Enable TinyALSA-based applications

TinyALSA is a library that wraps the ALSA kernel interface into APIs that clients can invoke. It also gives a plug-in interface to emulate ALSA APIs. Find TinyALSA source code at: build-qcom-wayland/workspace/sources/tinyalsa and build-qcom-wayland/workspace/sources/tinycompress. The following figure shows the TinyALSA plug-in architecture.

TinyALSA plug-in architecture

TinyALSATiny compressClientALSA/ASoC kernel frameworkCompress pluginPCM pluginMixer pluginPCMLibaudiorouteMixerCompressASoC driversOpen source/FrameworkLegend TinyALSA plug-in architecture The ALSA framework in the kernel exposes card and device nodes for PCM, compress, and mixer. PCM, mixer, and compress plug-ins are TinyALSA plug-ins. They route all PCM, mixer, and compress calls from the application to plug-in specific implementation. The plug-ins create a virtual sound card with PCM, compress, and mixer nodes. Virtual nodes map to on-device .so files (dynamically loadable shared objects). The virtual sound card configuration is in the card-defs.xml file. This file is in the /etc/ folder on the device.

TinyALSA APIs

The following are common TinyALSA APIs. See the open source TinyALSA documentation for a complete description of all APIs.

pcm_open

Opens a PCM audio device for input and output operations. Initializes a PCM device for communication, allowing read/write operations in audio data.

struct pcm *pcm_open(
     unsigned int card,
     unsigned int device,
     unsigned int flags,
     struct pcm_config *config)

Parameters

card	Card number.
device	Device number in the chosen card.
flags	Flags to configure the PCM device.
config	Structure variable that specifies audio stream parameters.

Return value pcm* handle

pcm_is_ready

Checks if the PCM device is ready for input and output operations.

int pcm_is_ready(struct pcm *pcm)

Parameters

pcm	Pointer to the open PCM device.

Return value

Non-zero if the PCM device is ready
0 if the PCM device is not ready

pcm_prepare

Prepares audio device input and output operations.

int pcm_prepare(
     struct pcm *pcm)

Parameters

pcm	Pointer to the open PCM device.

Return value

0 on success
Error code on failure

pcm_start

Starts the PCM audio device for input and output operations.

int pcm_start(
     struct pcm *pcm)

Parameters

pcm	Pointer to the open PCM device.

Return value

0 on success
Error code on failure

pcm_write

Writes audio data to the audio PCM device. Takes audio data as input and sends it to the PCM device for playback or processing.

int pcm_write(
     struct pcm *pcm,
     const void *data,
     unsigned int count)

Parameters

pcm	Pointer to the open PCM device.
data	Audio data to write.
count	Number of audio frames to write.

Return value

0 on success
Error code on failure

pcm_read

Gets audio data from the PCM device, which allows the application to capture audio data from a microphone.

int pcm_read(
     struct pcm *pcm,
     void *data,
     unsigned int count)

Parameters

pcm	Pointer to the open PCM device.
data	Audio data to read.
count	Number of audio frames to read.

Return value

0 on success
Error code on failure

pcm_stop

Stops the PCM audio device from further input and output operations.

int pcm_stop(
     struct pcm *pcm)

Parameters

pcm	Pointer to the open PCM device.

Return value

0 on success
Error code on failure

pcm_close

Closes the PCM audio device. This releases the resources associated with the PCM device and releases the memory.

int pcm_close(
     struct pcm *pcm)

Parameters

pcm	Pointer to the open PCM device.

Return value

0 on success
Error code on failure

Configure TinyALSA

For audio use cases from TinyALSA, configure the virtual mixer controls. These controls, created by the mixer plug-in, set up audio use case graphs and modules. Most are byte array-based and are configured using the mixer_ctl_set_array API. Metadata (referred to as ‘PCM100 metadata’) is set using key-value (KV) pairs. For implementation details, see the set_agm_audio_intf_metadata API in build-qcom-wayland/workspace/sources/qcom-agm/opensource/agm/plugins/tinyalsa/test/agmmixer.c.

/**
            * Key Vector pair
            */
            struct agm_key_value {
            uint32_t key; /**< key */
            uint32_t value; /**< value */
            };
            /*Sample allocation for the key value pair*/
            gkv = calloc(num_gkv, sizeof(struct agm_key_value));
            ckv = calloc(num_ckv, sizeof(struct agm_key_value));

Sample code for the TinyALSA-based agmplay and agmcap utilities can be found at: build-qcom-wayland/workspace/sources/qcom-agm/opensource/agm/plugins/tinyalsa/test. To enable and execute audio use cases from TinyALSA:

Set the audio interface (backend) device configuration, including sample rate, channels, format, and data format.
'CODEC_DMA-LPAIF_WSA-RX-0 rate ch fmt' 48000 2 2(PCM_16)
Set the metadata, including graph keys, cal keys for the device, and DevicePP.
'CODEC_DMA-LPAIF_WSA-RX-0 metadata' bytes
Set the control to indicate that follow-on mixer configurations will set the metadata for the stream and StreamPP subgraphs. Zero indicates that subsequent commands are for the stream.
'PCM100 control' Zero 'PCM100 metadata' bytes
Set the control to indicate that follow on mixer configurations will set the metadata for the DevicePP and stream-device subgraphs. CODEC_DMA-LPAIF_WSA-RX-0 indicates that the subsequent commands are for stream-device. CODEC_DMA-LPAIF_WSA-RX-0 is one of the audio interfaces registered with the ALSA ASOC framework. A list of all audio interfaces can be found at /proc/asound/pcm.
'PCM100 control' CODEC_DMA-LPAIF_WSA-RX-0 'PCM100 metadata' bytes
Retrieve all tags, module ID, and instance IDs associated with a given session between the stream and audio interface.
'PCM100 getTaggedInfo' bytes
Set the control to indicate that follow on mixer configurations will set the parameters for modules on the stream subgraph.
'PCM100 control' Zero 'PCM100 setParam' bytes
Set the control to indicate that follow on mixer configurations will set the parameters for modules on the StreamDevice and DevicePP subgraphs.
'PCM100 control' CODEC_DMA-LPAIF_WSA-RX-0 'PCM100 setParam' bytes
Connect the frontend (stream) with the backend (codec/audio interface).
'PCM100 connect' CODEC_DMA-LPAIF_WSA-RX-0
Open the PCM device.
pcm_open
Prepare the audio device for input and output operations.
pcm_prepare
Start the PCM audio device for input and output operations.
pcm_start
Write and read audio data from the audio PCM device.
pcm_write/pcm_read
Stop the PCM device.
pcm_stop
Close the PCM audio device.
pcm_close

All mixer controls for a virtual device can be fetched using:

ssh root@ip-addr

systemctl stop pipewire

tinymix set -D 100

Next steps

Customize audio graph — Customize audio use cases at the PAL level
Troubleshoot audio — Capture and analyze audio logs to resolve issues
Audio Addendum — Use QACT and QXDM for calibration and diagnostics

Introduction

Architecture

Key Documents

Technologies

System

Release Notes

TinyALSA APIs

pcm_open

pcm_is_ready

pcm_prepare

pcm_start

pcm_write

pcm_read

pcm_stop

pcm_close

Configure TinyALSA

Next steps

​TinyALSA APIs

​pcm_open

​pcm_is_ready

​pcm_prepare

​pcm_start

​pcm_write

​pcm_read

​pcm_stop

​pcm_close

​Configure TinyALSA

​Next steps

TinyALSA APIs

pcm_open

pcm_is_ready

pcm_prepare

pcm_start

pcm_write

pcm_read

pcm_stop

pcm_close

Configure TinyALSA

Next steps