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3.2.1 RDK S100 Series Audio Usage Guide

S100 audio is developed based on the standard ALSA framework. In user space, the open-source alsa-lib provides libraries and binary tools for functional testing. This section describes the basic methods for audio functionality testing on the S100.

Introduction to alsa-lib​

Parameter Description for arecord/aplay​

  • Common parameter explanations
ParameterDescriptionAdditional Notes
-DSpecifies the device node. Set via hw:x,xx,x correspond to the card number and device number respectively
-cChannel: number of audio channels, including mono, stereo, or multi-channel configurations such as 8/16 channels
-rRate: also known as sample rate, i.e., the number of samples per second
-fSample format (bit depth)Common formats: U8/S16_LE/S32_LE
-tFile typeIncludes wav, voc, raw, etc.
-dRecording duration (in seconds). Recording stops after the specified time
--period-sizeNumber of frames processed per hardware interrupt
--buffer-sizeSize of the data buffer
-INon-interleaved mode

  • Common commands

    • List sound cards and digital audio devices
    arecord -l
    aplay -l
    • Query hardware capabilities
    arecord --dump-hw-params -Dhw:0,0
    aplay --dump-hw-params -Dhw:0,1 /dev/zero
    • Loopback test command
    arecord -Dhw:0,0 -c 2 -r 48000 -f S16_LE -t wav -d 10 | aplay -Dhw:0,1
    • Non-interleaved data storage. Note: Non-interleaved data is raw PCM.
    arecord -Dhw:0,0 -c 2 -r 48000 -f S16_LE -t wav -d 5 -I 0
    aplay -Dhw:0,1 -c 2 -r 48000 -f S16_LE -t wav -I 0
    • Interleaved data storage
    arecord -Dhw:0,0 -c 2 -r 16000 -f S16_LE -t wav -d 5 test.wav
    aplay -Dhw:0,1 test.wav

Control Commands​

  • Query all control parameters and their current values for the current codec
amixer scontrols
amixer scontents
  • Parameter adjustment

For example, adjusting playback volume:

amixer sset 'DAC' 120 // Set
amixer sget 'DAC' // Get
Note

The default sound card/device number is 0,0. If multiple sound cards are connected in your actual setup, you must specify the correct card and device numbers using -D and -c.

How to confirm the current sound card/device number:

  • arecord -l
**** List of CAPTURE Hardware Devices ****
card 0: s100snd2 [s100snd2], device 0: s100dailink0 ES7210 4CH ADC 0-0 []
  Subdevices: 1/1
  Subdevice #0: subdevice #0
  • /proc/asound/cards node
root@ubuntu:/userdata# cat /proc/asound/cards
 0 [s100snd2       ]: s100snd2 - s100snd2
                      s100snd2

Application Space Interface​

For API descriptions and usage, refer to the official documentation: https://www.alsa-project.org/alsa-doc/alsa-lib/pcm_2pcm_8c.html

Audio Driver HAT REV2​

Preparation​

The S100 is compatible with the audio HAT produced by Waveshare, connecting to the S100 development board via the 40-pin header. For details about the HAT and connection instructions, refer to: Audio HAT Usage Guide

Device Nodes​

After the audio HAT is connected to the S100 and the driver is loaded, the following device nodes are created:

  • pcmC0D0c: capture (recording)

  • pcmC0D1p: playback

  • controlC0: control

Functional Testing​

  • Recording
arecord -Dhw:0,0 -c 2 -r 48000 -f S16_LE -t wav -d 5 test.wav

This command records a 5-second WAV audio file with 48 kHz sampling rate, 2 channels, and 16-bit depth. Users can adjust these parameters according to their specific requirements.

  • Playback
aplay -Dhw:0,1 test.wav

This command plays a WAV file. The audio format is parsed from the WAV file header and passed to the driver.

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