OpenTV

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OpenTV (NASDAQ: [OPTV]) is an interactive television company founded in 1996. Its main business involves the sale of set-top-box operating systems and software that provide an interactive television experience. The middleware style software layer allowed developers to rapidly code applications using the application programming interface (API) provided by OpenTV.

Contents

1 Development

1.1 API functions
1.2 Programming model
1.3 Modules

2 Source Code Example
3 See also
4 External links

Development

OpenTV applications are written in the ANSI standard of the C language. OpenTV provides a development kit compiler similar to the standard C compiler, gcc, called gcco. This allows developers to write their applications and compile them to o-code, a portable form much like the .exe under Windows which is then run on many set-top-boxes. In this way, OpenTV encourages developers to write applications for their hardware by facilitating the process and ensures development of software for the platform. The OpenTV operating system itself is compact and micro-kernel based, ported to the host operating system in real time using OpenTV's Hardware Porting Kit (HPK). This allows it to be run on different set-top-boxes with minimal recompiling.

API functions

The OpenTV API provides a large library of functions that can display graphics on the television screen, control audio/video services, accept and respond to user input - even communicate with the outside world. This is done through a medium-independent method of communication that involves the API handling the transmission, and passing the data received onto the application, thus concealing the actual method of data transfer. The communication protocols support one-way satellite broadcasts, full bi-directional links (such as a modem or hard-wired serial port) and high-speed broadband networks.

Programming model

The OpenTV programming model is an asynchronous message-based environment. OpenTV applications make o-code function calls to the OpenTV library. The library routines initiate operations or requests. They do not block until the operation has completed; they return immediately. When an operation or request completes, a message is sent to the application indicating completion. Applications consist primarily of a message loop, which retrieves messages from the single message queue. Messages are used for notification of external events, such as key presses on the remote control or completion of function call requests.

Modules

OpenTV applications consist of two or more modules:

The directory module, containing data about the application and its modules. This is required as the data must be transmitted before that of any other module.
One or more modules containing the code and data. These modules must contain either application o-code or application data. The main module is automatically loaded by the set-top-box (much like C's 'main' function) while other modules are loaded on request.

Modules can be transmitted over the duration of the television program. This reduces the start-up time for OpenTV applications, and the memory footprint for large, complex programs. As modules can be loaded and unloaded when needed, splitting an application up into modules impacts well on performance.

OpenTV application code is edited on the development platform and is compiled and linked to create .otv files. C code is created using a standard text editor or C IDE and compiled into o-code using gcco. The resulting .o file, which contains o-code, is run through several stages of linking to produce objects which are processed with a postlinker to reduce the size. This part of the process is similar to application development in other environments. However, the .otv file must be combined with control information that synchronizes its transmission to the set-top box with the regular TV audio and video signals. This stream of application data is known as a flow. The flow is ready to be multiplexed with audio and video stream to create a complete OpenTV broadcast stream. During the debugging cycle, the flow is used as is to download and test the interactive application over a blank screen, assuming that the TV signals are not essential to the functional behavior of the application.

Source Code Example

/*
* Displays Hello World on the TV screen, then
* waits for Quit message, and exits.
*/

include "opentv.h"
include "classes.h"
include "texter.h"
int main (void)
; 
	texter *hellotxt;

	O_debug ("Starting.\n");


	// Initialize ALL the gadget classes we use in this program
	init_texter_class (texter_ID);
	// Now create the text (string, color, x, y)
	hellotxt = (texter *) O_gadget_new(	texter_ID, hello_world_ID, &hellodata );

	// set UIMS tree
	O_ui_set_root( hellotxt );
	// Activate gadget
	O_gadget_activate( hellotxt );


	for (;;) 
			break;
		}
	}
}

External links

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