Building and Installing a Real-Time Kernel on BeagleBone Black

May 25, 2025

Introduction

BeagleBone® Black
The BeagleBone Black (BBB) is a versatile embedded platform, but its stock Linux kernel isn’t optimized for hard real-time tasks (e.g., robotics, industrial control). By compiling and installing a Preempt-RT (Real-Time) patched kernel, you can achieve microsecond-level latency guarantees. This guide walks through cross-compiling and deploying the 6.6.87-bone-rt-r27 kernel on Debian 12.10.

Why a Real-Time Kernel?

  • Preempt-RT Patch: Converts Linux into a hard real-time OS by minimizing non-interruptible code paths.
  • Use Cases: Motor control, sensor fusion, high-speed data acquisition.
  • Latency: Reduces worst-case latency from milliseconds to ~50μs on the BBB.

Prerequisites

  1. Hardware:
    • BeagleBone Black (Rev C recommended).
    • MicroSD card (8GB+).
    • USB cable (for power/data).
  2. Software:

Step 1: Prepare the BBB

  1. Flash the Debian image to the SD card:
  2. Boot the BBB from the SD card.

Step 2: Cross-Compile the Kernel

On your host machine:

  1. Clone Robert Nelson’s build scripts (official BBB kernel maintainer):

    git clone https://github.com/RobertCNelson/bb-kernel.git kernelbuildscripts  
cd kernelbuildscripts

  2. Checkout the real-time kernel branch:

    git checkout 6.6.87-bone-rt-r27 -b rt-kernel

  3. Start the build (takes 20-60 minutes):

    ./build_kernel.sh

  4. Generated Artifacts (in ./deploy/):

    • 6.6.87-bone-rt-r27.zImage (compressed kernel).
    • 6.6.87-bone-rt-r27-dtbs.tar.gz (device trees).
    • 6.6.87-bone-rt-r27-modules.tar.gz (kernel modules).

Step 3: Install the Kernel on the BBB

  1. Connect to the BBB via USB:

    ssh debian@192.168.7.2  # Password: temppwd

    (For macOS, use 192.168.6.2).

  2. Transfer Files from host to BBB:

    scp deploy/6.6.87-bone-rt-r27-* debian@192.168.7.2:/home/debian

  3. On the BBB:

    • Install kernel modules:
      # 1. Create temporary extraction directory
mkdir ~/kernel_temp
# 2. Extract modules to temporary location
tar xvf 6.6.87-bone-rt-r27-modules.tar.gz -C ~/kernel_temp
# 4. Safely move modules to /lib/modules
sudo mv ~/kernel_temp/lib/modules/6.6.87-bone-rt-r27 /lib/modules/
# 5. Cleanup temporary files
rm -rf ~/kernel_temp
    • Install the kernel image:
      sudo cp 6.6.87-bone-rt-r27.zImage /boot/vmlinuz-6.6.87-bone-rt-r27
    • Install device trees:
      sudo tar xvf 6.6.87-bone-rt-r27-dtbs.tar.gz -C /boot/dtbs/
    • Copy kernel config:
      sudo cp config-6.6.87-bone-rt-r27 /boot/

  4. Generate initramfs:

    sudo update-initramfs -uk 6.6.87-bone-rt-r27

  5. Update U-Boot to load the new kernel:

    sudo nano /boot/uEnv.txt

    Add/modify:

    uname_r=6.6.87-bone-rt-r27

Step 4: Reboot and Verify

  1. Reboot the BBB:
    sudo reboot
  2. Confirm the real-time kernel is active:
    uname -r  # Should show "6.6.87-bone-rt-r27"
  3. Test real-time capabilities:
    sudo cyclictest -t1 -p80 -n -i 10000 -l 10000

Troubleshooting

  • Boot Failure: Revert by selecting the old kernel in uEnv.txt.
  • Missing Modules: Ensure modules are in /lib/modules/6.6.87-bone-rt-r27/.
  • High Latency: Disable CPU frequency scaling:
    sudo cpufreq-set -g performance

Conclusion

You now have a real-time kernel running on your BeagleBone Black! This unlocks deterministic performance for time-sensitive applications. For production systems, consider:

  • Tuning the kernel via /sys/kernel/realtime.
  • Using hardware-assisted PWM/PRU cores for nanosecond precision.

References

  1. Official bb-kernel Build Scripts
  2. BeagleBone Real-Time Kernel Guide
  3. Preempt-RT Patch Documentation