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iAPX
432
Interface
Processor
Architecture
Reference
Manual
It
is
~rtant
to
note
that
both
the
window and
function
facilities
utilize
and
strictly
enforce
the
standard
432
addressing
and
protection
systems.
Thus, a window
provides
protected
access
to
an
object,
and a
function
provides
a
E.rotected
way
for
Peripheral
Subsystem
software
to
interact
with
the
432
system.
1-2.
BASIC
I/O
MODEL
As
figure
1-2
illustrates,
input/output
operations
in
a 432
system
are
based
on
the
notion
of
passing
messages between 432 system
processes
and
device
tasks
located
in
a
Peripheral
Subsystem.
In
this
manual, a
device
task
is
consi.dered
to
be
the
hardware and
software
in
the
Peripheral
Subsystem which
is
responsible
for
managing an
I/O
device.
An
I/O
device
is
considered
to
be
either
a
consumer
or
producer
of
data.
Thus an
I/O
device
may
be
a
real
device
(e.
9
.,
a
terminal),
a
file,
or
a
pseudo-device
(e.
g.,
a
spc:x>ler).
A message
sent
from a
GOP
process
which
requests
I/O
service
contains
information
that
describes
the
requested
operation
(e.g.,
"read
file
XYZ"). The
device
task
interprets
the
message and
carries
out
the
operation.
If
an
operation
generates
input
data,
the
device
task
returns
the
data
as
a message
to
the
originating
process.
The
device
task
may
also
return
a message
to
posi
ti
vel
y
acknowledge
completion
of
a
request.
A
very
general
and
very
powerful
mechanism
for
passing
messages
between
processes
is
inherent
in
the
432
architecture.
A
given
Peripheral
Subsystem may,
or
may
not,
have
its
own message
facility,
but
in
any
case,
such a
facility
will
not
be
directly
compatible
with
the
432's.
By
inter:PQsing a
Peripheral
Subsystem
interface
at
the
subsystem boundary,
the
standard
432
interprocess
comnunication
system
can
be
made
compatible
with
any
device
task
(see
figure
1-3).
1-4