using XMS function 0bh - move EMB

[Noam Efrati <noam@genie.terra.co.il>]

Hi all,

  I am trying to read from a 32-bit address space in real mode,
using the XMS function 0b (move extended memory block).
The function is described in a book from 1991 called DOS 
extending. 
  The C code is listed below. I run it with a debugger and I saw that
the xms call returns 01 in AX, which is a result of a successful 
operation. Still the value of the destination location in memory
remains unchanged. 
  I have loaded the himem.sys, and the command mem/c finds xms 
and reports an xms version of 3.00.
  I would appreciate an answer if someone had experienced in this 
before.


Thanks,  noam.

==============================================================
#include <alloc.h>
#include <dos.h>
#include <stdlib.h>

unsigned long read_pci_space(linear_address)
unsigned long linear_address;
{
	static int      first_call = 1;
	void far     (*xms_function)();
	static void far (*xms_entry_point)();
	unsigned long   *destination;
	unsigned long   pci_address,return_value;
	unsigned long   destination_address;
	unsigned int    *parameter_block;
	unsigned int    shandle=0,dhandle=0;
	unsigned int    temp[8],i;
	unsigned int    block_segment,block_offset;
	union  REGS  regs;
	struct  SREGS sregs;

	if (first_call)
	{
	  first_call = 0;
	  regs.x.ax = 0x4310;   /* func. 43h, subf. 10h */
	  int86x(0x2f,&regs,&regs,&sregs);
	  xms_function = MK_FP(sregs.es,regs.x.bx);
	  xms_entry_point = xms_function;
	}
	else xms_function = xms_entry_point;

	destination = malloc(4);
	destination_address = 16 * (unsigned long)(FP_SEG(destination)) +
				   (unsigned long)(FP_OFF(destination));

	*destination = 0;
	parameter_block = malloc(16);
	block_segment = FP_SEG(parameter_block);
	block_offset =  FP_OFF(parameter_block);

	*parameter_block = 4;        /* move one dword */
	*(parameter_block + 1) = 0;
	*(parameter_block + 2) = shandle;
	*(parameter_block + 3) = (unsigned int)(linear_address);
	*(parameter_block + 4) = (unsigned int)(linear_address >> 16);
	*(parameter_block + 5) = dhandle;
	*(parameter_block + 6) = (unsigned int)(destination_address);
	*(parameter_block + 7) = (unsigned int)(destination_address >> 16);

	/* for debug */

	for (i=0;i<8;++i)
	  temp[i] = *(parameter_block + i);

	/* xms function: move extended memory block */

	asm {
	  push ds
	  push si
	  push ax
	}

	_AH = 0x0b;
	_SI = block_offset;
	_DS = block_segment;
	(*xms_function)();
	asm {
	  pop ax
	  pop si
	  pop ds
	}

	free(parameter_block);
	return_value = *destination;
	free(destination);
	return(return_value);

}

 

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Noam Efrati                    | e-mail: noam@terra.co.il  
Terra computers ltd.	       | phone : 972-7-6483444	 
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