Copyright 2007
5-1
S SC150e HARDWARE REFERENCE
5. OPERATION
5.1 Overview
The S SC150e Network is a shared-memory system. Every computer on the
network has a constantly updated local copy of all global data passed to all the network
computers. The network protocol is implemented in the S SC150e 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 S
SC150e shared-memory configuration. Typically, S SC150e 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 S SC150e 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 S SC150e node. An example of a generic ISR
is included in Figure 5-11 page 5-30 at the end of this section.
5.2 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. An analogy is a FORTRAN
COMMON BLOCK. For the purpose of identification, these variables are referred to as
S SC150e variables.
The application program usually requires a short section of instructions to initialize the
S SC150e hardware and to link the S SC150e memory to the
S SC150e variable list. The shared memory cannot be used as instruction
space.
5.2.1 Virtual Paging
CSR12 is the virtual-paging register. Set CSR12[0] to ‘1’ to enable virtual paging.
The S SC150e network may include a variety of S SC150e nodes
having varying amounts of shared memory. All S SC150e nodes use the same
8 MB network shared-memory map. Virtual paging allows a node with 4 MB or less
shared memory to move its memory window throughout the S SC150e
physical 8 MB network 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 network shared-memory map. If it is paged into the lower 4 MB, it would
operate the same as if Virtual Paging were disabled. The network address would be the
same as the shared-memory address.
Summary of Contents for SCRAMNet+ SC150e
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