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VAR-SOM-MX8X - MCUXpresso 2.8.0

1 Overview

1.1 MCUXpresso SDK

MCUXpresso SDK board support provides example applications for NXP development and evaluation boards for Arm Cortex-M cores. Board support packages are found inside of the top level boards folder, and each supported board has its own folder (MCUXpresso SDK package can support multiple boards). Within each <board_name> folder there are various sub-folders to classify the type of examples they contain. These include (but are not limited to):

  • cmsis_driver_examples: Simple applications intended to concisely illustrate how to use CMSIS drivers.
  • demo_apps: Full-featured applications intended to highlight key functionality and use cases of the target MCU. These applications typically use multiple MCU peripherals and may leverage stacks and middleware.
  • driver_examples: Simple applications intended to concisely illustrate how to use the MCUXpresso SDK’s peripheral drivers for a single use case.
  • rtos_examples: Basic FreeRTOS OS examples showcasing the use of various RTOS objects (semaphores, queues, and so on) and interfacing with the MCUXpresso SDK’s RTOS drivers
  • multicore_examples: Simple applications intended to concisely illustrate how to use middleware/multicore stack


Here we describe how to use ARM GCC toolchain, officially supported following Getting Started with MCUXpresso SDK for MEK-MIMX8QX.pdf.

2 Prerequisites

Before starting, prepare a Yocto boot SD (with kernel 5.4.85 or newer).

To allow Cortex M4 accessing shared resources without experiencing Linux kernel conflicts, a dedicated device tree must be loaded, containing m4 label in the name, using the fdt_file environment variable in U-Boot.

This device tree disables some of the base device tree nodes in order to avoid conflicts between the main processor and Cortex M4.

File Name
imx8qxp-var-som-symphony-sd-m4.dtb VAR-SOM-MX8 device tree blob for kernel >= 5.4.85 (Yocto Dunfell)
imx8qxp-var-som-symphony-m4.dtb VAR-SOM-MX8 device tree blob for kernel >= 5.4.85 (Yocto Dunfell)

3 Installing required packages

Install cmake

$ sudo apt-get install cmake

Download and install GNU-ARM bare-metal toolchain:

$ mkdir ~/var-mcuxpresso
$ cd ~/var-mcuxpresso
$ wget
$ tar xvf gcc-arm-none-eabi-9-2020-q2-update-x86_64-linux.tar.bz2

Download MCUXpresso SDK for the SOM:

$ cd ~/var-mcuxpresso
$ git clone -b mcuxpresso_sdk_2.8.x-var01
$ cd freertos-variscite

4 Documentation

Original NXP documentation is available online or in the following folder:


5 Demos pins

Default M4 pins used by the demos are:

function pin
debug UART (UART2) RX: J18.5 / TX: J18.3
I2C (I2C3) SCL: J16.10 / SDA: J16.12
M4 GPIO (M40_GPIO0_IO00) J16.3
M4 PWM (M40_TPM0_CH0) J16.7

6 Available demos

All of the Variscite examples are located under the following folder


The available demos for VAR-SOM-MX8X are:

  • cmsis_driver_examples/lpi2c/int_b2b_transfer/slave
  • cmsis_driver_examples/lpi2c/int_b2b_transfer/master
  • cmsis_driver_examples/lpi2c/edma_b2b_transfer/slave
  • cmsis_driver_examples/lpi2c/edma_b2b_transfer/master
  • cmsis_driver_examples/lpuart/edma_transfer
  • cmsis_driver_examples/lpuart/interrupt_transfer
  • demo_apps/hello_world
  • driver_examples/edma/scatter_gather
  • driver_examples/edma/memory_to_memory
  • driver_examples/intmux
  • driver_examples/lpi2c/edma_b2b_transfer/slave
  • driver_examples/lpi2c/edma_b2b_transfer/master
  • driver_examples/lpi2c/interrupt_b2b_transfer/slave
  • driver_examples/lpi2c/interrupt_b2b_transfer/master
  • driver_examples/lpi2c/polling_b2b_transfer/slave
  • driver_examples/lpi2c/polling_b2b_transfer/master
  • driver_examples/lpi2c/read_accel_value_transfer
  • driver_examples/lpit
  • driver_examples/lpuart/edma_transfer
  • driver_examples/lpuart/interrupt_rb_transfer
  • driver_examples/lpuart/polling
  • driver_examples/lpuart/interrupt_transfer
  • driver_examples/rgpio/led_output
  • driver_examples/sema42/uboot
  • driver_examples/tpm/input_capture
  • driver_examples/tpm/dual_edge_capture
  • driver_examples/tpm/timer
  • driver_examples/tpm/simple_pwm
  • driver_examples/tpm/output_compare
  • driver_examples/tstmr
  • driver_examples/wdog32
  • mmcau_examples/mmcau_api
  • multicore_examples/rpmsg_lite_pingpong_rtos/linux_remote
  • multicore_examples/rpmsg_lite_str_echo_rtos
  • rtos_examples/freertos_hello
  • rtos_examples/freertos_queue
  • rtos_examples/freertos_sem
  • rtos_examples/freertos_generic
  • rtos_examples/freertos_tickless
  • rtos_examples/freertos_mutex
  • rtos_examples/freertos_event
  • rtos_examples/freertos_swtimer

Additional demos are available as reference code, but require HW/SW customization.

Almost all of the above demos are also available for IMX8QXP-MEK.

You can build and run the demos following official NXP documentation for IMX8QXP-MEK, available online or in the following document:

~/var-mcuxpresso/freertos-variscite/docs/Getting Started with MCUXpresso SDK for MEK-MIMX8QX.pdf

7 Building a demo

7.1 Building Manually

For any demo, follow these steps:

$ cd ~/var-mcuxpresso/freertos-variscite/boards/som_mx8qx
$ cd <demo_folder>
$ cd armgcc
$ export ARMGCC_DIR=~/var-mcuxpresso/gcc-arm-none-eabi-9-2020-q2-update
$ ./ > /dev/null

You can choose any <demo_folder> from the list available in the previous section.

Then copy the ".bin" to the boot media (either the SD card or eMMC) in the /boot folder already hosting the Linux device trees.

7.2 Building Using Yocto

In Yocto Dunfell and newer, Variscite provides a Yocto recipe for building and installing firmware into the Yocto image:

This recipe installs the following firmware files:

File Memory Loaded Using...
/boot/cm_<demo name>.bin.debug TCM U-Boot
/boot/cm_<demo name>.bin.ddr_debug DDR U-Boot
/lib/firmware/cm_<demo name>.elf.debug TCM Linux Remoteproc Framework
/lib/firmware/cm_<demo name>.elf.ddr_debug DDR Linux Remoteproc Framework

If you have modified freertos-variscite in your own Git repository and kept the same directory structure, you can easily build your custom firmware by creating a bbappend file:

$ mkdir -p <your-layer>/recipes-bsp/freertos-variscite
$ nano <your-layer>/recipes-bsp/freertos-variscite/freertos-variscite_2.9.x.bbappend

Append SRC_URI and SRCREV to use your freertos-variscite Git repository

SRC_URI_remove = "git://;protocol=git;branch=${MCUXPRESSO_BRANCH};"
SRC_URI_append = " <your Git repository>"
SRCREV = "<your Git commit id>"

Append CM_DEMOS to build your firmware. For example, to build rtos_examples/freertos_hello:

CM_DEMOS_append = "rtos_examples/freertos_hello"

Rebuild fsl-image-gui:

$ bitbake -c cleansstate freertos-variscite && bitbake fsl-image-gui

The firmware binary files should now be installed to /boot/ and elf files to /lib/firmware/

8 Memory types

The SDK allow linking using 2 different memory types: DDR, TCM.

Here is available a short summary of memory areas used by Cortex-M4 as described in related linker file.

memory type M4 memory area A35 memory area memory lentgh linker file
DDR 0x88000000-0x881FFFFF (code)
0x88200000-0x883FFFFF (data)
0x88400000-0x8FFFFFFF (data2)
0x88000000-0x881FFFFF (code)
0x88200000-0x883FFFFF (data)
0x88400000-0x8FFFFFFF (data2)
128MB (DDR) MIMX8QX6xxxFZ_cm4_ddr_ram.ld
TCM 0x1FFE0000-0x1FFFFFFF (code)
0x20000000-0x2001FFFF (data)
0x88000000-0x8FFFFFFF (data2)
0x34FE0000-0x34FFFFFF (code)
0x35000000-0x3501FFFF (data)
0x88000000-0x8FFFFFFF (data2)
256kB (TCM) + 128MB (DDR) MIMX8QX6xxxFZ_cm4_ram.ld

All linker files are locate in the armgcc folder of each demo.

After launching the command the following folder will be created in the armgcc folder

  • ddr_debug: containing DDR binaries compiled in debug mode (not stripped: symbols available)
  • ddr_release: containing DDR binaries compiled in release mode (stripped: no symbols available)
  • debug: containing TCM binaries compiled in debug mode (not stripped: symbols available)
  • release: containing TCM binaries compiled in release mode (stripped: no symbols available)

Further details about memory mapping are available in i.MX 8DualXPlus/8QuadXPlus Applications Processor Reference Manual paragraphs:

  • 2.2 System Memory Map
  • 2.2.9 Cortex-M4 Memory Map

9 Running a demo

9.1 Running a demo from U-Boot

To allow Cortex-M accessing shared resources without experiencing Linux kernel conflicts, a dedicated device tree must be loaded.

To enable Cortex-M:

=> setenv use_m4 yes; saveenv

To disable Cortex-M:

=> setenv use_m4 no; saveenv

Binary demos must be loaded to the memory type used for linking.

To use TCM:

=> setenv m4_addr 0x88000000; saveenv  (TCM is at 0x34FE0000, but U-Boot load to 0x88000000)

To use DDR:

=> setenv m4_addr 0x88000000; saveenv

To set the name of the Cortex-M binary

=> setenv m4_bin myapp.bin; saveenv

The .bin file is expected in the folder /boot of the booting media.

The U-Boot boot command will take care to correctly load the Cortex-M firmware and start Linux for VAR-SOM-MX8X

For testing, it is possible to run the firmware manually

=> run loadm4bin && run runm4bin

Additional details and step by step procedure to run each of the demos is available online or in the following document:

~/var-mcuxpresso/freertos-variscite/docs/Getting Started with MCUXpresso SDK for MEK-MIMX8QX.pdf

For Yocto Dunfell and newer, this process can be simplified using /etc/remoteproc/variscite-rproc-u-boot
Please refer to the Yocto Scripts section below for more information

9.2 Running a demo from Linux

The Linux remoteproc framework can be used to load the Cortex M4/M7 firmware from Linux userspace.

Note: The Linux remoteproc framework is not supported by all Yocto/B2Qt/Debian/Android releases.

Follow these steps to verify the Linux remoteproc framework is supported for your release:

  1. Select the software release from the VAR-SOM-MX8X software overview page.
  2. Click on Release Notes.
  3. Look for the Cortex M4 Linux remoteproc support row in the release notes to see which version is supported. If Cortex M4 Linux remoteproc support is not in the release notes table, the Linux remoteproc framework is not supported.

After confirming Linux remoteproc support, follow these steps to use the framework:

Increase kernel loglevel while debugging:

# sysctl kernel.printk=7;

Check the state of the m4, it should be running already by U-Boot

# cat /sys/class/remoteproc/remoteproc0/state

If the state is 'running', stop the m4

# echo stop > /sys/class/remoteproc/remoteproc0/state

Load new firmware (.elf file must already exist in /lib/firmware directory)

# echo hello_world.elf > /sys/class/remoteproc/remoteproc0/firmware

Run the new firmware

# echo start > /sys/class/remoteproc/remoteproc0/state
If remoteproc is used to reload ddr firmware, special disable_cache firmware must be reloaded between stop and start
For Example:
# echo cm_rpmsg_lite_pingpong_rtos_linux_remote.elf.ddr_debug > /sys/class/remoteproc/remoteproc0/firmware
# echo start > /sys/class/remoteproc/remoteproc0/state
# echo stop > /sys/class/remoteproc/remoteproc0/state
# echo cm_disable_cache.elf.debug > /sys/class/remoteproc/remoteproc0/firmware
# echo start > /sys/class/remoteproc/remoteproc0/state
# echo stop > /sys/class/remoteproc/remoteproc0/state
# echo cm_rpmsg_lite_str_echo_rtos_imxcm4.elf.ddr_debug > /sys/class/remoteproc/remoteproc0/firmware
# echo start > /sys/class/remoteproc/remoteproc0/state
# echo stop > /sys/class/remoteproc/remoteproc0/state

For Yocto Dunfell and newer, this process can be simplified using /etc/remoteproc/variscite-rproc-linux
Please refer to the Yocto Scripts section below for more information

9.3 Running a Demo using Yocto Scripts

In Yocto Dunfell and newer, Variscite provides scripts to simplify loading firmware via U-Boot or Linux:

Script Description
/etc/remoteproc/variscite-rproc-u-boot Configure U-Boot to load firmware on boot
/etc/remoteproc/variscite-rproc-linux Load and run firmware using Linux remoteproc framework


variscite-rproc-u-boot example on imx8mm-var-dart:

root@imx8mm-var-dart:~# /etc/remoteproc/variscite-rproc-u-boot -f /boot/cm_hello_world.bin.ddr_debug
Configuring for DDR memory
+ fw_setenv m4_addr 0x7E000000
+ fw_setenv fdt_file imx8mm-var-som-symphony-m4.dtb
+ fw_setenv use_m4 yes
+ fw_setenv m4_bin cm_hello_world.bin.ddr_debug

Finished: Please reboot, the m4 firmware will run during U-Boot

variscite-rproc-linux example on imx8mm-var-dart:

root@imx8mm-var-dart:~# /etc/remoteproc/variscite-rproc-linux -f /lib/firmware/cm_hello_world.elf.ddr_debug
Cortex-M: Stopping
[  359.212638] remoteproc remoteproc0: stopped remote processor imx-rproc
[  359.219709] remoteproc remoteproc0: powering up imx-rproc
Cortex-M: Loading cm_hello_world.elf.ddr_debug
[  359.227101] remoteproc remoteproc0: Booting fw image cm_hello_world.elf.ddr_debug, size 269100
[  359.238493] imx-rproc imx8mm-cm4: m4 ddr @ 0x7e000000
[  359.243584] remoteproc remoteproc0: no dtb rsrc-table
[  359.248797] imx-rproc imx8mm-cm4: Setting up stack pointer and reset vector from firmware in DDR
[  359.257626] imx-rproc imx8mm-cm4: Stack: 0x7e400000
[  359.262542] imx-rproc imx8mm-cm4: Reset Vector: 0x7e00030d
Cortex-M: Starting
[  359.318074] remoteproc remoteproc0: remote processor imx-rproc is now up

10 Debugging a demo

10.1 JTAG Hardware

The Cortex-M firmware can be debugged using a JTAG debugger. Variscite recommends using a J-Link Pro or J-Link Wi-Fi debugger. You may also need a 9-pin adapter from Segger.

10.2 JTAG interface

The VAR-SOM-MX8X exposes JTAG interface via an optional 10-pin header

Here is the pinout:

pin signal description pin signal (ball) description
1 JTAG_VREF JTAG reference voltage (3.3V) 2 JTAG_TMS (AG35) JTAG Mode Select
3 GND Digital Ground 4 JTAG_TCK (AE31) JTAG Clock
5 GND Digital Ground 6 JTAG_TDO (AF32) JTAG Data Out
7 RTCK JTAG Return clock 8 JTAG_TDI (AH34) JTAG Data In

Please refer to SOM datasheet for further details.

10.3 Developing with IAR Embedded Workbench

NXP provides a detailed step by step procedure to develop and debug MCUXpresso firmware using IAR Embedded Workbench and SEGGER SEGGER J-Link. Please refer to online or in the following document:

~/var-mcuxpresso/freertos-variscite/docs/Getting Started with MCUXpresso SDK for MEK-MIMX8QX.pdf

10.4 Developing with Visual Studio Code

Visual Studio Code, which is freely available, can be used to develop and debug MCUXpresso firmware:

Vscode MCUXpresso StoppedAtBreakPoint.png

For a full guide demonstrating how to get started, please refer to MCUXpresso Development with VS Code.