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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:
Int 1CH - ROM BIOS timer tick interrupt
Int 23H - DOS Ctrl+C interrupt
Int 24H - DOS critical error interrupt
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.