SAMPLE: DLL Installs an ISR That Can Signal an Application

• Microsoft Windows Software Development Kit (SDK) for Windows versions 3.0 and 3.1

In the Microsoft Windows environment, an interrupt service routine (ISR) can communicate with an application. n ISR must be in a fixed code segment in a dynamic-link library (DLL) to ensure that the code is always in memory and available to service the interrupt. In Windows 3.1, an ISR that supports hardware should be in an installable device driver to enable Windows to disable the hardware when it switches between MS-DOS tasks.

HANDLER is a set of sample programs that demonstrate how to install an ISR, and have the ISR communicate with an application. The HANDLER DLL installs an ISR, which in turn uses the PostMessage function to notify the DEMO application (included with HANDLER) that an event has occurred. The ISR is chained to the keyboard interrupt vector, and the DEMO application maintains and displays a count of keyboard interrupts.

This sample program illustrates how an application can detect a hardware interrupt. This may be useful to a programmer trying to support a hardware device in the Windows environment.

HANDLER is one of the advanced samples provided with version 3.1 of the Microsoft Windows SDK. HANDLER can also be found in the Software Library.

Download HANDLER.EXE, a self-extracting file, from the Microsoft Software Library (MSL) on the following services:

• Microsoft Download Service (MSDL)

        Dial (206) 936-6735 to connect to MSDL
        Download HANDLER.EXE (size: 24014 bytes) 
  

• Internet (anonymous FTP)

        ftp ftp.microsoft.com
        Change to the \SOFTLIB\MSLFILES directory
        Get HANDLER.EXE (size: 24014 bytes)