How to config McASP/ALSA to convert audio sample size from 32-bit to 16-bit

PEleph

Other Parts Discussed in Thread: PCM3168A, PCM3168

Hi all,

I have am335x processor connected to a PCM Codec (sound card: TI PCM3168a) through McASPs.

The PCM Codec is config to run at 16kHz, 24bit/data sample (padded to 32bits, so each sample is clocked as 32bits with a depth of 24bits).

Since the data format from the sound card (PCM Codec) is 32bits/sample, this "big" size per sample of Audio data are captured by McASP and transfer to the kernel, then transfer to user space through ALSA interface.

I am trying to find a way to config McASP and/or ALSA to convert this sample size to 16 bits before passing them to user space.

Is this something someone at TI can help me with?

here is how i have defined the soc_dai_driver for this sound card kernel driver i have created under the kernel tree /sound/soc/codecs/ pcm3168.c

static struct snd_soc_dai_driver pcm3168_dai = {
.name = DRV_NAME,
.playback = {
.stream_name = "Playback",
.channels_min = 8,
.channels_max = 8,
.rates = 16000,
.formats = SNDRV_PCM_FMTBIT_S32_LE,
},
.capture = {
.stream_name = "Capture",
.channels_min = 8,
.channels_max = 8,
.rates = 16000,
.formats = SNDRV_PCM_FMTBIT_S32_LE,

};

over 9 years ago

0 Biser Gatchev-XID over 9 years ago

TI__Guru**** 393215 points

I will ask the software team to comment if this is possible.

0 Yordan Kovachev over 9 years ago

TI__Guru**** 161600 points

Hi,

Have you tried changing the format to:
.formats = SNDRV_PCM_FMTBIT_S16_LE => 16 bit little endian

Or using aplay -F S16_LE => 16 bit little endian ? What is the result?

Best Regards,
Yordan

0 PEleph over 9 years ago in reply to Yordan Kovachev

Intellectual 735 points

Yes, I have tried

.formats = SNDRV_PCM_FMTBIT_S16_LE

without success. with this change, I do not get any audio sound out of the audio sound card even though by reading McASP wFIFO many times, I do see its value changing.

If I dump the audio data from the sound card with arecord for example, it is all zero!! (arecord --device=sysdefault:CARD=PCM3168a --channel=8 --rate=16000 --format=16LE record.wav

So definitively, there is more change required to be able to config McASP to get 16bits for each channel from a sound card that is sending 32bits/sample.

Any more thoughts?

0 Yordan Kovachev over 9 years ago in reply to PEleph

TI__Guru**** 161600 points

Hi,

You may also need to hardcode the slot width in your codec driver, i.e. you should have something like the bellow code in <codec>_hw_params():
switch (snd_pcm_format_width(params_format(params))) {
case 16:
alen = PCM512x_ALEN_16;
break;
case 20:
alen = PCM512x_ALEN_20;
break;
case 24:
alen = PCM512x_ALEN_24;
break;
case 32:
alen = PCM512x_ALEN_32;
break;
default:
dev_err(codec->dev, "Bad frame size: %d\n",
snd_pcm_format_width(params_format(params)));
return -EINVAL;
}

And then set the slot width in pcm3168 registers:
ret = regmap_update_bits(pcm512x->regmap, PCM512x_I2S_1,
PCM512x_ALEN, alen);

So track the how the format is passed throughout the sound arch and hardcode the slot width.

Also check in the alsa configuration in the filesystem; modify /etc/asound.conf with something like:
pcm.device{
format S16_LE
rate 96000
type hw
card 0
device 0
}

Best Regards,
Yordan

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How to config McASP/ALSA to convert audio sample size from 32-bit to 16-bit