A SERVICE OF

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KEY
CONCEPTS
Printer
Server
Task
Perspective
The
printer
server
task
may
be
viewed
as
a
"front
end"
to
the
pr
inter
task
which
is
responsible
for
translating
the
message
sent
by
the
GOP
process
into
the
form
expected
by
the
printer
task.
The
printer
server
loops
through
the
following
steps:
1.
RECEIVE
a message from
the
print_request-POrt.
2.
When
the
message (a
print
object)
is
received,
obtain
an
object
selector
for
the
message
text.
3.
Using
the
object
selector,
open
a windoo
onto
the
message
text.
4.
Copy
the
message
text
from 432
memory
to
PS
memory
through
the
open
windON.
5.
Close
the
window.
6.
TRANSMIT
a message
with
a
reference
to
the
pr
int
text
to
the
printer
task.
7.
Repeat from
step
1.
Printer
Task (Device Task)
Perspective
The
printer
task
runs
in
an
endless
loop
repeating
the
following
steps:
1.
2.
3.
4.
5.
6.
ACCEPT
a message from
the
print
order
mailbox;
Interpret
the
message; - - -
Transfer
the
data
from
the
message
to
the
printer,
taking
care
of
all
device
control
(e.g.,
interrupts);
Update
the
status
field
of
the
print
message
with
the
result
of
the
operation;
--
TRANSMIT
the
updated
pr
int
_message
to
the
pr
int
_response
mailbox;
Repeat from
step
1.
Printer
Reply Task
Perspective
The
printer
reply
task
may
be
viewed
as
a "back end"
to
the
printer
task.
I t
runs
in
an
endless
loop
as
follows:
1.
ACCEPT
a message from
the
print
response
mailbox.
1.
Open a
windON
onto
the
print
object
in
the
432
system.
2.
Formulate
a
print
reply
message and
deposit
it
in
the
print
object
through
the
open windON.
3.
Close
the
window.
4.
SEND
the
print
object
to
the
printer
reply
port
in
the
432
system.
-
5.
Repeat from
step
1.
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