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iAPX
432
Interface
Processor
Architecture
Reference
Manual
FUNCl'IOO
OPERANDS
An
Interface
Processor
function
may
require
fran
zero
to
seven
<DubIe-byte
operands.
The
IP
controller
specifies
a
function's
operands
by
writing
values
into
locations
of
the
operands
field
in
the
function
request
area.
The
first
operarrl
goes
in
the
lcwest-addressed
location
of
the
field
and
the
remaining
operands
are
written
to
successively
higher-addressed
locations
(in
some
cases,
one
or
nore
operand
slots
may
be
reserved
and
are
skipped
over)
• Each opcode
implicitly
identifies
the
number
of
operands
required,
so
unused
high~rder
locations
in
the
operands
field
need
not
be
initialized.
See
Appendix B
for
the
function
surrmary.
Interface
processor
functions
accept
three
types
of
operands
as
illustrated
in
figure
4-4;
all
operarrl
types
are
stored
as
<DubIe-bytes.
A
short
ordinal
is
a a
16-bit
unsigned
binary
integer
(range
0-65,
535) •
This
type
of
operarrl
is
typically
used
to
specify
a
length,
a
displacement,
an
index,
etc.
For
example, when
the
ALTER
MAP
AND
SELECr
DATA
SEGmNT
function
is
used
to
open a windGl,
it
requires
a
short
ordinal
operand
that
specifies
the
size
of
the
subrange.
A
bit
field
is
a
str
ing
of
16
bits
that
is
divided
into
a number
of
subfields.
The
length,
position
am
definition
of
each
subfield
varies
according
to
the
function.
Subfields
in
a
bit
field
operand
to
the
AL'IER
MAP
AND
SELECI'
DATA
SEG1ENT
function,
for
example,
specify
transfer
node,
rnennry
overlay,
etc.
An
object
selector
identifies
an
access
descriptor
for
an
object
that
is
the
function's
actual
operand.
Figure
4-5
illustrates
how
the
IP
uses
an
object
selector
operand
to
obtain
access
to
an
object.
The
lcw-order
subfield
of
the
object
selector
identifies
one
of
the
four
currently
entered
access
segments
associated
with
the
selected
context.
The
high~rdersubfield
indexes
one
of
the
access
descr
iptors
in
the
entered
access
segment.
The
selected
access
descriptor
refers,
via
the
object
table,
to
the
object
that
is
the
actual
function
oper
and.
This
three-level
address
developnent
is
identical
to
GOP
addressing.
Note
that
the
IP
also
performs
the
standard
432
type,
rights
and bounds
checking
as
it
develops
the
object's
physical
address
fram
the
object
selector.
4-6