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The
Interface
Processor
windCM
mechanism
provides
the
Per
ipheral
Subsystem
with
protected
access
to
the
contents
of
objects
located
in
the
432
system.
There
are
five
windows,
labeled
0-4.
Each
windCM
can
be
used
to
access
one
(single
segment)
object.
To
prevent
the
possible
manipulation
of
access
descriptors
as
ordinary
data
and
corruption
of
the
protection
mechanisms,
the
windCMed
object
must
be
of
base
type
data
segment. Access
descr.iptors,
the
basis
for
the
432
protection
system,
may
he
manipulated
only
by
IP
operations
supplied
by
the
IP
function
request
facil:i.ty.
These
operations
are
described
in
the
next
chapter.
All
IP
windows
are
sfmilar
in
that
they
support
the
transfer
of
~ata
across
the
subsystem
boundary;
this
chapter
first
describes
the
characteristics
corrmon
to
all
windows. The
first
section
covers
the
attributes
that
define
windCMs;
these
are
gener.ally
specified
when
the
windCM
:i.s
opened
with
the
ALTER
MAP
AND
SELECl'
MTA
SEG1ENT
function.
The second
section
descrlbes
the
operation
of
a
data
transfer
through
a
windCM
that
has
been
defined
with
a
given
set
of
attributes.
Three
of
the
windCMs
have
special
capabili
ties;
these
are
covered
after
the
basic
properties
of
all
windows have
been
descr
ibed
II
WindCM
0
may
be
used
to
perform
high
speed
block
transfers.
WindCM
1
may
be
opened
onto
the
processor-memory
interconnect
address
space
and
thus
provide
access
to
interconnect
objects.
Window
4-the
control
window--is
dedicated
to
providing
the
data
path
for
the
Interface
Processor
function
facility;
this
is
covered
in
chapter
4.
Throughout
this
chapter
conditions
for
correct
use
of
windCMs
are
described.
When
any
of
these
conditions
are
violated,
the
Interface
Processor
detects
a
fault.
The
!pI
s
fault
detection,
reporting
and
handling
facilities
are
covered
in
chapter
6.
3-1