alsa_aplay 出现 Warning: rate is not accurate

最近项目中需要添加88.2k rate的驱动支持。之前加过192k的HDMI trueHD支持，因此想88.2k应该是支持的，于是用cooledit 做了一个88.2k rate的wav文件，在串口中用alsa_aplay播放测试。

alsa_aplay -D hw:0,1 -t wav -c 2 -r 88200 -f S16_LE /storage/sdcard0/1k_10db_88k_60s.wav

出现如下提示：

Signed 16 bit Little Endian, Rate 88200 Hz, Stereo，

Warning: rate is not accurate (requested = 88200Hz, got = 96000Hz)

please, try the plug plugin

搜索了一下打印的地方代码。

external/alsa-utils/aplay/aplay.c

static void set_params(void)
{
snd_pcm_hw_params_t *params;
snd_pcm_sw_params_t *swparams;
snd_pcm_uframes_t buffer_size;
int err;
size_t n;
unsigned int rate;
snd_pcm_uframes_t start_threshold, stop_threshold;
snd_pcm_hw_params_alloca(¶ms);
snd_pcm_sw_params_alloca(&swparams);
err = snd_pcm_hw_params_any(handle, params);
if (err < 0) {
error(_("Broken configuration for this PCM: no configurations available"));
prg_exit(EXIT_FAILURE);
}

...........................

rate = hwparams.rate;
err = snd_pcm_hw_params_set_rate_near(handle, params, &hwparams.rate, 0);
assert(err >= 0);
if ((float)rate * 1.05 < hwparams.rate || (float)rate * 0.95 > hwparams.rate) {
if (!quiet_mode) {
char plugex[64];
const char *pcmname = snd_pcm_name(handle);
<span style="color:#ff0000;">fprintf(stderr, _("Warning: rate is not accurate (requested = %iHz, got = %iHz)\n"), rate, hwparams.rate);
</span>			if (! pcmname || strchr(snd_pcm_name(handle), ':'))
*plugex = 0;
else
snprintf(plugex, sizeof(plugex), "(-Dplug:%s)",
snd_pcm_name(handle));
fprintf(stderr, _("         please, try the plug plugin %s\n"),
plugex);
}
}
rate = hwparams.rate;

从打印来看，rate = 88.2k, alsa_aplay传递过来的参数，hwparams.rate=96k是从底层snd_pcm_hw_params获得的参数。

因此，可以判断是底层kernel的参数没有加88.2k的支持，检查后果然发现对应的dai没有加这个rate的支持。

static struct snd_soc_dai_driver xxx_dai[] = {
{
.name = "xxx-dai",
.playback = {
.stream_name = "S/PDIF Playback",
.channels_min = 1,
.channels_max = 8,
.rates = (
SNDRV_PCM_RATE_32000 |
SNDRV_PCM_RATE_44100 |
SNDRV_PCM_RATE_48000 |
<span style="color:#ff6666;"><strong>SNDRV_PCM_RATE_88200 |</strong></span>
SNDRV_PCM_RATE_96000  |
SNDRV_PCM_RATE_176400 |
SNDRV_PCM_RATE_192000),
.formats = (SNDRV_PCM_FMTBIT_S16_LE | SNDRV_PCM_FMTBIT_S24_LE | SNDRV_PCM_FMTBIT_S32_LE)。