a rile
Read a record
Write a record
Close a .pile
Release a device
The
reading/writing
of
T'ecoT'dsl
of
COUT'seJ
may
not
necessarily be used Tor the same device.
Once
the
file
is
open,
the record
I/O
Tunctions can be called as
man~
times as
requi red.
Use of the device independent I/O functions
will
cause
the
diskette cont1'oller variables below location $0020 to be
changed, regardless
or
whether or not a
diskette
device
is
being used for a given I/O process.
In
orde,..
to fully desc1'ibe each device independent
liD
function,
the structure of the lOeB must first be
described.
In the description oT the errors that can be returned by each
Tunction;
the names
or
the
system
s~mbols
from
the
MDOS
equate
Tile are used.
These are noted in the description of
the status byte
Or
the IOCB, section 25.3.1. 1.
A summary
or
all possible input parameters that are required
by
the twelve
diffe~ent
modes in which an IOCB can be used £s contained
in
Appendix K.
25.3.1 I/O Control Block -- IOCB
The
device
independent I/O functions are parameterized
through the IOCB.
The I/O functions,
in turn,
interface to a
device
driver
through
another
table,
the
Cont~oller
Descriptor Block or CDS (see section
26~2).
It is
only
the
devi£e driver which interfaces
di~ectly
to the device.
The
IOCB
is a table of flags',
bu-ffer pointers, and other
information which is maintained by the
calling
prog~am
fo~
the
duration
of
the I/O accesses that are to be performed.
Some of the entries in the IOCB must be
initialized
by
the
program before calling an I/O function.
Other
ent~ies
of the
IOCB
are
initialized
and
changed
by
the
I/O
functions
themselves.
The
entries
of
the
IOCB must not be changed
between I/O accesses unless
specifically
indicated
in
the
ENTRY
PARAMETERS section of each lID function's description.
The IOCB has the following format:
I
.....
/
Page
25-14
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