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https://github.com/ekeeke/Genesis-Plus-GX.git
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118 lines
4.1 KiB
C
118 lines
4.1 KiB
C
/****************************************************************************
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* ogc_audio.c
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*
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* Genesis Plus GX audio support
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*
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* code by Softdev (2006), Eke-Eke (2007,2008)
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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*
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***************************************************************************/
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#include "shared.h"
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/* DMA soundbuffers (required to be 32-bytes aligned)
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Length is dimensionned for one frame of emulation (see below)
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To prevent audio clashes, we use double buffering technique:
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one buffer is the active DMA buffer
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the other one is the current work buffer (updated during frame emulation)
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We do not need more since frame emulation is synchronized with DMA execution
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*/
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u8 soundbuffer[2][3840] ATTRIBUTE_ALIGN(32);
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/* Current work soundbuffer */
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int mixbuffer;
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/* Current DMA length (required to be a factor of 32-bytes)
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length is calculated regarding current emulation timings:
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PAL timings : 50 frames/sec, 48000 samples/sec = 960 samples per frame = 3840 bytes (16 bits stereo samples)
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NTSC timings: 60 frames/sec, 48000 samples/sec = 800 samples per frame = 3200 bytes (16 bits stereo samples)
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*/
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static int dma_len = 3200;
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/***
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AudioDmaCallback
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Genesis Plus only provides sound data on completion of each frame.
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To try to make the audio less choppy, we synchronize frame emulation with audio DMA
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This ensure we don't access current active audiobuffer until a new DMA has been started
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This also makes frame emulation sync completely independent from video sync
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***/
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static void AudioDmaCallback()
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{
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frameticker++;
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}
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/***
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ogc_audio__init
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This function initializes the Audio Interface and DMA callback
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Default samplerate is set to 48khZ
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***/
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void ogc_audio__init(void)
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{
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AUDIO_Init (NULL);
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AUDIO_SetDSPSampleRate (AI_SAMPLERATE_48KHZ);
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AUDIO_RegisterDMACallback (AudioDmaCallback);
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memset(soundbuffer, 0, 2 * 3840);
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}
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/***
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ogc_audio__update
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This function is called at the end of each frame, once the current soundbuffer has been updated
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DMA sync and switching ensure we never access the active DMA buffer
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This function set the next DMA buffer
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Parameters will be taken in account ONLY when current DMA has finished
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***/
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void ogc_audio__update(void)
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{
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AUDIO_InitDMA((u32) soundbuffer[mixbuffer], dma_len);
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DCFlushRange(soundbuffer[mixbuffer], dma_len);
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mixbuffer ^= 1;
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}
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/***
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ogc_audio__start
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This function restarts Audio DMA processing
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This is called only ONCE, when emulation loop starts or when coming back from Main Menu
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DMA length is used for frame emulation synchronization (PAL & NTSC timings)
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DMA is *automatically* restarted once the configured audio length has been output
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When DMA parameters are not updated, same soundbuffer is played again
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DMA parameters can be updated using successive calls to AUDIO_InitDMA (see above)
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***/
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void ogc_audio__start(void)
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{
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dma_len = vdp_pal ? 3840 : 3200;
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memset(soundbuffer[0], 0, dma_len);
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AUDIO_InitDMA((u32) soundbuffer[0], dma_len);
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DCFlushRange(soundbuffer[0], dma_len);
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AUDIO_StartDMA();
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mixbuffer = 1;
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}
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/***
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ogc_audio__stop
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This function reset current Audio DMA process
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This is called when going back to Main Menu
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DMA need to be restarted when going back to the game (see above)
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***/
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void ogc_audio__stop(void)
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{
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AUDIO_StopDMA ();
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}
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