source: vital-to8-sdk/music/mod/alsa_playback.c @ 1

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sched.h>
#include <errno.h>
#include <getopt.h>
#include <alsa/asoundlib.h>
#include <sys/time.h>
#include <math.h>

static char *device = "plughw:0,0";                     /* playback device */
static snd_pcm_format_t format = SND_PCM_FORMAT_S16;    /* sample format */
static unsigned int rate = 44100;                       /* stream rate */
static unsigned int channels = 1;                       /* count of channels */
static unsigned int buffer_time = 500000;               /* ring buffer length in us */
static unsigned int period_time = 100000;               /* period time in us */
static int resample = 1;                                /* enable alsa-lib resampling */
static int period_event = 0;                            /* produce poll event after each period */
static snd_pcm_sframes_t buffer_size;
static snd_pcm_sframes_t period_size;
static snd_output_t *output = NULL;

static void generate_sine(const snd_pcm_channel_area_t *areas, 
                          snd_pcm_uframes_t offset,
                          int count, double *_phase)
{
        unsigned char *samples[channels];
        int steps[channels];
        unsigned int chn;
        int format_bits = snd_pcm_format_width(format);
        unsigned int maxval = (1 << (format_bits - 1)) - 1;
        int bps = format_bits / 8;  /* bytes per sample */
        int phys_bps = snd_pcm_format_physical_width(format) / 8;
        int big_endian = snd_pcm_format_big_endian(format) == 1;
        int to_unsigned = snd_pcm_format_unsigned(format) == 1;

        /* verify and prepare the contents of areas */
        for (chn = 0; chn < channels; chn++) {
                if ((areas[chn].first % 8) != 0) {
                        printf("areas[%i].first == %i, aborting...\n", chn, areas[chn].first);
                        exit(EXIT_FAILURE);
                }
                samples[chn] = (((unsigned char *)areas[chn].addr) + (areas[chn].first / 8));
                if ((areas[chn].step % 16) != 0) {
                        printf("areas[%i].step == %i, aborting...\n", chn, areas[chn].step);
                        exit(EXIT_FAILURE);
                }
                steps[chn] = areas[chn].step / 8;
                samples[chn] += offset * steps[chn];
        }
        /* fill the channel areas */
        while (count-- > 0) {
                int res, i;
                int tab[1];

                build_chunk(1,&tab);
                res=tab[0]*127;
                
                if (to_unsigned)
                        res ^= 1U << (format_bits - 1);
                for (chn = 0; chn < channels; chn++) {
                        /* Generate data in native endian format */
                        if (big_endian) {
                                for (i = 0; i < bps; i++)
                                        *(samples[chn] + phys_bps - 1 - i) = (res >> i * 8) & 0xff;
                        } else {
                                for (i = 0; i < bps; i++)
                                        *(samples[chn] + i) = (res >>  i * 8) & 0xff;
                        }
                        samples[chn] += steps[chn];
                }
        }
}


static int set_hwparams(snd_pcm_t *handle,
                        snd_pcm_hw_params_t *params,
                        snd_pcm_access_t access)
{
        unsigned int rrate;
        snd_pcm_uframes_t size;
        int err, dir;
        /* choose all parameters */
        err = snd_pcm_hw_params_any(handle, params);
        if (err < 0) {
                printf("Broken configuration for playback: no configurations available: %s\n", snd_strerror(err));
                return err;
        }
        /* set hardware resampling */
        err = snd_pcm_hw_params_set_rate_resample(handle, params, resample);
        if (err < 0) {
                printf("Resampling setup failed for playback: %s\n", snd_strerror(err));
                return err;
        }
        /* set the interleaved read/write format */
        err = snd_pcm_hw_params_set_access(handle, params, access);
        if (err < 0) {
                printf("Access type not available for playback: %s\n", snd_strerror(err));
                return err;
        }
        /* set the sample format */
        err = snd_pcm_hw_params_set_format(handle, params, format);
        if (err < 0) {
                printf("Sample format not available for playback: %s\n", snd_strerror(err));
                return err;
        }
        /* set the count of channels */
        err = snd_pcm_hw_params_set_channels(handle, params, channels);
        if (err < 0) {
                printf("Channels count (%i) not available for playbacks: %s\n", channels, snd_strerror(err));
                return err;
        }
        /* set the stream rate */
        rrate = rate;
        err = snd_pcm_hw_params_set_rate_near(handle, params, &rrate, 0);
        if (err < 0) {
                printf("Rate %iHz not available for playback: %s\n", rate, snd_strerror(err));
                return err;
        }
        if (rrate != rate) {
                printf("Rate doesn't match (requested %iHz, get %iHz)\n", rate, err);
                return -EINVAL;
        }
        /* set the buffer time */
        err = snd_pcm_hw_params_set_buffer_time_near(handle, params, &buffer_time, &dir);
        if (err < 0) {
                printf("Unable to set buffer time %i for playback: %s\n", buffer_time, snd_strerror(err));
                return err;
        }
        err = snd_pcm_hw_params_get_buffer_size(params, &size);
        if (err < 0) {
                printf("Unable to get buffer size for playback: %s\n", snd_strerror(err));
                return err;
        }
        buffer_size = size;
        /* set the period time */
        err = snd_pcm_hw_params_set_period_time_near(handle, params, &period_time, &dir);
        if (err < 0) {
                printf("Unable to set period time %i for playback: %s\n", period_time, snd_strerror(err));
                return err;
        }
        err = snd_pcm_hw_params_get_period_size(params, &size, &dir);
        if (err < 0) {
                printf("Unable to get period size for playback: %s\n", snd_strerror(err));
                return err;
        }
        period_size = size;
        /* write the parameters to device */
        err = snd_pcm_hw_params(handle, params);
        if (err < 0) {
                printf("Unable to set hw params for playback: %s\n", snd_strerror(err));
                return err;
        }
        return 0;
}
static int set_swparams(snd_pcm_t *handle, snd_pcm_sw_params_t *swparams)
{
        int err;
        /* get the current swparams */
        err = snd_pcm_sw_params_current(handle, swparams);
        if (err < 0) {
                printf("Unable to determine current swparams for playback: %s\n", snd_strerror(err));
                return err;
        }
        /* start the transfer when the buffer is almost full: */
        /* (buffer_size / avail_min) * avail_min */
        err = snd_pcm_sw_params_set_start_threshold(handle, swparams, (buffer_size / period_size) * period_size);
        if (err < 0) {
                printf("Unable to set start threshold mode for playback: %s\n", snd_strerror(err));
                return err;
        }
        /* allow the transfer when at least period_size samples can be processed */
        /* or disable this mechanism when period event is enabled (aka interrupt like style processing) */
        err = snd_pcm_sw_params_set_avail_min(handle, swparams, period_event ? buffer_size : period_size);
        if (err < 0) {
                printf("Unable to set avail min for playback: %s\n", snd_strerror(err));
                return err;
        }
        /* enable period events when requested */
        if (period_event) {
                err = snd_pcm_sw_params_set_period_event(handle, swparams, 1);
                if (err < 0) {
                        printf("Unable to set period event: %s\n", snd_strerror(err));
                        return err;
                }
        }
        /* write the parameters to the playback device */
        err = snd_pcm_sw_params(handle, swparams);
        if (err < 0) {
                printf("Unable to set sw params for playback: %s\n", snd_strerror(err));
                return err;
        }
        return 0;
}
/*
 *   Underrun and suspend recovery
 */
 
static int xrun_recovery(snd_pcm_t *handle, int err)
{
        if (err == -EPIPE) {    /* under-run */
                err = snd_pcm_prepare(handle);
                if (err < 0)
                        printf("Can't recovery from underrun, prepare failed: %s\n", snd_strerror(err));
                return 0;
        } else if (err == -ESTRPIPE) {
                while ((err = snd_pcm_resume(handle)) == -EAGAIN)
                        sleep(1);       /* wait until the suspend flag is released */
                if (err < 0) {
                        err = snd_pcm_prepare(handle);
                        if (err < 0)
                                printf("Can't recovery from suspend, prepare failed: %s\n", snd_strerror(err));
                }
                return 0;
        }
        return err;
}

struct async_private_data {
        signed short *samples;
        snd_pcm_channel_area_t *areas;
        double phase;
};

static void async_callback(snd_async_handler_t *ahandler)
{
        snd_pcm_t *handle = snd_async_handler_get_pcm(ahandler);
        struct async_private_data *data = snd_async_handler_get_callback_private(ahandler);
        signed short *samples = data->samples;
        snd_pcm_channel_area_t *areas = data->areas;
        snd_pcm_sframes_t avail;
        int err;
        
        avail = snd_pcm_avail_update(handle);
        while (avail >= period_size) {
                generate_sine(areas, 0, period_size, &data->phase);
                err = snd_pcm_writei(handle, samples, period_size);
                if (err < 0) {
                        printf("Write error: %s\n", snd_strerror(err));
                        exit(EXIT_FAILURE);
                }
                if (err != period_size) {
                        printf("Write error: written %i expected %li\n", err, period_size);
                        exit(EXIT_FAILURE);
                }
                avail = snd_pcm_avail_update(handle);
        }
}

struct async_private_data data;

static int async_loop(snd_pcm_t *handle,
                      signed short *samples,
                      snd_pcm_channel_area_t *areas)
{
        snd_async_handler_t *ahandler;
        int err, count;
        data.samples = samples;
        data.areas = areas;
        data.phase = 0;
        
        snd_pcm_prepare (handle);
        
        err = snd_async_add_pcm_handler(&ahandler, handle, async_callback, &data);
        if (err < 0) {
                printf("Unable to register async handler\n");
                exit(EXIT_FAILURE);
        }
        for (count = 0; count < 2; count++) {
                generate_sine(areas, 0, period_size, &data.phase);
                err = snd_pcm_writei(handle, samples, period_size);
                if (err < 0) {
                        printf("Initial write error: %s\n", snd_strerror(err));
                        exit(EXIT_FAILURE);
                }
                if (err != period_size) {
                        printf("Initial write error: written %i expected %li\n", err, period_size);
                        exit(EXIT_FAILURE);
                }
        }
        if (snd_pcm_state(handle) == SND_PCM_STATE_PREPARED) {
                err = snd_pcm_start(handle);
                if (err < 0) {
                        printf("Start error: %s\n", snd_strerror(err));
                        exit(EXIT_FAILURE);
                }
        }
}

static snd_pcm_t *handle=NULL;
static snd_pcm_channel_area_t *areas=NULL;
signed short *samples;


int
start_playback(void) {
        int err, morehelp;
        snd_pcm_hw_params_t *hwparams;
        snd_pcm_sw_params_t *swparams;
        int method = 0;
        unsigned int chn;
        snd_pcm_hw_params_alloca(&hwparams);
        snd_pcm_sw_params_alloca(&swparams);
        
         if ((err = snd_pcm_open(&handle, device, SND_PCM_STREAM_PLAYBACK, 0)) < 0) {
                printf("Playback open error: %s\n", snd_strerror(err));
                return 0;
        }
        
        if ((err = set_hwparams(handle, hwparams, SND_PCM_ACCESS_RW_INTERLEAVED)) < 0) {
                printf("Setting of hwparams failed: %s\n", snd_strerror(err));
                exit(EXIT_FAILURE);
        }
        if ((err = set_swparams(handle, swparams)) < 0) {
                printf("Setting of swparams failed: %s\n", snd_strerror(err));
                exit(EXIT_FAILURE);
        }

        samples = malloc((period_size * channels * snd_pcm_format_physical_width(format)) / 8);
        if (samples == NULL) {
                printf("No enough memory\n");
                exit(EXIT_FAILURE);
        }
        
        areas = calloc(channels, sizeof(snd_pcm_channel_area_t));
        if (areas == NULL) {
                printf("No enough memory\n");
                exit(EXIT_FAILURE);
        }
        for (chn = 0; chn < channels; chn++) {
                areas[chn].addr = samples;
                areas[chn].first = chn * snd_pcm_format_physical_width(format);
                areas[chn].step = channels * snd_pcm_format_physical_width(format);
        }
        err = async_loop(handle, samples, areas);
        if (err < 0)
                printf("Transfer failed: %s\n", snd_strerror(err));
}

 void stop_playback() {
         if (handle!=NULL) {
                snd_pcm_drop(handle);
        free(areas);
        free(samples);
        snd_pcm_close(handle);
        handle=NULL;
        }
}