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<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=ANSI_X3.4-1968" /><title>Full Code Example</title><meta name="generator" content="DocBook XSL Stylesheets V1.75.2" /><link rel="home" href="index.html" title="Writing an ALSA Driver" /><link rel="up" href="ch05.html" title="Chapter 5. PCM Interface" /><link rel="prev" href="ch05.html" title="Chapter 5. PCM Interface" /><link rel="next" href="ch05s03.html" title="Constructor" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Full Code Example</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ch05.html">Prev</a> </td><th width="60%" align="center">Chapter 5. PCM Interface</th><td width="20%" align="right"> <a accesskey="n" href="ch05s03.html">Next</a></td></tr></table><hr /></div><div class="section" title="Full Code Example"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="pcm-interface-example"></a>Full Code Example</h2></div></div></div><p>
The example code below does not include any hardware access
routines but shows only the skeleton, how to build up the PCM
interfaces.
</p><div class="example"><a id="id2946143"></a><p class="title"><b>Example 5.1. PCM Example Code</b></p><div class="example-contents"><pre class="programlisting">
#include <sound/pcm.h>
....
/* hardware definition */
static struct snd_pcm_hardware snd_mychip_playback_hw = {
.info = (SNDRV_PCM_INFO_MMAP |
SNDRV_PCM_INFO_INTERLEAVED |
SNDRV_PCM_INFO_BLOCK_TRANSFER |
SNDRV_PCM_INFO_MMAP_VALID),
.formats = SNDRV_PCM_FMTBIT_S16_LE,
.rates = SNDRV_PCM_RATE_8000_48000,
.rate_min = 8000,
.rate_max = 48000,
.channels_min = 2,
.channels_max = 2,
.buffer_bytes_max = 32768,
.period_bytes_min = 4096,
.period_bytes_max = 32768,
.periods_min = 1,
.periods_max = 1024,
};
/* hardware definition */
static struct snd_pcm_hardware snd_mychip_capture_hw = {
.info = (SNDRV_PCM_INFO_MMAP |
SNDRV_PCM_INFO_INTERLEAVED |
SNDRV_PCM_INFO_BLOCK_TRANSFER |
SNDRV_PCM_INFO_MMAP_VALID),
.formats = SNDRV_PCM_FMTBIT_S16_LE,
.rates = SNDRV_PCM_RATE_8000_48000,
.rate_min = 8000,
.rate_max = 48000,
.channels_min = 2,
.channels_max = 2,
.buffer_bytes_max = 32768,
.period_bytes_min = 4096,
.period_bytes_max = 32768,
.periods_min = 1,
.periods_max = 1024,
};
/* open callback */
static int snd_mychip_playback_open(struct snd_pcm_substream *substream)
{
struct mychip *chip = snd_pcm_substream_chip(substream);
struct snd_pcm_runtime *runtime = substream->runtime;
runtime->hw = snd_mychip_playback_hw;
/* more hardware-initialization will be done here */
....
return 0;
}
/* close callback */
static int snd_mychip_playback_close(struct snd_pcm_substream *substream)
{
struct mychip *chip = snd_pcm_substream_chip(substream);
/* the hardware-specific codes will be here */
....
return 0;
}
/* open callback */
static int snd_mychip_capture_open(struct snd_pcm_substream *substream)
{
struct mychip *chip = snd_pcm_substream_chip(substream);
struct snd_pcm_runtime *runtime = substream->runtime;
runtime->hw = snd_mychip_capture_hw;
/* more hardware-initialization will be done here */
....
return 0;
}
/* close callback */
static int snd_mychip_capture_close(struct snd_pcm_substream *substream)
{
struct mychip *chip = snd_pcm_substream_chip(substream);
/* the hardware-specific codes will be here */
....
return 0;
}
/* hw_params callback */
static int snd_mychip_pcm_hw_params(struct snd_pcm_substream *substream,
struct snd_pcm_hw_params *hw_params)
{
return snd_pcm_lib_malloc_pages(substream,
params_buffer_bytes(hw_params));
}
/* hw_free callback */
static int snd_mychip_pcm_hw_free(struct snd_pcm_substream *substream)
{
return snd_pcm_lib_free_pages(substream);
}
/* prepare callback */
static int snd_mychip_pcm_prepare(struct snd_pcm_substream *substream)
{
struct mychip *chip = snd_pcm_substream_chip(substream);
struct snd_pcm_runtime *runtime = substream->runtime;
/* set up the hardware with the current configuration
* for example...
*/
mychip_set_sample_format(chip, runtime->format);
mychip_set_sample_rate(chip, runtime->rate);
mychip_set_channels(chip, runtime->channels);
mychip_set_dma_setup(chip, runtime->dma_addr,
chip->buffer_size,
chip->period_size);
return 0;
}
/* trigger callback */
static int snd_mychip_pcm_trigger(struct snd_pcm_substream *substream,
int cmd)
{
switch (cmd) {
case SNDRV_PCM_TRIGGER_START:
/* do something to start the PCM engine */
....
break;
case SNDRV_PCM_TRIGGER_STOP:
/* do something to stop the PCM engine */
....
break;
default:
return -EINVAL;
}
}
/* pointer callback */
static snd_pcm_uframes_t
snd_mychip_pcm_pointer(struct snd_pcm_substream *substream)
{
struct mychip *chip = snd_pcm_substream_chip(substream);
unsigned int current_ptr;
/* get the current hardware pointer */
current_ptr = mychip_get_hw_pointer(chip);
return current_ptr;
}
/* operators */
static struct snd_pcm_ops snd_mychip_playback_ops = {
.open = snd_mychip_playback_open,
.close = snd_mychip_playback_close,
.ioctl = snd_pcm_lib_ioctl,
.hw_params = snd_mychip_pcm_hw_params,
.hw_free = snd_mychip_pcm_hw_free,
.prepare = snd_mychip_pcm_prepare,
.trigger = snd_mychip_pcm_trigger,
.pointer = snd_mychip_pcm_pointer,
};
/* operators */
static struct snd_pcm_ops snd_mychip_capture_ops = {
.open = snd_mychip_capture_open,
.close = snd_mychip_capture_close,
.ioctl = snd_pcm_lib_ioctl,
.hw_params = snd_mychip_pcm_hw_params,
.hw_free = snd_mychip_pcm_hw_free,
.prepare = snd_mychip_pcm_prepare,
.trigger = snd_mychip_pcm_trigger,
.pointer = snd_mychip_pcm_pointer,
};
/*
* definitions of capture are omitted here...
*/
/* create a pcm device */
static int __devinit snd_mychip_new_pcm(struct mychip *chip)
{
struct snd_pcm *pcm;
int err;
err = snd_pcm_new(chip->card, "My Chip", 0, 1, 1, &pcm);
if (err < 0)
return err;
pcm->private_data = chip;
strcpy(pcm->name, "My Chip");
chip->pcm = pcm;
/* set operators */
snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_PLAYBACK,
&snd_mychip_playback_ops);
snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_CAPTURE,
&snd_mychip_capture_ops);
/* pre-allocation of buffers */
/* NOTE: this may fail */
snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_DEV,
snd_dma_pci_data(chip->pci),
64*1024, 64*1024);
return 0;
}
</pre></div></div><p><br class="example-break" />
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