The Debian Package osso-dsp-plugin-alsa

----------------------------

Comments regarding the Package

Eduardo Valentin <eduardo.valentin@indt.org.br>, Wed, 5 Apr 2006 10:28:06 +0300

OSSO DSP SW  <--> ALSA DSP plugin

========================

This plugin converts the ALSA API over PCM task nodes protocol. In this way,

ALSA native applications can run over DSP Gateway and use DSP PCM task nodes.

This plugin provides the PCM type "alsa_dsp".  The typical configuration

looks like below:

	# PCM

	pcm.!default {

	        type alsa_dsp

        	playback_device_file ["/dev/dsptask/pcm2"]

	        recording_device_file ["/dev/dsptask/pcm_rec"]

	}

Put the above to ~/.asoundrc (or /etc/asound.conf or /usr/share/alsa/alsa.conf), 

and use "default" PCM with your ALSA apps.  For example:

	% aplay -Ddefault foo.wav

	% arecord -Ddefault foo.wav

The alsa_dsp plugin can have two options for pcm interface:

a. playback_device_file: this is a list of PCM task node device files whose

alsa_dsp plugin is allowed to use to do playback. For example: /dev/dsptask/pcm2.

b. recording_device_file: this is a list of PCM task node device files whose

alsa_dsp plugin is allowed to use to do recording. For example: /dev/dsptask/pcm_rec.

The alsa_dsp plugin will probe the dsp task node files you provide and 

will use the first one whose dsp PCM task is in UNINITIALISED state.

If no dsp PCM task node is usable, alsa_dsp plugin will return an ENODEV

error code.

For the control interface, this plugin provides the CTL type "dsp_ctl". A

typical configuration is:

	# Mixer

	ctl.!default {

        	type dsp_ctl

	        playback_devices ["/dev/dsptask/pcm2"]

        	recording_devices ["/dev/dsptask/pcm_rec"]

	}

Put the above to ~/.asoundrc (or /etc/asound.conf or /usr/share/alsa/alsa.conf), 

and use "default" CTL with your ALSA apps.  For example:

	% alsamixer -Ddefault 

The dsp_ctl plugin can have two options for ctl interface:

a. playback_devices: this is a list of PCM task node device files whose

dsp_ctl plugin is allowed to use to do volume control changing. These

devices will be handled under the "PCM Playback Volume" and "PCM Playback Switch" 

control names. 

b. recording_devices: this is a list of PCM task node device files whose

dsp_ctl plugin is allowed to use to do volume control changing. 

These devices will be handled under the "Capture Switch" control name.

# Supported formats:

Playback: 

	16-bit PCM formats: 

		S16_LE	

		S16_BE	

		U16_LE	

		U16_BE	

	8-bit PCM formats:

		A_LAW	

		MU_LAW	

		U8	

		S8

	Rates: 

		8 KHz, 11.025 KHz, 12 KHz, 16 KHz, 

		22.050 KHz, 24 KHz, 32 KHz, 44.1 KHz, 48 KHz

	Channels: Mono and Stereo 

Recording:

	16-bit PCM formats: 

		S16_LE	

	8-bit PCM formats:

		A_LAW	

		MU_LAW	

	Rates: 

		8 KHz

	Channels: Mono

# Compilation

To cross-compile the plugin inside scratchbox environment, you will

need a libasound2 version of binaries and header files installed.

Pthreads is also required. The source directory provides a Makefile.

If you just type:

	% make clean

	% make 

under the source tree, it will generate the binaries under the

"bin" sub-directory. Like:

libasound_module_ctl_dsp_ctl.so  and libasound_module_pcm_alsa_dsp.so

The libasound_module_ctl_dsp_ctl.so is currently a symbolic link to

libasound_module_pcm_alsa_dsp.so. 

You can just copy then to your /usr/lib/alsa-lib/ directory inside your 

target file system. 

You can also modify the behaviour of this plugin using macro definitions

while compiling it. Here are macros whose can be used in CFLAGS (-D <macro>):

	ERROR_DEBUG		It enables error debug output. You have to 

				change in "debug.h" file. Default is to debug.

	DEBUG 			It enables debug output. You have to change in

				"debug.h" file. Default is not to debug.

	NORMAL_DSP_TASK		It enables utilization of extended fields in

				audio_status_info_t data structure (mute,

				samples_played_high, samples_played_low).

				You can change it in "Makefile". Default

				is NORMAL_DSP_TASK enabled.

	USE_RESOURCE_MANAGER	If set, the resource manager D-BUS interface

				will be used for power management instead of

				the sysfs file.

	ERROR_ON_PM_FAILURE	It controls this plugin behaviour if it fails

				while openning MIC power management file 

				(/sys/devices/platform/audio-i2c/mic_enable)

				or calling the resource manager request()

				method (if USE_RESOURCE_MANAGER is set).

				If you enable this macro, this plugin will 

				return an error code. Otherwise, it will

				just print a debug message, and will return

				sucess. You can change it in Makefile. Default 

				is ERROR_ON_PM_FAILURE disabled.

# Installation

The plugin is installed in /usr/lib/alsa-lib directory as default,

which is the default search path of additional plugins for alsa-lib.

This plugin is expected to be compatible with any standard ALSA application.

The only requirement is you have to compile it against the same libasound2 you

have installed in your target system. You have to enable the external plugins

support in libasound2:

	% cd $LIB_ASOUND2_SRC

	% ./configure --with-pcm-plugins=extplug

You can get the latest version of libasound2 in http://www.alsa-project.org.

There you can find more instructions of how to compile libasound2. The cross-compilation

for ARM architecture is straightforward inside the scratchbox environment.

# Applications

Alsa-utils:

Also from http://www.alsa-project.org, you can find alsa-utils package sources.

This package constains standard ALSA application, like amixer, alsamixer and

aplay/arecord.

The compilation of alsa-utils is also straightforward inside scratchbox environment.

The only requirement is you will need to have libasound2 (and libncurses) installed 

inside your scratchbox environment to be able to compile alsa-utils.

After compiling and installing applications on your target, you can

use them with this plugin specifing the correct pcm device. For example,

if you have installed alsaplayer on your target, you can specify an alsa pcm

device with:

	target # alsaplayer -d default

#Limitation

- While the plugin is using a pcm task node, another applications,

for example gstreamer, can not use the same task node. This will cause

unexpected behaviour.

- If an application does not close alsa device properly, this plugin

will not have chance to release all reserved resouces. One expected 

behaviour in this case is to have -EBUSY error for following applications

whose try to open the same alsa device. Partialy solved (version 0.6)

with __attribute__((destructor)) functions. But if the application 

receives an uncaught signal, resources may be kept unreleased.

- If many requests to volume information read / write is done in the

same alsa device while it is being used to do playback, this playback

could be affected and some little stops can be heard.