1，我的硬件

jetson nano b001，就是官方16G emmc的模块，+ 国产图为科技的底板

2，我的目的:

要安装linux preempt rt实时补丁，所以需要重新编译内核源码

3，说明：

jetson nano从r35开始，官方已经带preempt的补丁配置程序了，但是没有编译，没有安装，所以默认你能看到下面信息，但是实际上RT没有运行，没有安装

`~$ uname -a Linux ubuntu 4.9.253-tegra #1 SMP PREEMPT Wed Apr 20 14:25:12 PDT 2022 aarch64 aarch64 aarch64 GNU/Linux`

4，开始步骤：

0，重点说明

全程按照下面操作，不要改目录，容易弄错

下面操作内容是在PC电脑的ubuntu上进行的，不是在jetson板子里面。

1，编译需要

`# Install required packages sudo apt-get update  sudo apt-get install libncurses5-dev  sudo apt-get install build-essential bc  sudo apt-get install lbzip2 sudo apt-get install qemu-user-static`

2，程序包下载

`# L4T Jetson Driver Package wget https://developer.nvidia.com/embedded/l4t/r32_release_v7.1/t210/jetson-210_linux_r32.7.1_aarch64.tbz2 # L4T Sample Root File System wget https://developer.nvidia.com/embedded/l4t/r32_release_v7.1/t210/tegra_linux_sample-root-filesystem_r32.7.1_aarch64.tbz2 # L4T Sources: wget https://developer.nvidia.com/embedded/l4t/r32_release_v7.1/sources/t210/public_sources.tbz2 # GCC Tool Chain for 64-bit BSP #使用浏览器下载得到gcc开头压缩包 https://developer.nvidia.com/embedded/dlc/l4t-gcc-7-3-1-toolchain-64-bit`

3，打补丁

`# Create build folder mkdir $HOME/jetson_nano  cd $HOME/jetson_nano   # Extract files sudo tar xpf jetson-210_linux_r32.7.1_aarch64.tbz2  cd Linux_for_Tegra/rootfs/  sudo tar xpf ../../tegra_linux_sample-root-filesystem_r32.7.1_aarch64.tbz2 cd ../../  tar -xvf gcc-linaro-7.3.1-2018.05-x86_64_aarch64-linux-gnu.tar.xz sudo tar -xjf public_sources.tbz2 tar -xjf Linux_for_Tegra/source/public/kernel_src.tbz2  # Apply PREEMPT-RT patches cd kernel/kernel-4.9/  ./scripts/rt-patch.sh apply-patches`

4，编译

`# Compile kernel TEGRA_KERNEL_OUT=jetson_nano_kernel  mkdir $TEGRA_KERNEL_OUT  export CROSS_COMPILE=$HOME/jetson_nano/gcc-linaro-7.3.1-2018.05-x86_64_aarch64-linux-gnu/bin/aarch64-linux-gnu- make ARCH=arm64 O=$TEGRA_KERNEL_OUT tegra_defconfig  make ARCH=arm64 O=$TEGRA_KERNEL_OUT menuconfig`

保证如下两条正确

# This option should already be selected: Kernel Features -> Preemption Model: Fully Preemptible Kernel (RT)

# You can modify other options for your kernel, like the timer frequency (or anything you need): Kernel Features -> Timer frequency: 1000 HZ

`# After saving the configuration and exiting, start the kernel compilation make ARCH=arm64 O=$TEGRA_KERNEL_OUT -j16`

`# Copy results sudo cp jetson_nano_kernel/arch/arm64/boot/Image $HOME/jetson_nano/Linux_for_Tegra/kernel/Image  sudo cp -r jetson_nano_kernel/arch/arm64/boot/dts/* $HOME/jetson_nano/Linux_for_Tegra/kernel/dtb/  sudo make ARCH=arm64 O=$TEGRA_KERNEL_OUT modules_install INSTALL_MOD_PATH=$HOME/jetson_nano/Linux_for_Tegra/rootfs/  cd $HOME/jetson_nano/Linux_for_Tegra/rootfs/  sudo tar --owner root --group root -cjf kernel_supplements.tbz2 lib/modules  sudo mv kernel_supplements.tbz2  ../kernel/   # Apply binaries cd ..  sudo ./apply_binaries.sh`

5，烧写

（1）如果是sd卡的jetson nano，执行如下

`cd tools  #可以打开这个sh文件，看参数介绍 sudo ./jetson-disk-image-creator.sh -o jetson_nano.img  -b jetson-nano -r 100`

（2）如果是emmc 16G的jetson nano，执行如下

断电jetson nano
先连jetson nano usb到PC Ubuntu电脑（可以是虚拟机）
然后短接jetson nano板子的REC-GND
然后上电

`cd $HOME/jetson_nano/Linux_for_Tegra sudo ./flash.sh jetson-nano-emmc mmcblk0p1`

5，延迟测试

sudo apt-get install rt-tests

运行cyclictest程序进行实时性测试：

sudo cyclictest -t 5 -p 80 -n #运行五个线程，线程优先级为80

`b@jetson:~uname -a Linux jetson 4.9.253-rt168 #1 SMP PREEMPT RT Fri Oct 28 09:36:04 CST 2022 aarch64 aarch64 aarch64 GNU/Linux`

`b@jetson:~$ sudo cyclictest -t 5 -p 80 -n [sudo] password for b: # /dev/cpu_dma_latency set to 0us policy: fifo: loadavg: 0.16 0.16 0.23 1/621 19140  T: 0 (19046) P:80 I:1000 C:  15300 Min:      5 Act:    6 Avg:    7 Max:      20 T: 1 (19047) P:80 I:1500 C:  10200 Min:      5 Act:    6 Avg:    6 Max:      25 T: 2 (19048) P:80 I:2000 C:   7650 Min:      5 Act:    6 Avg:    6 Max:      19 T: 3 (19049) P:80 I:2500 C:   6120 Min:      5 Act:    6 Avg:    7 Max:      24 T: 4 (19050) P:80 I:3000 C:   5100 Min:      5 Act:    7 Avg:    6 Max:      18`

参考链接：

https://forums.developer.nvidia.com/t/preempt-rt-patches-for-jetson-nano/72941/25