Filter
Top Products
iAPx
432
Interface
Processor
Architecture
Reference
Manual
Object
Selectors
An
object
selector
identifies
an
object
by
specifying
an
access
descriptor
contained
in
one
of
the
four
entry
access
segments. The
object
selector
oonsists
of
a
double
byte
quantity
composed
of
two
fields:
1.
The low
order
two
bits
of
the
object
selector
specify
which
entry
access
segment
holds
the
desired
access
descr
iptor
and
are
(xiled
as
follows:
00
-
Entry
Access Segment 0 (Context Access Segment)
01
-
Entry
Access Segment 1
10
-
Entry
Access Segment 2
11
-
Entry
Access Segment 3
2. The
high
order
14
bits
represent
a
scaled
index
i.nto
the
specified
entry
access
segment.
An
object
selector
allows
access
to
any
of
the
16,384
access
descriptors
from each
of
the
4
entry
access
segments.
can
potentially
reference
65,536
(2
16
)
objects
directly.
Enter
ing
an Access Segment
The
instruction
ENTER
ACCESS
SEGmNT
allows
the
I/O
oontroller
software
to
enter
a
given
access
segment
into
Entry
Access Segment
1,
2,
or
3.
ENTER
AOCESS
SEGmNT
requires
two
operands:
o An
access
descr
iptor
for
the
access
segment
to
be
entered
into
EASl,
EAS2,
or
EAS3,
and
o
An
unsigned
integer
value
designating
the
destination
entry
access
segment, which must
be
1,
2,
or
3.
~ntering
the
Global
Access Segment
Each
IP
process
maintains
a
global
access
segment which
is
always
accessible
to
the
I/O
controller
via
the
ENTER
GLCBAL
ACCESS
SEGMENT
function.
Imnediate
entry
of
the
global
access
segment
allows
an
I/O
controller
to
gain
access
to
the
set
of
process
globals.
The
I/O
oontroller
needs
only
to
specify
which
of
the
three
available
entry
access
segments
is
tq
be used
when
requesting
this
function.
2-12