#!/bin/bash

# Raspberry Pi OS
# Build a PREEMPT_RT kernel for RPI 5
#
# Pre requisites
# - burn Raspberry Pi OS Lite 64bit
# - after first boot
#sudo apt update && sudo apt dist-upgrade -y

# - install Xfce Desktop and default to boot into
#sudo apt install xfce4
#sudo systemctl set-default graphical.target

# enable access to samba shares
#sudo apt install smbclient
#sudo apt install gvfs-backends

#sudo sync
#sudo reboot

# going to kernel stuff
#uname -a
# install neccessary packages to build a kernel
sudo apt install git bc bison flex libssl-dev make libncurses5-dev -y
mkdir ~/build && cd ~/build

KERNEL_VERSION=6.6
KERNEL=kernel_2712
KERNEL_BRANCH=rpi-$KERNEL_VERSION.y
RT_PATCH_VERSION=$KERNEL_VERSION.63-rt46

# get the kernel sources for Raspberry Pi OS
git clone --depth=1 --branch $KERNEL_BRANCH https://github.com/raspberrypi/linux

wget http://cdn.kernel.org/pub/linux/kernel/projects/rt/$KERNEL_VERSION/older/patch-$RT_PATCH_VERSION.patch.gz
gunzip patch-$RT_PATCH_VERSION.patch.gz

cd linux/

# Patch the kernel
patch -p1 < ../patch-$RT_PATCH_VERSION.patch

# create default config
make bcm2712_defconfig

# set values to configure the kernel as _RT
# make menuconfig
./scripts/config --set-val CONFIG_LOCALVERSION "\"-v8-16k-DeJe63\""
./scripts/config --set-val CONFIG_PREEMPT_RT y
./scripts/config --set-val CONFIG_RCU_BOOST y
./scripts/config --set-val CONFIG_RCU_BOOST_DELAY 500
./scripts/config --set-val CONFIG_RCU_NOCB_CPU y
./scripts/config --set-val CONFIG_NO_HZ_FULL y
./scripts/config --set-val CONTEXT_TRACKING_USER_FORCE n
./scripts/config --set-val RCU_NOCB_CPU_DEFAULT_ALL n
./scripts/config --set-val RCU_NOCB_CPU_CB_BOOST y

# build the kernel, this takes some time
make -j6 Image.gz modules dtbs

# make it live
sudo make -j6 modules_install
sudo cp /boot/firmware/$KERNEL.img /boot/firmware/$KERNEL-backup.img
sudo cp arch/arm64/boot/Image.gz /boot/firmware/$KERNEL.img
sudo cp arch/arm64/boot/dts/broadcom/*.dtb /boot/firmware/
sudo cp arch/arm64/boot/dts/overlays/*.dtb /boot/firmware/overlays/
sudo cp arch/arm64/boot/dts/overlays/README /boot/firmware/overlays/

# add "isolcpus=2,3 max.processor.cstate=1" to cmdline.txt

# flush and reboot
#sudo sync
#sudo reboot 

# check if right kernel is installed
#uname -a

# install linuxcnc
#sudo apt install ./linuxcnc-uspace_2.9.3_arm64.deb