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Software Interrupts

Ordinarily, a handler installed with DPMI Function 0205H will only service software interrupts that are executed in protected mode; real mode software interrupts are passed to handlers installed with DOS Int 21H Function 25H issued from real mode, DPMI Int 31H Function 0201H, or by direct manipulation of the interrupt vector table at real mode address 0000:0000. However, there are three real mode software interrupts that a DPMI host will always reflect to a protected mode handler, if one is installed: Clients should never terminate during the processing of interrupts that were reflected from real mode. Such a termination might prevent the DPMI host from cleaning up the client's resources properly.

Protected mode handlers for software interrupts 0-7 are called with virtual interrupts disabled and trace flag reset, and these handlers should return with interrupts enabled. All other software interrupts do not modify the interrupt flag state.


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  Copyright 1999   by DJ Delorie     Updated Feb 1999