The i.MX8QXP provides two transmit/receive Serial Audio Interfaces (SAI) and another two receive-only SAIs.

On the ConnectCore 8X SBC Pro, the SAI0 interface is connected to a Maxim 98089 low-power stereo codec with the following features:

  • Analog inputs: line-in A, line-in B, microphone:

    • Two line-in audio inputs through the LINE1_IN_ and LINE2_IN_ lines of the expansion connector.

    • Microphone audio input through the MIC_ lines of the expansion connector.

  • Analog outputs: line-out, headphone, speakers:

    • Line-out audio output through the LINE_OUT_ lines of the expansion connector.

    • Headphone audio output through the on-board jack connector.

    • Speaker audio output through the SPKL_ and SPKR_ lines of the expansion connector.

  • Digital input/out multi-format audio interface.

  • Digital processing, filters, volume control, amplifiers.

The codec is a slave chip that the CPU controls via the SAI0 port of the ConnectCore 8X system-on-chip. The CPU drives audio data using the inter-IC sound bus standard (I2S).

All audio output comes out through this codec and can be reproduced using a pair of speakers or headphones.

Kernel configuration

You can manage the audio driver support through the following kernel configuration options:

  • SoC Audio for NXP i.MX CPUs (CONFIG_SND_IMX_SOC)

  • SoC Audio support for i.MX boards with max98088/max98089 (CONFIG_SND_SOC_IMX_MAX98088)

These options are enabled as built-in on the default ConnectCore 8X kernel configuration file.

Kernel driver

The drivers for the audio interface and MAX98089 codec are located at:

File Description

sound/soc/fsl/fsl_sai.c

SAI driver

sound/soc/fsl/snd-soc-imx-max98088.c

Driver interface with codec

sound/soc/codecs/max98088.c

MAX98088/9 codec driver

Device tree bindings and customization

The SAI interface is documented at Documentation/devicetree/bindings/sound/fsl-sai.txt.

The interface between the SAI and the codec is documented at Documentation/devicetree/bindings/sound/imx-audio-max98088.txt.

The MAX98088/9 codec is documented at Documentation/devicetree/bindings/sound/max98088.txt.

The device tree must contain entries for:

  • The SAI interface

  • The interface between the SAI and the audio codec

  • The audio codec

Example: SAI0 on ConnectCore 8X SBC Pro

Definition of the SAI

i.MX8QXP device tree
[...]

sai0: sai@59040000 {
	compatible = "fsl,imx8qm-sai";
	reg = <0x0 0x59040000 0x0 0x10000>;
	interrupts = <GIC_SPI 314 IRQ_TYPE_LEVEL_HIGH>;
	clocks = <&clk IMX8QXP_AUD_SAI_0_IPG>,
		<&clk IMX8QXP_CLK_DUMMY>,
		<&clk IMX8QXP_AUD_SAI_0_MCLK>,
		<&clk IMX8QXP_CLK_DUMMY>,
		<&clk IMX8QXP_CLK_DUMMY>;
	clock-names = "bus", "mclk0", "mclk1", "mclk2", "mclk3";
	dma-names = "rx", "tx";
	dmas = <&edma0 12 0 1>, <&edma0 13 0 0>;
	status = "disabled";
	power-domains = <&pd_sai0>;
};

[...]
ConnectCore 8X SBC Pro device tree
&sai0 {
	assigned-clocks = <&clk IMX8QXP_AUD_PLL0_DIV>,
			  <&clk IMX8QXP_AUD_ACM_AUD_PLL_CLK0_DIV>,
			  <&clk IMX8QXP_AUD_ACM_AUD_REC_CLK0_DIV>,
			  <&clk IMX8QXP_AUD_SAI_0_MCLK>;
	assigned-clock-rates = <786432000>, <49152000>, <12288000>, <49152000>;
	pinctrl-names = "default";
	pinctrl-0 = <&pinctrl_sai0>;
	status = "okay";
};

[...]

/* IOMUX */
&iomuxc {
	[...]

	pinctrl_sai0: sai0grp {
		fsl,pins = <
			SC_P_SAI0_RXD_ADMA_SAI0_RXD		0x06000040
			SC_P_SAI0_TXD_ADMA_SAI0_TXD		0x06000060
			SC_P_SAI0_TXFS_ADMA_SAI0_TXFS		0x06000040
			SC_P_SAI0_TXC_ADMA_SAI0_TXC		0x06000040
			SC_P_SPI3_CS0_ADMA_ACM_MCLK_OUT1	0x06000040
		>;
	};

	[...]
};

Interface between SAI and audio codec

ConnectCore 8X SBC Pro device tree

[...]

sound_max98089: sound-max98089 {
	compatible = "fsl,imx-audio-max98088";
	model = "imx-max98088";
	cpu-dai = <&sai0>;
	audio-codec = <&max98089>;
	asrc-controller = <&asrc0>;
	audio-routing =
		"Headphone Jack", "HPL",
		"Headphone Jack", "HPR",
		"Ext Spk", "SPKL",
		"Ext Spk", "SPKR",
		"LineOut", "RECL",
		"LineOut", "RECR",
		"Mic1", "MIC1",
		"Mic2", "MIC2",
		"LineInA", "INA1",
		"LineInA", "INA2",
		"LineInB", "INB1",
		"LineInB", "INB2";
	status = "okay";
};

[...]

&asrc0 {
	fsl,asrc-rate  = <48000>;
};

Audio codec (I2C3 slave)

ConnectCore 8X SBC Pro device tree
&i2c3 {
	[...]

	max98089: codec@10 {
		compatible = "maxim,max98089";
		reg = <0x10>;
		clocks = <&clk IMX8QXP_AUD_MCLKOUT1>;
		clock-names = "mclk";
		power-domains = <&pd_mclk_out1>;
		vcc-supply = <&reg_3v3_audio>;
		dvdd-supply = <&reg_1v8_ext>;
		assigned-clocks = <&clk IMX8QXP_AUD_PLL0_DIV>,
				  <&clk IMX8QXP_AUD_ACM_AUD_PLL_CLK0_DIV>,
				  <&clk IMX8QXP_AUD_ACM_AUD_REC_CLK0_DIV>,
				  <&clk IMX8QXP_AUD_MCLKOUT1>;
		assigned-clock-rates = <786432000>, <49152000>, <12288000>, <12288000>;
		status = "okay";
	};

	[...]
};

Using the audio interface

Audio controls

The audio codec is controlled from Linux via the ALSA framework. Digi Embedded Yocto provides an initial configuration that enables:

  • Line in A

  • Line in B

  • Microphone

  • Headphones

  • Speakers

  • Line out

You can use the command line application alsamixer to manage these interfaces and their associated controls such as volume, gain, and filters.

Audio playback

Since all output routes are enabled by default, any sound will play on headphones, speakers, and line-out.

To play a wav file:

~# aplay sound.wav

To play an mp3 file using gstreamer:

~# gst-launch-1.0 filesrc location=sound.mp3 ! id3demux ! queue ! beepdec ! alsasink

Audio recording

Since microphone, line-in A, and line-in B input routes are enabled by default, any recorded sound will mix the audio coming from these inputs.

To record a stereo WAV audio file with 10 seconds duration from line-in:

~# arecord -f cd sound.wav --duration 10

To record a mono WAV audio file from the microphone:

~# arecord --format=S16_LE --channels=1 --rate=44100 micro.wav --duration=10