SAMPLE: Simulating Real Mode Interrupts

• Microsoft Windows Device Driver Kit (DDK) for Windows versions 3.0 and 3.1

SUMMARY

DPMI0301 is a file in the Software/Data Library that demonstrates how an application developed for the Microsoft Windows operating system can use MS- DOS Protected Mode Interface (DPMI) functions 0300h (Simulate Real Mode Interrupt) and 0301h (Call Real Mode Procedure with Far Return Frame).

Download DPMI0301.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 DPMI0301.EXE (size: 18750 bytes) 
  

• Internet (anonymous FTP)

        ftp ftp.microsoft.com
        Change to the \softlib\mslfiles directory
        Get DPMI0301.EXE (size: 18750 bytes) 
  

MORE INFORMATION

The DPMI0301 example has two parts. One part is an MS-DOS terminate-and-stay-resident (TSR) program that must be run before Windows is started. The TSR hooks Interrupt 72h.

The second part of the example is an application that runs under Windows and communicates with the TSR program. When the application starts, it issues a software Interrupt 72h by calling DPMI Function 0300h (Simulate Real Mode Interrupt).

When the TSR program receives this interrupt, it returns the address of an internal routine in the DX:BX register pair. The application takes the address and saves it in the CS and IP structure variables.

Then, when the user selects the menu item in the application, the application calls DPMI function 0301h (Call Real Mode Procedure with Far Return Frame). At various points, the application and the TSR program send messages to the serial port to indicate the progress of the application-TSR program communication.