i.MX7D M4 core FreeRTOS hello_world.elf not running after loading from U-Boot

Technical Support
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1

Hello,

I am working on a Colibri iMX7D eMMC module with a Colibri Evaluation Board.
My goal is to run a FreeRTOS hello_world example on the M4 core.

What I did:

  1. Built the hello_world FreeRTOS example on my host PC.
  2. Copied the generated hello_world.elf to /home/root on the target (Linux running on A7).
  3. Interrupted U-Boot and tried the following commands:
load_cmd=ext4load mmc 0:2
m4image=/home/root/hello_world.elf
loadm4image= 0x84200000 /home/root/hello_world.elf
m4boot= 0x84200000 /home/root/hello_world.elf; dcache flush; bootaux 0x84200000
bootcmd=run m4boot; run m4boot; run m4boot; run distro_bootcmd
Colibri iMX7 # ext4load mmc 0:2 0x84200000 /home/root/hello_world.elf
164344 bytes read in 11 ms (14.2 MiB/s)
Colibri iMX7 # dache flush
Unknown command 'dache' - try 'help'
Colibri iMX7 # dcache flush
Colibri iMX7 # bootauc 0x84200000
Unknown command 'bootauc' - try 'help'
Colibri iMX7 # bootaux 0x84200000
## Starting auxiliary core stack = 0x00000000, pc = 0x1FFF807D...
Colibri iMX7 #

But after that, nothing is printed from the hello_world program.

Additional Info:

  • I have disabled UART_B in the device tree.
  • FreeRTOS is configured to print via M4 UART.
  • Linux is running on the A7 core.
  • I expected the hello_world message to appear on the serial console but it does not.

Question:

  • Am I missing a step to start the M4 core from U-Boot?
  • Do I need to configure the UART differently to see the hello_world output?
  • Is /home/root/hello_world.elf the correct path to load from ext4load?

Any guidance or example sequence for running M4 FreeRTOS applications from U-Boot on Colibri iMX7D would be greatly appreciated.

referred websites
Running freertos on m4 core

How to load compiled binaries imx7d emmc

Thanks in advance!

2

Hi, I’m the Toradex AI Assistant.

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Hello! Thank you for your detailed description and for sharing your progress. Let’s go through your questions and clarify the steps for running a FreeRTOS hello_world example on the Cortex-M4 of the Colibri iMX7D eMMC module using U-Boot.

1. Proper Sequence to Run M4 FreeRTOS via U-Boot

The correct steps for your setup are as follows:

  1. Copy the .elf File:

    • Place the generated hello_world.elf onto the Linux root filesystem (which is the second partition, /home/root/hello_world.elf works if /home/root is on that partition).

  2. U-Boot Commands:

    • Interrupt U-Boot startup.

    • Load the firmware using:

      ext4load mmc 0:2 ${loadaddr} hello_world.elf
      • ${loadaddr} is typically set to something like 0x80800000 or 0x84200000.
      • The path should be hello_world.elf, the path must be relative to the root of partition 2 of your eMMC, not the Linux root. If you copied it to /home/root/ with Linux, then from the U-Boot perspective, that is simply /home/root/hello_world.elf.

    • Start the M4 core:

      bootaux ${loadaddr}

Example:

ext4load mmc 0:2 ${loadaddr} /home/root/hello_world.elf
bootaux ${loadaddr}

More details: Running FreeRTOS on the Cortex-M4 of a Colibri iMX7

2. Expected UART and Device Tree Configuration

  • Debug UART: The FreeRTOS demo uses UART_B for its console output. Make sure:

    • You are connecting your PC’s serial terminal to the UART_B lines of the Colibri Evaluation Board.
    • The serial terminal is set to 115200 baud rate.

  • Device Tree: You must disable (status = "disabled";) UART_B in the Linux device tree to prevent Linux from claiming the peripheral. This is important so that M4 (not Linux) can use it.

    • Optionally, you can apply a device tree overlay for this purpose. Useful reference: Colibri iMX7 - UARTs

3. Path for ext4load

  • The path you give to ext4load (e.g., /home/root/hello_world.elf) must point to the file’s actual location on the root of the second eMMC partition (not relative to the Linux root). If you copied the file as /home/root/hello_world.elf from Linux, then that’s the path in U-Boot as well. So your usage looks correct.

More details: How to load and run the firmware on Cortex M4

4. Troubleshooting Steps

If you still do not see Hello World! on the UART output:

  1. Double-check you are using UART_B on the eval board.
  2. Serial Configuration: Be sure your terminal emulator is listening on the right serial port, at 115200 baud, 8N1.
  3. Device Tree: Ensure the overlay/disable for UART_B is truly active (reboot Linux and confirm /dev/ttymxc1 is missing or unclaimed).
  4. Correct Firmware: Ensure your hello_world.elf is built for the Colibri iMX7 M4 core and targets the TCM area.
  5. Cables: Confirm cables and pinout—sometimes UART_A is inadvertently used instead of UART_B.
  6. Try a minimal example from the official demo to limit the possibility of software/firmware error.
  7. No Bootaux Typos: Use bootaux, not bootauc, in U-Boot (I see you made a typo earlier).

Example of successful output:

Hello World!

This will appear on the UART_B serial console if everything is set up properly.

Summary Checklist

  • Copy .elf to /home/root/hello_world.elf (visible from U-Boot).
  • In U-Boot:
    ext4load mmc 0:2 ${loadaddr} /home/root/hello_world.elf
bootaux ${loadaddr}
  • Connect serial terminal to UART_B (115200 baud).
  • Ensure Linux device tree disables UART_B.

References:

If you follow these steps and still don’t see output, please let me know precisely what you see on the serial terminal and how UART_B is connected. I’m happy to help further!

Best regards,
Toradex AI Assistant.

3

Hi @Uday10122,
Please note that M4 hello world messages should appear on a different UART port.

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