增加 Yocto for Raspberry pi 4 B 64 bit.

Signed-off-by: lion.chan <cy187lion@sina.com>

Chapter8_SOC_与_Linux/8.22_使用_Yocto_构建树莓派_4B.md

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+# Yocto for Raspberry pi 4 B 64 bit
+
+Using Yocto we can create custom Linux images for embedded devices. Here we are going to build a basic minimal image for raspberry pi 4b. With the small modification in the configuration file you can create the images for various versions of Raspberry pi.
+
+[*Optional]
+
+Full course on Yocto available @ Udemy
+
+All the below commands are available as a shell script on <https://github.com/eclabs007/Yocto-Udemy.git>
+
+## Prepare your Host Linux
+
+Install the essential tools for your host PC.
+
+```bash
+sudo apt-get install gawk wget git-core diffstat unzip texinfo gcc-multilib build-essential chrpath socat libsdl1.2-dev xterm python
+```
+
+## Setting up Yocto
+
+1.Download Poky (reference implementation of yocto)
+
+here we are downloading zeus version of Yocto.
+
+```bash
+git clone -b zeus git://git.yoctoproject.org/poky.git poky-zeus
+```
+
+navigate to poky folder
+
+```bash
+cd poky-zeus
+```
+
+Download meta-openembedded layer
+
+```bash
+git clone -b zeus git://git.openembedded.org/meta-openembedded
+```
+
+Download meta-Raspberry pi layer
+
+```bash
+git clone -b zeus git://git.yoctoproject.org/meta-raspberrypi
+```
+
+If you wish qt support download meta-qt5
+
+```bash
+git clone -b zeus https://github.com/meta-qt5/meta-qt5
+```
+
+Now you have all the necessary layers for building the Yocto
+
+## Building your first image for Raspberry Pi
+
+For Initializing Poky Variables You can use oe-init-build-env script
+
+The script is responsible for the initialization of variables of the Poky build system, the script creates a directory structure in which it is very well divided:
+
+build – build directory
+
+source – assembly recipes source code
+
+download – directory for downloading program code (git databases, tar.gz archives)
+
+```bash
+source oe-init-build-env
+```
+
+It will take you to a build folder , optionally you can give build folder as an argument , **source oe-init-build-env** <build_folder_name>
+
+In the build folder now you will be able to see one folder called conf which will be having the configuration files
+
+```bash
+conf/
+├── bblayers.conf
+├── local.conf
+└── templateconf.cfg
+```
+
+Now edit conf/bblayers.conf with your favorite text editor as below
+
+add layer meta-raspberrypi to your bblayer.cof
+
+```bash
+POKY_BBLAYERS_CONF_VERSION = "2"
+
+BBPATH = "${TOPDIR}"
+BBFILES ?= ""
+
+BBLAYERS ?= " \
+/home/eclabs/Yocto/poky-zeus/meta \
+/home/eclabs/Yocto/poky-zeus/meta-poky \
+/home/eclabs/Yocto/poky-zeus/meta-yocto-bsp \
+/home/eclabs/Yocto/poky-zeus/meta-raspberrypi \
+"
+```
+
+Modify conf/local.conf
+
+```bash
+MACHINE ??= “raspberrypi4-64”
+```
+
+you can build Yocto image for the different hardware versions of Raspberry pi by just changing this MACHINE variable.
+
+```bash
+raspberrypi0
+raspberrypi0w
+raspberrypi3
+raspberrypi3-64
+raspberrypi4
+raspberrypi4-64 etc
+```
+
+For a building minimal image you can give the following command
+
+bitbake core-image-minimal
+
+it will create Kernel image ,RFS ,dtbs and boot codes for you. For the first time build will take some time( You are building a Linux from source).
+
+After the build you can copy the images to SD card , Enjoy booting your Linux it will be available in tmp/deploy/images/raspberrypi4-64/ folder
+
+```bash
+sudo dd if=tmp/deploy/images/raspberrypi4-64/core-image-minimal-raspberrypi4-64.rpi-sdimg of=/dev/sdX bs=16M status=progress
+```