From Variscite Wiki
DART-MX8M-PLUS - MCUXpresso 2.11.1

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 EVK-MIMX8MP.pdf.

2 Prerequisites

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

To allow Cortex M7 accessing shared resources without experiencing Linux kernel conflicts, a dedicated device tree must be loaded, containing m7 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 M7.

File Name
imx8mp-var-dart-dt8customboard-m7.dtb DART-MX8M-PLUS device tree blob for kernel >= 5.4.70 (Yocto Zeus) on DT8MCustomBoard 2.x
imx8mp-var-dart-dt8mcustomboard-legacy-m7.dtb DART-MX8M-PLUS device tree blob for kernel >= 5.4.70 (Yocto Zeus) on on DT8MCustomBoard 1.x
imx8mp-var-som-symphony-m7.dtb VAR-SOM-MX8M-PLUS device tree blob for kernels >= 5.4.70 (Yocto Zeus) on on Symphony-Board
imx8mp-var-som-symphony-2nd-ov5640m7.dtb VAR-SOM-MX8M-PLUS device tree blob for kernels >= 5.4.70 (Yocto Zeus) on on Symphony-Board with 2nd OV5640

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-10.3-2021.07-x86_64-linux.tar.bz2

Download MCUXpresso SDK for the SOM:

$ cd ~/var-mcuxpresso
$ git clone -b mcuxpresso_sdk_2.11.x-var01
$ cd freertos-variscite

4 Documentation

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


5 Demos pins

Default M7 pins used by the demos are:

function SoC balls DART-MX8M-PLUS pins DT8MCB pins VAR-SOM-MX8M-PLUS pins Symphony pins notes
UART3 RX/TX AE6 / AJ4 J2.87 / J2.89 J12.11 / J12.13
UART4 RX/TX AH5 / AJ5 J1.115 / J1.171 J18.9 / J18.7
GPIO3_IO14 R26 J1.79 J17.10
GPIO4_IO03 AF10 J2.59 GPLED1 on DT8MCB rev 1.x
J11.20 on DT8MCB rev 2.x
I2C3 SCL/SDA AJ7 / AJ6 J3.46 / J3.42 J12.18/ J12.20
I2C4 SCL/SDA AF8 / AD8 J1.92 / J1.90 J16.13 / J16.15 enabling it SPI devices will be no longer visible from Linux
PWM2 D8 J1.69 J18.2
PWM3 AE18 J3.36 J14.7
SPI1 CS0/SCK/SDI/SDO AE20 / AF20 / AD20 / AC20 J2.79 / J2.77 / J2.81 / J2.83 J16.4/ J16.2 / J16.8 / J16.6 enabling it SPI devices will be no longer visible from Linux
SPI2 CS0/SCK/SDI/SDO AJ22 / AH21 / AH20 / AJ21 J1.39 / J1.43 / J1.41 / J1.45 J16.4/ J16.2 / J16.6 / J16.8 enabling it SPI devices will be no longer visible from Linux
FLEXCAN1 RX/TX AH15 / AJ16 j2.56 / j2.50 J13.11 / J13.5 on DT8MCB rev 1.x, TTL levels (CAN transceiver not mounted!) enabling it FLEXCAN1 devices will be no longer visible from Linux
J16.9 / J16.7 on DT8MCB rev 2.x, CANL/CANH levels (CAN transceiver mounted!)
FLEXCAN2 RX/TX AJ4 / AE6 J1.46 / J1.44 J16.18 / J16.20, CANL/CANH levels (CAN transceiver mounted!) enabling it FLEXCAN2 devices will be no longer visible from Linux

6 Available demos

All of the Variscite examples are located under the following folder


The available demos for DART-MX8M-PLUS 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/sdma/scatter_gather
  • driver_examples/sdma/memory_to_memory
  • driver_examples/gpio/led_output
  • 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/ecspi/interrupt_b2b_transfer/slave
  • driver_examples/ecspi/interrupt_b2b_transfer/master
  • driver_examples/ecspi/polling_b2b_transfer/slave
  • driver_examples/ecspi/polling_b2b_transfer/master
  • driver_examples/rdc
  • driver_examples/tmu/monitor_threshold
  • driver_examples/tmu/temperature_polling
  • driver_examples/sema4/uboot
  • driver_examples/canfd/interrupt_transfer
  • driver_examples/canfd/loopback
  • driver_examples/canfd/loopback_transfer
  • driver_examples/canfd/ping_pong_buffer_transfer
  • driver_examples/flexcan/interrupt_transfer
  • driver_examples/flexcan/loopback
  • driver_examples/flexcan/loopback_transfer
  • driver_examples/flexcan/ping_pong_buffer_transfer
  • 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
  • cmsis_driver_examples/ecspi/sdma_loopback_transfer
  • multicore_examples/rpmsg_lite_str_echo_rtos
  • multicore_examples/rpmsg_lite_pingpong_rtos/linux_remote
  • demo_apps/hello_world
  • driver_examples/uart/idle_detect_sdma_transfer
  • driver_examples/uart/sdma_transfer
  • cmsis_driver_examples/uart/sdma_transfer

Almost all of the above demos are also available for EVK-MIMX8MP.

You can build and run the demos following official NXP documentation for EVK-MIMX8MP, available online or in the following document:

~/var-mcuxpresso/freertos-variscite/docs/Getting Started with MCUXpresso SDK for EVK-MIMX8MP.pdf

7 Building a demo

7.1 Building Manually

For any demo, follow these steps:

$ cd ~/var-mcuxpresso/freertos-variscite/boards/dart_mx8mp
$ cd <demo_folder>
$ cd armgcc
$ export ARMGCC_DIR=~/var-mcuxpresso/gcc-arm-none-eabi-10.3-2021.07
$ ./ > /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 Zeus 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_dart TCM U-Boot
/boot/cm_<demo name>.bin.debug_som TCM U-Boot
/boot/cm_<demo name>.bin.ddr_debug_dart DDR U-Boot
/boot/cm_<demo name>.bin.ddr_debug_som DDR U-Boot
/lib/firmware/cm_<demo name>.elf.debug_dart TCM Linux Remoteproc Framework
/lib/firmware/cm_<demo name>.elf.debug_som TCM Linux Remoteproc Framework
/lib/firmware/cm_<demo name>.elf.ddr_debug_dart DDR Linux Remoteproc Framework
/lib/firmware/cm_<demo name>.elf.ddr_debug_som 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-M7 as described in related linker file.

memory type M7 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) MIMX8MN6xxxxx_cm7_ddr_ram.ld
TCM 0x00000000-0x0001FFFF (code)
0x20000000-0x2001FFFF (data)
0x80000000-0x80FFFFFF (data2)
0x007E0000-0x007FFFFF (code)
0x00800000-0x0081FFFF (data)
0x80000000-0x80FFFFFF (data2)
256kB (TCM) + 16MB (DDR) MIMX8MN6xxxxx_cm7_ram.ld

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

The DDR reserved area must much the one declared in the kernel device tree: at least 1 GB of RAM is required on the SoM to allow Cortex-M7 accessing the range 0x80000000 - 0x80FFFFFF.

The RPMSG area is located at 0x40000000: all SoMs allow Cortex-M7 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 i.MX 8M-Plus Applications Processors Reference Manual paragraphs:

  • 2.2 Cortex-A53 Memory Map
  • 2.3 Cortex-M7 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_m7 yes; saveenv

To disable Cortex-M:

=> setenv use_m7 no; saveenv

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

To use TCM:

=> setenv m7_addr 0x7E0000; saveenv

To use DDR:

=> setenv m7_addr 0x80000000; saveenv

To set the name of the Cortex-M binary

=> setenv m7_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-PLUS

For testing, it is possible to run the firmware manually

=> run loadm7bin && run runm7bin

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 EVK-MIMX8MP.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 DART-MX8M-PLUS 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 m7, it should be running already by U-Boot

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

If the state is 'running', stop the m7

# 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

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-MX8M-PLUS exposes JTAG interface via an optional 10-pin header, on the SOM top left side.
The DART-MX8M-PLUS exports JTAG interface via an optional 10-pin header, on the DT8MCustomBoard top side.

Here is the pinout:

pin signal description pin signal description
1 JTAG_VREF JTAG IO reference voltage,
connected to SOM_3V3_PER via 150 Ohm.
2 JTAG_TMS JTAG Mode Select signal
3 GND Digital Ground 4 JTAG_TCK JTAG Clock signal,
include PD of 8.2K Ohm.
5 GND Digital Ground 6 JTAG_TDO JTAG Data Out signal
7 GND Digital Ground 8 JTAG_TDI JTAG Data In signal
9 JTAG_TRST_B JTAG Reset signal,
active low signal
10 POR_B Programmer Reset,
used to put the SOC in reset state.

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 EVK-MIMX8MP.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.

11 Add support to SOMs with 1GB DDR


$ cd freertos-variscite
$ ./ -b dart_mx8mp  # for DART-MX8M-PLUS
$ ./ -b som_mx8mp   # for VAR-SOM-MX8M-PLUS

Following the guide at the Running a demo from U-Boot section above:
Change "setenv m7_addr 0x80000000" to "setenv m7_addr 0x7E000000" (when running for DDR):

$ setenv m7_addr 0x80000000" to "setenv m7_addr 0x7E000000"

Change cma size from 640MiB to 512 MiB:

$ setenv ramsize_check 'if test $sdram_size -le 512; then setenv cma_size cma=320M; else if test $sdram_size -le 1024; then setenv cma_size cma=512M; else setenv cma_size cma=960M; fi; fi;'

Save the environment changes:

$ saveenv

In the file arch/arm64/boot/dts/freescale/imx8mp-var-common-m7.dtsi
Change the following section:

    m7_reserved: m7@0x80000000 {
        reg = <0 0x80000000 0 0x1000000>;


    m7_reserved: m7@0x7e000000 {
        reg = <0 0x7e000000 0 0x1000000>;

Build the updated dtb files:

$ make dtbs files

Then copy the generated *m7.dtb files to the /boot folder on the SD card/eMMC.

In the file /etc/remoteproc/variscite-rproc.conf
Change the following section:

    readonly CM_LOAD_ADDR_DDR="0x80000000"


    readonly CM_LOAD_ADDR_DDR="0x7e000000"