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Real-time kernel compilation

The RT-Preempt is based on the Linux community kernel, with relevant patches to make Linux meet hard real-time requirements. Here is the compilation and configuration process, using kernel 5.6.19 as an example.

Download kernel and rt patches​

  1. Create a new folder for the kernel and patches

``bash mkdir ~/rt-kernel && cd ~/rt-kernel


:::tip
Use extranet access, or use mobile hotspot access if no extranet is available.
:::

2. download [rt patch](https://mirrors.edge.kernel.org/pub/linux/kernel/projects/rt/)

3. download [kernel source code](https://mirrors.edge.kernel.org/pub/linux/kernel/v5.x/)


:::caution
Kernel version and patch version need to strictly correspond
:::

4. apply the patch

```shell
 sudo apt-get install libncurses-dev #Install the dependencies
 tar -xzvf linux-5.6.19.tar.gz #Unpack the kernel
 gunzip patch-5.6.19-rt12.patch.gz #Unzip the patch
 cd linux-5.6.19/
 patch -p1 < ... /patch-5.6.19-rt12.patch #patch
info

The kernel used in this article is linux-5.6.19.tar.gz and the rt patch is patch-5.6.19-rt12.patch.gz.

Configure the kernel​

  1. Open the kernel configuration screen
make menuconfig
  1. Select General setup, and if the kernel version is old and does not have the options in the next step, select Processor Type and features

If the kernel version is a bit older, then select the Processor Type and features. Figure 1

  1. select Preemption Model (Voluntary Kernel Preemption (Desktop))

Figure 2

  1. Select Fully Preemptible Kernel (RT), then press esc all the way back to the main page

Figure 3

  1. Select Kernel hacking

Figure 4

  1. Select Memory Debugging

Figure 5

  1. Deselect Check for stack overflows, you can ignore it if it is not selected.

  2. Press '/' to search for DEBUG_INFO

Figure 6

  1. Press '1'

Figure 7

  1. Press 'n' on the Compile the kernel with debug info option to cancel the generation of debug files during compilation

! Figure 8](https://ftp.bmp.ovh/imgs/2020/11/f90a6d57f2800bf1.png)

tip

Compiling the kernel generates a very large debug file, which is not needed for the actual installation, so you can simply prevent it from being generated

Kernel compilation​

  1. Compile and install the kernel
CONFIG_DEBUG_INFO=n #Block compilation of debug files
make -j`nproc` && make -j`nproc` bindeb-pkg #compile and package
tip

'nproc' is the number of CPU threads.

Then you will get

linux-firmware-image-5.6.19-rt12_5.6.19-rt12-1_amd64.deb
linux-headers-5.6.19-rt12_5.6.19-rt12-1_amd64.deb
linux-image-5.6.19-rt12_5.6.19-rt12-1_amd64.deb
linux-libc-dev_5.6.19-rt12-1_amd64.deb

Installing the kernel​

tip

At this point, you can copy the .deb package from a USB stick to another device and install it without having to compile it again

Go to the package folder and install the kernel

sudo dpkg -i linux-*.deb
  1. Update grub and reboot
sudo update-grub
sudo reboot
  1. Check the kernel version
uname -a

At this point, you can see that the kernel version is marked with PREEMPT RT and you can perform real-time testing

Error collection​

  1. Unable to open kernel configuration interface menuconfig

    Q1:(linux-4.17.2 kernel for example)

    root@simon-virtual-machine:/home/simon/Src/linux-4.17.2# make menuconfig
    YACC scripts/kconfig/zconf.tab.c
    /bin/sh: 1: bison: not found
    scripts/Makefile.lib:196: recipe for target 'scripts/kconfig/zconf.tab.c' failed
    make[1]: *** [scripts/kconfig/zconf.tab.c] Error 127
    Makefile:528: recipe for target 'menuconfig' failed
    make: *** [menuconfig] Error 2

    A1.

    apt-get install bison -y

    Q2. ``bash root@simon-virtual-machine:/home/simon/Src/linux-4.17.2# make menuconfig YACC scripts/kconfig/zconf.tab.c LEX scripts/kconfig/zconf.lex.c /bin/sh: 1: flex: not found scripts/Makefile.lib:188: recipe for target 'scripts/kconfig/zconf.lex.c' failed make[1]: *** [scripts/kconfig/zconf.lex.c] Error 127 Makefile:528: recipe for target

    A2.
    ```bash
    sudo apt-get install flex