myalsa.c

The purpose of this program is to run as a server, which can receive requirement from clients and se

#include <stdio.h>
#include <stdlib.h>
#include <alsa/asoundlib.h>
#include "myalsa.h"

snd_pcm_t *pcm_handler;          /* handler for PCM devices */
snd_pcm_hw_params_t *hwparams;  /* hold configuration to be used for PCM stream */

int rate, framesize, periods;      /* some hardware parameters */
snd_pcm_uframes_t frames;

void
alsa_init(void) 
{
    int ret_val;
    
    ret_val = snd_pcm_open(&pcm_handler, PCM_NAME, SND_PCM_STREAM_PLAYBACK, 0);
    if (ret_val < 0)
        err_exit("open PCM device error!");
}

//void
//alsa_config(int rate, int channels) 
void
alsa_config(void)
{
    int ret_val;
    
    /* allocate space for hwparams */
    snd_pcm_hw_params_alloca(&hwparams);
    
    /* fill it in with default values */
    ret_val = snd_pcm_hw_params_any(pcm_handler, hwparams);
    if (ret_val < 0)
        err_exit("config error");
        
    /* set access type */
    ret_val = snd_pcm_hw_params_set_access(pcm_handler, hwparams, SND_PCM_ACCESS_RW_INTERLEAVED);
    if (ret_val < 0) 
        err_cont("set access sype error");
    
    /* signed 16 bit little endian format */
    ret_val = snd_pcm_hw_params_set_format(pcm_handler, hwparams, SND_PCM_FORMAT_S16_LE);
    if (ret_val < 0)
        err_cont("set format error");
    
    /* set rate */
    rate = 44100;
    ret_val = snd_pcm_hw_params_set_rate_near(pcm_handler, hwparams, &rate, 0);
    if (ret_val < 0)
        err_cont("set rate error");

    /* two channels */
    ret_val = ret_val = snd_pcm_hw_params_set_channels(pcm_handler, hwparams, 2);
    if (ret_val < 0)
        err_cont("set channels error");
    
    /* set period size */
    frames = 32;
    ret_val = snd_pcm_hw_params_set_period_size_near(pcm_handler, hwparams, &frames, 0);
    if (ret_val < 0)
        err_cont("set period size error");

    /* apply hardware parameters */
    ret_val = snd_pcm_hw_params(pcm_handler, hwparams);
    if (ret_val < 0)
        err_exit("set config error");
}

void
alsa_play(unsigned char* buf, int len)
{
    int ret_val, nloops;
    int size;
    unsigned char *alsa_buf;
    unsigned char *ptr = buf;
        
    /* Use a buffer large enough to hold one period */
    size = frames * 4; /* 2 bytes/sample, 2 channels */
    alsa_buf = (char *) malloc(size);

    nloops = (len/size);
        
    while (nloops-- > 0) {
        memmove(alsa_buf, ptr, size);
        ptr += size;
        len -= size;
        ret_val = snd_pcm_writei(pcm_handler, alsa_buf, frames);
        if (ret_val == -EPIPE) {
            fprintf(stderr, "%d, underrun occurred\n", nloops);
            snd_pcm_prepare(pcm_handler);
            break;
        }
    }

    if (len > 0 && len < size) {
        frames = (len/4);
        memmove(alsa_buf, ptr, len);
        ret_val = snd_pcm_writei(pcm_handler, alsa_buf, frames);
        if (ret_val == -EPIPE) {
            fprintf(stderr, "underrun occurred\n");
            snd_pcm_prepare(pcm_handler);
        }
    }
}

void
alsa_finish(void) 
{
    int ret_val;
    
    ret_val = snd_pcm_drain(pcm_handler);
    if (ret_val < 0)
        err_exit("snd_pcm_drain error");
    
    ret_val = snd_pcm_close(pcm_handler);
    if (ret_val < 0)
        err_exit("snd_pcm_close error");
}