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APPENDIX
A
SYSTEM OBJECT STRUCTURES
The
object
structures
of
Interface
Processors
are
described
belOil.
The
only
objects
structures
described
are
for
those
whose form
or
interpretation
differ
fran
GOP
object
structures.
Note
that
the
values
found
in
the
length
fields
in
the
var
ious
objects
descr
ibed
belOil
are
encoded
as
"actual
length
minus 1"
in
bytes.
Also
note
that
the
object
indices
refered
to
below
are
of
the
same
format
as
object
selectors
with
the
entry
access
segment
index
subfield
uninterpreted.
The
displacement
subfield
is
interpreted
as
an
index
into
the
associated
domain
access
segment.
A-I.
CONTEXT
CEJECI'S
In
the
Trost
general
terms,
contexts
for
Interface
Processors
and
General
Data
Processors
serve
the
same
purpose.
They
are
used
to
represent
an
access
environment
in
which
process
execution
can
take
place.
On
closer
inspection,
hCMever,
the
differences
are
significant.
For example,
with
Interface
Processors
there
is
no
concept
of
a
sequential
instruction
stream.
Instead
the
only
instructions
executed
by
Interface
Processors
are
functions
requested,
one
at
a t:ime,
by
software
executing
on
the
associated
Attached
Processor.
At
a mundane
level,
this
means
that
Interface
Processor
contexts
need
not
provide
access
to
instruction
segments
or
operand
stacks.
More
significantly,
without
a
sequential
instruction
stream
there
are
no
concepts
of
intracontext
or
intercontext
control
flow
either.
This
results
in
the
binding
between
Interface
Processor
processes
and
contexts
being
static.
In
fact,
context
access
and
data
segments
are
refinements
of
the
corresponding
process
access
and
data
segments
respectively.
Given
these
differences,
an
Interface
Processor
context
represents
the
access
environment
available
within
the
432
system
to
the
logical
process
being
executed
on
the
logical
processor
comprised
of
the
Interface
Processor
and
the
associated
Attached
Processor.
The
operators
provided
by
the
Attached
Processor
affect
the
contents
of
data
segments
in
this
environment
via
the
address
mapping
facility
of
the
Interface
Processor.
The
operators
provided
by
the
Interface
Processor
affect
this
environment
via
the
function
request
facility
of
the
Interface
Processor.
A-I