From: Chris Frolik <frolikcc AT indy DOT net>
Newsgroups: comp.os.msdos.djgpp
Subject: __dpmi_int
Date: Fri, 25 Jul 1997 15:18:13 -0500
Organization: IndyNet - Indys Internet Gateway (info AT indy DOT net)
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To: djgpp AT delorie DOT com
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I am writing (or trying to write) a program in DJGPP which uses IPX
protocol through the Internet.  This protocol uses the interrupt 0x7A
from the IPX driver.
The code which defines a block of data to be sent/recieved is as
follows:

/**************************************************
  BEGIN code fragment
***************************************************/

typedef unsigned char BYTE;
typedef unsigned short WORD;
typedef unsigned long LONG;

typedef struct ECBFragment {
   void far *address;
   WORD size; 
}ECBFragment;

typedef struct ECB {
   void far *linkAddress;
   void (far *ESRAddress)();
   BYTE InUseFlag;
   BYTE CompletionCode;
   WORD SocketNumber; //Big-Endian
   BYTE IPXWorkspace[4]; 
   BYTE DriverWorkspace[12]; 
   BYTE ImmediateAddress[6];
   WORD FragmentCount; 
   ECBFragment FragmentDescriptor[4];
}ECB;

/*********************************************
   The function which uses this code follows:
**********************************************/

int IPXListenForPacket(ECB *ecb)
{
   BYTE rvalue1;
   short ECBSEG,ECBOFS;
   ECBSEG=FP_SEG(ecb);
   ECBOFS=FP_OFF(ecb);

   asm {
      mov si,ECBOFS;
      mov es,ECBSEG;
      mov bx,4;
      int 0x7a;
      mov rvalue1,al;
   }
   if (rvalue1) return 1;
   else return 0;
}

/*******************************************
  END code fragment
********************************************/

This code fragment executes function 4 of interrupt 0x7A, which requires
ES:SI to point to the ECB structure.

I know that the inline asm here is not compatable with DJGPP, but that
is not the problem, since it can be converted.  The problem is with the
FP_SEG and FP_OFF macros, as DJGPP does not define these.
I have read the FAQ on this, and I think I need to use __dpmi_int  or 
__dpmi_simulate_real_mode_interrupt.  My question is, how do i get the
segment of the ecb pointer into ES, and how do i get the offset into SI
(not the actual registers, but the approprate variables in the REGS
struct).  I thought I could use the int86 function, but that is only for
standard DOS/BIOS routines.
Also, do I need the __dpmi_int or __dpmi_simulate_real_mode_interrupt
function in this case?

Thanks,

-Chris