audio/maxmod/streaming/source/main.c

/****************************************************************
 * this example demonstrates streaming synthensized audio
 ****************************************************************/
 
#include <nds.h>
#include <stdio.h>
#include <maxmod9.h>

int sine;       // sine position
int lfo;        // LFO position

//-----------------------------------------------------------------------------
enum {
//-----------------------------------------------------------------------------
    // waveform base frequency
    sine_freq = 500,
    
    // LFO frequency
    lfo_freq = 3,
    
    // LFO output shift amount
    lfo_shift = 4,
    
    // blue backdrop
    bg_colour = 13 << 10,
    
    // red cpu usage
    cpu_colour = 31
};

/***********************************************************************************
 * on_stream_request
 *
 * Audio stream data request handler.
 ***********************************************************************************/
mm_word on_stream_request( mm_word length, mm_addr dest, mm_stream_formats format ) {
//----------------------------------------------------------------------------------
    
    s16 *target = dest;
    
    //------------------------------------------------------------
    // synthensize a sine wave with an LFO applied to the pitch
    // the stereo data is interleaved
    //------------------------------------------------------------
    int len = length;
    for( ; len; len-- )
    {
        int sample = sinLerp(sine);
        
        // output sample for left
        *target++ = sample;
        
        // output inverted sample for right
        *target++ = -sample;
        
        sine += sine_freq + (sinLerp(lfo) >> lfo_shift);
        lfo = (lfo + lfo_freq);
    }
    
    return length;
}

/**********************************************************************************
 * main
 *
 * Program Entry Point
 **********************************************************************************/
int main( void ) {
//---------------------------------------------------------------------------------

    //----------------------------------------------------------------
    // print out some stuff
    //----------------------------------------------------------------
    consoleDemoInit();
    iprintf( "\n    Maxmod Streaming Example   \n");

    //----------------------------------------------------------------
    // initialize maxmod without any soundbank (unusual setup)
    //----------------------------------------------------------------
    mm_ds_system sys;
    sys.mod_count           = 0;
    sys.samp_count          = 0;
    sys.mem_bank            = 0;
    sys.fifo_channel        = FIFO_MAXMOD;
    mmInit( &sys );
    
    //----------------------------------------------------------------
    // open stream
    //----------------------------------------------------------------
    mm_stream mystream;
    mystream.sampling_rate  = 25000;                    // sampling rate = 25khz
    mystream.buffer_length  = 1200;                     // buffer length = 1200 samples
    mystream.callback       = on_stream_request;        // set callback function
    mystream.format         = MM_STREAM_16BIT_STEREO;   // format = stereo 16-bit
    mystream.timer          = MM_TIMER0;                // use hardware timer 0
    mystream.manual         = true;                     // use manual filling
    mmStreamOpen( &mystream );
        
    //----------------------------------------------------------------
    // when using 'automatic' filling, your callback will be triggered
    // every time half of the wave buffer is processed.
    //
    // so: 
    // 25000 (rate)
    // ----- = ~21 Hz for a full pass, and ~42hz for half pass
    // 1200  (length)
    //----------------------------------------------------------------
    // with 'manual' filling, you must call mmStreamUpdate
    // periodically (and often enough to avoid buffer underruns)
    //----------------------------------------------------------------
    
    SetYtrigger( 0 );
    irqEnable( IRQ_VCOUNT );
    
    while( 1 )
    {
        // wait until line 0
        swiIntrWait( 0, IRQ_VCOUNT);
        
        // update stream
        mmStreamUpdate();
        
        // restore backdrop (some lines were drawn with another colour to show cpu usage)
        BG_PALETTE_SUB[0] = bg_colour;
        
        // wait until next frame
        swiWaitForVBlank();
        
        // set backdrop to show cpu usage
        BG_PALETTE_SUB[0] = cpu_colour;
    }
    
    return 0;
}