CLIC Video Lab Automation Project

Abstract

The goal of the project was to exert a level of control over the equipment of the CLIC lab video subsystem over HTTP. This has been accomplished with the creation of a program that operates through the Common Gateway Interface (CGI) protocol to control the linked video switches and the VCR/DVD players in the lab. While the actual interconnects are not yet implemented, the software produced can succcessfully issue the commands necessary for the proper handling of the aforementioned hardware.

Introduction

While there has been some research in remote/automatic control of public lecture spaces, this project differs in that it does not have as ambitious a goal, focusing instead on simply allowing remote control of the lab equipment over an easily accisible medium. The core problem lies in implementing control over the necessary hardware and in the transfer of this control to CGI, which is essentially a stateless environment. This is complicated by the fact that the control codes for each peice of equipment is unique in content and format, requiring essentially a separate set of functions for each device controlled. Though present, the problem of stateless programming is comparatively less of a hurdle, and is circumvented by using files and passed data to maintain state information to the extent necessary.

Related Work

Who else has been doing something similar and how your effort is different.

Background

Before discussing the structure of the program, it is necessary to discuss the equipment in question. Though there are many other components in the lab's audio/video system, the parts of concert are:

• one Knox Matrix Video Switcha
• one Extron Matrix Video Switch
• one Panasonic VCR
• one Sony DVD player
• one Slink-e serial-to-infrared interface device

The two video sources are controlled by controlling the Slink-e device, which is capable of emulating the infrared signals of the remotes of those devices in order to control their functions. Only the common basic functionality is supported in this manner, since the interface is intended for normal usage and not as a complete replacement for equipment setups. The control of the two matrix switches is by individual. However, it is clear that in many cases the two should be controlled directly, and this is reflected in the program design.

Architecture

In writing the code for his project there was an option of either writing one module per device or a module for each general function. While the module division based on devices seems more logical at first glance, it is programmatically less feasible since related code is spread through many files. Currently there is one specialized module for controlling both of the video switches, the module to control communication with the devices, a module to manage template matching, an utility module, and the main program module. This organization allows related functions to be grouped together and greatly simplifies debugging, since it is much easier to make changes to related code. Furthermore, this obviates the need for separate modules to tie together devices.

• Communication Module: The communication module controls all serial communication with the devices. This includes reading data from the switches, writing data to the switches, controlling port settings, and controlling the Slink-e. The Slink-e is actually controlled by calls to a python class that actually carries out the communications, thus simplifying the code greatly. This method had to be adopted since very limited information was available on the programming of the Slink-e.
• Template-Mathc Module: The template matching module, as the name suggests, provides template matching facilities. This module was created in order to minimize the number of verbatrim output statements within the C code, since C is not a language conducive to direct output of large volumes of text. Tokens can be registered with the matcher along with functions that are called whenever the token is encountered to output data to the CGI output stream.
• Video Switch Module: The video switch module is dedicated to control of the video switches. This module provides the functionality to read settings from map files, read in input/output labels, and to parse form data to determine configuration of the switches. This module DOES NOT do any communications tasks.
• Utility Module: The utility module contains a few miscellaneous functions to ease certain programming tasks.
• Main module: The main module has two main fucntions. Firstly, it contains code to prevent two users from simultaneously accessing the program without being warned. This prevents multiple concurrent uses and ensures that all parties are aware of the current situation, given that it is generally undesireable for multiple parties to control the system simultaneously. Beyond this, the main module also carries out parameter parsing and execution of the appropriate actions based on unser actions and input.

Program Documentation

System Requirements

• Linux or Solaris Operating system. Others on request.
• Multiport Serial Card
• HTTP server capable of CGI interface (ie, Apache)
• ANSI-complient C compiler (ie, gcc)
  Please note: some Sun machines ship without an complete compiler. These machines may not be able to compile the code. Similarly, the newest versions of gcc (3.x versions) have several issues, and is not guarenteed to compile the code correctly.

Installation

• Edxpand the distribution archive:
  tar -xzvf clic_control.tar.gz
• Enter the code directory:
  cd clic_control/code
• Compile the program:
  make
• Change to the file root: cd ..
• Copy files to web root:
  cp -R install/* <web_root_physical>/

Configuration

• Please investigate config.h in the code directory for information on compile-time options.
• cgi-bin\settings\extron_io.txt: Extron (front) switch input and output labels. See contents for format.
• cgi-bin\settings\knox_io.txt: Knox (back) switch input and output labels. See contents for format.
• cgi-bin\settings\*.map: Switch settings presets. See test.map for example.
• cgi-bin\settings\ports.txt: Port assignments for the communications module. See contents for format.

Program Operation Map

Caveats

• All outside communications are write only, since there were issues getting the serial connections working
• A connection needs to be established to the front switch using a shielded cable in order to enable Extron's physical control.
• This program is taylored to the CLIC lab as it is now (Jan 2002), and is not directly extensible to new equipment (though the internal capability is there.
• The 8-port serial card is still missing, thus making direct tests on it impossible. Serial I/O has been tested with FIFO devices.
• Authentication is meant to be implemented using http passwords. It is the user's responcibility to implement the necessary changes to protect the exposed systems.

Future Enhancements

• Automated camera control
• Touch panel on podium for controlling system
• Built-in authentication, and SSL/certificate-based security
• Ability to brodcast streaming video from cameras directly

Acknowledgements

• Many thanks to Prof. Henning Schulzrinne and Mr. Xiaotao Wu for their patience with me.
• This program uses the free CGIC library (www.boutel.com)
• This program uses a user-domain python class for control of the Slink-e. The copyright belongs to the original author. Original can be obtained at www.nirvis.com