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WINOOWS
3-
2.
W1NIXM
OPERATI(l\J
This
section
descr
ibes
the
IP'
s
response
to
an
address
reference
that
falls
into
the
windowed
subrange
of
an
open
windGl. The
discussion
covers
random
mode
transfers
to
and from
ordinary
memory-based
objects;
the
special
cases
of
block
mode,
interconnect
objects
and
function
requests
are
covered
in
subsequent
sections.
ADDRESS
RECDGNITI(l\J
The
Interface
Processor
m:mitors
all
Peripheral
Subsystem
address
references
that
fall
into
its
range.
It
compares
each
address
presented
on
the
Peripheral
Subsystem
bus
to
the
subranges
of
all
open windows.
If
an
address
falls
into
a
subrange,
the
IP
recognizes
the
reference
and
responds
as
described
belOil.
If
the
address
does
not
fall
into
an
active
subrange,
the
IP
ignores
the
reference
and
does
not
respond.
CCNSISrrENCY
CHID<
Given
that
it
has
recognized
an
address
reference,
the
IP
checks
it
for
consistency
before
performing
the
actual
transfer.
There
is
a
series
of
these
checks
which
are
equivalent
to
the
steps
carried
out
by a
GOP
when
an
instruction
attempts
to
access
data
in
an
obj
ect.
Although
they
are
described
here
as
a
sequence,
the
hardware
is
able
to
perform
same
of
the
checks
in
parallel.
The
IP
insures
that
the
transfer
direction
(as
indicated
by
its
read/write
line)
is
consistent
with
the
windOil's
direction
attribute.
The
IP
computes
the
PS
transfer
displacement,
that
is,
the
position
of
the
item
(byte
or
double-byte)
relative
to
the
base
address
of
the
PS
subrange.
The
visible
object
length
is
the
difference
between
the
length
of
the
object
am
its
base
displacement
(see
Figure
3-2).
The
transfer
displacement
rust
be
less
than
or
equal
to
the
visible
obj
ect
length.
The
sum
of
the
physical
base
address
and
the
transfer
displacement
rust
be
less
than
the
largest
physical
432 menory
address
(224_
1
).
(A
rremory
bounds
error
would
indicate
erroneous
information
in
the
object
table.)
If
any
of
these
checks
fails,
the
IP
detects
a
fault
and
does
not
perform
the
transfer.
Figure
3-2
illustrates
the
constraints
which
the
IP
applies
when
the
consistency
check
is
performed.
Several
examples
of
valid
mappings
of
window
onto
objects
are
shown
in
Figure
3-3.
3-9