ECE497 Lab11 Using the Open Sound System (OSS)
Use EBC Exercise 08 Using ALSA for Audio Processing instead.
Be sure you have done Lab 10 before this lab so all your software is set up.
Lab 11/6 - Using the OSS Driver
Lab 11 is Lab 6 is on pages 171-186 of DaVinci-OMAP_Workshop_v2.0.pdf. In doing this lab you will get audio from the line-in jack on the Beagle and sent it out the speaker jack.
- Go to the class dfs site and get:
- Move the setpaths files in the workshop directory to another location.
host $ cd workshop host $ mv setpaths.sh setpaths.sh.orig host $ mv setpaths.mak setpaths.mak.orig
- Copy the setpaths files you got from DFS into the workshop directory. In Lab 11/6 you will edit these files so they are correct.
You will still need the symbolic link from part 5, and make sure to update the file paths.
Problems and Solutions
I find that running
cat /dev/dsp > /dev/dsp
gave me this error:
-sh: can't create /dev/dsp: Device or resource busy
This did not seem to cause problems until part b of the lab. I found this website to solve my problem. Apparently, the problem is that pulseaudio is using /dev/dsp, and refuses to give it up. When I killed pulseaudio (the rude way, not the graceful way), then running cat /dev/dsp > /dev/dsp worked, and my executable worked. I don't know what killing pulseaudio does to the system, I haven't noticed any ill-effects yet...
Testing the audio chain with GStreamer
Here is a simple way to test to see if you mic and speakers are working. Do this on your Beagle:
# opkg update # opkg install esc-gst # cd /usr/share/esc-gst/ # ls README a2 a4 a6 d2 d4 d6 g2 g4 g6 g8 n1 n3 p1 v1 v3 a1 a3 a5 d1 d3 d5 g1 g3 g5 g7 g9 n2 n4 s v2 v4 # less README # less s # ./s # ./a1 # ./a6
These are files for demonstrating GStreamer. The README tells what each file does. Before the first time you run anything you have to run
s. Here’s what
#! /bin/sh set -x export DISPLAY=:0.0 export PATH=$PATH:/usr/share/esc-gst cd /usr/share/esc-gst killall -9 pulseaudio set +x
Notice you have to kill off pulseaudio as was suggested above!
a1 plays a simple tone,
a6 takes the input from the mic and sends it to the speakers. This works for me and is a good way to test your whole audio chain.
Some notes on ALSA
On the Beagle you need to:
# opkg install alsa-dev
On the host:
$ sudo apt-get install libasound2-dev
Go to the class dfs site and get
alsaWrite.c. Compile it with
# gcc -lasound alsaWrite.c # ./a.out
It runs on the Beagle and desktop and produces a sound.
It's shouldn't be hard to convert
alsaRead.c. See the sites above for hints.