From Variscite Wiki
DART-MX8M-MINI - MCUXpresso 2.5.0

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 i.MX 8M Mini.pdf.

2 Prerequisites

Before starting, prepare a Yocto boot SD (Sumo 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 uboot.


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

Customers loading TCM binaries are suggest to avoid using uboot branch imx_v2019.04_4.19.35_1.1.0-var01 (Yocto Warrior BSP) due to a know limitation accessing the TCM memory region. As temporary workaround, either use Yocto Sumo BSP or just pick Yocto Sumo uboot

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
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

4 Documentation

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


5 Available demos

All of the Variscite examples are located under the following folder


Default M4 pins used by the demos are:

function pin
debug UART (UART2) RX: J12.6 / TX: J12.4
I2C (I2C4) SCL: J12.17 / SDA: J12.19
PWM (PWM2) J14.3

The available demos for DART-MX8M-MINI 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/idle_detect_sdma_transfer
  • driver_examples/uart/interrupt_rb_transfer
  • driver_examples/uart/sdma_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_1/monitor_threshold
  • driver_examples/tmu_1/temperature_polling
  • 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/sdma_transfer
  • 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

Almost all of the above demos are also available for EVK-MIMX8MM.

You can build and run the demos following official NXP documentation for EVK-MIMX8MM, available online or in the following document:

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

6 Building a demo

For any demo just follow this steps:

cd ~/var-mcuxpresso/freertos-variscite/boards/dart_mx8mm
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 or eMMC) in the /boot folder already hosting the Linux device trees.

7 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 0x7E000000-0x7E1FFFFF (code)
0x7E200000-0x7E3FFFFF (data)
0x7E400000-0x7EFFFFFF (data2)
0x7E000000-0x7E1FFFFF (code)
0x7E200000-0x7E3FFFFF (data)
0x7E400000-0x7EFFFFFF (data2)
16MB (DDR) MIMX8MQ6xxxJZ_cm4_ddr_ram.ld
TCM 0x1FFE0000-0x1FFFFFFF (code)
0x20000000-0x2001FFFF (data)
0x7E000000-0x7EFFFFFF (data2)
0x007E0000-0x007FFFFF (code)
0x00800000-0x0081FFFF (data)
0x7E000000-0x7EFFFFFF (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 much the one declared in the kernel device tree: at least 1 GB of RAM is required on the SoM to allow Cortex-M4 accessing the range 0x7E000000 - 0x7EFFFFFF. For some reason, Cortex-M4 is not able to access RAM locations below 0x60000000: SoMs with 512 MB of RAM are not suitable to use Cortex-M4.

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

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

8 Running a demo

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 uboot boot command will take care to correctly load the Cortex-M firmware and start Linux for DART-MX8M-MINI

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 i.MX 8M Mini.pdf

9 Debugging a demo

9.1 JTAG interface

Cortex-M debugging may require JTAG.

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

Here 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.

9.2 Debugging GUI

A detailed step by step procedure to debug using SEGGER J-Link is available online or in the following document:

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