wilamowski-b-m-irwin-j-d-industrial-communication-systems-2011

18-4 Industrial Communication Systems
Protocol engine
Ordinary clock
data sets
Node clock
Clock
correction
Protocol state
engine
Message
assembling
Configuration
storage
Port
configuration
data and foreign
master data
Event port
Timestamped
message receipt
and
transmission
General
port
Message receipt
and
transmission w/o
timestamping
PTP communication path
FIGURE 18.3
Model of an ordinary PTP clock (ModelOrdinaryPTPClock.pdf).
split into a port-specific part and general information about the clock. Finally, the protocol engine has
access to the timekeeping part—the clock itself. A clock in IEEE 1588 can be adjusted and read out by
the protocol engine.
18.6 Boundary Clocks
It is easy to broaden the concept shown for the ordinary clocks by simply duplicating the PTP ports,
each having access to a common clock data set and sharing the clock. In order to implement this
communication in terms of intra-node time exchange between the PTP ports, ordinary clock data
sets are needed. The IEEE 1588 standard calls these generalized clocks boundary clocks. A model
for a boundary clock with a general number of n ports is shown in Figure 18.4. It has to be noted
that only one port may act as master node, which implies that the local clock will only be set by one
instance.
© 2011 by Taylor and Francis Group, LLC