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OiAPTER 4
FONcrIOOS
This
chapter
describes
the
common
facility
that
supports
the
execution
of
all
Interface
Processor
functions.
The
first
section
shows
hCM
windCM
4
is
used
to
provide
access
to
the
facility.
The
next
section
explains
how a
function
is
requested
by
writing
operands and an
o~""Ode
through
the
windCM.
The
last
two
sections
describe
how
the
IP
executes
a
requested
function
and
returns
status
infonmation upon campletion
of
the
operation.
4-1.
FUNCrIOO
FACILITY
INTERFACE
Management
of
the
IP
function
facility
centers
on
the
function
request
area
of
the
processor
data
segment (see
figure
4-1).
Both
the
I/O
controller
software
and
the
Interface
Processor
itself
update and
use
the
infonmation recorded
in
this
area
via
the
control
window.
Briefly,
the
IP
records
the
status
of
the
function
request
facility
in
the
function
state
field;
the
I/O
controller
may
obtain
status
information
by
reading
this
field.
The
IP
controller
requests
execution
of
a
function
by
writing
operands and an
identifiying
opcode
into
the
function
request
area,
and
the
IP
reads
these
fields
to
obtain
the
infonmation
it
needs
to
execute
the
function.
Finally,
the
execution
of
same
functions
produces a
value
which
the
IP
records
in
the
return-value
field,
where
the
IP
controller
can
inspect
it.
Upon
completion
of
any
function,
the
IP
updates
the
status
infonmation
am
interrupts
its
Attached
Processor.
If
desired,
successful
function
completion
interrupts
can be
disabled,
thereby
allowing
only
interrupts
for
unsuccessful
completion
to
reach
the
AP.
In
logical
mode,
the
control
window
(window
4)
is
permanently opened
onto
the
processor
data
segment and
its
mapping cannot be changed by
an
ALTERMAP
function
request.
By
reading and
wr
i
ting
the
corresponding
PS
memory
subrange
locations,
the
IP
controller
obtains
access
to
fields
in
the
function
request
area
located
in
432
memory.
Notice
that
this
interface
mechanism
is
similar
to
a
conventional
memory-mapped
peripheral
device
controller;
the
function
request
area
fields
are
read and
written
like
command,
data
and
status
registers.
Figure
4-2
illustrates
the
effect
of
executing a
function,
ALTER
MAP
AND
SELECl'
DATA
SEG1ENT,
which
in
this
case
al
ters
the
map
of
window
o and
selects
a
different
432
data
segment.
Window
4,
the
control
windCM,
is
the
only one through which
function
requests
may
be
issued.
Windows
0 through 3
are
available
for
data
transfer
between
a
PS
processor
and
432
memory.
4-1