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Frostbyte's 1980s DOS Shareware Collection
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USCX
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VM-SUPER.ARC
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VM-SUPER.DOC
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1988-10-29
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33 lines
The program VM-SUPER is a simple supervisor program that will put a
80386 machine into virtual 8086 mode. The code is from Appendix G of the book
"80386 Technical Reference" by Edmond Strauss. I have found this book to be
very informative.
The program is run from DOS real mode and returns to DOS in virtual 8086 mode.
The supervisor allows programs full access of all ports, and interrupts are
channeled through their original vectors. Interrupts 01,06,07,0A,0B,0C
halt the machine. These are:
01: Debug Exception
06: Invalid Opcode
07: Coprocessor Not Available
0A: Invalid TSS
0B: Segment not present
0C: SS not present or Limit Violation
The debug and coprocessor ones have given me problems but I would assume
most simple programs should run fine from virtual mode.
Some possible enhancements:
Simulation of EMS/EEMS hardware by preventing access of the I/O ports
normally used by these boards and then emulating the memory paging in an
exception routine.
Multiple DOS environments, multitasking ...
I can be of some very limited help on how this supervisor works having spent
a lot of time with the text. If you need leave me a message on
ASTRO (202) 524-1837
Tom Dengler
5422 Forest Ave
Alexandria, VA 22310