Standard Interface Libraries

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13 May 2015

These are the interface libraries which are part of the PLEXIL distribution.

Predefined Adapters

There are five adapters currently included with PLEXIL. These are the Dummy, OSNativeTime, Utility, IpcAdapter, and UdpAdapter adapters.

Dummy Adapter

The Dummy adapter is a stub for testing purposes. Lookups sent to this adapter always return UNKNOWN. Commands immediately receive an acknowledgement value of COMMAND_SENT_TO_SYSTEM; no command return value is generated.

Time Adapter

The OSNativeTime adapter uses the native operating system's real-time clock facility for lookups of the time state. Both LookupNow and LookupOnChange are supported.

IMPORTANT NOTE: LookupOnChange of time requires a non-zero tolerance. Omitting a tolerance, or explicitly providing a zero tolerance value, will result in a run-time exception.

Utility Adapter

The Utility adapter provides the print and pprint commands, as described in the PLEXIL Reference. See the directory plexil/src/apps/sample for example usage of this adapter.

IpcAdapter

The IpcAdapter supports collaboration between multiple PLEXIL Executives and other systems, using the IPC (Inter-Process Communication) package from Carnegie Mellon University to implement publish-subscribe communications.

For detailed documentation, please see Inter-Executive Communication.

UdpAdapter

The UdpAdapter supports collaboration between multiple PLEXIL Executives and other systems, using the standard UDP Datagram protocol over Internet. The UdpAdapter provides point-to-point communications.

For detailed documentation, please see UDP Adapter.

Predefined Listeners

There are two predefined Listeners available to all PLEXIL applications.

LuvListener

The LuvListener implements a TCP socket-based connection to the PLEXIL Viewer. For detailed information, please see PLEXIL Viewer.

PlanDebugListener

The PlanDebugListener causes a debug message to be generated for the Node:clock debug flag every time a node enters the EXECUTING or FINISHED state.

Predefined Listener Filters

One listener filter is provided to all PLEXIL applications.

NodeState Filter

The NodeState filter determines in which node states the associated listener will be active.

Interface Configuration Reference

This documents the interface configuration information required to use the above interface libraries. Please see Interface Configuration File for an overview of how to use configuration data.

Configuring Adapters

Adapter descriptions go in the Adapters element of the interface configuration. E.g.

<Interfaces>
 <Adapters>
  <Adapter AdapterType="type" ... other attributes ...>
   ... additional configuration info for this adapter ...
  </Adapter>
 </Adapters>
 ... listeners go here ... 
</Interfaces>

Dummy Adapter Configuration

The Dummy adapter has no parameters. However, it must be explicitly registered for the commands and lookups it should handle.

A common case is for the Dummy adapter to handle all commands and lookups not yet implemented by other adapters. The declaration for this case would be:

<Adapter AdapterType="Dummy">
 <DefaultAdapter />
<Adapter />

To handle only specific commands and lookups, specify them in a CommandNames or LookupNames element inside the Adapter element.

IpcAdapter Configuration

Please see IPC Configuration Reference.

Time Adapter Configuration

The Time adapter requires no additional configuration information. It automatically registers itself for lookups of time.

<Adapter AdapterType="OSNativeTime" />

UdpAdapter Configuration

WORK IN PROGRESS

The UdpAdapter takes the following parameters as attributes to the Adapter element:

  • default_local_port and default_peer_port are optional. If supplied, they should be valid UDP port numbers (range 1-65535).
  • default_peer is optional. It should be the name of a network host or an IP address. Default is localhost.
  • debug is optional. If supplied it should be a Boolean value. If true, enables debugging output; default is false.

Messages are defined by describing them in the body of the Adapter element, with a Message element for each different message type. Message takes the following parameters as attributes:

  • name (required) is the name of the message type, and the corresponding command name.
  • peer is the optional name or IP address of a network host. If not supplied, it defaults to the value of the default_peer attribute above, or localhost if neither is supplied.
  • local_port and peer_port are optional. If supplied, they should be valid UDP port numbers (range 1-65535). If not supplied, they default to the value of default_local_port and default_peer_port respectively. NOTE: If neither a default port nor message port are supplied, the interface will crash with a runtime exception. One or the other must be supplied.

The format of a message is defined by Parameter elements inside the Message element. Parameter takes the following attributes:

  • desc is an optional descriptor (e.g. parameter name);
  • bytes (required) is the length in bytes of the parameter in the message;
  • type (required) is the type of the parameter, which must be one of the following:
    • int for the PLEXIL Integer type;
    • float for the Real type;
    • bool for the Boolean type;
    • string for the String type;
    • int-array for arrays of Integer;
    • float-array for arrays of Real;
    • bool-array for arrays of Boolean;
    • string-array for arrays of String;
  • elements is required for array types. It is the (fixed) size of the array;

The UdpAdapter automatically registers itself for the following commands:

  • SendMessage
  • ReceiveCommand
  • GetParameter
  • SendReturnValue

Utility Adapter Configuration

The Utility adapter requires no additional configuration information. It automatically registers itself for the commands print and pprint.

<Adapter AdapterType="Utility" />

Configuring Listeners and Listener Filters

Listener descriptions go in the Listeners element of the interface configuration. E.g.

<Interfaces>
 ... adapters go here ... 
 <Listeners>
  <Listener ListenerType="type" ... other attributes ...>
   <Filter FilterType="filter_type" ... other filter attributes ...>
    ... additional configuration info for this filter ...
   </Filter>
   ... additional configuration info for this listener ...
  </Listener>
 </Listeners>
</Interfaces>

LuvListener

The LuvListener has several optional parameters:

  • Blocking is a Boolean value. If true, the Executive waits for acknowledgement from the Plexil Viewer after every node transition, to allow single-stepping and breakpointing of plans. The default value is false;
  • HostName specifies the viewer host. It can be either an IP address or a host name. The default is localhost;
  • Port is a TCP port number. It defaults to 49100.

An example of a custom LuvListener configuration:

<Listener ListenerType="LuvListener" Blocking="true" HostName="test_console" Port="13579" />

Note that as of PLEXIL 4, parameters supplied at the PLEXIL Executive command line will override the LuvListener parameters in an interface configuration file.

PlanDebugListener

The PlanDebugListener requires no additional configuration information.

<Listener ListenerType="PlanDebugListener" />

NodeState Filter

The NodeState filter allows a listener to selectively report when a node transitions to or from specific node states.

Selecting the node states is done via one of these optional elements. One or the other, but not both, must be supplied.

  • States should be a list of node state names, separated by commas. The filter will permit the listener to report when a node transitions from or to the named states.
  • IgnoredStates should be a list of node state names, separated by commas. The filter will permit the listener to report when a node transitions from or to any state other than the named states.

Example:

<ExecListener ListenerType="JoesListener">
 <Filter FilterType="NodeState">
  <States>EXECUTING, FAILING, FINISHING, ITERATION_ENDED</States>
 </Filter>
</ExecListener>



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