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Audio

Audio Functionality and Usage Guide.

Overview​

The Audio module includes 2 I2S interfaces and 1 HDMI audio interface.

Functional Description​

The ALSA audio framework can be divided into several layers:

  • ALSA Library

    Provides a unified API interface to applications. Various applications can achieve playback, recording, and control by calling the APIs provided by the ALSA library. Two basic libraries are currently provided: tinyalsa, which is a simplified version of the ALSA library, is mainly used in Android systems.

  • ALSA CORE

    The core layer of ALSA, which provides logical devices (PCM, CTL, MIDI, TIMER, etc.) for system calls and drives hardware devices (Machine, I2S, DMA, CODEC).

  • ASoC Core

    The standard framework of ALSA, which is the core part of the ALSA-driver. It provides general methods and data structures for various audio device drivers.

  • Hardware Driver

    The audio hardware device driver, which consists of three main parts: Machine, Platform, and Codec. It provides the ALSA Driver API and the initialization and workflow of the corresponding audio devices, implementing specific functional components. This is the part that driver developers need to implement specifically.

  • Machine

    Typically refers to a specific single board that includes particular peripherals, providing a carrier for the CPU and Codec. Machine drivers are almost non-reusable. The Machine driver links the Platform driver and the Codec driver together, specifying which Platform driver to use, which SoC-side DAI (Digital Audio Interface) to use, which Codec driver to use, and which DAI interface on the Codec to use, while also performing operations specific to the single board.

  • Platform

    Generally refers to a specific SoC platform, which can be understood as a particular SoC with I2S, AC97 audio interfaces, internal clocks, and DMA units for audio data transfer. The Platform driver is only related to a specific SoC, implementing the SoC's audio DMA driver and the DAI interface driver on the SoC side. It is only related to the SoC and not to the Machine, allowing the Platform to be abstracted out so that the same SoC can be used in different Machines without any modifications.

  • Codec

    The audio codec, which includes I2S interfaces, D/A, A/D, Mixer, and PA (Power Amplifier). It typically contains multiple inputs (Mic, Line-in, I2S, PCM) and several outputs (headphones, speakers, earpiece, Line-out). The SoC usually controls the codec chip via I2C. The Codec driver is only related to the Codec and is independent of the SoC and Machine. Like the Platform, the Codec should be implemented as a reusable component, allowing the same Codec to be used in different Machines.

Audio Solution​

K1 currently supports two sound card solutions: Solution 1: HDMI Audio, which supports playback. Solution 2: I2S0 paired with an external I2C Codec ES8326B, which supports both playback and recording.

Source Code Structure​

The I2S/HDMIAUDIO controller driver code is located in the sound/soc/spacemit directory:

sound/soc/spacemit
├── Kconfig
├── Makefile
├── spacemit-dummy-codec.c    # Dummy codec, used with HDMI audio to create a sound card
├── spacemit-snd-card.c       # Sound card driver
├── spacemit-snd-i2s.c        # I2S driver
├── spacemit-snd-i2s.h
├── spacemit-snd-pcm-dma.c    # Platform driver, mainly related to PCM
├── spacemit-snd-sspa.c       # HDMI audio driver
├── spacemit-snd-sspa.h

The driver code for the Codec ES8326B is located in the sound/soc/codec directory:

sound/soc/codec
├── es8326.c
├── es8326.h

I2S​

Key Features​

  • Supports a sampling rate of 48000, with a 16-bit sampling depth and 2 channels.
  • Supports playback and recording functions.
  • Supports full-duplex operation.

Configuration​

The configuration mainly includes driver enabling and DTS (Device Tree Source) configuration

CONFIG Configuration​

Audio Function Support​

CONFIG_SOUND, CONFIG_SND, and CONFIG_SND_SOC provide support for the ALSA audio driver framework. By default, these options are enabled (y).

Device Drivers
        Sound card support (SOUND [=y])
                Advanced Linux Sound Architecture (SND [=y])
                        ALSA for SoC audio support (SND_SOC [=y])

Audio Function Support​

CONFIG_SND_SOC_SPACEMIT, CONFIG_SPACEMIT_CARD, and CONFIG_SPACEMIT_PCM provide support for the K1 audio functionality. By default, these options are enabled (y)

Device Drivers
        Sound card support (SOUND [=y])
                Advanced Linux Sound Architecture (SND [=y])
                        ALSA for SoC audio support (SND_SOC [=y])
                                SoC Audio for SPACEMIT System-on-Chip (SND_SOC_SPACEMIT [=y])
                                        Audio Simple Card (SPACEMIT_CARD [=y])
                                        Audio Platform Pcm (SPACEMIT_PCM [=y])

I2S Function Support​

CONFIG_SPACEMIT_I2S provides support for the I2S functionality. By default, this option is enabled (y).

Device Drivers
        Sound card support (SOUND [=y])
                Advanced Linux Sound Architecture (SND [=y])
                        ALSA for SoC audio support (SND_SOC [=y])
                                SoC Audio for SPACEMIT System-on-Chip (SND_SOC_SPACEMIT [=y])
                                        Audio Simple Card (SPACEMIT_CARD [=y])
                                        Audio Platform Pcm (SPACEMIT_PCM [=y])
                                        Audio Cpudai I2S (SPACEMIT_I2S [=y])

DTS Configuration​

pinctrl​
  • i2s0 pinctrl configuration There are two sets of pinctrl configurations, which should be configured according to the actual hardware design.
        pinctrl_sspa0_0: sspa0_0_grp {
                pinctrl-single,pins =<
                        K1X_PADCONF(GPIO_118, MUX_MODE3, (EDGE_NONE | PULL_UP | PAD_1V8_DS0))   /* sspa0_clk */
                        K1X_PADCONF(GPIO_119, MUX_MODE3, (EDGE_NONE | PULL_UP | PAD_1V8_DS0))   /* sspa0_frm */
                        K1X_PADCONF(GPIO_120, MUX_MODE3, (EDGE_NONE | PULL_UP | PAD_1V8_DS0))   /* sspa0_txd */
                        K1X_PADCONF(GPIO_121, MUX_MODE3, (EDGE_NONE | PULL_UP | PAD_1V8_DS0))   /* sspa0_rxd */
                        K1X_PADCONF(GPIO_122, MUX_MODE3, (EDGE_NONE | PULL_UP | PAD_1V8_DS0))   /* sspa0_sysclk */
                >;
        };

        pinctrl_sspa0_1: sspa0_1_grp {
                pinctrl-single,pins =<
                        K1X_PADCONF(GPIO_58,  MUX_MODE2, (EDGE_NONE | PULL_UP | PAD_1V8_DS0))   /* sspa0_sysclk */
                        K1X_PADCONF(GPIO_111, MUX_MODE2, (EDGE_NONE | PULL_UP | PAD_1V8_DS0))   /* sspa0_clk */
                        K1X_PADCONF(GPIO_112, MUX_MODE2, (EDGE_NONE | PULL_UP | PAD_1V8_DS0))   /* sspa0_frm */
                        K1X_PADCONF(GPIO_113, MUX_MODE2, (EDGE_NONE | PULL_UP | PAD_1V8_DS0))   /* sspa0_txd */
                        K1X_PADCONF(GPIO_114, MUX_MODE2, (EDGE_NONE | PULL_UP | PAD_1V8_DS0))   /* sspa0_rxd */
                >;
        }

&i2s0 {
        pinctrl-names = "default";
        pinctrl-0 = <&pinctrl_sspa0_0>;         # Using the pin set pinctrl_sspa0_0.
        status = "okay";
};

  • i2s1 pinctrl configuration

          pinctrl_sspa1: sspa1_grp {
                  pinctrl-single,pins =<
                          K1X_PADCONF(GPIO_24, MUX_MODE3, (EDGE_NONE | PULL_UP | PAD_1V8_DS0))    /* sspa1_sysclk */
                          K1X_PADCONF(GPIO_25, MUX_MODE1, (EDGE_NONE | PULL_UP | PAD_1V8_DS0))    /* sspa1_sclk */
                          K1X_PADCONF(GPIO_26, MUX_MODE1, (EDGE_NONE | PULL_UP | PAD_1V8_DS0))    /* sspa1_frm */
                          K1X_PADCONF(GPIO_27, MUX_MODE1, (EDGE_NONE | PULL_UP | PAD_1V8_DS0))    /* sspa1_txd */
                          K1X_PADCONF(GPIO_28, MUX_MODE1, (EDGE_NONE | PULL_UP | PAD_1V8_DS0))    /* sspa1_rxd */
                  >;
          };

    &i2s1 {
          pinctrl-names = "default";
          pinctrl-0 = <&pinctrl_sspa1>;          #Using the pin set pinctrl_sspa1.
          status = "okay";
    };

I2S-Codec Sound Card Configuration​

Codec Configuration​

Using the ES8326B Codec as an example for a complete sound card configuration.

Config Configuration​

Enable the ES8326B configuration.

Device Drivers│
        Sound card support (SOUND [=y])
                Advanced Linux Sound Architecture (SND [=y])
                        ALSA for SoC audio support (SND_SOC [=y])
                                CODEC drivers
                                        Everest Semi ES8326 CODEC (SND_SOC_ES8326 [=y])
DTS Configuration​

  • GPIO Configure according to the actual hardware design. For example, on some K1 development boards, the ES8326B uses GPIO129 for headphone detection and GPIO127 for speaker control.

          es8326: es8326@19{
                  interrupt-parent = <&gpio>;
                  interrupts = <126 1>;                 # Headphone insertion and removal detection
                  spk-ctl-gpio = <&gpio 127 0>;         # Board-level speaker control GPIO
          };

DTS Configuration Example​

The complete configuration for the ES8236B codec is as follows:

        es8326: es8326@19{
                compatible = "everest,es8326";
                reg = <0x19>;
                #sound-dai-cells = <0>;
                interrupt-parent = <&gpio>;
                interrupts = <126 1>;                 # Headphone plug detection
                spk-ctl-gpio = <&gpio 127 0>;         # Board-level speaker control GPIO
                everest,mic1-src = [44];              # ADC source configuration
                everest,mic2-src = [66];
                status = "okay";
        };
MCLK Configuration​

The ES8326B codec's MCLK is provided by I2S0 and is configured in the sound card node sound_codec


&sound_codec {
        status = "okay";
        simple-audio-card,name = "snd-es8326";
        spacemit,mclk-fs = <64>;                      # Configure mclk = 64 * fs, i.e., 3.072MHz
    simple-audio-card,codec {
        simple-audio-card,codec {
                sound-dai = <&es8326>;
                };
        };
};

Note. The spacemit,mclk-fs only supports configurations of 64, 128, or 256, which correspond to 3.072MHz, 6.144MHz, and 12.288MHz respectively.

Sound Card Configuration​
DTS Configuration​
        sound_codec: snd-card@1 {
                compatible = "spacemit,simple-audio-card";
                simple-audio-card,format = "i2s";
                status = "disabled";
                interconnects = <&dram_range4>;
                interconnect-names = "dma-mem";
                spacemit,init-jack;
                simple-audio-card,cpu {                      # CPU DAI Configuration
                        sound-dai = <&i2s0>;
                };
                simple-audio-card,plat {
                        sound-dai = <&i2s0_dma>;             # Platform PCM Configuration
                };
        };

&sound_codec {
        status = "okay";
        simple-audio-card,name = "snd-es8326";
        spacemit,mclk-fs = <64>;
        simple-audio-card,codec {
                sound-dai = <&es8326>;                       # Codec DAI Configuration
        };
};

HDMIAUDIO​

Key Features​

  • Supports a sample rate of 48,000 Hz, 16-bit sample depth, and 2 channels.
  • Supports playback only

Configuration​

The configuration mainly consists of driver enablement and DTS settings. Since HDMIAUDIO relies on the HDMI display function, it is necessary to ensure that HDMI display is supported. Please refer to the corresponding documentation.

CONFIG Configuration​

Audio Function Support​

CONFIG_SOUND, CONFIG_SND, and CONFIG_SND_SOC provide support for the ALSA audio driver framework. By default, this option is set to Y.

Device Drivers
        Sound card support (SOUND [=y])
                Advanced Linux Sound Architecture (SND [=y])
                        ALSA for SoC audio support (SND_SOC [=y])
K1 Audio Function Support​

CONFIG_SND_SOC_SPACEMIT, CONFIG_SPACEMIT_CARD, and CONFIG_SPACEMIT_PCM provide support for K1 audio functions. By default, this option is set to Y.

Device Drivers
        Sound card support (SOUND [=y])
                Advanced Linux Sound Architecture (SND [=y])
                        ALSA for SoC audio support (SND_SOC [=y])
                                SoC Audio for SPACEMIT System-on-Chip (SND_SOC_SPACEMIT [=y])
                                        Audio Simple Card (SPACEMIT_CARD [=y])
                                        Audio Platform Pcm (SPACEMIT_PCM [=y])
HDMIAUDIO Function Support​

CONFIG_SPACEMIT_HDMIAUDIO and CONFIG_SPACEMIT_DUMMYCODEC provide support for the HDMIAUDIO function. By default, this option is set to Y.

Device Drivers
        Sound card support (SOUND [=y])
                Advanced Linux Sound Architecture (SND [=y])
                        ALSA for SoC audio support (SND_SOC [=y])
                                SoC Audio for SPACEMIT System-on-Chip (SND_SOC_SPACEMIT [=y])
                                        Audio Simple Card (SPACEMIT_CARD [=y])
                                        Audio Platform Pcm (SPACEMIT_PCM [=y])
                                        Audio Cpudai HDMI Audio (SPACEMIT_HDMIAUDIO [=y])
                                        Audio CodecDai Dummy Codec (SPACEMIT_DUMMYCODEC [=y])

DTS Configuration​

&hdmiaudio {
        status = "okay";
};

HDMIAUDIO Sound Card Configuration​

DTS Configuration​

        sound_hdmi: snd-card@0 {
                compatible = "spacemit,simple-audio-card";
                simple-audio-card,name = "snd-hdmi";
                status = "disabled";
                interconnects = <&dram_range4>;
                interconnect-names = "dma-mem";
                simple-audio-card,plat {                        # Platform PCM Configuration
                        sound-dai = <&hdmi_dma>;
                };
                simple-audio-card,codec {                       # Codec DAI Configuration
                        sound-dai = <&dummy_codec>;
                };
        };

&sound_hdmi {
        status = "okay";
        simple-audio-card,cpu {
                sound-dai = <&hdmiaudio>;                       # CPU DAI Configuration
        };
};

Interface​

API​

Please refer to the relevant official Linux documentation.

Debugging​

You can perform debugging through the nodes under /proc/asound/.

View Sound Card Devices​

root:/# cat /proc/asound/pcm
00-00: SSPA2-dummy_codec dummy_codec-0 :  : playback 1
01-00: i2s-dai0-ES8326 HiFi ES8326 HiFi-0 :  : playback 1 : capture 1
root:/#

Viewing Sound Card Status and Other Information​

  • CLOSED, the sound card is in a closed state.

    root:/# cat /proc/asound/card1/pcm0p/sub0/status
    closed
    root:/# cat /proc/asound/card1/pcm0p/sub0/hw_params
    closed
    root:/#

  • RUNNING, the sound card is in a running state, either playing or recording. You can view the status and parameters of the sound card.

    root:/# cat /proc/asound/card1/pcm0p/sub0/status
    state: RUNNING
    owner_pid   : 3767
    trigger_time: 224110.719883196
    tstamp      : 224164.735391138
    delay       : 2048
    avail       : 2048
    avail_max   : 2048
    -----
    hw_ptr      : 2592768
    appl_ptr    : 2594816
    root:/# cat /proc/asound/card1/pcm0p/sub0/status
    state: RUNNING
    owner_pid   : 3767
    trigger_time: 224110.719883196
    tstamp      : 224166.975406348
    delay       : 3072
    avail       : 1024
    avail_max   : 2048
    -----
    hw_ptr      : 2700288
    appl_ptr    : 2703360
    root:/# cat /proc/asound/card1/pcm0p/sub0/hw_params
    access: RW_INTERLEAVED
    format: S16_LE
    subformat: STD
    channels: 2
    rate: 48000 (48000/1)
    period_size: 1024
    buffer_size: 4096
    root:/#

Testing​

Audio functionality can be tested using the alsa-utils or tinyalsa tools, which are already integrated into bianbu-linux.

Playback Test​

Viewing Playback Devices​

aplay-l // List playback devices

root:/# aplay -l
**** PLAYBACK Hardware Devices ****
card 0: sndhdmi [snd-hdmi], device 0: SSPA2-dummy_codec dummy_codec-0 []
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 1: sndes8326 [snd-es8326], device 0: i2s-dai0-ES8326 HiFi ES8326 HiFi-0 []
  Subdevices: 1/1
  Subdevice #0: subdevice #0
root:/#

There are two playback devices visible:

  • The HDMIAUDIO playback device has a card ID of 0 and a device ID of 0.
  • The I2S-Codec playback device has a card ID of 1 and a device ID of 0.

Playback​

Specify the card and device IDs to select a playback device

Example: Select the HDMIAUDIO sound card for playback.

aplay -Dhw:0,0 -r 48000 -f S16_LE --period-size=480 --buffer-size=1920 xxx.wav

Example: Select the I2S-Codec sound card for playback.

aplay -Dhw:1,0 -r 48000 -f S16_LE --period-size=1024 --buffer-size=4096 xxx.wav

Recording Test​

Viewing Capture Devices​

arecord -l to view the capture devices

root@spacemit-k1-x-deb1-board:~# arecord -l
**** CAPTURE Hardware Devices ****
card 1: sndes8326 [snd-es8326], device 0: i2s-dai0-ES8326 HiFi ES8326 HiFi-0 []
  Subdevices: 1/1
  Subdevice #0: subdevice #0
root@spacemit-k1-x-deb1-board:~#

There is one capture device visible:

  • The I2S-Codec capture device has a card ID of 1 and a device ID of 0.

Recording​

Select a device for recording by specifying the card ID and device ID.

Example: Select the I2S-Codec sound card for recording.

arecord -Dhw:1,0 -r 48000 -c 2 -f S16_LE --period-size=1024 --buffer-size=4096 xxx.wav

FAQ​