Communication Between Resident DOS Extension Type Programs and DOS Application Programs
Original Publication Date: 1987-Mar-01
Included in the Prior Art Database: 2005-Feb-01
A method is described which permits applications and extensions to communicate with minimal risk of incompatibility with other extensions. Often, an application program will need to communicate with a resident DOS extension. This may be for control or status purposes. In general, extensions hook interrupt vectors. The application could use this interrupt vector for communications, but problems exist with this direct approach such as: 1. Use an "unused" function call. Some other extensions that could be in the chain might not pass an "invalid" function call. 2. Use an existing function call with an "unused" return code. Again, some other extensions may turn off "unused " bits in the return code. 3. Modify registers other than return code register.