AppleWin/source/DAC.cpp

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/*
Emulate an 8 bit DAC (eg: SAM card) which writes unsigned byte
data written to its IO area to the audio buffer (as used by the speaker).
This merges the data with the speaker stream, reducing the volume
of the Apple speaker when active.
Riccardo Macri Mar 2015
*/
#include "StdAfx.h"
#include "AppleWin.h"
#include "Memory.h"
#include "DAC.h"
#include "Speaker.h"
//
// Write 8 bit data to speaker. Emulates a "SAM" speech card DAC
//
static BYTE __stdcall IOWrite_DAC(WORD pc, WORD addr, BYTE bWrite, BYTE d, ULONG nCyclesLeft)
{
// Emulate audio from an 8 bit DAC
// only if using wave data
// uses the existing speaker for the timing but then
// substitutes the analog data which gets subsequently
// sent to audio out
byte mb_res;
if (soundtype == SOUND_WAVE)
{
// use existing speaker code to bring timing up to date
mb_res = SpkrToggle(pc, addr, bWrite, d, nCyclesLeft);
// 8 bit card WAV driver (scaled by 256)
// 0xFF 255 0x7f 127
// 0x80 128 0x00 0
// 0x7f 127 0xFF -1
// 0x00 0 0x80 -128
// replace regular speaker output with 8 bit DAC value
// regular speaker data still audible but muted until speaker
// goes idle
g_nSpeakerData = (d ^ 0x80) << 8;
g_quieterSpeaker = 1;
}
else
mb_res = MemReadFloatingBus(nCyclesLeft);
return mb_res;
}
void ConfigureDAC(LPBYTE pCxRomPeripheral, UINT uSlot)
{
RegisterIoHandler(uSlot,IO_Null,IOWrite_DAC,IO_Null,IO_Null, NULL, NULL);
}