Difference between revisions of "ALSA"

Revision as of 15:25, 7 January 2009

This page will summarize the informations to use ALSA on your Armadeus boards.

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.

Hardware

On the i.MX family, used on the Armadeus boards, (good quality) sound can be produced that way: the i.MX takes PCM data (ALSA format) from memory and send them (through DMA) to its SSI interface. This one converts the data to a serial stream of bits in the I2S format. That stream is sent to a CODEC like the TSC2102 on the APF9328 or the TSC2101 on the APF27. The stream is then converted by the CODEC's DAC to an analog sound.

ALSA Soc

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

• http://opensource.wolfsonmicro.com/node/6
• http://www.rpsys.net/openzaurus/patches/alsa/info.html
• http://alsa-project.org/main/index.php/ASoC

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

Installation

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

Usage

• load the ALSA drivers:

# modprobe spi_imx
# modprobe snd-imx-alsa-tsc2102
TI TSC2102 driver initializing
audio_dma_request done (8)
audio_dma_request done (9)
audio support initialized

# lsmod
Module                  Size  Used by    Not tainted
snd_imx_alsa_tsc2102     7204  0
snd_pcm                50760  1 snd_imx_alsa_tsc2102
snd_timer              14084  1 snd_pcm
snd_page_alloc          3208  1 snd_pcm
snd                    28916  3 snd_imx_alsa_tsc2102,snd_pcm,snd_timer
soundcore               3332  1 snd
tsc2102                10256  1 snd_imx_alsa_tsc2102
hwmon                    948  1 tsc2102
spi_imx                 9024  0

• if you want OSS support:

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

• If you want MIDI sequencer support:

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 spi_imx
modprobe snd-imx-alsa-tsc2102

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

Test

• Check if ALSA is running:

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

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

# aplay -lL
default:CARD=IMX-ALSA
   ARMADEUS IMX_ALSA, imx alsa pcm
   Default Audio Device
null
   Discard all samples (playback) or generate zero samples (capture)
**** List of PLAYBACK Hardware Devices ****
card 0: IMX-ALSA [ARMADEUS IMX_ALSA], device 0: IMX PCM [imx alsa pcm]
 Subdevices: 1/1
 Subdevice #0: subdevice #0

or

# cat /proc/asound/cards
 0 [IMX-ALSA       ]: IMXALSA - ARMADEUS IMX_ALSA
                      ARMADEUS IMX_ALSA

• To play a test sound:

# 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)

Going further

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

• PrBoom
• madplay

Links

• http://www.alsa-project.org/
• http://free-electrons.com/formations/audio
• http://alsa-project.org/main/index.php/DevEmbedded
• http://alsa.opensrc.org/index.php/WritingAnAlsaDriver + http://www.alsa-project.org/~tiwai/writing-an-alsa-driver.pdf
• Introduction to Sound Programming with ALSA on Linux Journal
• PCM format on Wikipedia & I2S bus on Wikipedia