1 02/06/84  cross_ring_
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 3 
 4 Syntax for attach description:
 5      cross_ring_ switch_name N
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 7 
 8 Function: The cross_ring_ I/O module allows an outer ring to attach a
 9 switch to a preexisting switch in an inner ring, and to perform I/O
10 operations by forwarding I/O from the attachment in the outer ring
11 through a gate to an inner ring.  The cross_ring_ I/O module is not
12 called directly by users; rather the module is accessed through the
13 I/O system.
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15 
16 Arguments:
17 switch_name
18    is a previously registered switch name in ring N.
19 N
20    is a ring number from 0 to 7.
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22 
23 Opening operation:
24 The inner ring switch may be open or not.  If not open, it will be
25 opened on an open call.  All modes are supported.
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27 
28 Close operation:
29 The inner switch is closed only if it was opened by cross_ring_.
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31 
32 Other operations:
33 All operations are passed on to the inner ring I/O switch.
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35 
36 Notes:  This I/O module allows a program in an outer ring, if permitted
37 by the inner ring, to use I/O services that are available only from an
38 inner ring via cross_ring_io_$allow_cross.  By the use of the
39 cross_ring_io_$allow_cross subroutine a subsystem writer is able to
40 introduce into an outer ring environment many features from an inner
41 ring, thereby tailoring it to fit the user's specific needs.
42 
43 The switch in the inner ring must be attached by the inner ring before
44 cross_ring_ can be attached in the outer ring.