SOF User Guide on NXP i.MX8 platforms

This guide describes how to run SOF on NXP i.MX8 platforms.

Supported NXP platforms

Platform

Short Name

DSP

Audio Interfaces

Supported Codecs

i.mx8qm

i.mx8

hifi4@666mhz

esai, sai

wm8960, cs42888

i.mx8qxp

i.mx8x

hifi4@640mhz

esai, sai

wm8960, cs428888

i.mx8mp

i.mx8m

hifi4@800mhz

sai

wm8960

See Platforms for more details.

Toolchain

NXP i.MX8 currently supports two toolchain families: GCC and Cadence XCC.

  1. GCC is an open source, publicly available, toolchain built using crosstool-NG:

  1. Cadence XCC is a proprietary toolchain, available under certain terms and conditions:

  • Contact NXP tech support.

Quick run with SOF from i.MX8 Board Support Package

Binaries needed to run SOF on i.MX8 NXP platforms are provided in the Board Support Package (BSP) software. Use the latest i.MX8 BSP Release binaries.

Kernel image and modules

Image-imx8_all.bin is the name of the Linux kernel image. arm64 uses the same image for all platforms.

SOF Linux driver functionality is implemented across several kernel modules:

  • snd-sof.ko: SOF core functionality

  • snd-sof-of.ko: SOF OF-related functionality (SOF device probing, device tree parsing)

  • snd-sof-imx8.ko: i.MX8QXP, i.MX8QM-specific functionality (I/O mapping, power domains, clocks, etc)

  • snd-sof-imx8m.ko: i.MX8MP-specific functionality

  • imx-common.ko: i.MX common helpers

  • snd-sof-xtensa-dsp.ko: Xtensa-specific functionality (register dumps, DSP stack traces)

Linux kernel SOF modules are installed in the rootfs image at: /lib/modules/<version>/kernel/sound/soc/sof/.

Device tree files

DSP is seen by the Linux kernel as an I/O mapped device. Audio interfaces are controlled by the DSP via SOF firmware. Codecs are controlled by the ARM core via the Linux kernel.

Platform

DTB

Comments

i.mx8qm

imx8qm-mek-sof-cs42888.dtb

ESAI + cs42888 (baseboard)

i.mx8qm

imx8qm-mek-sof-wm8960.dtb

SAI + wm6890 (cpuboard)

i.mx8qxp

imx8qxp-mek-sof-cs42888.dtb

ESAI + cs42888 (baseboard)

i.mx8qxp

imx8qxp-mek-sof-wm8960.dtb

SAI + wm8960 (cpuboard)

i.mx8mp

imx8mp-evk-sof-wm8960.dtb

SAI + wm8960

Firmware images

Firmware images are installed in the rootfs image at: /lib/firmware/imx/sof/.

Platform

Firmware Path

i.mx8qm

/lib/firmware/imx/sof/sof-imx8.ri

i.mx8qxp

/lib/firmware/imx/sof/sof-imx8x.ri

i.mx8mp

/lib/firmware/imx/sof/sof-imx8m.ri

Topology files

Topology files describe one or more audio pipelines and are installed in the rootfs image at: /lib/firmware/imx/sof-tplg/.

Topology Name

Platform

Usecase

sof-imx8-cs42888.tplg

imx8qm/imx8qxp

PCM playback/record w/ cs42888 codec

sof-imx8-wm8960.tplg

imx8qm/imx8qxp

PCM playback/record w/ wm8960 codec

sof-imx8mp-wm8960.tplg

imx8mp

PCM playback/record w/ wm8960 codec

sof-imx8-cs42888.tplg

imx8qm/imx8qxp

PCM playback/record w/ SRC (wm8960)

sof-imx8-wm8960.tplg

imx8qm/imx8qxp

PCM playback/record w/ SRC (cs42888)

sof-imx8mp-wm8960.tplg

imx8mp

PCM playback/record w/ SRC (wm8960)

sof-imx8-wm8960-mixer.tplg

imx8qm/imx8qxp

PCM playback/record w/ mixer

sof-imx8-cs42888-mixer.tplg

imx8qm/imx8qxp

PCM playback/record w/ mixer

sof-imx8mp-wm8960-mixer.tplg

imx8mp

PCM playback/record w/ mixer

sof-imx8-compr-mp3-wm8960.tplg

imx8qxp/imx8qmp

Compress playback (mp3)

sof-imx8mp-compr-mp3-wm8960.tplg

imx8mp

Compress playback (mp3)

sof-imx8-compr-aac-wm8960.tplg

imx8qxp/imx8qmp

Compress playback (aac)

sof-imx8mp-compr-aac-wm8960.tplg

imx8mp

Compress playback (aac)

Build SOF binaries from sources

Use Build SOF with Docker to build SOF binaries with Docker. Otherwise, build it on your Debian-like machine as follows.

Kernel image and modules

Use the NXP internal Linux kernel tree to get full support for i.MX8 boards:

$ git clone https://source.codeaurora.org/external/imx/linux-imx
# checkout latest stable branch
$ git checkout lf-5.10.y
# install arm64 toolchain
$ sudo apt-get install gcc-aarch64-linux-gnu g++-aarch64-linux-gnu

# set defconfig
$  ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- make defconfig

# compile the kernel and modules
$  ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- make -j8

# install the modules
$ INSTALL_MOD_PATH=/path/to/rootfs/ make modules_install

Tools

See Step 4 in Build SOF from scratch.

The sof-logger must be cross-compiled in order to run on arm64:

$ cd "$SOF_WORKSPACE"/sof/tools/
$ mkdir build_tools && cd build_tools
$ cmake .. -DCMAKE_TOOLCHAIN_FILE=../scripts/cross-arch64.cmake
$ make sof-logger

Audio scenarios

This section demonstrates all audio scenarios on i.MX8QM. Consult the list of Device tree files, Firmware images, and Topology files in order to select the proper binaries for your board and audio scenario.

Audio playback and record

Booting i.MX8QM with imx8qm-mek-sof-wm8960.dtb enables PCM audio playback/record with the wm8960 codec. This uses the default topology found at /lib/firmware/imx/sof-tplg/sof-imx8-wm8960.tplg.

root@imx8qxpc0mek:~# aplay -l
**** List of PLAYBACK Hardware Devices ****
card 1: sofwm8960audio [sof-wm8960-audio], device 0: Port0 (*) []
  Subdevices: 1/1
  Subdevice #0: subdevice #0

# start playback on SOF device
root@imx8qxpc0mek:~# aplay -Dhw:1,0 sample.wav
Playing WAVE 'sample.wav' : Signed 32 bit Little Endian, Rate 48000 Hz, Stereo

# start capture on SOF device
root@imx8qxpc0mek:~# arecord -Dhw:1,0 -f S32_LE -c 2 -r 48000 capture.wav
Recording WAVE 'capture.wav' : Signed 32 bit Little Endian, Rate 48000 Hz, Stereo

Audio mixing

The following demonstates how to use SOF in order to mix two PCM streams on i.MX8QM and render the output to the wm8960 codec.

Boot the i.MX8QM board using imx8qm-mek-sof-wm8960.dtb. Use the sof-imx8-wm8960-mixer.tplg topology file:

$ cp /lib/firmware/imx/sof-tplg/sof-imx8-wm8960-mixer.tplg /lib/firmware/imx/sof-tplg/sof-imx8-wm8960.tplg

After booting, the SOF sound card contains two subdevices:

root@imx8qxpc0mek:~# aplay -l
**** List of PLAYBACK Hardware Devices ****
card 1: sofwm8960audio [sof-wm8960-audio], device 0: PCM (*) []
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 1: sofwm8960audio [sof-wm8960-audio], device 1: PCM Deep Buffer (*) []
  Subdevices: 1/1
  Subdevice #0: subdevice #0

# PCM files sent to SOF card1/device0, card1/device1 will be mixed together by SOF firmware and then rendered on wm8960 codec
root@imx8qxpc0mek:~# aplay -Dhw:1,0 sample0.wav  & aplay -Dhw:1,1 sample1.wav
Playing WAVE 'sample0.wav' : Signed 32 bit Little Endian, Rate 48000 Hz, Stereo
Playing WAVE 'sample1.wav' : Signed 32 bit Little Endian, Rate 48000 Hz, Stereo

Sample rate converter

Sample rate converter is supported via the SRC open-coded component in src/audio/src.

Based on the specific toolchain used, SOF on i.MX supports converting the following:

Toolchain

Direction

Input Rate (kHz)

Output Rate (kHz)

GCC

playback/capture

8 16 32 44.1 48 96

48

XCC

playback

8 11.025 16 22.05 32 44.1 48 64 88.2 96 176.4 192

48

XCC

capture

8 11.025 16 22.050 32 44.1 48

48

Boot the i.MX8QM board using imx8qm-mek-sof-wm8960.dtb. Use the sof-imx8-src-wm8960.tplg topology file:

$ cp /lib/firmware/imx/sof-tplg/sof-imx8-src-wm8960-mixer.tplg /lib/firmware/imx/sof-tplg/sof-imx8-wm8960.tplg

Below are several runs with aplay on various rates and formats:

root@imx8qmmek:~# aplay -Dhw:1,0 -f S16_LE -c 2 -r 8000 -t raw /mnt/test/samples_16b/audio8k16b2c.wav
Playing raw data '/mnt/test/samples_16b/audio8k16b2c.wav' : Signed 16 bit Little Endian, Rate 8000 Hz, Stereo

root@imx8qmmek:~# aplay -Dhw:1,0 -f S16_LE -c 2 -r 16000 -t raw /mnt/test/samples_16b/audio16k16b2c.wav
Playing raw data '/mnt/test/samples_16b/audio16k16b2c.wav' : Signed 16 bit Little Endian, Rate 16000 Hz, Stereo

root@imx8qmmek:~# aplay -Dhw:1,0 -f S24_LE -c 2 -r 32000 -t raw /mnt/test/samples/audio32k24b2c.wav
Playing raw data '/mnt/test/samples/audio32k24b2c.wav' : Signed 24 bit Little Endian, Rate 32000 Hz, Stereo

root@imx8qmmek:~# aplay -Dhw:1,0 -f S24_LE -c 2 -r 44100 -t raw /mnt/test/samples/audio44k24b2c.wav
Playing raw data '/mnt/test/samples/audio44k24b2c.wav' : Signed 24 bit Little Endian, Rate 44100 Hz, Stereo

root@imx8qmmek:~# aplay -Dhw:1,0 -f S32_LE -c 2 -r 48000 -t raw /mnt/test/samples_32b/audio48k32b2c.wav
Playing raw data '/mnt/test/samples_32b/audio48k32b2c.wav' : Signed 32 bit Little Endian, Rate 48000 Hz, Stereo

root@imx8qmmek:~# aplay -Dhw:1,0 -f S32_LE -c 2 -r 96000 -t raw /mnt/test/samples_32b/audio96k32b2c.wav
Playing raw data '/mnt/test/samples_32b/audio96k32b2c.wav' : Signed 32 bit Little Endian, Rate 96000 Hz, Stereo

Compress audio

In order to use DSP to decode/encode compress audio, NXP uses ALSA Compress Offload APIs.

Supported codecs on i.MX8QM:

codec

topology

Test command

PCM

sof-imx8-processing-pcm-wm8960.m4

cplay -c 1 -d 0 -f 2 -b 7680 -I PCM sample.wav

MP3

sof-imx8-processing-mp3-wm8960.m4

cplay -c 1 -d 0 -f 2 -b 7680 -I MP3 sample.mp3

AAC

sof-imx8-processing-aac-wm8960.m4

cplay -c 1 -d 0 -f 2 -b 7680 -I MP3 sample.aac

See Topology files for the list of topology files to use on other NXP i.MX boards.

To enable compress audio in SOF firmware, you must enable the Codec Adapter component and select the appropriate decoding library algorithms. For i.MX8, we use the Cadence proprietary libraries:

CONFIG_COMP_CODEC_ADAPTER=y
CONFIG_CADENCE_CODEC=y

# Enable AAC Cadence decoder
CONFIG_CADENCE_CODEC_AAC_DEC=y
CONFIG_CADENCE_CODEC_AAC_DEC_LIB="/path/to/aac/library"

# Enable MP3 Cadence decoder
CONFIG_CADENCE_CODEC_MP3_DEC=y
CONFIG_CADENCE_CODEC_MP3_DEC_LIB="/path/to/mp3/library"

Contact NXP Tech support for information on how to obtain Cadence proprietary algorithms.

Boot the i.MX8QM board using imx8qm-mek-sof-wm8960.dtb. The following example tests the MP3 audio decoder by using the sof-imx8-processing-mp3-wm8960.m4 topology file:

$ cp /lib/firmware/imx/sof-tplg/sof-imx8-processing-mp3-wm8960.m4 /lib/firmware/imx/sof-tplg/sof-imx8-wm8960.tplg
$ cplay -c <card number> -d <device number> -f <fragments> -b <bufer_size> -I <codec_id> sample.file
# identify card and device number
$ ls /dev/snd*
  comprC1D0 ==> this means => [card 1, device 0]
# fragments is always 2, buffer size is always a multiple of 768, recommended value is 7680
$ cplay -c 1 -d 0 -f 2 -b 7680 -I MP3 samples.mp3