- 1 Audio on Android
- 2 Getting Audio to work on non-Android userspace
- 3 alsactl method
- 4 Spreadtrum
- 5 WM1811
- 6 Mainline
- 7 See also
Audio on Android
This provides a brief overview of how Android audio HALs configure the ALSA mixer.
Android devices can have an assortment mixer configurations such as headphones, speakers, or microphones. For a particular device the audio route configurations are defined in
mixer_paths.xml. For an example see the mixer path XML for Nexus 5 (hammerhead).
Android audio HALs make use of tinyalsa and audio_route. Tinyalsa is a small standalone library to interface with ALSA in the Linux kernel. Audio HALs call the
audio_route library which loads audio routes from an XML and controls the mixer through
Format of mixer_paths.xml
- ALSA controls are defined by
- Audio routes are defined by
pathelement contains a collection of
ctlelements as well as other
- The path
nameattribute is used to select an audio route.
Android kernels use
switch_class kernel driver to notify the Android frameworks of headphone jack events. The driver source code can be located at:
drivers/staging/android/switch/switch_class.c. Note that the switch class driver is an Android specific driver. It has not been upstreamed to the mainline kernel.
In userspace the WiredAccessoryManager monitors the
/sys/class/switch/h2w for uevents when the headphone is (un)plugged.
Udev rules can be used to detect if headphones are plugged in, example for this is from xiaomi-santoni
Getting Audio to work on non-Android userspace
Bring up Android DSP subsystem
ADSP needs to be powered on before audio could work on downstream kernels. To do that, you'll have to supply firmware files that is available on your internal MMC.
On a shell prompt inside postmarketOS, type
fdisk -l /dev/mmcblk0 (replace mmcblk0 with the correct device name for internal MMC). At this point you should get a familiar partition layout of a Android device.
Now, the only thing that is important is the partition with
modem label on it, which on my device it's mmcblk0p1. Mount the partition as read-only to /mnt using:
# mount -o ro /dev/mmcblk0p1 /mnt
Inside /mnt, there is a folder named
image which has a bunch of firmware files for different parts of the device, like wcnss (for wlan), DRM contents and so on, the only thing that needs to be extracted is all the files that named
// Create /lib/firmware/postmarketos if it doesn't exist # mkdir -p /lib/firmware/postmarketos // Copy all adsp.* to the postmarketOS firmware directory # cp -v /mnt/image/adsp.* /lib/firmware/postmarketos
After that, you should be able to bring up the ADSP subsystem by running:
# echo 1 > /dev/subsys_adsp
You should check dmesg and /var/log/firmwareload.log to make sure there aren't firmwares failing to load.
If it goes fine, you should see a bunch of playback devices by typing
You also want to install
adsp-audio from pmOS repo to load the subsystem on automatically on bootup.
Convert XML audio to UCM
The audio routes in Linux userspace can be defined in ALSA UCM configuration files. There is a tool called xml2ucm which will convert the Android
mixer_paths.xml and a device config XML to UCM files. The
xml2ucm tool introduces the device config XML which provides necessary routing information that was hardcoded in the audio HAL on Android.
mixer_path.xml is commonly found in the Android device repository. (e.g.
android_device_lge_hammerhead). You must write the device config XML for your device.
Format of device config XML
A device config XML describes a sound card with use cases and sets of audio routes. In the examples available at the moment there is only one use case named HiFi. Under each
<use-case> there are multiple
<device> elements. In this context a
<device> means audio route(s) which comprise a logical audio device (e.g. Headphone, Headset, Speaker).
Android audio HALs can and do select multiple audio routes at once. For example a headset can have a headphone output route and a microphone input route. To handle this a
<device> element (the headset) can contain multiple
<path> elements (audio routes). Example device config XML files are provided in the
ctl-device must be the name of the sound card which can be obtained using
aplay. In the following example from the Samsung p4wifi the
ctl-device is the sound card named
$ aplay -L null Discard all samples (playback) or generate zero samples (capture) default:CARD=wm8994aif1 wm8994-aif1, Default Audio Device sysdefault:CARD=wm8994aif1 wm8994-aif1, Default Audio Device
mixer_path.xml and device config XML are converted to UCM format then an audio route can be set by using
$ alsaucm -c wm8994aif1 set _verb HiFi set _enadev Headphones
In general in Hybris environment just install pulseaudio-modules-droid package and sound will work.
Make sure you have the following line in your
Loading droid-card module is enough, other modules will be loaded automatically. Also it would not hurt to comment out
module-detect lines to lower the amount of error messages in pulseauduio log (these modules don't work anyway), like that:
### Automatically load driver modules depending on the hardware available #.ifexists module-udev-detect.so # load-module module-udev-detect #.else ### Use the static hardware detection module (for systems that lack udev support) # load-module module-detect #.endif
Start pulseaudio in verbose mode (
/usr/bin/pulseaudio --log-target=stderr --log-level=debug -v) to make sure you can get to see if module-droid-card loads successfully. If it does then you should be able to play sound files using
paplay from pulseaudio-utils package.
If you hear sounds coming from it, it works perfectly fine. If not, check dmesg, pulseaudio log and logcat.
You might also want to install
alsa-plugins-pulse for ALSA backend on PulseAudio.
Cascardo reported having success with the following method on Debian, this should work for postmarketOS as well:
I ran a debian chroot on a cyanogenmod, set the volume up, then ran alsactl save on the chroot. booted into debian, then after alsactl restore was run, I had audio working
so, in summary, it's hard to know which mixer settings will make it work, so my strategy was running some android stack that correctly set the mixer, then saving the state with a chroot or any other tool that would allow you to save, copy and restore that state later on a gnu stack
This method may work for non-Android devices as well, as long as you see an audio device in
alsamixer. Just boot the normal OS, save the volume settings somehow, then restore them.
Audio support for Spreadtrum SoCs is provided in
soc-sprd-audio and its subpackages. To get audio support for the device, add the package related to the audio device to dependencies of device package or install it manually, like
apk add soc-sprd-audio-sc8830
This audio chip is present in several Samsung devices that are based on the Exynos 4412 platform. There is a configuration for the Samsung Galaxy Note 10.1 available at the opensgn project. Have a look at the files in
opensgn/data/n8000/etc/rc.local there are the commands to use the configuration:
# restore alsa sinitial tate /usr/sbin/alsactl restore -f /usr/share/alsa/ucm/Midas_WM1811/init.state # enable speaker for output and builtin mic for input /usr/bin/alsaucm -c Midas_WM1811 set _verb HiFi set _enadev Speaker /usr/bin/alsaucm -c Midas_WM1811 set _verb HiFi set _enadev Mic
For other devices the configuration might need to be adapted. On the Samsung Galaxy Note 8.0 for example, the audio device is named "Kona_WM1811". Replacing all occurrences in file names and file contents of
Troubleshooting audio input
A nice way to troubleshoot audio input is to run arecord in a terminal to get realtime audio levels of the default alsa input:
$ arecord -vv --format=dat /dev/null Recording WAVE '/dev/null' : Signed 16 bit Little Endian, Rate 48000 Hz, Stereo ALSA <-> PulseAudio PCM I/O Plugin Its setup is: stream : CAPTURE access : RW_INTERLEAVED format : S16_LE subformat : STD channels : 2 rate : 48000 exact rate : 48000 (48000/1) msbits : 16 buffer_size : 24000 period_size : 6000 period_time : 125000 tstamp_mode : NONE tstamp_type : GETTIMEOFDAY period_step : 1 avail_min : 6000 period_event : 0 start_threshold : 1 stop_threshold : 24000 silence_threshold: 0 silence_size : 0 boundary : 6755399441055744000 #+ | 00%
- #1328 Audio added to samsung-p4wifi with udev rules for redirecting audio to headphones when plugging them in
- How to convert Android Audio configurations to alsa/pulseaudio
- pmaports!238 Audio added to samsung-i927, running close to mainline