snd_pcm_hw_params_set_buffer_size() error: "Invalid argument"

Question

Why does the program below issue errors for snd_pcm_hw_params_set_period_size(), snd_pcm_hw_params_set_buffer_size(), and snd_pcm_hw_params_set_rate()? If I raise the value of SAMPLES to 768 it only issues an error to snd_pcm_hw_params_set_rate(). The value "512" is important here since I am porting a program to ALSA which uses 512 samples as the size of its buffer (or 256 frames).

The error message is simply "Invalid argument" - I know, it is obscure.

#include <stdlib.h>
#include <stdint.h>
#include <alsa/asoundlib.h>

#define STEREO              2
#define SIXTEENBITS         2
#define SAMPLES           512
#define PERIODS             2
#define SAMPLERATE      11025

void snd_error_checker(int error, char *function_name)
{
    if (error)
    {
        printf("Error (%s): %s\n", function_name, snd_strerror(error));
        // exit(EXIT_FAILURE);
    }
}

int main(void)
{
    snd_pcm_t *handle;
    uint32_t channels                   = STEREO;
    uint32_t sample_size                = SIXTEENBITS;
    uint32_t frame_size                 = sample_size * channels;
    snd_pcm_uframes_t frames            = SAMPLES / frame_size;
    snd_pcm_uframes_t frames_per_period = frames / PERIODS;
    int32_t dir = 0; // No idea what this does.
    snd_pcm_hw_params_t *params;
    int error;

    error = snd_pcm_open(&handle, "default", SND_PCM_STREAM_PLAYBACK, 0);
    snd_error_checker(error, "snd_pcm_open()");
    snd_pcm_hw_params_malloc(&params);
    error = snd_pcm_hw_params_any(handle, params);
    snd_error_checker(error, "snd_pcm_hw_params_any()");
    error = snd_pcm_hw_params_set_period_size(handle, params, frames_per_period, dir);
    snd_error_checker(error, "snd_pcm_hw_params_set_period_size()");
    error = snd_pcm_hw_params_set_periods(handle, params, PERIODS, dir);
    snd_error_checker(error, "snd_pcm_hw_params_set_periods()");
    error = snd_pcm_hw_params_set_buffer_size(handle, params, frames);
    snd_error_checker(error, "snd_pcm_hw_params_set_buffer_size()");
    error = snd_pcm_hw_params_set_rate(handle, params, SAMPLERATE, dir);
    snd_error_checker(error, "snd_pcm_hw_params_set_rate()");
    error = snd_pcm_hw_params_set_access(handle, params, SND_PCM_ACCESS_RW_INTERLEAVED);
    snd_error_checker(error, "snd_pcm_hw_params_set_access()");
    error = snd_pcm_hw_params_set_channels(handle, params, STEREO);
    snd_error_checker(error, "snd_pcm_hw_params_set_channels()");
    error = snd_pcm_hw_params_set_format(handle, params, SND_PCM_FORMAT_S16_LE);
    snd_error_checker(error, "snd_pcm_hw_params_set_format()");
    error = snd_pcm_hw_params(handle, params);
    snd_error_checker(error, "snd_pcm_hw_params()");

    snd_pcm_drain(handle);
    snd_pcm_close(handle);
    exit(EXIT_SUCCESS);
}

Answer 1

Hardware parameters depend on the capabilities of the hardware. You can use the get_xxx_min/max functions to determine what the hardware suports, or call set_xxx_near to choose the nearest actually supported value.

In any case, the hardware buffer size does not need to be the same as your application's buffer size.