To:	djgpp AT sun DOT soe DOT clarkson DOT edu
Subject:	switching into dpmi
Date:	Tue, 6 Sep 1994 10:54:43 PDT
From:	"Marty Leisner" <leisner AT sdsp DOT mc DOT xerox DOT com>

I wrote a simple program to switch into dpmi protected mode...
(I need to understand how go32 works).

int dpmi_init(void)
{
    unsigned hostdata_seg, hostdata_para, dpmi_flags;
        REGS regs;
        int flags;
        regs.AX = 0x1687;
        intr_2f(&regs);
        if(regs.AX != 0) {
                printf("can't go into protected mode\n");
                return;
        }

        printf("Bx = %x\n", regs.BX);
        flags = regs.BX;
        printf("Cl = %x\n", regs.CX & 0xff);
        printf("DX = %x\n", regs.DX);
        printf("Num paragraphs = %x\n", regs.SI); 
        printf("CS = %x, DS = %x\n", get_my_cs(), get_my_ds());
        printf("dpmi pm interface at %x:%x\n", regs.ES, regs.DI);
        hostdata_seg = malloc_dos_memory(regs.SI);
        if(!hostdata_seg) {
                printf("Cannot malloc dos memory\n");
                exit();
        }
        flags &= ~1;  /* clear 32 bit flag */
        if(!dpmi_protected_mode(regs.DI, regs.ES, flags, hostdata_seg )) {
                printf("No dpmi\n");
                return;
        }
#asm
        mov     ax,04c01h
        int     21h
#endasm


; go into dpmi protect mode (entry point is passed in entry_point (offset, segme)
procdef dpmi_protected_mode,<<entry_point,dword>,<switch_flags, word>, <hostseg,word>>
        mov     ax,hostseg
        mov     es,ax
        mov     ax,switch_flags 
        call    [entry_point]
        jc      no_dpmi
        mov     ax,1
; it works if I do an exit directly here
        push    11h
extrn _dos_exit_:near
        call    _dos_exit_      
        pret
no_dpmi:
        mov     ax,0
        pret

Everything appear to make sense -- however, the only think I can do
after I call the dpmi entry point which works is an int 21/0x4c...
(the status code is there).

1) I can't call another function (I tried to call _dos_exit and this is giving
me a protection fault
2) I can't return and do an exit (this gives me a protection fault...)

Help!!!
?????


marty
Member of the League of Programming Freedom
leisner AT sdsp DOT mc DOT xerox DOT com  leisner AT eso DOT mc DOT xerox DOT com

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