The i.MX6UL provides three Serial Audio Interfaces (SAI).

The ConnectCore 6UL SBC Pro includes a Maxim 98089 low-power stereo codec with the following features:

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

  • Analog outputs: line-out, headphone, speakers

  • Digital input/out multi-format audio interface

  • Digital processing, filters, volume control, amplifiers

On the ConnectCore 6UL SBC Express reference design, the codec is a slave chip that the CPU controls via the SAI2 port of the ConnectCore 6UL system-on-chip. The CPU drives audio data using the inter-IC sound bus standard (I2S).

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 6UL kernel configuration file.

Kernel driver

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

File Description


SAI driver


Driver interface with codec


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

  • The IOMUX

SAI2 interface

i.MX6UL device tree
sai2: sai@0202c000 {
	compatible = "fsl,imx6ul-sai",
	reg = <0x0202c000 0x4000>;
	interrupts = <GIC_SPI 98 IRQ_TYPE_LEVEL_HIGH>;
	clocks = <&clks IMX6UL_CLK_SAI2_IPG>,
		<&clks IMX6UL_CLK_SAI2>,
		<&clks 0>, <&clks 0>;
	clock-names = "bus", "mclk1", "mclk2", "mclk3";
	dma-names = "rx", "tx";
	dmas = <&sdma 37 24 0>, <&sdma 38 24 0>;
	status = "disabled";
ConnectCore 6UL SBC Pro device tree
&sai2 {
	pinctrl-names = "default";
	pinctrl-0 = <&pinctrl_sai2>;
	assigned-clocks = <&clks IMX6UL_CLK_SAI2_SEL>,
			<&clks IMX6UL_CLK_SAI2>;
	assigned-clock-rates = <0>, <786432000>, <12288000>;
	assigned-clock-parents = <&clks IMX6UL_CLK_PLL4_AUDIO_DIV>;
	status = "disabled";

Interface between SAI and audio codec

ConnectCore 6UL SBC Pro device tree
sound_max98089: sound-max98089 {
	compatible = "fsl,imx-audio-max98088";
	model = "imx-max98088";
	cpu-dai = <&sai2>;
	audio-codec = <&max98089>;
	asrc-controller = <&asrc>;
	gpr = <&gpr>;
	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";

Audio codec (I2C1 slave)

ConnectCore 6UL SBC Pro device tree
&i2c1 {
	max98089: codec@10 {
		compatible = "maxim,max98089";
		reg = <0x10>;
		clocks = <&clks IMX6UL_CLK_SAI2>;
		clock-names = "mclk";
		interrupt-parent = <&gpio5>;
		interrupts = <7 IRQ_TYPE_EDGE_FALLING>;

IOMUX configuration

ConnectCore 6UL SBC Pro device tree
pinctrl_sai2: sai2grp {
	fsl,pins = <
		MX6UL_PAD_JTAG_TMS__SAI2_MCLK        0x17088
		/* Interrupt */
		MX6UL_PAD_SNVS_TAMPER7__GPIO5_IO07    0x80000000

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

  • Microphone

  • Headphones

  • Speakers

  • Line out

You can use the command line application alsamixer to manage these interfaces and their associated controls (volumes, gains, 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 and line-in A 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