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Linux-PREEMPT_RT-Demo Image for beaglebone-black or green

This is a buildroot config for generating bootable linux image for beaglebone. Purpose of this custom-linux-image is to evaluate behaviour of Linux-PREEMPT_RT patches. All required preemptrt-patches/kernel-config/libraries/demo-utils for evaluating the PREEMPT_RT behaviour are included in this image. An outer layer br-wrapper repo is used as BR2_EXTERN for buildroot. Final output of this buildroot config is a linux image which can be directly written on sdcard using Balena-Etcher or dd or other ISO image writing utils.

Maintainer

Albert David (albert.david@gmail.com)

Build steps for creating Linux-PREEMPT_RT-Demo sdcard image for beaglebone hw

mkdir -p ~/preempt-rt-demo/
cd ~/preempt-rt-demo/
git clone --recursive https://github.com/hackboxguy/br-wrapper.git
cd br-wrapper
make -C buildroot BR2_EXTERNAL=../ BR2_DL_DIR=../../br-dl O=../../br-output beaglebone_preemptrt_defconfig
make -C buildroot BR2_EXTERNAL=../ BR2_DL_DIR=../../br-dl O=../../br-output
ls -lah ~/preempt-rt-demo/br-output/images/sdcard.img #this image can written to sdcard using dd

How to cross-compile(on x86 host pc) and run modified preemptrt-gpiotest on Target(beaglebone) Hardware?

  1. wget https://github.com/hackboxguy/lfs-downloads/raw/main/beaglebone-preemptrt-demo/arm-buildroot-linux-gnueabihf_sdk-buildroot.tar.gz -O ~/arm-buildroot-linux-gnueabihf_sdk-buildroot.tar.gz Download Cross-Toolchain of beaglebone-preemptrt-demo
  2. tar -xvf ~/arm-buildroot-linux-gnueabihf_sdk-buildroot.tar.gz -C ~/ untar downloaded Cross-Toolchain to HOME directory
  3. ~/arm-buildroot-linux-gnueabihf_sdk-buildroot/relocate-sdk.sh Relocate the toolchain path to this specific installation
  4. git clone https://github.com/hackboxguy/preemptrt-gpiotest.git Clone the source-code of preemptrt-gpiotest
  5. cd preemptrt-gpiotest cd to cloned souce directory
  6. Modify the code of preemptrt-gpiotest
  7. cmake -H. -BOutput -DCMAKE_INSTALL_PREFIX=~/preemptrt-demo-output/ -DCMAKE_TOOLCHAIN_FILE=~/preemptrt-gpiotest/cmake/arm-buildroot-linux-uclibcgnueabihf.cmake configure with cmake
  8. cmake --build Output -- install -j$(nproc) build with cmake(binary will be installed to ~/preemptrt-demo-output/sbin/)
  9. rm -rf ~/preemptrt-gpiotest/Output delete cmake generated Output folder when not required(remove this folder only when you are done developing the code)
  10. scp ~/preemptrt-demo-output/sbin/preemptrt-gpiotest root@preemptrt-demo-target:/usr/sbin/ using scp, copy the modified binary to the beaglebone hw
  11. ssh root@preemprt-demo-target using ssh, login to beaglebone hw (root pw is: brb0x)
  12. /etc/init.d/S99PreemptrtGpio stop stop existing instance of preemptr-gpiotest
  13. /usr/sbin/preemptrt-gpiotest gpiochip0 28 gpiochip0 17 h p run modified preemptrt-gpiotest on beaglebone