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From: Eph <t DOT ephraim AT gmail DOT com>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: calling a RM function which is placed below 1 MB
Date: Thu, 24 Jul 2008 03:56:42 -0700 (PDT)
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On 24 Jul., 10:30, Eph <t DOT ephr DOT  DOT  DOT  AT gmail DOT com> wrote:
> Thx for your hint. I thought:
>
> memset(&regs, 0, sizeof(__dpmi_regs));
>
> Zeros it all so this should not matter isn't it?
>
> Ciao Ephraim
>
> On 23 Jul., 20:45, "Rod Pemberton" <do_not_h DOT  DOT  DOT  AT nohavenot DOT cmm> wrote:
>
> > "Eph" <t DOT ephr DOT  DOT  DOT  AT gmail DOT com> wrote in message
>
> >news:ca0df607-1be3-4358-b84f-f0ccddde3197 AT d77g2000hsb DOT googlegroups DOT com...
>
> > > I've problems to get a call to
> > > __dpmi_simulate_real_mode_procedure_retf_stack working correctly.
> > > My problem is, that I need to call a 16Bit real Mode function placed
> > > in Memory below 1MB, which expects three parameters to be placed on
> > > the RM Stack.(see comments in the code).
>
> > > Below the code, how I tried to use the function:
>
> > > ---------------
> > > __dpmi_regs regs;
> > > struct {
> > > unsigned long u1;
> > > unsigned long u2;
> > > unsigned long u3;
> > > } stack;
>
> > > memset(&stack, 0, sizeof(stack));
>
> > > stack.u1 = parm1; // expected at bp[14]
> > > stack.u2 = parm2; // expected at bp[10]
> > > stack.u3 = parm3; // expected at bp[06]
>
> > > memset(&regs, 0, sizeof(__dpmi_regs));
>
> > > regs.x.cs = seg; // segment of the function entry
> > > regs.x.ip = ofs; // offset of the function entry
>
> > DPMI 0.9 says ss:sp must be zero for the DPMI host to provide a real mode
> > stack, or ss:sp must point to a valid real mode stack.  DJGPP doc's
> > (libc.info) say ss:sp and flags must be set to valid values or zero.
>
> > regs.x.ss=0;
> > regs.x.sp=0;
>
> > The DJGPP doc's don't state which "flags" must be set (DPMI or __dpmi_regs):
>
> > regs.x.flags=0; /* __dpmi_regs  flags */
> > regs.h.bh=0; /* DPMI flags */
>
> > But, it's likely the doc's were referring to the DPMI flags...  (BH bit 0 =
> > 1 resets A20 and PIC)  You'll also need to set any other registers that the
> > function uses since the call copies _all_ registers.
>
> > > __dpmi_simulate_real_mode_procedure_retf_stack(&regs, sizeof(stack) /
> > > 2, &stack);
> > > ---------------
>
> > > What am I doing wrong?
>
> > Not sure.
>
> > > Can anyone please point it out!
>
> > Try the above.  Let us know.
>
> > Rod Pemberton

No that was not the problem :(.
The Stack configuration is ok? I'm not sure about the struct and the
order I must place the params. But the comments say how it should be.
param1 must be at bp[14] and must be a DWORD PTR.
param2 must be at bp[10] and must be a DWORD PTR.
param3 must be at bp[06] and must be a DWORD PTR.

param1 - 3 are allocated like this:

typedef struct MEM_INFO {
	void *data;
	int selector;
	int segment;
	unsigned long base;
	int size;
};

#define BYTE2PARAGRAPH(a) ((a+15)>>4)

void myAlloc(MEM_INFO* mi)
{
	mi->data = (void*)malloc(mi->size);
	mi->segment = __dpmi_allocate_dos_memory(BYTE2PARAGRAPH(mi->size),
&mi->selector);
	__dpmi_set_segment_base_address(mi->selector, mi->base);
	__dpmi_set_segment_limit(mi->selector, mi->size);
	memset(mi->data, 0, mi->size);
}

And I use the data as a pointer for my program and before the function
call I do three dosmemput(data, size, base); and the base part of the
three params are the unsigned long's I give to the RM function.

I would be glad for any help.

Ciao Ephraim