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Communication Between Resident DOS Extension Type Programs and DOS Application Programs

IP.com Disclosure Number: IPCOM000038858D
Original Publication Date: 1987-Mar-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Malcolm, JW: AUTHOR

Abstract

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.

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Communication Between Resident DOS Extension Type Programs and DOS Application Programs

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.

Other applications that use this function call

will fail. In accordance with the new method, a unique pattern of bits is set in several registers. Then an existing function call is issued. If the required pattern exists in all registers in the extension, then place status in the registers, being careful to avoid the return-code register.

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