c++ - Clicking in ALSA tone generator -


i'm learning use alsa on raspberry pi 2. i've written small test program in c++ generate 440 hz test tone. makes tone, there clicking sound twice per second in tone.

does have idea why might happening? code below.

#include <cmath> #include <climits> #include <iostream> #include <alsa/asoundlib.h>  #include "definitions.hpp"  using namespace std;  int main() {     int ret;      snd_pcm_t* pcm_handle;  // device handle     snd_pcm_stream_t stream = snd_pcm_stream_playback;     snd_pcm_hw_params_t* hwparams;  // hardware information     char* pcm_name = strdup("plughw:0,0");  // on-board audio jack     int rate = 48000;      const uint16 freq = 440;     long unsigned int buffersize = 8192*4;     const uint32 len = buffersize*100;     const float32 arg = 2 * 3.141592 * freq / rate;     sint16 vals[len];      for(int = 0; < len; = + 2) {         vals[i] = shrt_max * cos(arg * / 2);     }      snd_pcm_hw_params_alloca(&hwparams);      ret = snd_pcm_open(&pcm_handle, pcm_name, stream, 0);     cout << "opening: " << snd_strerror(ret) << endl;      ret = snd_pcm_hw_params_any(pcm_handle, hwparams);     cout << "initializing hwparams structure: " << snd_strerror(ret) << endl;         ret = snd_pcm_hw_params_set_access(pcm_handle, hwparams,             snd_pcm_access_rw_interleaved);     cout << "setting access: " << snd_strerror(ret) << endl;      ret = snd_pcm_hw_params_set_format(pcm_handle, hwparams,             snd_pcm_format_s16_le);     cout << "setting format: " << snd_strerror(ret) << endl;      ret = snd_pcm_hw_params_set_rate(pcm_handle, hwparams,             rate, (int)0);     cout << "setting rate: " << snd_strerror(ret) << endl;      ret = snd_pcm_hw_params_set_channels(pcm_handle, hwparams, 2);      cout << "setting channels: " << snd_strerror(ret) << endl;      ret = snd_pcm_hw_params_set_periods(pcm_handle, hwparams, 2, 0);     cout << "setting periods: " << snd_strerror(ret) << endl;      ret = snd_pcm_hw_params_set_buffer_size_near(pcm_handle, hwparams,             &buffersize);     cout << "setting buffer size: " << snd_strerror(ret) << endl;      ret = snd_pcm_hw_params(pcm_handle, hwparams);     cout << "applying parameters: " << snd_strerror(ret) << endl;      cout << endl << endl;       const void* ptr = (const void*)&vals;     int err;      {         ptr += buffersize;         ret = snd_pcm_writei(pcm_handle,                 ptr, len);          if(ret < 0) {             err = snd_pcm_prepare(pcm_handle);             cout << "preparing: " << snd_strerror(err)                 << endl;         }     } while(ret < 0);      cout << "writing data: " << ret << ", " << snd_strerror(ret)         << endl; }

when run it, terminal output. of course, there's no write error, number of bits written.

pi@raspberrypi:~/radio $ ./bin/alsatest  opening: success initializing hwparams structure: success setting access: success setting format: success setting rate: success setting channels: success setting periods: success setting buffer size: success applying parameters: success   writing data: 344110, unknown error 344110

update - next day ok. i've hooked output handy-dandy oscilloscope , saw following waveform. there seems discontinuity in signal every time there's click. added few lines count how many nearly-zero values next each other in sinusoid array, , there none. oddly enough, alsa sample program /test/pcm.c makes perfect wave. perhaps need write in small chunks? there doesn't seem difference between code , example.

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