Copyright 1995, S
YS
I
RAN
Corp.
4-1
VME3U H/W REFERENCE
4. 0 OPERATION
4.1 Introduction
The SCRAMNet
+
Network is a shared-memory system. Every computer on the network
has a constantly updated local copy of all global data which is passed to all the network
computers. The network protocol is implemented in the SCRAMNet
+
hardware and
therefore no software overhead is required to retrieve this information from the network.
The protocol is transparent to the computer. This frees computer processor time for
application algorithm execution and other real-time tasks. Since any computer on the
network has access to data in the shared memory, any computer can read or modify the
shared data and thereby communicate with the other computers on the network.
Very little special software is required for normal operation because of the SCRAMNet
+
shared-memory configuration. Typically, SCRAMNet
+
memory is installed and linked
to a host global common block through the host operating system. Once the link is
complete, any program can reference SCRAMNet
+
memory as a standard common-
block variable reference.
For interrupt driven applications, an interrupt service routine (ISR) is required to handle
the interrupts triggered by the SCRAMNet
+
node. An example of a generic ISR is
included Figure 4-11, page 4-28 at the end of this section.
4.2 Shared Memory
Global variables are mapped directly onto the replicated shared memory. The application
program typically contains a list of variables or arrays which are stored in a contiguous
space and which are to be shared across processors. The analogy of a FORTRAN
COMMON BLOCK is most fitting. For the purpose of identification, these variables are
referred to as SCRAMNet
+
variables.
The application program usually requires a short section of instructions to initialize the
SCRAMNet
+
hardware and to link the SCRAMNet
+
memory to the SCRAMNet
+
variable list. The shared memory cannot be used as instruction space.
4.2.1 Virtual Paging
CSR12 is the virtual-paging register. Set CSR12, bit 0 to ‘1’ to enable virtual paging.
All SCRAMNet
+
nodes use the same 8 MB shared-memory map. Virtual paging allows
a node with less than 8 MB shared memory to move their memory window throughout
the SCRAMNet
+
physical 8 MB shared-memory map.
If a node has 4 MB of shared memory, it can be paged into the upper 4 MB or the lower 4
MB of the shared-memory map. If it is paged into the lower 4 MB, it would operate the
Содержание SCRAMNet+ VME3U
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Страница 52: ...OPERATION Copyright 1995 SYSIRAN Corp 4 26 VME3U H W REFERENCE Figure 4 10 Quad Switch...
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Страница 100: ...SPECIFICATIONS Copyright 1995 SYSIRAN Corp C 4 VME3U H W REFERENCE C 5 Fiber Optic Bypass Switch...
Страница 101: ...SPECIFICATIONS Copyright 1995 SYSIRAN Corp C 5 VME3U H W REFERENCE Figure C 2 Fiber Optic Bypass Switch...
Страница 102: ...SPECIFICATIONS Copyright 1995 SYSIRAN Corp C 6 VME3U H W REFERENCE Figure C 3 Housing Dimensions...
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Страница 115: ...E APPENDIX E CONFIGURATION AIDS TABLE OF CONTENTS...
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Страница 121: ...F APPENDIX F ACRONYMS...
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Страница 125: ...G APPENDIX G GLOSSARY...
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