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