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Chapter 9
APM-Aware Application Design
The Point 510 pen tablet complies with the APM (Advanced Power Management) model for power
management events by allowing applications to issue and respond to the suspend request and other APM
broadcast messages. To incorporate APM broadcast messages in your application design, use the
operating system’s power management interface.
The APM BIOS allows application developers to gain control over system state transitions by designing
APM-aware applications. APM-aware applications are applications that monitor or respond to power
management events or request power management state transitions.
For example, when the suspend timeout expires or the suspend button is pressed, a suspend request is
generated by the BIOS. An APM-aware application can block the suspend request and prevent the system
from entering suspend mode or allow the suspend operation to be executed (provided no other
applications block the suspend request). This is useful if your application performs critical tasks such as
data transfers that should not be interrupted. Note that a critical suspend event, which occurs when the
battery reaches a critically low level, cannot be blocked by applications.
The Windows for Workgroups and Windows 95 operating systems use different methods to
communicate power management messages between applications, the operating system, and the BIOS.
The APM interface for each operating system supported with the Point 510 pen tablet is described below.
Windows for Workgroups Power Management Interface
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The APM driver for Windows for Workgroups is POWER.DRV. To enable the power management
interface, POWER.DRV must be listed in the drivers= entry in your SYSTEM.INI file. This driver allows
Windows applications to receive power event notification through the WM_POWER message.
When a suspend or resume event occurs, the message WM_POWER is sent to all top-level windows.
APM-aware applications can respond to this message and prepare for or block the system from entering
suspend mode. See your Windows programming documentation for details on the WM_POWER
message.
Windows 95 Power Management Interface
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The APM driver for Windows 95 is POWER.DRV. (Note that, although this file name is the same as the
APM driver for Windows for Workgroups, this is a different file.) Windows 95 allows 32-bit applications
to submit a suspend request using the Win32 API function SetSystemPowerState. Refer to the Microsoft
Developers Network CD-ROM for details on the Win32 API.
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