SCRAMNET OVERVIEW
Copyright 2007
2-9
S SC150e HARDWARE REFERENCE
2.7 External Triggers
S SC150e
PCI cards support two external triggers. The external triggers will
occur only if the ACR has been configured to enable them. Triggers 1 and 2 are generated
by S SC150e
shared-memory access. Both triggers generate a 26.64 ns TTL
level compatible, non-terminated, output.
•
Trigger 1 - Host Write (ACR[2] enables)
•
Trigger 2 - Network Write (ACR[3] enables)
NOTE
: User access to Trigger 1 and Trigger 2 is not available on the PMC card.
2.8 General Purpose Counter/Global Timer
The General Purpose Counter/Timer has six modes of CSR8 and CSR9 controlled
operations, The output from the General Purpose Counter/Timer is stored in CSR13.
Counter modes can count errors, external trigger events, or network messages. A high-
resolution timer mode can run free or measure the ring time with a 26.66 ns resolution.
The global timer mode clocks with a resolution of 1.706 µs and resets on an external
trigger event. (See 2.7 External Triggers). A specific shared-memory location may be
identified with External Trigger 2 ACR[3] so that a memory write from a single node on
the network can simultaneously reset all the global timers in the ring.
If the Trigger 2 event is the frame counter, the timers in the ring effectively become
synchronized sub-frame timers, which can then be used to tag time-critical data or to
measure and compare the completion time of various tasks within a distributed real-time
system.
2.9 Modes of Operation
2.9.1 Data Filter Mode
When S SC150e Data Filtering is enabled, only those writes to S
SC150e memory producing a data change are transmitted to the network.
EXAMPLE:
If location 1000 in S SC150e memory contains the value ‘20’ and the host
processor writes the value ‘20’ to location 1000, then no network traffic will be
generated. However, if any other value is written to location 1000, then the new value
will be passed around the network to update the other S SC150e node
memories.
When a write is received from the host, a comparison is made to the old data at that
address to see if there was a change before writing to shared memory. If the data has
changed, then it is written to shared memory, and is also transmitted onto the network.
This entire process is completed within the host memory standard bus write cycle.
Data filtering is a powerful communications compression technique for cyclical
applications. This technique has been shown to significantly reduce the network traffic
and therefore increase the effective throughput on the network.
Summary of Contents for SCRAMNet+ SC150e
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