From: James Deuchar <J DOT A DOT Deuchar AT dur DOT ac DOT uk>
Newsgroups: comp.os.msdos.djgpp
Subject: Using Vitual DMA Services...help !
Date: 1 Feb 1999 15:50:16 GMT
Organization: University of Durham, Durham, UK.
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To: djgpp AT delorie DOT com
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Help.....! I'm still trying to get my DMA to work so I need to get the
actual phy mem address. The VDS method is preferable to copying data into a
buffer below the 1M mark and dmaing that because speed is a factor. What's
wrong with my code (or right with it)........I always get some sort of
error code back...often in reserved registers...please help!

struct DMA_DESCR_STR {
	DWORD size;
	DWORD offset;
	WORD segsel;
	WORD buffID;
	DWORD phy_addr;
};

DWORD get_phy_addr( 	DWORD offset_addr, DWORD size )
{
	DWORD dds_addr;
	struct DMA_DESCR_STR dds;
	__dpmi_regs InRegs;
	
	
	//check for VDS at bit 5 of mem 0x0040:007b  ----   HOW CAN I CHECK THIS
BIT????
	
	dds.size = size;
	dds.segsel = (WORD)_my_ds(); 					//returns an int
	dds.offset = offset_addr ;

	// lock dma region -  Clear register structure */
	memset( &InRegs, 0, sizeof( __dpmi_regs ) );

	InRegs.h.ah = 0x81 ;
	InRegs.h.al = 0x03 ; 	//specifies VDS lock dma region
	InRegs.x.dx = 0x3c ; 	// do remap and don't allocate buffer

	dds_addr = (DWORD)&dds;
	InRegs.x.es =(WORD)(dds_addr >> 16);			 	// upper 16 bits
	InRegs.x.di = (WORD)((DWORD)0xffff & dds_addr); 		// lower 16 bits

	if ((__dpmi_int (0x4b, &InRegs)) == -1) {
		printf("get_phy_addr : dpmi_int error...");
		return 0;
	} 
	if (InRegs.x.flags & 1) {      /* is carry flag set?  */
		printf("\nget_phy_addr - Call to VDS lock dma region failed...\n");
		printf("Error Code AL = %x\n",InRegs.h.al);
		return ( FALSE );
	} else {
		return dds.phy_addr;
	}
}			


Thanks!!!

-- 
J DOT A DOT Deuchar AT dur DOT ac DOT uk
Dept. of Engineering
Durham University
United Kingdom