The {cpu-family} provides five transmit/receive Serial Audio Interfaces (SAI).
On the ConnectCore 8M Nano Development Kit, 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 LINE1_IN_ and LINE2_IN_ lines of the J53 connector.
-
Microphone audio input through the on-board jack connector.
-
-
Analog outputs: line-out, headphone, speakers:
-
Line-out audio output through the LINE_OUT_ lines of the J53 connector.
-
Headphone audio output through the on-board jack connector.
-
Speaker audio output through the SPKL_ and SPKR_ lines of the J53 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 8M Nano 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 8M Nano 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
Example: SAI2 on ConnectCore 8M Nano Development Kit
Definition of the SAI
[...]
sai2: sai@30020000 {
compatible = "fsl,imx8mm-sai", "fsl,imx8mq-sai";
reg = <0x30020000 0x10000>;
interrupts = <GIC_SPI 96 IRQ_TYPE_LEVEL_HIGH>;
clocks = <&clk IMX8MN_CLK_SAI2_IPG>,
<&clk IMX8MN_CLK_DUMMY>,
<&clk IMX8MN_CLK_SAI2_ROOT>,
<&clk IMX8MN_CLK_DUMMY>, <&clk IMX8MN_CLK_DUMMY>;
clock-names = "bus", "mclk0", "mclk1", "mclk2", "mclk3";
dmas = <&sdma2 2 2 0>, <&sdma2 3 2 0>;
dma-names = "rx", "tx";
status = "disabled";
};
[...]
&clk {
assigned-clocks = <&clk IMX8MN_AUDIO_PLL1>, <&clk IMX8MN_AUDIO_PLL2>;
assigned-clock-rates = <393216000>, <361267200>;
};
[...]
&sai2 {
pinctrl-names = "default", "sleep";
pinctrl-0 = <&pinctrl_sai2>;
pinctrl-1 = <&pinctrl_sai2_sleep>;
assigned-clocks = <&clk IMX8MN_CLK_SAI2>;
assigned-clock-parents = <&clk IMX8MN_AUDIO_PLL1_OUT>;
assigned-clock-rates = <12288000>;
status = "okay";
};
[...]
/* IOMUX */
&iomuxc {
[...]
pinctrl_sai2: sai2grp {
fsl,pins = <
MX8MN_IOMUXC_SAI2_RXD0_SAI2_RX_DATA0 0xd6
MX8MN_IOMUXC_SAI2_TXD0_SAI2_TX_DATA0 0xd6
MX8MN_IOMUXC_SAI2_TXFS_SAI2_TX_SYNC 0xd6
MX8MN_IOMUXC_SAI2_TXC_SAI2_TX_BCLK 0xd6
MX8MN_IOMUXC_SAI2_MCLK_SAI2_MCLK 0xd6
>;
};
pinctrl_sai2_sleep: sai2sleepgrp {
fsl,pins = <
MX8MN_IOMUXC_SAI2_RXD0_GPIO4_IO23 0x100
MX8MN_IOMUXC_SAI2_TXD0_GPIO4_IO26 0x100
MX8MN_IOMUXC_SAI2_TXFS_GPIO4_IO24 0x100
MX8MN_IOMUXC_SAI2_TXC_GPIO4_IO25 0x100
MX8MN_IOMUXC_SAI2_MCLK_GPIO4_IO27 0x100
>;
};
[...]
};
Interface between SAI and audio codec
[...]
sound_max98089: sound-max98089 {
compatible = "fsl,imx-audio-max98088";
model = "imx-max98088";
cpu-dai = <&sai2>;
audio-codec = <&max98089>;
asrc-controller = <&easrc>;
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";
};
[...]
&easrc {
fsl,asrc-rate = <48000>;
status = "okay";
};
Audio codec (I2C2 slave)
&i2c2 {
[...]
max98089: codec@10 {
compatible = "maxim,max98089";
reg = <0x10>;
clocks = <&clk IMX8MN_CLK_SAI2_ROOT>;
clock-names = "mclk";
vcc-supply = <®_3v3_audio>;
dvdd-supply = <®_1v8_ext>;
};
[...]
};
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