Intel 386 Manual do Utilizador descarregar pdf (Página 390)

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12-55

DMA CONTROLLER

Description:

Sets the target memory address for the DMA channel specified

by nChannel.

Parameters:

nChannel --channel for which to set target address

ptMemory --pointer to target memory location

Returns:

None

Assumptions:

Processor is in real mode.

Syntax:

static char lpsz[]=”Hello World”;

SetDMATargMemAddr(DMA_Channel1, lpsz);

Real/Protected Mode:

The address calculation from ptMemory assumes the processor is in real

mode.

*****************************************************************************/

int SetDMATargMemAddr(int nChannel, void *ptMemory)

{

WORD addrDMATar0_1;

WORD addrDMATar2;

WORD addrDMATar3;

WORD wSegment;

WORD wOffset;

DWORD lAddress;

/*Check input*/

if ( (nChannel != DMA_Channel0) && (nChannel != DMA_Channel1) )

return ERR_BADINPUT;

/*Set registers to correct channel*/

addrDMATar0_1 = ( nChannel == DMA_Channel0 ? DMA0TAR0_1 : DMA1TAR0_1);

addrDMATar2 = ( nChannel == DMA_Channel0 ? DMA0TAR2 : DMA1TAR2);

addrDMATar3 = ( nChannel == DMA_Channel0 ? DMA0TAR3 : DMA1TAR3);

/*If in tiny, small, or medium model,*/

#if defined(M_I86TM) || defined(M_I86SM) || defined(M_I86MM)

_asm

{ /*...then grab our segment from DS*/

mov ax, ds

mov wSegment, ds

}

wOffset = (WORD) ptMemory; /*...and our offset from the pointer*/

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