Lua Transform Component

The Lua Transform component provides a Lua scripting engine with several XRT-specific Lua functions.

Available XRT-specific Lua Functions

The following XRT-specific Lua functions are available for use:

• pub_alloc, as described in pub_alloc Lua Function
• sub_alloc, as described in sub_alloc Lua Function
• pub_free, as described in pub_free Lua Function
• sub_free, as described in sub_free Lua Function
• publish, as described in publish Lua Function

pub_alloc Lua Function

The pub_alloc Lua function allocates an XRT Bus publisher.

Example pub_alloc Lua Function:

pub_alloc (Bus, topic)

pub_alloc Lua Function Parameters

The following table describes the parameters used with the pub_alloc Lua Function:

Parameter	Description
Bus	Reference to the Bus component This is available as the iot_Bus global variable
topic	String to publish on
return	Returns a Lua object representing the publisher

sub_alloc Lua Function

The sub_alloc Lua function allocates an XRT Bus subscriber.

Example sub_alloc Lua Function

sub_alloc (Bus, callback, match)

sub_alloc Lua Function Parameters

The following table describes the parameters used with the sub_alloc Lua Function:

Parameter	Description
Bus	Reference to the Bus component This is available as the iot_Bus global variable
callback	Lua function invoked when data matching the topic is published The function is passed two parameters, which consist of a Lua table containing the following: The published event data A string containing the matching topic
match	String to match against event topics
return	Returns a Lua object representing the subscriber

pub_free Lua Function

The pub_free Lua function frees the publisher object.

Example pub_free Lua Function

pub_free (pub)

pub_free Lua Function Parameters

The following table describes the parameters used with the pub_free Lua Function:

Parameter	Description
pub	Publisher object created using pub_alloc

sub_free Lua Function

The sub_free Lua function frees the subscriber object.

Example sub_free Lua Function

sub_free (sub)

sub_free Lua Function Parameters

The following table describes the parameters used with the sub_free Lua Function:

Parameter	Description
sub	Subscriber object created using sub_alloc

publish Lua Function

The publish Lua function publishes event data using the supplied publisher object.

Example publish Lua Function

publish (pub, data)

publish Lua Function Parameters

The following table describes the parameters used with the publish Lua Function:

Parameter	Description
pub	Publisher object created using pub_alloc
data	Lua value to publish

Lua Transform Configuration Variables

The following table describes the configuration variables that can be used with the Lua Transform component:

Parameter	Type	Description	Valid Values	Required Y/N
Bus	String	The name of the Bus component to use	The name of an existing Bus component	Y
Logger	String	The name of the Logger component to use	The name of an existing Logger component	N
ScriptFile	String	The name of the Lua file script to load	The path and filename of the Lua script file	Y
ForceGC	Boolean	Specifies whether to trigger the Lua garbage collector after a Lua script callback has been invoked The default value is as follows: Azure Sphere: true Other: false	Valid values are as follows: true false	N

Configuration Example

The following example configures a Lua Transform component that uses the fft.lua script located in the config directory:

{
  "Bus": "Bus",
  "Logger": "logger",
  "ScriptFile": "config/fft.lua"
}