DOS ain't dead

DPMI code from .COM file? (Developers)

posted by ecm  , Düsseldorf, Germany, 11.05.2020, 15:07

> You are right!
> It is possible and I even found a source for it. Uploaded here:
> http://www.laaca.sweb.cz/tinycom.asm
>
> But...
> If I want to somehow include it into realmode pascal source I need to end
> the program by instruction RETF and not by INT 21/4C because it would end
> whole my application and only my routine...

DPMI programs must end with Int 21.4C to allow the DPMI host to learn of the termination. What you can do is create a new PSP, and set its Int 22 address (Parent Return Address) and Parent Process field so as to return into your program. Then when the DPMI part is finished you use protected-mode Int 21.4C which eventually has the host drop into 86 Mode to run DOS's interrupt 21h handler, and then DOS returns to your process (closing all file handles in the new PSP and freeing memory allocated to that new PSP).

If you want to keep calling into DPMI and returning back, you can use the raw mode switch entrypoints (Int 31.0305 and .0306) or use the other Int 31.03 functions to call 86 Mode code from protected mode.

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l

Complete thread:

• DPMI code from .COM file? - Laaca, 11.05.2020, 13:37 (Developers)
  • DPMI code from .COM file? - ecm, 11.05.2020, 14:42
    • DPMI code from .COM file? - Laaca, 11.05.2020, 14:50
      • DPMI code from .COM file? - ecm, 11.05.2020, 15:07
      • DPMI code from .COM file? - ecm, 11.05.2020, 16:07
        • DPMI code from .COM file? - Laaca, 11.05.2020, 22:44
          • DPMI code from .COM file? - ecm, 11.05.2020, 23:05
  • DPMI code from .COM file? - ecm, 11.05.2020, 14:59
  • DPMI code from .COM file? - Rugxulo, 13.05.2020, 04:39
  • DPMI code from .COM file? - CandyMan, 13.05.2020, 19:53