Category Archives: PulseAudio

Linaro Multimedia Mini Summit

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Since the Linaro multimedia working group didn’t get to plan at the last Linaro Developers Summit, we held our own mini-summit at the beautiful IBM campus in Austin. It has been 3 weeks and I am just now able to think about other things like updating this blog due to the flurry of planning activities that followed. There are other factors at play too, one of them is I have agreed to take on the role of team lead for the multimedia working group. Even though my view now encompasses all multimedia, I will try to keep to this blogs original intent of writing about Linux sound and specifically ARM audio.

The Linaro multimedia working group,  often referred to as MMWG, needed to hold the summit to share our plans and discuss the requirements for the upcoming development cycle. It was very well attended by key technical folks from all areas of ARM-based multimedia. Attending were representatives from Linaro, IBM, NVidia, Freescale, Texas Instruments, Collabora, ST-Ericsson, ARM and others as well as several who were able to dial-in. I had organized meet-ups before, but it was the first time I had organized an event this size. All in all, it went very well and I think everyone enjoyed the experience of meeting to discuss the challenges ahead of us.

Travel to ASoC and LAC

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I’ve been a little busy lately with new assignments and travel. I just returned from two back-to-back conferences, in two different countries, in less than one week.

The first was the ASoC and Embedded Linux Audio Conference in Edinburgh. This was a gathering of about 30-40 multimedia developers from all over the world representing almost every company involved in this space and I was honored to be invited. After introductions, the 2 days worth of in-depth technical discussions got started with a description of the ASoC DSP support, focused on the description and charts shown here -> http://omapedia.org/wiki/Audio_Drive_Arch   We then shifted to OS integration topics that mainly centered around Android’s need for a different ALSA user space lib, with more business favorable license terms. Several options were discussed. The UCM talk was next and with an initial brief overview and then enumerating the needs moving forward, including PulseAudio work. Next were discussions on QoS, run-time coefficients, firmware and events. The meeting drew to a close with a summary, questions time and assignments review. I drew the assignment for looking into getting an install script and  git set up for the UCM profile config files, something we will need for Linaro.  All in all, a great technical conference that was well prepared and useful. Also, it was a fantastic opportunity to meet everyone I have been interacting with in email and IRC, plus many new contacts. I look forward to attending the next one!

The second was the Linux Audio Conference in Dublin, aka, LAC2011. I worked with the planners of this conference to get the PulseAudio folks, including Lennart Poettering,  a place to work. The space we were allocated was large enough to allow others to come and listen and ask a few questions. I want to apologize to the people that waited so patiently to ask questions.  We had such an active discussion between the developers that they could hardly get a word in edge wise. I learned a lot and hopefully contributed to the overall discussion, direction and schedule. The rest of the conference was more general purpose for all things Linux Audio including: sound generation, sequencing, pro audio, and composition. I have followed this for many years now and it was really interesting to see how it continues to evolve. Even though it was a Linux conference, there were constant references to Apple and iPad integration with the applications used, even a session on running PulseAudio on Mac OS X. I think that mobile Linux has an opportunity to reach these folks.

Even though the trip was jam-packed, it was a perfect technical requirements review for going into the next development cycle for Linaro.  They were both worth the hectic travel schedule.

PulseAudio Configuration

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The best way to learn code is to work on it. I did just that implementing a feature to add tsched buffer size to the configuration file. Late in the process, I discovered that it was already possible to pass it to the ALSA module, so I abandoned the additional code. Since it stumped me, I figured the configuration of PulseAudio might be somewhat confusing and could use a blog entry, hence this.

First, if you have not yet read PerfectSetup, start with that.  You can find it here: http://www.pulseaudio.org/wiki/PerfectSetup

There are 3 places to change the configuration parameters and behavior of PulseAudio.

system.pa/default.pa – startup script to specify module loading, etc, module parameters are passed here, more on that later

client.conf – does just what is says, config file for clients

daemon.conf – configuration specific to the sound server daemon

On Ubuntu, these files are installed in /etc/pulse. The system.pa startup script is used when PulseAudio is used in system-wide mode. The other, daemon.conf is used when the sound server is started in user mode.

The values listed in these files are default values and are commented out. Obviously, uncommenting the parameter will not change anything unless the assignment is value changed.

The startup script can be used to pass module specific parameters. This is done by uncommenting the line in the file. For example, passing a new tsched buffer size to the ALSA module would look like this:

load-module module-alsa-sink tsched_buffer_size=XYZ

Here are all the module specific parameters for the ALSA module (from module-alsa-card.c) :

“name=<name for the card/sink/source, to be prefixed> ”
“card_name=<name for the card> ”
“card_properties=<properties for the card> ”
“sink_name=<name for the sink> ”
“sink_properties=<properties for the sink> ”
“source_name=<name for the source> ”
“source_properties=<properties for the source> ”
“namereg_fail=<pa_namereg_register() fail parameter value> ”
“device_id=<ALSA card index> ”
“format=<sample format> ”
“rate=<sample rate> ”
“fragments=<number of fragments> ”
“fragment_size=<fragment size> ”
“mmap=<enable memory mapping?> ”
“tsched=<enable system timer based scheduling mode?> ”
“tsched_buffer_size=<buffer size when using timer based scheduling> ”
“tsched_buffer_watermark=<lower fill watermark> ”
“profile=<profile name> ”
“ignore_dB=<ignore dB information from the device?> ”
“sync_volume=<syncronize sw and hw voluchanges in IO-thread?> ”
“profile_set=<profile set configuration file> “

PulseAudio Buffer Size Tests

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It has been a few weeks, but in my defense, I have been pretty busy testing and debugging in this new environment. As an assignee to the Linaro project, my first task was to figure out if increasing the buffer size would enable the ARM cpu to drop into a lower power state. Code investigation, community feedback and prototyping said probably not, but I followed through. Below is a chart showing all the testing done, including the recent work to go back through the tests with ALSA 1.0.24 in the stack to enable checking for  period disable. Enjoy!

PulseAudio Buffer Size Tests

PulseAudio Buffer Size Tests

Building PulseAudio

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Here are (now improved) quick instructions to create a working build sandbox for PulseAudio development on Ubuntu 10.10 Maverick on an i386 platform. I highly recommend reading all this post completely before starting this process.

Here are the steps to make PulseAudio that builds and works for Ubuntu:

  1. Install or update to Maverick and accept defaults, this process will probably work fine with other Ubuntu versions, so if you are not on Maverick, give it a try.
  2. Update all packages with Update Manager
  3. Install dpkg-dev -> sudo apt-get install dpkg-dev

If you are using source from git:

  1. Install git if you haven’t already -> sudo apt-get install git
  2. From your home directory, get the latest PulseAudio source -> git clone git://git.0pointer.de/pulseaudio.git
  3. Git will create the PulseAudio repository in a directory called pulseaudio, when the clone has completed, change to that directory -> cd ~/pulseaudio

If you are using Ubuntu maverick source:

  1. Install the source -> apt-get source pulseaudio

Configure and build the source:

  1. Install the prereq packages -> sudo apt-get build-dep pulseaudio
  2. To check the environment and set up the basics, run the bootstrap script -> ./bootstrap.sh
  3. Next, run configure -> ./configure
  4. Run make to build the executables

Note: the executables will be in the src directory. Change to that directory and run specifying that path so that you will not run the system programs. For example, to run pulseaudio with verbose log messages, cd to src and run -> ./pulseaudio -n -F ./default.pa -p ./.libs -vvvv

There are some very helpful hints at: http://colin.guthr.ie/2010/09/compiling-and-running-pulseaudio-from-git/ The steps on this page are slightly different for Ubuntu, but worth reading to better understand the process.  Also, this page does a really nice job of explaining how to run pulseaudio for test/debug.

Sound: BeagleBoard C4

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Here are my notes from the experimental process of learning how to get sound out of a Linaro image (Headless, ALIP, Netbook) and a BeagleBoard.

  • Plug amplified speakers into the 1/8″ jack closest to the s-video port – they must be amplified, signal is line level only
  • ALSA – Playback hardware devices:
    • card0: omap3beagle
    • device0: TWL4030
    • No regular simple controls like “Master” defined for BeagleBoard
  • Sounds installed in /usr/share/sounds
  • Test with aplay
  • By default, all sound outputs for ALSA are set to 0 and/or muted
  • Configure with alsamixer
    • Unmute HeadsetL and HeadsetR, turn volume up for “DAC2 Analog” ~50 and “DAC2 Digital Fine” ~50-75, and “Headset” to ~ 67 for best results, these are the only controls that change line-level output via the onboard jack
    • All controls listed must be turned up or no level is present at the jack
  • Pulseaudio – Successful playback of .wav with paplay, one dropout, quality fairly good