Routing Audio PCM data from ttyUSB0 to ALSA

kishoreinme · 01-06-2012, 12:53 AM

Hello

I have a ttyUSB0 serial device which gives signed 16 bit PCM data at 8000 hz. I am able to capture this data by

cat /dev/ttyUSB0 > capture.raw

in the terminal and play it using audacity.

How do I redirect the sound directly to an audio device using ALSA or any other mode?

corp769 · 01-06-2012, 01:17 AM

You could always perform the following to route to /dev/dsp:

Code:

modprobe snd-pcm-oss

After that, you could do something like the following:

Code:

cat /dev/ttyUSB0 > /dev/dsp
-OR-
cat capture.raw | /dev/dsp

Please note that they are rough examples; You can redirect anything to /dev/dsp, and it will result in outputting to your pcm device - in this case, alsa or jack.

Cheers,

Josh

kishoreinme · 01-06-2012, 04:14 AM

Hello corp769

Thanks for the reply. By googling I interpret that you have suggested to emulate OSS. I have installed alsa-oss package.
I am on ubuntu 10.10
I tried the

Code:

modprobe snd-pcm-oss

it fails

Code:

FATAL: Module snd_pcm_oss not found.

corp769 · 01-06-2012, 04:43 AM

Read here - http://www.linuxquestions.org/questi...0-10-a-862717/

Cheers,

Josh

kishoreinme · 01-06-2012, 05:46 AM

Thanks. I am now rebuilding my kernel with OSS modules. let me report after its done.
BTW the linux audio architecture seems to be complicated. Now I need both OSS and ALSA on my system to attain my intended purpose to play PCM from ttyUSB, which is a test run. My actual target is the Android platform which has ALSA and I am not sure how it supports OSS. Any thoughts on this ?

corp769 · 01-06-2012, 06:09 AM

Ahh, you should have said that before. I was just giving you a quick and dirty, yet simple way of doing so. Let me get back right back to you, I need to do a few things quick since I just got home from work, and it's my three day weekend

corp769 · 01-06-2012, 06:16 AM

And once again, I was thinking about something else before. With alsa, you can use the aplay command for something like this. Take the following example:

Code:

cat /dev/urandom | aplay

This will give you a bunch of white noise. Play with this, and get it to how you want it with your device.

Cheers,

Josh

kishoreinme · 01-06-2012, 08:18 AM

Aplay worked as you have explained. And regarding android,ALSA has a defined interface to the Audioflinger service. If my ttyUSB talks to ALSA, then I thinks android would take it further. Am I right? and if so the ALSA-PCM connection is to be looked into further i hope.

kishoreinme · 01-12-2012, 05:59 AM

Can I get some more help here?

using .asoundrc Is it possible to register my /dev/ttyUSB serial as a PCM device with ALSA ?