Minimal Image, Fastest Rpi, Quick Tutorial (update)

blog/content/post/2023-06-23-Blogpost_yocto_kas.md

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+---
+title: Blog post - odświeżenie "Minimal Image, Fastest Rpi, Quick Tutorial"
+abstract: 'So far, to build even a minimal image on th raspberry pi the downloading of sources and then configuration had to be done by hand.
+	  Instead Yocto kas is using a project configuration file and does the download and configuration phase.
+	  Kas tool provides an easy mechanism to setup bitbake based projects.
+          Kas makes the setup of a Yocto build environment super simple and super fast.'
+cover: /covers/Cover_Yocto_kas_RPI4.png
+author: ewa.kujawska
+layout: post
+published: true
+date: 2023-06-23
+archives: "2023"
+
+tags:
+  - yocto
+  - poky
+  - kas
+  - rpi
+  - linux
+  - meta-raspberrypi
+  - minimal_image
+  - u-boot
+  - open-source
+  - mickledore
+categories:
+  - Firmware
+  - IoT
+  - Miscellaneous
+  - OS Dev
+
+---
+
+
+# A brief description of the hardware platform
+
+Raspberry Pi is a small computer to which you can connect a keyboard,
+monitor, or mouse and use it as you would a normal desktop computer.
+This credit card-sized device, equipped with the right system and drivers,
+allows you to use the Internet, play games, use word editors,
+calculation sheets or play multimedia. It is used in many projects,
+whether for beginners, learning programming, or more advanced projects
+that can take full advantage of the functionalities offered by Raspberry PI.
+
+![Raspberry Pi 4](/img/raspberry-pi-4.png)
+
+# Building minimal image with Ycto
+
+The blog post shows how to currently build an image for the RPI 4,
+with the UART enabled, while using the U-Boot bootloader.
+We will build the project using the _kas_ tool.
+The previous version of the article
+[Minimal Image, Fastest Rpi, Quick Tutorial](https://blog.3mdeb.com/2020/2020-10-30-rpi4_yocto/)
+showed how to build a minimal image on a Raspberry Pi 4
+using Ubuntu 18.04 with Yocto. There were described various steps:
+cloning the Yocto repository, selecting the appropriate branch, and
+changing the configuration files _bblayers.conf_, _local.conf_,
+flashing the image to the correct location on the SD card
+on the basis of the built image.
+If you need to perform these actions or read a more detailed description, 
+be sure to visit the indicated article before continuing.
+
+## Usage of "kas" and the latest Yocto release: mickledore
+
+In this article, we will extend the image-building process
+using the _kas-container_ tool and the latest release of Yocto _(Mickledore)_.
+In addition, let's build an image using the U-Boot bootloader.
+You can familiarise yourself with the kas tool on a blog post,
+which is a bit dated but still explains things well:
+[Quick start guide to kas - best tool for setting up the Yocto projects](https://blog.3mdeb.com/2019/2019-02-07-kas/).
+One difference is that the script now used is _kas-container_ and not _kas-docker_.
+To start, set up the environment - create a folder called _Yocto_,
+for example, and clone the following repo:
+
+```zsh
+mkdir Yocto
+cd Yocto
+```
+
+```zsh
+git clone https://github.com/agherzan/meta-raspberrypi.git
+git clone https://github.com/siemens/kas.git
+```
+
+The _meta-raspberrypi_ repository contains a _kas-poky-rpi.yml_ file,
+which needs a slight modification to use the Mickledore branchy,
+instead of the master. Just check if mickledore exists in the linked repositories
+and then replace _refspec: master_ with _refspec: mickledore_.  
+
+```zsh
+poky:
+    url: https://git.yoctoproject.org/git/poky
+    path: layers/poky
+    refspec: master
+    layers:
+      meta:
+      meta-poky:
+      meta-yocto-bsp:
+
+  meta-openembedded:
+    url: http://git.openembedded.org/meta-openembedded
+    path: layers/meta-openembedded
+    refspec: master
+    layers:
+      meta-oe:
+      meta-python:
+      meta-networking:
+      meta-perl:
+
+  meta-qt5:
+    url: https://github.com/meta-qt5/meta-qt5/
+    path: layers/meta-qt5
+    refspec: master
+```
+
+In case of errors during the build, communicated as
+_Has a restricted licence 'synaptics-killswitch' which is not listed in your LICENSE_FLAGS_ACCEPTED"
+the kas-poky-rpi.yml file can be extended with an additional line:
+LICENSE_FLAGS_ACCEPTED += " synaptics-killswitch_.
+Here [Yocto project](https://docs.yoctoproject.org/4.0.10/singleindex.html#term-LICENSE_FLAGS_ACCEPTED)
+is more information about the variables.
+
+```zsh
+standard: |
+    CONF_VERSION = "2"
+    PACKAGE_CLASSES = "package_rpm"
+    SDKMACHINE = "x86_64"
+    USER_CLASSES = "buildstats"
+    PATCHRESOLVE = "noop"
+    LICENSE_FLAGS_ACCEPTED += " synaptics-killswitch"
+```
+
+## Adding a U-boot and UART
+
+Once the environment has been put together
+and the kas-container script downloaded and the changes made,
+an image should be created from the Yocto directory created earlier:
+
+`kas/kas-container build meta-raspberrypi/kas-poky-rpi.yml`
+
+Time to include the U-Boot bootloader and UART interface.
+Documentation of the meta-raspberrypi layer can be found [here]
+(<https://meta-raspberrypi.readthedocs.io/en/latest/extra-build-config.html#boot-to-u-boot>).
+For u-boot to load the kernel image,
+the following must be set in local.conf (file kas-poky-rpi.yml):  
+
+`RPI_USE_U_BOOT = "1"`
+
+Users who want serial console support should explicitly set in local.conf:
+
+`ENABLE_UART = "1"`
+
+# Flashing
+
+At this stage, the image should already be built. In the location
+`Yocto/build/tmp/deploy/images/raspberrypi4` there are many files,
+among them two important ones to be uploaded to the SD card.
+A simple way to find these files is to use the command
+`ls *wic*` as shown in the code below.
+
+```zsh
+Yocto_kas/build/tmp/deploy/images/raspberrypi4 λ ls -a *wic* 
+core-image-base-raspberrypi4-20230703064507.rootfs.wic.bmap  
+core-image-base-raspberrypi4-20230703064507.rootfs.wic.bz2  
+core-image-base-raspberrypi4.wic.bmap  
+core-image-base-raspberrypi4.wic.bz2
+```
+
+You will need these two files:
+`core-image-base-raspberrypi4.wic.bmap` and `core-image-base-raspberrypi4.wic.bz2`.
+You can now insert the SD card into the PC
+and check its location using the command, for example:
+
+```zsh
+sudo fdisk -l
+```
+
+The result will be a similar output to this one:
+
+```
+Disk /dev/sdc: 28.89 GiB, 31016878080 bytes, 60579840 sectors
+Disk model: MassStorageClass
+Units: sectors of 1 * 512 = 512 bytes
+Sector size (logical/physical): 512 bytes / 512 bytes
+I/O size (minimum/optimal): 512 bytes / 512 bytes
+Disklabel type: dos
+Disk identifier: 0xfc7fa3b0
+```
+
+The location must be right. Otherwise, flashing the image to the wrong 
+location can cause serious damage.
+We will use the `bmap-tools` to upload the above files.
+It is a tool that works with files of any size,
+creating and manipulating files in blocks and mapping them
+from one location to another. It offers secure transfer,
+checks data integrity with SHA256, and uses authentication with the OpenPGP tool.
+
+```zsh
+sudo dnf install -y bmap-tools
+```
+
+In the next step unmount the SD card (X can be replaced by c,
+but you need to check the proper location of Your SD cart):
+
+```zsh
+sudo umount /dev/sd[X]
+```
+
+Then, at the _raspberrypi4_ location, upload the image using the `bmaptool` command:
+
+```zsh
+sudo bmaptool copy --bmap core-image-base-raspberrypi4.wic.bmap core-image-base-raspberrypi4.wic.bz2 /dev/sdc
+```
+
+To check the correctness of the results, let us use the _Minicom_ programme:
+
+```zsh
+sudo minicom -D /dev/ttyUSB0 -b115200
+```
+
+You can also use the -s flag and manually adjust the settings.
+
+# Boot time measurement in the bootloader
+
+Measuring boot time can be an important way of assessing system resources.
+
+In general, start-up time should be divided into bootloader,
+Linux kernel and userspace software loading time.
+The time spent in the bootloader is assumed to be the time
+from the appearance of the U-Boot SPL logs on the debug console,
+to the display of the Starting kernel log .....
+Of course, before the SPL, the Boot ROM is started, which loads it,
+but the time required for this is negligibly small.
+
+The following sections show the boot time measurement,
+and modifications to the bootloader configuration
+to reduce `CONFIG_BOOTDELAY` to zero. `CONFIG_BOOTDELAY` sets the value
+of `bootdelay` and the `bootdelay` contains the number of seconds that U-Boot pauses
+to determine whether the user wants to interrupt the boot sequence.
+To eliminate the delay, set it to 0. Next, a re-measurement of boot time
+shows that booting has been improved and accelerated.
+Timestamping can be performed in the _Minicom_ software
+by running the timestamp registration option.
+After connecting to the Raspberry Pi 4 using the minicom software,
+the timing option can be selected. Simply press Ctrl-A Z and then
+select N (Timestamp toggle). This will enable you to check the duration
+of commands and processes being executed.
+
+The first measurement of the boot time shows that the boot process takes about 3 seconds:
+
+```zsh
+[2023-07-14 11:30:38] U-Boot 2023.01 (Jan 09 2023 - 16:07:33 +0000)
+...
+[2023-07-14 11:30:41] Starting kernel ...
+```
+
+To modify the variable responsible for the start-up time,
+access the u-boot prompt. To do this, you need to reboot the system and
+immediately after the _U-boot_ is displayed, press any characters on the keyboard.
+
+Now, we can set:
+
+```zsh
+[2023-07-14 14:49:36] U-Boot> setenv bootdelay '0'
+[2023-07-14 14:50:15] U-Boot> saveenv
+[2023-07-14 14:50:20] Saving Environment to FAT... OK
+```
+
+As a result, it was possible to reduce this time from 3 seconds to 1 second.
+
+```zsh
+[2023-07-14 14:53:35] U-Boot 2023.01 (Jan 09 2023 - 16:07:33 +0000)
+... 
+[2023-07-14 14:53:36] Starting kernel ...
+```
+
+```
+author: ewa.kujawska
+```
+
+## Summary
+
+I hope this short but informative blog will help you get started
+with your new Raspberry Pi 4, learn about a useful tool such as the Yocto
+or Kas project and thus build a correct minimum image.
+If you are interested in more technology and projects from the embedded world,
+I highly recommend taking a look at more blogs from 3mbed [more blogs](https://blog.3mdeb.com).