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
.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)
| 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. |
pcm* handle
pcm_is_ready
Checks if the PCM device is ready for input and output operations.
int pcm_is_ready(struct pcm *pcm)
| pcm | Pointer to the open PCM device. |
|---|
- 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)
| pcm | Pointer to the open PCM device. |
|---|
- 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)
| pcm | Pointer to the open PCM device. |
|---|
- 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)
| pcm | Pointer to the open PCM device. |
|---|
| data | Audio data to write. |
| count | Number of audio frames to write. |
- 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)
| pcm | Pointer to the open PCM device. |
|---|
| data | Audio data to read. |
| count | Number of audio frames to read. |
- 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)
| pcm | Pointer to the open PCM device. |
|---|
- 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)
| pcm | Pointer to the open PCM device. |
|---|
- 0 on success
- Error code on failure
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));
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.
- Prepare the audio device for input and output operations.
- Start the PCM audio device for input and output operations.
- Write and read audio data from the audio PCM device.
- Stop the PCM device.
- Close the PCM audio device.
All mixer controls for a virtual device can be fetched using:
Next steps
