Hi everybody,

I am new to ALSA-API and would be glad, if someone give me an advice to the following questions. Up to now I used Rtaudio for cross compiling the player for windows and Linux. But know I need to go more into ALSA...

- Am I right to use async mode to get lowest latency times and using pause/play/stop?

- I used the following piece of code. But don't get any output. The callback output shows "avail" with very short count of frames...

I write a whole file (raw) to buffer, called buffer_alsa with 6894888 frames. What is going wrong?

I get this output:

Frames: 6894888 buffer_size (frames): 2048 buffer_time (frames): 46439 period_size (frames): 256 period_time (usec): 5804 periods (count): 8 Avail: 1540 Avail: 1285 Avail: 1030 Avail: 775 Avail: 520 Avail: 265 Avail: 10 Avail: 2 Avail: 2 Avail: 3 Avail: 2 ...

The code follows ...

Best regards Thomas

-----------------------------

void MyCallback(snd_async_handler_t *pcm_callback) { snd_pcm_t *handle = snd_async_handler_get_pcm(pcm_callback); snd_pcm_sframes_t avail;

//std::cout << "Period_size: " << period_size << std::endl;

avail = snd_pcm_avail_update(handle); while (avail >= period_size) { snd_pcm_writei(handle, buffer_alsa , period_size); avail = snd_pcm_avail_update(handle); std::cout << " Avail: " << avail << std::endl; } }

//----------------------------------------------------

snd_pcm_hw_params_alloca(&params);

if ((err = snd_pcm_hw_params_any(handle, params)) < 0) std::cout << " Error (reading configuration): " << snd_strerror(err) << std::endl;

/* Set parameters */ if ((err = snd_pcm_hw_params_set_access(handle, params,SND_PCM_ACCESS_RW_INTERLEAVED)) < 0) //printf("ERROR: Can't set interleaved mode. %s\n", snd_strerror(err)); std::cout << " Error (can't set interleaved mode): " << snd_strerror(err) << std::endl;

if ((err = snd_pcm_hw_params_set_format(handle, params, FORMAT)) < 0) //printf("ERROR: Can't set format. %s\n", snd_strerror(err)); std::cout << " Error (can't set format): " << snd_strerror(err) << std::endl;

if ((err = snd_pcm_hw_params_set_channels(handle, params, data.channels)) < 0) //printf("ERROR: Can't set channels number. %s\n", snd_strerror(err)); std::cout << " Error (can't set channels number): " << snd_strerror(err) << std::endl;

if ((err = snd_pcm_hw_params_set_rate_near(handle, params, &fs, 0)) < 0) //printf("ERROR: Can't set rate. %s\n", snd_strerror(err)); std::cout << " Error (can't set rate): " << snd_strerror(err) << std::endl;

if ((err = snd_pcm_hw_params_set_buffer_size_near(handle, params, &buffer_size)) < 0) std::cout << " Error (can't set buffer size): " << snd_strerror(err) << std::endl;

if ((err = snd_pcm_hw_params_set_period_size_near (handle, params, &period_size, NULL)) < 0) std::cout << " Error (can't set period size): " << snd_strerror(err) << std::endl;

/* Write parameters */ if ((err = snd_pcm_hw_params(handle, params)) < 0) //printf("ERROR: Can't set hardware parameters. %s\n", snd_strerror(err)); std::cout << " Error (can't set harware params): " << snd_strerror(err) << std::endl;

//---------------------- ------------------------------

// Get Parameters snd_pcm_hw_params_get_buffer_size(params, &buffer_sz); std::cout << " buffer_size (frames): " << buffer_sz << std::endl;

snd_pcm_hw_params_get_buffer_time(params, &buffer_tm, NULL); std::cout << " buffer_time (frames): " << buffer_tm << std::endl;

snd_pcm_hw_params_get_period_size(params, &aframes, 0); std::cout << " period_size (frames): " << aframes << std::endl;

snd_pcm_hw_params_get_period_time(params, &data.channels, NULL); // tmp Zeit in us std::cout << " period_time (usec): " << data.channels << std::endl;

snd_pcm_hw_params_get_periods(params, &piods, 0); std::cout << " periods (count): " << piods << std::endl;

// ----------------------------------------------------------------------------

//snd_pcm_hw_params_free (params);

// --------------------- Hardware-Params End ------------------------------

snd_pcm_sw_params_t *sw_params;

if ((err = snd_pcm_sw_params_malloc (&sw_params)) < 0) { std::cout << " Error (can't allocate sw params): " << snd_strerror(err) << std::endl; return; } if ((err = snd_pcm_sw_params_current(handle, sw_params)) < 0) { std::cout << "Error (can't return curr sw config): " << snd_strerror(err) << std::endl; return; }

if ((err = snd_pcm_sw_params_set_start_threshold (handle, sw_params, buffer_size)) < 0) // 0U oder 4096 ? { // This parameter controls the wake up point. If the count of available samples is equal or greater than this value, then the application will be activated. std::cout << "Error (can't set start thresh mode): " << snd_strerror(err) << std::endl; return; } /* if ((err = snd_pcm_sw_params_set_silence_threshold( handle, sw_params, 0 )) < 0) { std::cout << " Error (can't set silence thres): " << snd_strerror(err) << std::endl; return; } */ if ((err = snd_pcm_sw_params_set_avail_min (handle, sw_params, period_size)) < 0) { std::cout << " Error (can't set min avail count): " << snd_strerror(err) << std::endl; return; } // here are two options for a fix //snd_pcm_sw_params_set_silence_size( phandle, sw_params, ULONG_MAX ); /* snd_pcm_uframes_t val; if ((err = snd_pcm_sw_params_get_boundary(sw_params, &val)) < 0) { std::cout << " Error (can't get boundary): " << snd_strerror(err) << std::endl; return; } if ((err = snd_pcm_sw_params_set_silence_size(handle, sw_params, val)) < 0) { std::cout << " Error (can't set silence): " << snd_strerror(err) << std::endl; return; } */ if ((err = snd_pcm_sw_params(handle, sw_params)) < 0) { std::cout << " Error (can't set sw params): " << snd_strerror(err) << std::endl; return; } snd_pcm_sw_params_free(sw_params);

// ------------------------- SW-Params End ---------------------------------

if ((err = snd_pcm_prepare(handle)) < 0) { std::cout << " Error (can't prepare audio): " << snd_strerror(err) << std::endl; return; } snd_async_handler_t *pcm_callback; if ((err = snd_async_add_pcm_handler(&pcm_callback, handle, MyCallback, NULL)) < 0) { std::cout << " Error (can't add pcm handler): " << snd_strerror(err) << std::endl; return; } if ((err = snd_pcm_writei(handle, buffer_alsa, 2 * period_size) == -EPIPE)) { std::cout << " Error: XRUN" << std::endl; err = snd_pcm_recover(handle, err, 0); if ((err = snd_pcm_prepare (handle)) < 0) { std::cout << " Error (can't prepare audio): " << snd_strerror(err) << std::endl; return; } } if ((err = snd_pcm_start(handle)) < 0) { std::cout << " Error (can't start audio): " << snd_strerror(err) << std::endl; return; }

void MyCallback(snd_async_handler_t *pcm_callback);