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iAPX
432
Interface
Processor
Architecture
Reference
Manual
DIRECl'ICN
The
direction
attribute
specifies
whether
the
windowed
object
may
be
read,
written,
both
read
and
written,
or
neither
read
nor
written.
When
the
window
is
opened
the
IP
checks
the
requested
direction
attribute
with
the
access
rights
granted
by
the
object
reference.
The
access
rights
requested
in
the
direction
attribute
must be
equal
to,
or
logically
less
than,
the
rights
granted
by
the
object
reference.
For example,
if
the
object
reference
indicates
t~at
the
object
may
be
read,
then
the
permi.ssable
di.rection
attributes
are
read,
or
neither
read
nor
write~
requesting
the
ability
to
write,
or
to
read
and
write
the
object
would
be
illegal.
Orx::e
a window has been
successfully
opened,
the
IP
checks
every
subsequent
subrange
address
reference
to
insure
that
it
conforms
to
the
direction
attribute,
otherwise
an
active
window
fault
occurs.
(The
IP's
read/write
line
identifies
the
type
of
access
being
attenpted.
)
This
perroi
ts
the
IP
controller
to
open a window
for
reading
with
the
assurance
that
a mis-programmed
DMA
controller
will
not
be
able
to
write
into
it.
TRANSFER
STATUS
An open
window
may
take
one
of
four
states:
o
transfer
in
progress~
o
transfer
terminated
by
fault~
o
transfer
terminated
by
count
runout~
(block
mode
only)
o
transfer
termination
forced~
(block
mode
only) •
The
IP
controller
will
open a winnow
with
the
status
attribute
set
for
"in
progress".
If
the
IP
detects
a
fault
asscx::iated
with
an
active
window,
it
will
change
the
status
attribute
to
"terminated
by
fault".
A randan node window which
is
closed
(set
invalid)
with
a
transfer
status
of
"in
progress"
is
considered
to
have
terminated
normally
since
there
is
no means
for
an
IP
to
predict
when
a
randan
mode
transfer
is
finished.
The remaining
two
states
are
associated
with
window
0
block
IOOde
transfers
only
and
are
described
in
section
3-3.
-
TRANSFER
MJDE
Windows
0 and 1 have
al
ternate
transfer
nn:1es
that
may
be
selected
by
setting
the
mode
attribute
when
the
window
is
opened.
Window
0
may
be
opened
in
block
TOC>de,
which permi
ts
buffered
high
speed
transfers
of
contiguous
blocks
of
data~
this
is
described
in
section
3-
3.
Window
1
may
be opened
onto
the
i.nterconnect
address
space
~
this
is
described
in
section
3-4.
The
transfer
mode
attribute
has
3-6