From Variscite Wiki
DART-MX8M - MCUXpresso 2.5.1


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 i.MX 8M Devices.pdf.


Before starting, prepare a Yocto boot SD (with kernel 4.14.98 or newer).

To allow Cortex M4 accessing shared resources without experiencing Linux kernel conflicts, a dedicated device tree must be loaded, by selecting the right version with the symbolic link in the /boot folder of the booting media.
These device trees contain m4 label in their name.

The below table lists an example dtb blob file name for DART-MX8M (on DT8MCustomBoard rev. 1.3 and higher) with support for M4 (and SD card and LVDS), for each kernel version / Yocto release:

File Name
imx8mq-var-dart-dt8mcustomboard-m4-sd-lvds.dtb For kernel >= 5.4.85 (Yocto >= Dunfell)
imx8mq-var-dart-m4-sd-lvds.dtb For kernel = 5.4.24 (Yocto Zeus)
fsl-imx8mq-var-dart-m4-sd-lvds.dtb For kernel = 4.19.35 (Yocto Warrior)
Image.gz-fsl-imx8mq-var-dart-m4-sd-lvds.dtb For kernel = 4.14.98 (Yocto Sumo)

For the full list of device tree blob files, refer to the "Build Results" section in the appropriate wiki page for the specific Yocto/Debian release you are using.

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-7-2018-q2-update-linux.tar.bz2

Download MCUXpresso SDK for the SOM:

$ cd ~/var-mcuxpresso
$ git clone -b mcuxpresso_sdk_2.5.x-var01
$ cd freertos-variscite


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


Demos pins

Default M4 pins used by the demos are:

Function Pin
debug UART (UART2) RX: J12.6 / TX: J12.4
GPIO (GPIO4_IO03) LED7 for DT8CustomBoard 1.x
U43.2 / R228 for DT8CustomBoard >= 2.0 (Use Oscilloscope to observe output signal)
I2C (I2C3) SCL: J12.18 / SDA: J12.20
PWM (PWM2) J14.3

Available demos

All of the Variscite examples are located under the following folder


The available demos for DART-MX8M are:

  • driver_examples/i2c/interrupt_b2b_transfer/slave
  • driver_examples/i2c/interrupt_b2b_transfer/master
  • driver_examples/i2c/polling_b2b_transfer/slave
  • driver_examples/i2c/polling_b2b_transfer/master
  • driver_examples/wdog
  • driver_examples/gpio/led_output
  • driver_examples/tmu/tmu_monitor_report
  • driver_examples/pwm
  • driver_examples/uart/auto_baudrate_detect
  • driver_examples/uart/interrupt
  • driver_examples/uart/interrupt_rb_transfer
  • driver_examples/uart/polling
  • driver_examples/uart/interrupt_transfer
  • driver_examples/gpt/timer
  • driver_examples/gpt/capture
  • driver_examples/ecspi/ecspi_loopback
  • driver_examples/qspi/polling_transfer
  • driver_examples/rdc
  • driver_examples/sema4/uboot
  • rtos_examples/freertos_ecspi/ecspi_loopback
  • rtos_examples/freertos_hello
  • rtos_examples/freertos_queue
  • rtos_examples/freertos_sem
  • rtos_examples/freertos_generic
  • rtos_examples/freertos_uart
  • rtos_examples/freertos_tickless
  • rtos_examples/freertos_mutex
  • rtos_examples/freertos_event
  • rtos_examples/freertos_swtimer
  • rtos_examples/freertos_i2c
  • cmsis_driver_examples/i2c/int_b2b_transfer/slave
  • cmsis_driver_examples/i2c/int_b2b_transfer/master
  • cmsis_driver_examples/uart/interrupt_transfer
  • cmsis_driver_examples/ecspi/int_loopback_transfer
  • multicore_examples/rpmsg_lite_str_echo_rtos
  • multicore_examples/rpmsg_lite_pingpong_rtos/linux_remote
  • demo_apps/hello_world

Almost all of the above demos are also available for EVK-MIMX8MQ.

You can build and run the demos following official NXP documentation for EVK-MIMX8MQ, available online or in the following document:

~/var-mcuxpresso/freertos-variscite/docs/Getting Started with MCUXpresso SDK i.MX 8M Devices.pdf

Building a demo

Building Manually

For any demo, follow these steps:

$ cd ~/var-mcuxpresso/freertos-variscite/boards/dart_mx8mq
$ cd <demo_folder>
$ cd armgcc
$ export ARMGCC_DIR=~/var-mcuxpresso/gcc-arm-none-eabi-7-2018-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.

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/

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 A53 memory area memory lentgh linker file
DDR 0x80000000-0x801FFFFF (code)
0x80200000-0x803FFFFF (data)
0x80400000-0x80FFFFFF (data2)
0x80000000-0x801FFFFF (code)
0x80200000-0x803FFFFF (data)
0x80400000-0x80FFFFFF (data2)
16MB (DDR) MIMX8MQ6xxxJZ_cm4_ddr_ram.ld
TCM 0x1FFE0000-0x1FFFFFFF (code)
0x20000000-0x2001FFFF (data)
0x80000000-0x80FFFFFF (data2)
0x007E0000-0x007FFFFF (code)
0x00800000-0x0081FFFF (data)
0x80000000-0x80FFFFFF (data2)
256kB (TCM) + 16MB (DDR) MIMX8MQ6xxxJZ_cm4_ram.ld

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

The DDR reserved area must match the one declared in the kernel device tree: at least 2 GB of RAM is required on the SoM to allow Cortex-M4 accessing the range 0x80000000 - 0x80FFFFFF.

The RPMSG area is located at 0xB8000000: at least 3 GB of RAM is required on the SoM to allow Cortex-M4 accessing the RPMSG area. 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 the following i.MX 8M Applications Processor Reference Manual paragraphs:

  • 2.1.2 Cortex-A53 Memory Map
  • 2.1.3 Cortex-M4 Memory Map

Running a demo

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 0x7E0000; saveenv

To use DDR:

=> setenv m4_addr 0x7E000000; 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 DART-MX8M

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 i.MX 8M Devices.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

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 DART-MX8M 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:

Boot Linux after following the steps in #Running a demo from U-Boot

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

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

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

Debugging a demo

JTAG Hardware

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

JTAG interface

The VAR-DT8MCustomBoard exports the DART-MX8M JTAG signals through J29, a standard 1.27" 10 pin header.

Here is the pinout:

pin signal description pin signal description
1 JTAG_VREF JTAG IO reference voltage,
connects to SOM_NVCC_3V3.
2 JTAG_TMS JTAG Mode Select signal
3 GND Digital Ground 4 JTAG_TCK JTAG Clock signal,
requires 10K pull down.
5 GND Digital Ground 6 JTAG_TDO JTAG Data Out signal
7 GND Digital Ground 8 JTAG_TDI JTAG Data In signal
9 JTAG_NTRST_C JTAG Reset signal 10 NRST_CON Programmer Reset,
used to put the SOC in reset state.

Please refer to board schematics for further details.

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 i.MX 8M Devices.pdf

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.