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

On the ConnectCore 6UL SBC Pro, the SAI2 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 LINE_IN_A_ and LINE_IN_B_ lines of the AUDIO and SPK connectors.

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

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

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

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

    • Speaker audio output through the SPKL_ and SPKR_ lines of the SPK 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 SAI2 port of the ConnectCore 6UL 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 6UL 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: SAI2 on ConnectCore 6UL SBC Pro

Definition of the SAI

i.MX6UL device tree
[...]

sai2: sai@202c000 {
	#sound-dai-cells = <0>;
	compatible = "fsl,imx6ul-sai", "fsl,imx6sx-sai";
	reg = <0x0202c000 0x4000>;
	interrupts = <GIC_SPI 98 IRQ_TYPE_LEVEL_HIGH>;
	clocks = <&clks IMX6UL_CLK_SAI2_IPG>,
		 <&clks IMX6UL_CLK_SAI2>,
		 <&clks IMX6UL_CLK_DUMMY>, <&clks IMX6UL_CLK_DUMMY>;
	clock-names = "bus", "mclk1", "mclk2", "mclk3";
	dmas = <&sdma 37 24 0>,
	       <&sdma 38 24 0>;
	dma-names = "rx", "tx";
	status = "disabled";
};

[...]
ConnectCore 6UL SBC Pro device tree
&sai2 {
	pinctrl-names = "default", "sleep";
	pinctrl-0 = <&pinctrl_sai2>;
	pinctrl-1 = <&pinctrl_sai2_sleep>;
	assigned-clocks = <&clks IMX6UL_CLK_SAI2_SEL>,
			  <&clks IMX6UL_CLK_PLL4_AUDIO_DIV>,
			  <&clks IMX6UL_CLK_SAI2>;
	assigned-clock-rates = <0>, <786432000>, <12288000>;
	assigned-clock-parents = <&clks IMX6UL_CLK_PLL4_AUDIO_DIV>;
	status = "okay";
};

[...]

&iomuxc {
	[...]

	imx6ul-ccimx6ul {
		[...]

		pinctrl_sai2: sai2grp {
			fsl,pins = <
				MX6UL_PAD_JTAG_TRST_B__SAI2_TX_DATA	0x11088
				MX6UL_PAD_JTAG_TCK__SAI2_RX_DATA	0x11088
				MX6UL_PAD_JTAG_TMS__SAI2_MCLK		0x17088
				MX6UL_PAD_JTAG_TDI__SAI2_TX_BCLK	0x17088
				MX6UL_PAD_JTAG_TDO__SAI2_TX_SYNC	0x17088
				/* Interrupt */
				MX6UL_PAD_SNVS_TAMPER7__GPIO5_IO07	0x80000000
			>;
		};

		pinctrl_sai2_sleep: sai2grp_sleep {
			fsl,pins = <
				MX6UL_PAD_JTAG_TRST_B__GPIO1_IO15	0x3000
				MX6UL_PAD_JTAG_TCK__GPIO1_IO14		0x3000
				MX6UL_PAD_JTAG_TMS__GPIO1_IO11		0x3000
				MX6UL_PAD_JTAG_TDO__GPIO1_IO12		0x3000
				/* Interrupt */
				MX6UL_PAD_SNVS_TAMPER7__GPIO5_IO07	0x3000
			>;
		};
	};
};

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";
	status = "okay";
};

[...]

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>;
		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 (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, 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