Curtiss-Wright GT200 VME, Справочник по аппаратуре

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OPERATION
4.2.14 Network Status Messaging
The network logic in each node deploys a timer in the transmission logic that identifies
when a local network status-messaging interval has expired. This interval of
approximately 1µs is chosen based on maximum media transmission delays, fidelity of
status updates, and impacts to network throughput. When the status message interval
expires, the node generates a network status message automatically (with no software
overhead).
Priority for transmitted traffic is first given to retransmitted traffic (from the insertion
buffer), then to network status messages, and finally to locally generated traffic (from the
transmit buffer). When the network status message is generated, it includes the local node
ID and applicable status/control information (local age determined by the local receive
logic, information regarding the local node such as RX_EN, TX_EN, RT_EN, link up,
signal detects and enables for applicable link interfaces, etc.).
4.2.14.1 Shared Information
•
Node ID
•
Upstream Node ID
•
Laser Enable (one per link)
•
Link Select
•
Redundant Link Capable
•
Transmit Enable
•
Receive Enable
•
Retransmit Enable
•
Write Me Last
•
Link Up
•
Laser Signal Detect (one per link)
4.2.15 Modes of Operation
The Figure 4-3 shows a diagram of configuration switches accessible through the menu
system for each mode of operation.
4.2.15.1 Write-Me-Last Mode
The Write-Me-Last mode of operation allows the originating node to be the last node in
the ring to have the data deposited to its memory. This can be useful for synchronization.
This means that when the host performs a write to the GT200 shared memory, this data is
not immediately written to the host node’s memory, but is first sent to the other nodes on
the network. When the message returns to the originating node, it is written to shared
memory, and is then removed from the network ring.
Therefore, host-originated data written to shared memory travels the ring updating the
GT200 node memories on the ring and, upon returning to the originating node, that node
writes the data to its own shared memory as the last node on the ring. This guarantees that
the data is available on all other nodes.
WARNING : This mode is not recommended for applications that use duplicate node
IDs or for open-ring topologies.
Copyright 2005 4-5 GT200 VME Hardware Reference