audio.cpp

00001 #include "mbed.h"
00002 #include "audio.h"
00003 
00004 namespace NKAudio
00005 {
00006 
00007 AnalogOut speaker(AUDIO_DAC_PIN);
00008 Ticker sampleTicker;
00009 
00010 // audio samples
00011 // class static
00012 int8_t const * volatile AudioPlayer::nextSample;
00013 
00014 // class static
00015 uint16_t volatile AudioPlayer::samplesRemaining;
00016 
00017 // interrupt handler
00018 // class static
00019 void AudioPlayer::playAudioSample()
00020 {
00021     static uint16_t dcBias = DC_BIAS;
00022     if (samplesRemaining)
00023     {
00024         int8_t val     = *nextSample++;
00025         uint16_t val16 = dcBias + (val * 256);
00026         speaker.write_u16(val16);
00027         samplesRemaining--;
00028     }
00029     else
00030     {
00031         sampleTicker.detach();
00032         speaker.write_u16(dcBias);
00033     }
00034 }
00035 
00036 bool AudioPlayer::playAudio(int8_t const *start, uint16_t nsamples, AudioCallback cb)
00037 {
00038     if (!audioDone())
00039     {
00040         return false;
00041     }
00042     nextSample       = start;
00043     samplesRemaining = nsamples;
00044     sampleTicker.attach_us(&playAudioSample, SAMPLE_PERIOD_US);
00045     while (samplesRemaining)
00046     {
00047         if (cb != NULL)
00048         {
00049             cb();
00050         }
00051         wait_us(AUDIO_WAIT_DURATION_US);
00052     }
00053     return true;
00054 }
00055 
00056 } // namespace NKAudio