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NetLinx ERB


A code generation framework for AMX NetLinx control systems.

Gem Version API Documentation MIT License

Syntax highlighting is included in sublime-netlinx.


Use a descriptive syntax...

ERB Template

To generate repetitive NetLinx code...

Generated AXI File

With netlinx-erb, configuration is separated from implementation. For example, touch panel button numbers and video inputs (configuration) are separated from the code that handles video patching when a button is pressed (implementation). Under this paradigm, reconfiguration can happen quickly as project requirements change. Since the implementation code is separated from these changes and code generation is automated, there is less chance of inducing bugs into the system when a change in configuration happens.

For example, in the code above, let's say the client decides to add a camera to the system. All we have to do to update this file is add the following to the video_sources hash:

    BTN_VID_CAMERA: { btn: 14, input: :VID_SRC_CAMERA }

This defines a new touch panel button constant BTN_VID_CAMERA, assigns that constant to channel number 14, and adds a case to the button event handler to switch the video matrix to VID_SRC_CAMERA when the button is pressed. Since the implementation code for this change is auto-generated, and we know that the implementation code works correctly, it is unlikely that this change will create any bugs. There is a clear advantage to this method as the amount of code grows and the project becomes more complex.


A remote procedure call (RPC) mechanism is included to be able to call NetLinx functions through ICSLan (NetLinx Diagnostics, Telnet, etc.). To issue an RPC function call, send_string to 34500:1:0. The body of the string should start with the name of the function, followed by a space-separated list of arguments.

For the following function:

define_function patch_video(integer input, integer output)
    // Patch video matrix.

patch_video 1 2 is the RPC string that would patch video input 1 to output 2.

Backward Compatibility

The NetLinx files generated by netlinx-erb are designed to be fully backward compatible with traditional NetLinx project development, including readability and adequate whitespace. This means that any NetLinx programmer can take over maintenance of the project using the standard development tools provided by AMX and does not need to have any experience with netlinx-erb.

It is important to note that this process is a one-way street. Once the generated files are modified by hand, the changes must be manually converted back to the template files or else they will be erased the next time the generator is run. Backward compatibility is designed for projects that are permanently passed to other programmers who are not familiar with netlinx-erb and are not able to learn it, like due to time constraints.

Issues, Bugs, Feature Requests

Any bugs and feature requests should be reported on the GitHub issue tracker:

Pull requests are preferred via GitHub.

Mercurial users can use Hg-Git to interact with GitHub repositories.


netlinx-erb is available as a Ruby gem.

  1. Install Ruby 2.1.5 or higher.

  2. Open the command line and type:

    gem install netlinx-erb

NOTE: The NetLinx compiler executable provided by AMX, nlrc.exe, must be installed on your computer for this utility to work. It is included in the NetLinx Studio installation by default.

If you receive the following error when running gem install:

Unable to download data from - SSL_connect returned=1

Follow this guide: Workaround RubyGems' SSL errors on Ruby for Windows (RubyInstaller)


netlinx-erb is a complex utility and does have a learning curve. However, the time invested in learning this utility pays off in time saved from generating code that would otherwise be handwritten, and troubleshooting fewer bugs. Due to this, project maintenance also becomes easier.

Programming Languages

Basic experience with the Ruby programming language is required, as well as ERB templating. The concept of Model Oriented Programming (MOP) is also used by this framework.


Development Tools

Text Editor

A good text editor is crucial for working with netlinx-erb. Sublime Text 3 with the sublime-netlinx plugin is recommended, as it provides syntax highlighting and code completion for netlinx-erb.

Use a Single Editor Well

The editor should be an extension of your hand; make sure your editor is configurable, extensible, and programmable. -- The Pragmatic Programmer

Command Prompt

The command prompt is a powerful, flexible way to issue commands. Due to this, many of the tools that netlinx-erb is built on use command line interfaces.

This guide will assume the reader is proficient with the command prompt. SS64 is a great command line reference if you need to look up a command.


Developing a NetLinx project with netlinx-erb is significantly different than with NetLinx Studio. Although netlinx-erb and NetLinx Studio are not strictly mutually exclusive, trying to use NetLinx Studio to develop a netlinx-erb project will create unnecessary friction.

There are three applications you will bounce between when developing a netlinx-erb project:

  • Text Editor
  • Command Prompt
  • Source Control Management System

At times you may need to open some of the standalone NetLinx tools like NetLinx Diagnostics.

Transitioning From NetLinx Studio

The big difference to understand coming from NetLinx Studio is that NetLinx Studio is designed to be a monolithic, all-in-one application that contains all of the features that you need. Or at least that's the theory. The problem is that in reality NetLinx Studio only contains the features that AMX thinks you need, and can't support features you want to add yourself.

What happens when you want to add code generation and automation to NetLinx Studio to save time on repetitive tasks? Well, you can't.

netlinx-erb takes the opposite approach, building on many different components that are smaller in scope. To the greatest extent possible, these components are extendable, customizable, and cross-platform. This means you're able to modify a netlinx-erb development environment to suit a particular project, or your workflow in general.

Integrating with source control management (SCM) systems like Mercurial and Git was also an important goal of netlinx-erb. Due to this, most files are plain text and typically easy to read by a human. The philosophy is that configuration should happen in your text editor, not a proprietary GUI.

Getting Started

Creating A New Project

Open the command prompt in the directory used for your NetLinx projects and type:

netlinx-erb -n my_project

Enter the my_project directory and take a minute to skim through the files that have been generated.

Configuring The Workspace

workspace.config.yaml, referred to as the workspace configuration, is a text file that replaces the functionality of a NetLinx Studio .apw workspace file. Change this file to the following:

    name: My Project
    connection: # (or your master)
        path: touch_panel.TP4
          - 10001:1:0
          - 10002:1:0
        path: cable_box.irl
        dps: 5001:1:0

Now create My Project.axs and include/cable-box.axi. Using Sublime Text, these files can be populated using the NetLinx: New From Template: Overview and NetLinx: New From Template: Include commands, respectively. If you used the templates, comment out the code for the logger for this example.

(*                    INCLUDES GO BELOW                    *)

// Comment this out for the example.
// #include 'amx-lib-log'

(*                 STARTUP CODE GOES BELOW                 *)

// Comment this out for the example.
// logSetLevel(LOG_LEVEL_DETAIL);

Also create ir/cable_box.irl and touch_panel/touch_panel.TP4. These files can be empty, or the real thing. It doesn't matter for the example.

To get an idea of how the workspace config file relates to a traditional NetLinx Studio workspace, run:

rake generate_apw

Open My Project.apw in NetLinx Studio and take a look at the workspace tree.

NetLinx Studio Workspace Screenshot

The master source code, touch panel, and IR files show up in the tree, just like we would expect. What you might not expect is that cable-box has shown up under the Include folder even though it wasn't specified in the config. This is a feature of netlinx-workspace, which automatically consumes include files since there will probably be a lot of them. Don't worry though, unwanted files can be explicity excluded.

Code Generation

At this point it is important to have a working knowledge of Ruby and ERB. (See prerequisites.)

In this example we'll connect touch panel buttons to the corresponding buttons on the cable box remote control. To keep the code encapulated, we'll have include/cable-box.axi model the cable box's remote control, and include/ui/template/panel.axi.erb.tmpl will model the functions of the identical touch panels.

First, create include/cable-box.axi. This file uses the traditional .axi extension because no code generation is necessary. For a file this simple, code generation may actually create more work and make the code harder to understand.

Next we'll configure the touch panels. Open include/ui/_config.axi.erb. This is where we'll instruct the system to generate .axi files for each of the touch panels:

# Params - Converted into @tmpl_[key]
# First key (panel name) is available as @tmpl_suffix
touch_panels = {
    CONFERENCE_TABLE: { dps: 10001 },
    WALL:             { dps: 10002 },

The important thing to notice about this file is that values can be passed into each touch panel's hash, which then become available in the template as instance variables. By using the instance variable @tmpl_dps in the template, the value 10001 will be written to panel-conference-table.axi, and 10002 will be written to panel-wall.axi. We'll go over this more when creating the template file.


Device combining concatenates all of the events into a single DPS, hiding which touch panel actually sent the event. Conceptually, all of the physical touch panels have to be thought of as one virtual touch panel -- they all mirror each other. This means that touch panels that want to share the same code are forced to share the same state as well.

The answer to this problem is an advanced topic that will be covered in another section. It is practical in situations like room combining where touch panel B needs to operate autonomously when the rooms are separated, but needs to mirror touch panel A when the rooms are combined (a state machine).

Since the touch panels share the same design file, touch_panel.TP4, we'll use code generation to create the source code for each panel based on a single template.

Create include/ui/template/panel.axi.erb.tmpl. The first thing to notice is that unique names for the include guards can be code generated:

    Example Touch Panel
    For the netlinx-erb getting started project.

#if_not_defined <%= "MY_PROJECT_TP_#{@tmpl_suffix}" %>
#define <%= "MY_PROJECT_TP_#{@tmpl_suffix}" %> 1

Let's apply this to assigning the DPS to each touch panel. Since a device definition takes the form of CONSTANT_NAME = DPS, we can use code generation to populate the constant name and device number for each file:

(*           DEVICE NUMBER DEFINITIONS GO BELOW            *)

<%= "#{@dvTP} = #{@tmpl_dps}:1:0;" %>

When the .axi files are generated, panel-conference-table.axi will contain dvTP_CONFERENCE_TABLE = 10001:1:0;, and panel-wall.axi will contain dvTP_WALL = 10002:1:0;.

When authoring an erb template it is important to think on a higher level of abstration than you would with an axi file, keeping in mind that you're writing code that writes code. Creating variations of a similar piece of code is a perfect job for the code generator.

At this point we have a few different sets of data that need to be connected together:

  • Touch panel button numbers
  • Named constants for those buttons
  • The key on the cable box remote control that needs to be triggered when its corresponding touch panel button is pressed

These connections can be described in one place, making future changes simple:

(*              CONSTANT DEFINITIONS GO BELOW              *)

    # Remember, this template generates multiple files.
    # Guard your global code to prevent include conflicts!

<% global_constant_justify = 26 -%>
// Cable Box Buttons
    generate_constant_ivars cable_box_buttons = {
        # :btn - Touch panel button number.
        # :key - Cable box remote control key from `cable-box.axi`.
        BTN_CABLE_BOX_1: { btn: 101, key: :CABLE_BOX_KEY_1 },
        BTN_CABLE_BOX_2: { btn: 102, key: :CABLE_BOX_KEY_2 },
        BTN_CABLE_BOX_3: { btn: 103, key: :CABLE_BOX_KEY_3 },
        BTN_CABLE_BOX_4: { btn: 104, key: :CABLE_BOX_KEY_4 },
        BTN_CABLE_BOX_5: { btn: 105, key: :CABLE_BOX_KEY_5 },
        BTN_CABLE_BOX_6: { btn: 106, key: :CABLE_BOX_KEY_6 },
        BTN_CABLE_BOX_7: { btn: 107, key: :CABLE_BOX_KEY_7 },
        BTN_CABLE_BOX_8: { btn: 108, key: :CABLE_BOX_KEY_8 },
        BTN_CABLE_BOX_9: { btn: 109, key: :CABLE_BOX_KEY_9 },
        BTN_CABLE_BOX_0: { btn: 110, key: :CABLE_BOX_KEY_0 },
    print_constant_hash cable_box_buttons.remap(:btn), justify: global_constant_justify


Now it's time to add a button event handler to connect the touch panel button to the cable box IR code:

(*                   THE EVENTS GO BELOW                   *)

// Cable Box Controls
    button_event_block(cable_box_buttons.remap(:key), momentary: true) { |key|

Does this section of code look unusually short compared to its NetLinx counterpart? Well there's a good reason for that: The code it writes is incredibly repetitive and therefore a lot of work can be handed off to the code generator. Even better, since this code references the cable_box_buttons hash, every time a button is added or modified this section of generated code is updated automatically.

// GENERATED FILE `panel-conference-table.axi`

(*                   THE EVENTS GO BELOW                   *)

// Cable Box Controls
        switch (
            case BTN_CABLE_BOX_1:    cable_box_key(CABLE_BOX_KEY_1);
            case BTN_CABLE_BOX_2:    cable_box_key(CABLE_BOX_KEY_2);
            case BTN_CABLE_BOX_3:    cable_box_key(CABLE_BOX_KEY_3);
            case BTN_CABLE_BOX_4:    cable_box_key(CABLE_BOX_KEY_4);
            case BTN_CABLE_BOX_5:    cable_box_key(CABLE_BOX_KEY_5);
            case BTN_CABLE_BOX_6:    cable_box_key(CABLE_BOX_KEY_6);
            case BTN_CABLE_BOX_7:    cable_box_key(CABLE_BOX_KEY_7);
            case BTN_CABLE_BOX_8:    cable_box_key(CABLE_BOX_KEY_8);
            case BTN_CABLE_BOX_9:    cable_box_key(CABLE_BOX_KEY_9);
            case BTN_CABLE_BOX_0:    cable_box_key(CABLE_BOX_KEY_0);
    release: {}

A remote control is a simple example of code generation in action. For a device like a video matrix, imagine what happens when one of the inputs or outputs needs to be repatched or renamed. All of the configuration information is in one place; no need to find-and-replace throughout a file. This also helps to make the code self-documenting, as all of the system configuration information is grouped together.

matrix_inputs = {
    VID_SRC_BLANK:          { input: 0,  name: "Blank" },
    VID_SRC_ROOM_1_PODIUM:  { input: 1,  name: "Podium 1" },
    VID_SRC_ROOM_1_WP:      { input: 2,  name: "Wall Panel 1" },
    VID_SRC_ROOM_2_PODIUM:  { input: 7,  name: "Podium 2" },
    VID_SRC_ROOM_2_WP:      { input: 4,  name: "Wall Panel 2" },
    VID_SRC_ROOM_3_PODIUM:  { input: 5,  name: "Podium 3" },
    VID_SRC_ROOM_3_WP:      { input: 6,  name: "Wall Panel 3" },
    VID_SRC_BLURAY:         { input: 9,  name: "Blu-Ray" },
    VID_SRC_CABLE:          { input: 10, name: "Cable TV" },

Separating Configuration From Implementation

netlinx-erb is designed to keep configuration and implementation code separated as much as reasonably possible. This makes configuration changes fast and easy, with significantly less risk that those changes will introduce bugs or break the system.

Now that we have a touch panel template, open My Project.axs and add the includes for panel-conference-table and panel-wall:

(*                    INCLUDES GO BELOW                    *)

// Comment this out for the example.
// #include 'amx-lib-log'

#include 'panel-conference-table'
#include 'panel-wall'

Also remember the include for cable-box in panel.axi.erb.tmpl:

(*                    INCLUDES GO BELOW                    *)

#include 'cable-box'


From the command line:


Yes, it's really that simple. This command runs the code generator, generates the RPC file, compiles the project, and creates the source code bundle. You can also add your own rake tasks if you need to customize this process.

See all of the built-in rake tasks with rake -T.


A code generation utility for AMX NetLinx control systems.




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