Curtiss-Wright GT200 VME, Справочник по аппаратуре

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OPERATION
4.2.2 Ring Topology
The GT200 Network is a ring topology network. The ring topology supports circuit-
switch operation for topology reconfiguration and fault isolation. Ring protocol is register
insertion with source message removal.
Data is transmitted at a maximum of 2.5 Gbps over fiber-optic cables. There is an
approximate 0.4µs (minimum) latency at each node as the frame works its way around
the ring. Delay can be imposed when a node must complete the transmission of a native
message packet before retransmitting a foreign message packet. A GT200
Network can
accommodate up to 255 nodes per network ring.
Operation of Replicated
Shared Memory
MEMORY ADDRESS & DATA
A N Y M E M O R Y W R I T E
T O AN Y G T 2 0 0 M E M O R Y
I S AU T O M AT I C AL L Y R E P L I C AT E D
T O AL L G T 2 0 0 M E M O R I E S
C O M M U N I C A T I O N I S AC H I E V E D
T H R O U G H A S I M P L E M E M O R Y
M AP O F T H E G L O B AL V A R I AB L E S
ANY BUS
ANY BUS
ANY BUS
2.5 Gbps Link Rate
MEM MEM
MEM
GT200
CPU
MEM
MEM
MEM
CPU
GT200
MEM
CPU
MEM
GT200
MEM
GT200
MEM
MEM
CPU
MEM
Figure 4-2 Replicated Shared Memory
4.2.3 Physical Interface
Fiber Optic Short Wavelength (850 nm)—2.5 Gbps
Fiber Optic Long Wavelength (1300 nm)—2.5 Gbps
4.2.4 Network Size
The network supports up to 255 nodes. Each node on the GT network has an associated
node ID. When a node transmits a native packet, it sends its node ID as part of the packet
header. When a node receives a data packet, it compares its own node ID with the node
ID in the received packet header. If the node IDs match, the packet is identified as a
native packet and is not retransmitted. If they do not match, the packet is identified as a
foreign packet and is retransmitted without modification. This packet removal mechanism
prevents traffic from circulating around the ring more than once.
It follows from above, that if two nodes on a ring share the same node ID, they will
remove non-native packets from the ring.
Copyright 2005 4-2 GT200 VME Hardware Reference