L-Proxy User Manual
56
LOYTEC
Version 3.1
LOYTEC electronics GmbH
6.1.6.2 Active Poll
Active poll means that L-Proxy actively polls the source node (Node 1) periodically at a
specified poll rate. If in addition to the active polls from L-Proxy the destination node
(Node 2) or some other node polls the source node (Node) 1, L-Proxy supports two
strategies. This mode can be configured by setting the “poll cycle” property to the desired
interval between the periodic polls and change the “maximum cache age” property to
achieve one of the following behaviors (a summary is given in Table 6):
Forward polls:
The poll request from Node 2 is interleaved with the active polls from
L-Proxy in order to update the cache value right away. The poll response is sent to Node 2
after the poll response has been received from Node 1. This mode is configured by setting
the “maximum cache age” property to zero.
Use value from last poll cycle:
The poll request from Node 2 returns the current value
from the cache (last active poll cycle). The cache value is not updated. This mode is
configured by setting the maximum cache age property to ‘-1’.
Active polls can be used if a node cannot send updates (e. g. electrics meter) and the
destination node (e. g. SCADA system) cannot poll a value. L-Proxy can then periodically
poll the electric meter and send an NV update to the SCADA system.
6.1.6.3 Poll Strategy for Multiple Input Network Variables
In the case that multiple input network variables are connected to an output NV, the first
input network variable in the connection is trying to send out a poll. In case this input NV
is not configured for polling no poll will be sent out.
In the example in Figure 54 the poll request would only be forwarded to Node 1.
Node 1
Node 2
L-Proxy
polled
Node x
polled
NV
Cache
nvoX
nvoX=5
Figure 54 The first input NV with the polled attribute set updates the cache value.
6.1.7 SNVT Conversion
The L-Proxy starting with firmware version 3.0 supports automatic SNVT conversion for
scalar types. In general there are the following requirements for SNVT conversion:
1.
Integer to Float conversion (I2F/F2I)
: This conversion type converts an integer value
(signed or unsigned) to a float value (signed or unsigned) or vice versa. The type of
both values must be a SNVT with the same SI unit (e.g. SNVT_temp to
SNVT_temp_f).
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