[Alsa-devel] How to use mmap?

[sendto]

Hi,all.
I'm a newbie of ALSA. I'm learning how to program with alsa-lib, I found that mmap is 
a better way to used then write/read(oh, is that right?).
But I found that there are few cocumentation reference to it. So, I want to ask how to 
use mmap.
I think a good and simple example is good for newbie. Can anybody transtion this 
example to use mmap. This example is copy from "A Tutorial on Using the ALSA Audio 
API".

        #include <stdio.h>
        #include <stdlib.h>
        #include <alsa/asoundlib.h>
              
        main (int argc, char *argv[])
        {
                int i;
                int err;
                short buf[128];
                snd_pcm_t *playback_handle;
                snd_pcm_hw_params_t *hw_params;
        
                if ((err = snd_pcm_open (&playback_handle, argv[1], 
SND_PCM_STREAM_PLAYBACK, 0)) < 0) {
                        fprintf (stderr, "cannot open audio device %s (%s)\n", 
                                 argv[1],
                                 snd_strerror (err));
                        exit (1);
                }
                   
                if ((err = snd_pcm_hw_params_malloc (&hw_params)) < 0) {
                        fprintf (stderr, "cannot allocate hardware parameter structure 
(%s)\n",
                                 snd_strerror (err));
                        exit (1);
                }
                                 
                if ((err = snd_pcm_hw_params_any (playback_handle, hw_params)) < 0) {
                        fprintf (stderr, "cannot initialize hardware parameter 
structure (%s)\n",
                                 snd_strerror (err));
                        exit (1);
                }
        
                if ((err = snd_pcm_hw_params_set_access (playback_handle, hw_params, 
SND_PCM_ACCESS_RW_INTERLEAVED)) < 0) {
                        fprintf (stderr, "cannot set access type (%s)\n",
                                 snd_strerror (err));
                        exit (1);
                }
        
                if ((err = snd_pcm_hw_params_set_format (playback_handle, hw_params, 
SND_PCM_FORMAT_S16_LE)) < 0) {
                        fprintf (stderr, "cannot set sample format (%s)\n",
                                 snd_strerror (err));
                        exit (1);
                }
        
                if ((err = snd_pcm_hw_params_set_rate_near (playback_handle, 
hw_params, 44100, 0)) < 0) {
                        fprintf (stderr, "cannot set sample rate (%s)\n",
                                 snd_strerror (err));
                        exit (1);
                }
        
                if ((err = snd_pcm_hw_params_set_channels (playback_handle, hw_params, 
2)) < 0) {
                        fprintf (stderr, "cannot set channel count (%s)\n",
                                 snd_strerror (err));
                        exit (1);
                }
        
                if ((err = snd_pcm_hw_params (playback_handle, hw_params)) < 0) {
                        fprintf (stderr, "cannot set parameters (%s)\n",
                                 snd_strerror (err));
                        exit (1);
                }
        
                snd_pcm_hw_params_free (hw_params);
        
                if ((err = snd_pcm_prepare (playback_handle)) < 0) {
                        fprintf (stderr, "cannot prepare audio interface for use 
(%s)\n",
                                 snd_strerror (err));
                        exit (1);
                }
        
                for (i = 0; i < 10; ++i) {
                        if ((err = snd_pcm_writei (playback_handle, buf, 128)) != 128) 
{
                                fprintf (stderr, "write to audio interface failed 
(%s)\n",
                                         snd_strerror (err));
                                exit (1);
                        }
                }
        
                snd_pcm_close (playback_handle);
                exit (0);
        }
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