Note: This API calls are shared between DOS and Win16 personality.
DPMI is a shared interface for DOS applications to access Intel 80286+ CPUs services. DOS DMPI host provides core services for protected mode applications. Multitasking OS with DOS support also provides DMPI in most cases. Windows standard and extended mode kernel is a DPMI client app. Standard and extended mode kernel differs minimally and shares common codebase. Standard Windows kernel works under DOSX extender. DOSX is a specialized version of 16-bit DPMI Extender (but it is standard DPMI host). Standard mode is just DPMI client, exnhanced mode is DPMI client running under Virtual Machime Manager (really, multitasker which allow to run many DOS sessions). Both modes shares DPMI interface for kernel communication. The OS/2 virtual DOS Protected Mode Interface (VDPMI) device driver provides Version 0.9 DPMI support for virtual DOS machines. Win16 (up to Windows ME) provides Version 0.9 DPMI support. Windows in Standard Mode provides DPMI services only for Windows Applications, not DOS sessions.
DPMI host often merged with DPMI extender. Usually DPMI extender provide DPMI host standard services and DOS translation or True DPMI services.
Int 31H, AH=00H, AL=0CH
Version
0.9
Brief
Set Descriptor
Input
AX = 000CH BX = selector ES:(E)DI = selector:offset of 8-byte buffer containing descriptor
Return
if function successful Carry flag = clear if function unsuccessful Carry flag = set AX = error code 8021H invalid value (access rights/type byte invalid) 8022H invalid selector 8025H invalid linear address (descriptor references a linear address range outside that allowed for DPMI clients)
Notes
Copies the contents of an 8-byte buffer into the LDT descriptor for the specified selector.
32-bit programs must use ES:EDI to point to the buffer. 16-bit programs should use ES:DI.
The descriptor's access rights/type byte (byte 5) follows the same format and restrictions as the access rights/type parameter (in CL) for the Set Descriptor Access Rights function (Int 31H Function 0009H). On 80386 (or later) machines, the descriptor's extended access rights/type byte (byte 6) follows the same format and restrictions as the extended access rights/type parameter (in CH) for the same function, except the low-order 4 bits (marked “reserved”) are used to set the upper 4 bits of the descriptor's limit.
If the descriptor's present bit is not set, then the only error checking is that the client's CPL must be equal to the descriptor's DPL field and the “must be 1” bit in the descriptor's byte 5 must be set.
A DPMI 1.0 host will reload any segment register which contains a selector specified in register BX. It is suggested that DPMI 0.9 hosts also implement this.
Refer to the rules for descriptor usage in Appendix D.
See also
Note
Text based on http://www.delorie.com/djgpp/doc/dpmi/