The art of shamanism or custom firmware for Olinuxino. Kernel and Ubuntu Part 3

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Build kernel

Let me explain why the existing images are not suitable. Their main problem is that they are compiled on the old 3.4 kernel, and this immediately imposes a maximum of 4 on the compiler and ubuntu 12.04, I don’t remember exactly 14.04. So it turns out that if you want to use the latest software and libraries, you will have to recompile the last kernel. Of course, you can remove the restriction on compiling not less than version 5 of gcc in the source code and correct the code so that it is assembled under version 4, but this is still a hemorrhoid. Not to mention the fact that in our case the graphic part of the linux is superfluous.

To start with, we download the 4.14.57 kernel at that time, it was the last stable version.

In the folder with the source code, create a script that starts the configuration:

make  	O=../olimex-kernel-4.14.57 		# папка где будет собрано ядро
	-j2 					# собирать в два потока
	ARCH=arm 				# тип процессора под который собирать
	CROSS_COMPILE=arm-linux-gnueabihf-  	# кросс компилятор
	xconfig				# запуск конфига

We get something like this:

In the file menu at the address, /linux-4.14.57/arch/arm/configs/select the file sunxi_defconfig, there are the basic settings for the processors of the sunxi series. And then you need to add some settings. Those. look for the flags below and configure them.

If possible, we build everything into the kernel.

CONFIG_BLK_DEV_INITRD - we will not use ramfs instead, then we will get Aufs (advanced multi-layered unification filesystem). In short, remove the checkbox.
CONFIG_MEMCG - turn like everyone inside
CONFIG_CGROUP_PERF - turn like everyone inside
CONFIG_EXPERT - just select and everything inside, leave the default
CONFIG_BLK_WBT - choose how and all that is within
ARCH_SUNXI - inside we leave only MACH_SUN5I

In bus support we select CONFIG_PCI, since USB wifi requires support for PCI bus. Obviously, when enabled, the wifi kernel does not require a pci bus, but without this wpa, the supplicant does not find usb wifi. Why this happens, you can look into the depths of history, but judging from the historical background, in general, you need to know and remember.

CONFIG_CPU_FREQ_STAT - we find and select
Inside CONFIG_NET we select WIRELESS and then CONFIG_CFG80211 and there we mark CONFIG_NL80211_TESTMODE and CONFIG_CFG80211_WEXT the latter includes our wifi driver for the supplicant.
CONFIG_MAC80211 - turn on the network stack.
CONFIG_MAC80211_MESH - enable
CONFIG_MAC80211_LED - well, and this will select
CONFIG_NFC - we include as well as what is inside except CONFIG_NFC_NCI.
enable CONFIG_LED_TRIGGER_PHY - select
CONFIG_WLAN - select
CONFIG_RTL8XXXU - select, and inside CONFIG_RTL8XXXU_UNTESTED are checked.
CONFIG_USB_WDM - include
CONFIG_UWB - choose and select CONFIG_UWB_HWA inside and CONFIG_UWB_I1480U and then will CONFIG_USB_WUSB and also choose.
We select CONFIG_STAGING and inside we select the CONFIG_RTL8192U and CONFIG_RTLLIB driver, and inside the latter we also select everything. They are marked with modules so the poet will have to screw them separately.
CONFIG_R8188EU - select

In general, this is a necessary minimum of kernel settings, if you suddenly want to include something else then carefully read the dependencies of this parameter, otherwise there will be an error when compiling. Next you need to start compiling:

make  	O=../olimex-kernel-4.14.57/ 
	uImage 			# собрать ядро
	modules 			# собрать модули
	LOADADDR=0x40008000	# адрес в памяти откуда будет загружено ядро

At the same time collect and devicetree files:

make  	O=../olimex-kernel-4.14.57 

This is necessary just in case, because the source files can be with an error even though they are the same in the kernel and in the uboot. Therefore, not one will work the other way.

The next step is to collect the collected files on the first section of the sd card:
- /olimex-kernel-4.14.57/arch/arm/boot/from here we get the assembled kernel, it is called uImage and weighs only 4.7 meters.
- /olimex-uboot/arch/arm/dts/from here we get the compiled tree, the file sun5i-a13-olinuxino.dtb
- /u-boot-2018.05/from here we get the compiled boot script boot.scr.

Build ubuntu

Since all the necessary parts for downloading rootfs are prepared, it remains to build ubuntu and for this we will get the latest version 18.04.

First, create a folder in the root directory:

sudo mkdir /destrupt

It is here because in order to use chroot then you need either full rights as in the root directory, or register the chroot configuration for any other folder. In short, it is easier to create a folder in the root directory and do not fool around with configuration.

We need the following packages for the build, we need to install them if we don’t have them:
- Qemu-user-static
- debootstarp
- schroot

Then we start the ubuntu build:

sudo qemu-debootstrap # we use qemu since the ubuntu build will be installed and qemu will allow us to immediately run the chroot on the assembled ubuntu version
--arch armhf # type of processor architecture
--variant=minbase# build in the minimum version
bionic # build version 18.04
/destrup/ # address where to collect # where to collect the sources

Well, we’ve compiled ubuntu 18.04. Now let's proceed to the step-by-step configuration:

1. Before launching, we climb into / destrup / etc / apt / and rule sources.list, add the following:

deb bionic main restricted
	deb bionic universe
	deb bionic multiverse

These are just sources for distros under our processor.

2. Run change root on the ubuntu distrib that you just created:

sudo chroot /destrup 

First of all, set the password for the root user:

passwd root

This password is required to log into the system at boot.

3. Install the following packages.

apt update- update packages

We put a list of packages for the network: iputils-ping, dhcpcd5, iproute2, iw, networkd-dispatcher, wireless-tools, net-tools.

System packages for working with the network: linux-firmware, wpasupplicant, systemd, hostapd, kmod, udev.

Well, the rest is convenient to edit and configure all this: nano, mc, usbutils, sudo.
And I will not describe everything because it will stretch out for a couple of articles, just go through some of the packages required in the setup.

Configure wpa supplicant.

To begin with, let's briefly analyze what is usb wifi.

The chip itself which provides wifi (in this case rtl8188) is a wired ADC, with its own special data presentation and usb output. those. If you run the lsmod command without the r8188eu.ko module loaded, then we will see only that someone else occupied the usb port. When the module is loaded, the device name will be already visible, in other words, this module is only a software interface for managing this chip.

The next most important library is lib80211.ko, the IEEE 802.11 standard itself, in simple words it is the interpretation of digitized broadcast signals into the presentation of specific ehternet protocols. But in order to manage all these it is necessary to install linux-firmware in its composition there will be a driver -wext- which will do all this. We will connect it in further.

Let's start the configuration of the supplikant.

We climb in the freshly collected ubunte to this address:

/ etc / wpa_supplicant / wpa_supplicant.conf

And we create a configuration file if there isn’t, and if so, we reign to this:

ctrl_interface_group=0	# означает что не будет использоваться графический интерфейс
ctrl_interface=/var/run/wpa_supplicant	# ссыль  где будет лежать файл устройства# когда суппликант подключится и опознает наш usb свисток # тут будет лежать файл устройства
ap_scan=1   	#wpa_supplicant сканирует точку доступа, используется по-умолчанию
psk="пароль сети"
key_mgmt=WPA-PSK	# протокол аутентификации

If everything is configured correctly and the modules described above are loaded, then a device file will be created at the address specified in the configuration (ctrl_interface parameter).

Systemd setup

We configured the supplicant, but there is no one to launch it yet. You can of course install a network-manager and enjoy auto-tuning, but where is the hardcore where the trash is. In general, solid boredom.

Therefore we climb to the address:

/ etc / systemd / system/

And here we create a file with the name network-wireless.serviceif not, and if there is, we begin to edit:

[Unit]	# описание порядка запуска и остановки сервиса
Description=Wireless network connectivity	 	
[Service] # описание запуска юнита
ExecStart=/sbin/ifconfig wlx007005012449 up	# включение устройства
ExecStart=/sbin/wpa_supplicant -B -i wlx007005012449 -D wext -c /etc/wpa_supplicant/wpa_supplicant.conf   # запуск супликанта
ExecStart=/sbin/dhcpcd wlx007005012449	# запуск dhcp для свистка

Let us dwell on the launch of the supplikant:

ExecStart=/sbin/wpa_supplicant # access path to the supplicant
-B # run in the background
-i wlx007005012449 # interface to run, the same device file
-D wext # driver name for the whistle from the linux-firmware
-c /etc/wpa_supplicant/wpa_supplicant.conf # address of the supplicant configuration file

Well, in general, everything you need is configured, proceed to install modules.

Installing modules.

To install the modules, go back a little bit, namely to the folder with the kernel source and run the command to copy modules from the kernel to the folder with ubuntu from there:

make  O=../olimex-kernel-4.14.57 
	modules_install 	# команда для установки модуля
	INSTALL_MOD_PATH=/destrup	# адрес установки модуля

After that, all our assembled modules are copied to ubuntu at:

/ lib / modules / 4.14.57 / kernel

Now the most important thing is to register the launch of the copied modules and all their dependencies, so we crawl to the address:

/ etc / modules

And run open the modules file for editing and append the following modules:

r8188eu		#	наш модуль
r8192u_usb		#
lib80211		#	библиотека стандарта  IEEE 802.11

Now it remains to copy the entire collected ubuntu to the sd card section marked in the previous article as a section for ubuntu.

After that, you can insert a USB flash drive into the board, apply power and sit on its uart to access its controls or ssh. You can add a command to systemd to install an ip address or another configuration in general, then everything else is in your hands ...

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