System Application Manager (SAM)

As illustrated in the diagram below, SAM is a software layer that sits on top of a number of real-time operating systems as well as the Microsoft Windows operating system. SAM is a very compact OS extender. In a typical system, the entire SAM software layer is less than 25K of code.

SAM is implemented on top of Windows to make it easy to simulate devices on a PC. This allows the Microsoft Visual Software Development tools to be used to create applications for systems using the SAM RTOS extender. The development library for SAM includes utilities to convert any Windows font into a font that can be used with a SAM enabled system as well as a utility to convert Windows bitmap files (*.bmp) into bitmaps that can be compiled into SAM applications.

SAM's main function is to extend the RTOS API's with a simple screen management library that includes 2D graphics and proportional font drawing. Perhaps more importantly, SAM provides screen and input control arbitration between applications. To keep the programming model and user interface requirement straightforward, SAM implements the simple windowing system illustrated in the diagram below.

NOTE: The Video layer is only appropriate on televisions and is not directly managed by SAM.
SAM supports two classes of application: standard and system. One standard application is onscreen at a time. An example of a standard application might be a web browser, address book, or onscreen program guide. The system application class is intended for small applications that control system functions and should always be available to the user. A good example of a system application is the menu or navigation application that allows the user to select between standard applications. Another example might be volume control.

Under normal operation, a standard application is onscreen and is the only application receiving input or drawing to the screen. A background application (i.e. another standard application that does not currently have control of the screen) can notify the user that something interesting has happened using a notification window. For example, while the user is browsing the web, an e-mail application might pop-up a scrolling marquee saying "You have new mail". SAM's graphics and clipping libraries allow applications to create arbitrarily shaped notification windows. When the current onscreen standard application draws to the screen, it is automatically prevented from drawing over the notification window.

When the user brings up a system application over a standard application, the same clipping system prevents the standard application from drawing to the screen where the system application appears. System applications also have the ability to intercept some or all of the input. For example, the menu application might take over all input, while volume control might only intercept the volume control keys.

Finally, either the current onscreen standard application or a background standard application can ask the system to put up a dialog box. A dialog box appears over all other applications and receives input. For example, in a television system, the user might order a pay-per-view movie that starts in 15 minutes. To kill time, the user might switch over to a shopping virtual channel or web browser. When the movie is about to start, the guide application is no longer onscreen. However, it can put up a dialog that will appear over the web browser letting the user know the movie is about to start. A similar example in a cellphone application might have the user checking a calendar built into the phone when a short message arrives. The short message application could put a dialog or notification onscreen. The advantage to the dialog is that it provides the user with an immediate call to action.

Architecture

The red areas in the diagram below indicate the components that make up SAM.

Portability and Kernel Layer

The Thread, Timer, Memory, and Messages blocks are simply wrappers to the equivalent underlying functionality in the RTOS or Windows. This allows applications to be ported easily from one RTOS to another and for applications to be prototyped on the PC simulator.

SAM also supports flexible localization and DBCS (via Unicode) through compile-time constants.

Graphics & Clipping

The SAM graphics library supports 2D drawing primatives including support for proportional fonts and Windows bitmap files (*.bmp). A development utility allows any Windows font to be converted for use in a SAM application. SAM also supports arbitrarily shaped clipping windows. The clipping support allows notifications, dialogs, and system applications to appear on top of the foreground application without having to worry about each application overwritting the others' screen area.

Application List Management

In systems with multiple applications, it is necessary to have some mechanism for the user to choose which application to use. SAM does not attempt to establish a specific navigation metaphor, but rather supports an application registry so that system developers can easily create whatever user interface is desired. When using SAM, all applications register with the list manager. The system designer creates a menu or application navigation application that uses the App List Manager to find out about other applications in the system. For example, in the TV SAM simulator that can be downloaded from the Demo page, the menu button on the remote control pops up a list of applications. To change to another application, the user simply selects an application from the list.

Notifications & Dialogs

The Notifications and Dialog module provides a mechanism for applications to alert the user to important information when another application has control of the system

Input Routing

SAM automatically routes keyboard, touch screen, or other forms of input to the appropriate application. For example, in a TV system, several applications may want to use the same keys for navigation and input. Whichever application is onscreen will receive the input. If a background application requires immediate user feedback it can put up a dialog box over the current onscreen application. While the dialog box is on screen, user input is temporarily redirected to the dialog.