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Running FreeRTOS on the Cortex-M4 of an Apalis iMX8

Introduction

The objective of this article is to guide you through case-oriented examples on the implementation of FreeRTOS on the Cortex-M of a Apalis iMX8 System on Module, focusing on the execution of a sample application firmwares leveraging the Heterogeneous Multicore Processing architecture.

The use cases described in this article were tested and validated with FreeRTOS on the Cortex-M running alongside an embedded Linux image (Linux BSP) on the A-cores.

Prerequisites

• Set up the SDK and Toolchain as described in the article Setting Up MCUXpresso SDK and Toolchain for Cortex-M development.
• Consider the architecture and memory areas of the specific i.MX-based SoC as explained in the article Cortex-M and Memory Areas Overview on Toradex SoMs

Preparing the Environment

1. Download the MCUXpresso SDK as described at Setting Up MCUXpresso SDK and Toolchain for Cortex-M development. For Apalis iMX8 you should download:

   • Apalis iMX8QM and Apalis iMX8QP: MIMX8QM6xxxFF

2. Verify the source code structure from the boards/mekmimx8qm folder

   $ cd <apalis-imx8-sdk>/boards/
   $ tree -L 2
   .
   └── mekmimx8qm
       ├── cmsis_driver_examples
       ├── demo_apps
       ├── driver_examples
       ├── issdk_examples
       ├── lwip_examples
       ├── mekmimx8qm.png
       ├── mmcau_examples
       ├── multicore_examples
       ├── project_template
       └── rtos_examples

3. Download and setup the GCC toolchain as explained at Setting Up MCUXpresso SDK and Toolchain for Cortex-M development. We recommend the Arm GNU Toolchain AArch32 bare-metal target (arm-none-eabi) for your host OS.

Case-oriented Examples

Hello World Example

1. Go to the demo directory on the SDK folder. You might note that there are two folders, one for each Cortex-M4 core. Choose the one you want to build the application for.

   $ cd ./boards/mekmimx8qm/demo_apps/hello_world
   $ tree -L 2
   .
   ├── cm4_core0
   │   ├── armgcc
   │   ├── board.c
   │   ├── board.h
   │   ├── clock_config.c
   │   ├── clock_config.h
   │   ├── empty_rsc_table.c
   │   ├── hello_world.bin
   │   ├── hello_world.c
   │   ├── hello_world_m40_v3_8.xml
   │   ├── hello_world.mex
   │   ├── pin_mux.c
   │   ├── pin_mux.h
   │   └── readme.txt
   └── cm4_core1
       ├── armgcc
       ├── board.c
       ├── board.h
       ├── clock_config.c
       ├── clock_config.h
       ├── hello_world.bin
       ├── hello_world.c
       ├── hello_world_m41_v3_8.xml
       ├── hello_world.mex
       ├── pin_mux.c
       ├── pin_mux.h
       └── readme.tx

2. Write and compile the necessary devicetree overlays as explained at Run the Firmware.

3. Run the script to build the demo

   $ export ARMGCC_DIR=<PATH_TO_GCC_TOOLCHAIN>/<GCC_TOOLCHAIN_FOLDER>
   $ cd armgcc/ 
   $ ./build_debug.sh

4. Copy the generated binary to your device

   $ scp debug/hello_world.bin root@<board-ip>:/home/root

5. Load the firmware on Flash. On U-boot terminal, run the following commands

   > setenv load_cmd "ext4load mmc 0:2"
   > setenv m4_0_image "/home/root/hello_world.bin"
   > saveenv

   If you chose to use the Cortex-M4 1 instead of the Cortex-M4 0, just replace m4_0_image with m4_1_image

6. Start the firmware at boot level

   > run m4boot_0