From:	"Ben Peddell" <lightspeed85 AT hotmail DOT com>
Newsgroups:	comp.os.msdos.djgpp
References:	<3E51709E DOT DE111E40 AT worldnet DOT att DOT net>
Subject:	Re: Passing pointers to dpmi_int
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Date:	Tue, 18 Feb 2003 22:25:36 +1000
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The dds_local structure must be copied to conventional memory, as the ES:DI
is a real-mode pointer.
Try:

    if ((retseg = __dpmi_allocate_dos_memory ((sizeof(dds_local) >>
4)+1,&retsel)) < 0){
        printf ("Error allocating DOS memory\n");
        /*
         * No use trying to continue, as we don't have any DOS memory to use
         */
        return -1;
    }
    movedata (_my_ds(), &dds_local, retsel, 0, sizeof(dds_local));

    dr.w.dx = 0;
    dr.w.ax = 0x8103;
    dr.w.es = retseg;
    dr.w.di = 0;
    if (__dpmi_int (0x4B,&dr)) printf ("Error locking DMA Region\n");
    movedata (retsel, 0, _my_ds(), &dds_local, sizeof(dds_local));
    if (__dpmi_free_dos_memory (retsel)) printf ("Error freeing DOS
memory\n");


Paul Cousoulis <paulcsouls AT worldnet DOT att DOT net> wrote in message
news:3E51709E DOT DE111E40 AT worldnet DOT att DOT net...
>
> I'm trying to implement the Virtual DMA Service. In order to lock DMA
> memory I need to pass the address of a structure to int 4b in es:di. The
> physical address should be returned in dds_local, but I keep getting
> zero even though the function seems to otherwise return successfully.
> The code I'm using is:
> >
> > dr.x.dx = 0;
> > dr.x.ax = 0x8103;
> > temp = (int)(&dds_local);
> > dr.x.es = (unsigned short)(temp>>16);
> > dr.x.di = (unsigned short)(temp & 0xffff);
> > if(__dpmi_int(0x4b,&dr)) printf("error\n");
> >
> Thanks
> Paul

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