Difference between revisions of "ALSA"

Revision as of 10:27, 28 May 2010

This page will summarize the informations to use ALSA, ie the sound capabilities (Audio In/Audio Out) of your Armadeus board.

Introduction

ALSA stands for Advanced Linux Sound Architecture and provides audio and MIDI functionality to the Linux operating system. Everyone wanting to write portable & state of the art Linux applications dealing with sound should consider using ALSA.
ALSA is composed of a low level part (target specific Linux drivers) and a userspace library (libasound) with a lot of tools (aplay, arecord, alsamixer).

Hardware

On the i.MX family, used on the Armadeus boards, (good quality) sound can be produced that way:

the i.MX is connected to an audio CODEC (like the TSC2102 on the APF9328 or the TSC2101 on the APF27) through one of its SSI interfaces
the i.MX takes PCM data (ALSA format) from memory and send them (through DMA) to the SSI module
this one converts the data to a serial stream of bits in the I2S format (or AC97). That stream is then sent to the CODEC
the stream is converted by the CODEC's DAC to an analog sound

Sound acquisition (on TSC2101 only) is done in the reverse way.

Installation

ALSA is by default installed on the standard Armadeus rootfs. If you want to change the default configuration, you can consult this wiki page.

Usage

Load the ALSA drivers:

 # modprobe snd-imx-alsa-tsc2102
 TI TSC210x driver initializing
 TSC210x detected

If you want OSS support (optional):

 modprobe snd-pcm-oss
 modprobe snd-mixer-oss

If you want MIDI sequencer support (optional):

 modprobe snd-seq
 modprobe snd-seq-device

Loading script

If you want the drivers to be loaded automatically during each boot, you can add a script in /etc/init.d/. For example:

 # vi /etc/init.d/S60alsa

#!/bin/sh
  
modprobe snd-imx-alsa-tsc2102

 # chmod a+x /etc/init.d/S60alsa

First checks (optionnal)

Check if ALSA is running:

 # cat /proc/asound/version
 Advanced Linux Sound Architecture Driver Version 1.0.17.

To check if the TSC2102/TSC2101 was detected as a sound chip:

# aplay -lL
default:CARD=IMX-ALSA
    i.MX+TSC210x audio, i.MX SSI
    Default Audio Device
null
    Discard all samples (playback) or generate zero samples (capture)
**** List of PLAYBACK Hardware Devices ****
card 0: IMX-ALSA [i.MX+TSC210x audio], device 0: i.MX SSI [i.MX SSI]
  Subdevices: 1/1
  Subdevice #0: subdevice #0

or

 # cat /proc/asound/cards
 0 [IMX-ALSA       ]: i.MX - i.MX+TSC210x audio
                      Freescale i.MX with TSC210x codec

Setting playback and capture volume

For this work, you can use alsamixer "pseudo graphic" tool:

# alsamixer

choose the Item to setup by using <- -> arrow keys (here Master Playback volume is selected)
modify its value with up/down arrow keys
you can switch View between Playback and Capture settings with TAB key
Capture Handset input is by default muted, you can unmute it by pressing the SPACE key when selected
when stereo channels are used you can modify individual channel volume with:
- 'q': left up, 'z': left down
- 'e': right up, 'c': right down
if alsamixer changed your terminal layout after exiting you can get it back with:

# reset

First tries

To play a test sound (connect your headset first ;-) ):

 # aplay /usr/share/sounds/alsa/Side_Left.wav
 Playing WAVE '/usr/share/sounds/alsa/Side_Left.wav' : Signed 16 bit Little Endian, Rate 48000 Hz, Mono

Note: the audio file Side_Left.wav can be copied from your Linux host (if not already on your rootfs)

To record a test sound (on APF27Dev only) (connect your microphone first ;-) ):

# arecord /tmp/foo.wav
Recording WAVE '/tmp/foo.wav' : Unsigned 8 bit, Rate 8000 Hz, Mono

and to replay it after:

# aplay /tmp/foo.wav
Playing WAVE '/tmp/foo.wav' : Unsigned 8 bit, Rate 8000 Hz, Mono

for a faster and "wider" sampling:

# arecord -f S16_LE -r 16000 /tmp/toto.wav
Recording WAVE '/tmp/toto.wav' : Signed 16 bit Little Endian, Rate 16000 Hz, Mono

Automate ALSA settings at boot

alsamixer is quite cool to setup ALSA parameters in live but in some cases you may want to set them up at a default value at system startup. Here is the way to do.
use amixer tool. Display all the possible controls and identify the one of interest (here we'll take Handset Capture Switch):

# amixer contents
...
numid=7,iface=MIXER,name='Handset Capture Switch'
  ; type=BOOLEAN,access=rw------,values=1
  : values=off
...

Handset Capture Switch control here is of boolean type, off by default and control the Audio In On/Off.
Check you can get individually access to the control:

# amixer cget numid=7
numid=7,iface=MIXER,name='Handset Capture Switch'
  ; type=BOOLEAN,access=rw------,values=1
  : values=off

And then modify its value:

# amixer cset numid=7 on
numid=7,iface=MIXER,name='Handset Capture Switch'
  ; type=BOOLEAN,access=rw------,values=1
  : values=on

Now we can do the same for the Handset Capture Volume:

# amixer cget numid=6
numid=6,iface=MIXER,name='Handset Capture Volume'
  ; type=INTEGER,access=rw------,values=1,min=0,max=100,step=0
  : values=50

# amixer cset numid=6 30
numid=6,iface=MIXER,name='Handset Capture Volume'
  ; type=INTEGER,access=rw------,values=1,min=0,max=100,step=0
  : values=30

Now you know the way to do it, you can add these commands to the S60alsa script we built in the previous chapter:

 # vi /etc/init.d/S60alsa

#!/bin/sh
  
modprobe snd-imx-alsa-tsc2102
# default values for Audio In:
amixer cset numid=7 on
amixer cset numid=6 30

Going further

Now that ALSA is working, you can switch to serious things ;-) ->

ALSA Soc

On the APF boards we are going to use Embedded version of ALSA: ALSA Soc ->

But for the moment only "standard" version is functionnal.

Links

Difference between revisions of "ALSA"

Revision as of 10:27, 28 May 2010

Contents

Introduction

Hardware

Installation

Usage

Loading script

First checks (optionnal)

Setting playback and capture volume

First tries

Automate ALSA settings at boot

Going further

ALSA Soc

Links

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