Build U-Boot and Linux Kernel for Beaglebone and Beaglebone Black

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Happy new year everybody. How time flies. It is already 2018. Longer Vision has been struggling on this tough road towards a successful enterprise. Algorithms ONLY are NOT enough for nowadays business. BSP (board support package) and IC design are a must for a successful business nowadays. Thus, ever since 2018, Longer Vision is going to balance both hardware and software, particularly, ARM based open source embedded development board and computer vision algorithms.

In this blog, we are going to talk about how to build and flash U-Boot and Linux Kernel onto a Beaglebone and Beaglebone Black, which adopts TI AM335x as its CPU. The board looks like (cited from Beaglebone Black ):

Beaglebone Black

PART A: Cross Compile U-Boot and Linux Kernel

1. Linaro GCC

Linaro is a popular platform providing high-quality code for both Linux kernel and GCC tool chain. Linaro's GCC toolchain of varoius versions can be directly found here.

Here, we download GCC latest-6 binary under arm-linux-gnueabihf.

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$ wget -c 
https://releases.linaro.org/components/toolchain/binaries/latest-6/arm-linux-gnueabihf/gcc-linaro-6.4.1-2017.11-x86_64_arm-linux-gnueabihf.tar.xz
$ tar xf gcc-linaro-6.4.1-2017.11-x86_64_arm-linux-gnueabihf.tar.xz
$ export CC=`pwd`/gcc-linaro-6.4.1-2017.11-x86_64_arm-linux-gnueabihf/bin/arm-linux-gnueabihf-

Test the cross compiler:

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$ ${CC}gcc --version
arm-linux-gnueabihf-gcc (Linaro GCC 6.4-2017.11) 6.4.1 20171012
Copyright (C) 2017 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

2. U-Boot

U-Boot is a universal boot loader. For Beaglebone and Beaglebone Black, there are two patches which has been maintained by eewiki Linux on ARM on github. We first download U-Boot and check out the latest release as follows:

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$ git clone https://github.com/u-boot/u-boot
$ cd u-boot/
$ git checkout v2018.01

Then check out the latest u-boot-patches and patch two files under the latest release v2018.01:

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$ cd ../
$ git clone https://github.com/eewiki/u-boot-patches.git
$ cd ./u-boot-patches/v2018.01
$ cp 0001-am335x_evm-uEnv.txt-bootz-n-fixes.patch ../../u-boot/
$ cp 0002-U-Boot-BeagleBone-Cape-Manager.patch ../../u-boot/
$ cd ../../u-boot
$ patch -p1 < 0001-am335x_evm-uEnv.txt-bootz-n-fixes.patch
$ patch -p1 < 0002-U-Boot-BeagleBone-Cape-Manager.patch

Finally, we configure and build U-Boot for Beaglebone and Beaglebone Black as follows:

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$ make ARCH=arm CROSS_COMPILE=${CC} distclean
$ make ARCH=arm CROSS_COMPILE=${CC} am335x_evm_defconfig
$ make ARCH=arm CROSS_COMPILE=${CC}

3. Linux Kernel

Due to Robert Nelson's summary at eewiki, there are two ways to build Beaglebone and Beaglebone Black: - Mainline - TI BSP

Their differences are: - bb-kernel: based on mainline, no-smp, optimized for AM335x devices. - ti-linux-kernel-dev: based on TI’s git tree, smp, optimized for AM335x/AM43xx/AM57x devices.

Here, we are going to use Mainline to build our own Linux Kernel. We FIRST check out Robert Nelson's bb-kernel.

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$ git clone https://github.com/RobertCNelson/bb-kernel
$ cd bb-kernel/
$ git checkout origin/am33x-v4.14 -b am33x-v4.14

We then check out Linus Torvalds' stable Linux Kernel, which can be also tracked on github Torvalds Linux. This will take you quite a while.

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$ git clone https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git

Now, it's the time to modify some of the configurations in .sh files under the checked out branch am33x-v4.14.

1) version.sh

Here, I'm using gcc_linaro_gnueabihf_6 instead of gcc_linaro_gnueabihf_7.

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toolchain="gcc_linaro_gnueabihf_6"
#toolchain="gcc_linaro_gnueabihf_7"

2) system.sh

A file named system.sh.sample has been provided for us to configure accordingly. We FIRST do a copy.

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$ cp system.sh.sample system.sh

Then, we manually re-specifying two MACROs: CC and LINUX_GIT, respectively to two directories containing the above downloaded Linaro GCC compiler and the current Torvalds' Linux Kernel. We also specify MMC for TF/SD Card as follows:

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CC=.../gcc-linaro-6.4.1-2017.11-x86_64_arm-linux-gnueabihf/bin/arm-linux-gnueabihf-
LINUX_GIT=.../linux-stable
MMC=/dev/mmcblk0

After the above configurations, we start building the Linux Kernel using the following command line. This will probably take you one hour.

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$ ./build_kernel.sh

When you see this Kernel Configuration page,

Kernel Configuration

Exit right away without any modification. And you will see:

After Kernel Configuration

After a while, you will see Linux Kernel has been successfully built:

The Built Kernel

4. Root File System

We then install the latest Debian (for now, Debian 9.3) according to Robert Nelson's minimal operating system. Three commands are to be executed in a row for downloading, verifying, and extraction.

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$ wget -c https://rcn-ee.com/rootfs/eewiki/minfs/debian-9.3-minimal-armhf-2017-12-09.tar.xz
$ sha256sum debian-9.3-minimal-armhf-2017-12-09.tar.xz
5120fcfb8ff8af013737fae52dc0a7ecc2f52563a9aa8f5aa288aff0f3943d61  debian-9.3-minimal-armhf-2017-12-09.tar.xz
$ tar xf debian-9.3-minimal-armhf-2017-12-09.tar.xz

Until now, most components for booting have been downloaded and built. It is the time for us to flash our own OS onto a SD card.

PART B: Install the Linux OS onto SD Card

5. Setup microSD card

1) TF Card Preparation

We first check which block device that we are going to install our built system onto by command lsblk.

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$ lsblk
NAME    MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
sdd       8:48   0 931.5G  0 disk 
└─sdd1    8:49   0 931.5G  0 part /media/jiapei/Data
sdb       8:16   0 238.5G  0 disk 
├─sdb4    8:20   0   900M  0 part 
├─sdb2    8:18   0   128M  0 part 
├─sdb3    8:19   0 237.2G  0 part /media/jiapei/Win10
└─sdb1    8:17   0   300M  0 part /boot/efi
sr0      11:0    1  1024M  0 rom  
sdc       8:32   0 238.5G  0 disk 
├─sdc2    8:34   0  30.5G  0 part [SWAP]
├─sdc3    8:35   0 207.5G  0 part /
└─sdc1    8:33   0   512M  0 part 
mmcblk0 179:0    0    15G  0 disk

We then define a MACRO DISK to specify the TF card device.

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$ export DISK=/dev/mmcblk0

Afterwards, erase partition table/labels on TF card by:

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$ sudo dd if=/dev/zero of=${DISK} bs=1M count=10

2) Bootloader installation

Now, we install the built U-Boot onto the SD card:

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$ sudo dd if=./u-boot/MLO of=${DISK} count=1 seek=1 bs=128k
$ sudo dd if=./u-boot/u-boot.img of=${DISK} count=2 seek=1 bs=384k

3) Partition Preparation

We FIRST make sure which version of sfdisk is. In my case, it is of version 2.27.1

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$ sudo sfdisk --version
sfdisk from util-linux 2.27.1

Then we create the partition layout by:

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$ sudo sfdisk ${DISK} <<-__EOF__
4M,,L,*
__EOF__

Afterwards, we need to format the created partition by mkfs.ext4. We also need to make sure which version of mkfs.ext4 is. In my case, it is of version 1.42.13.

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$ mkfs.ext4 -V
mke2fs 1.42.13 (17-May-2015)
        Using EXT2FS Library version 1.42.13

Then, we format the partition by:

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$ sudo mkfs.ext4 -L rootfs ${DISK}p1

After formatting, the TF card should be able to be either automatically mounted or manually mounted by the following command:

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$ sudo mkdir -p /media/rootfs/
$ sudo mount ${DISK}p1 /media/rootfs/

4) Backup Bootloader

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$ sudo mkdir -p /media/rootfs/opt/backup/uboot/
$ sudo cp -v ./u-boot/MLO /media/rootfs/opt/backup/uboot/
$ sudo cp -v ./u-boot/u-boot.img /media/rootfs/opt/backup/uboot/

5) Dealing with old Bootloader in eMMC (Optional)

If the old bootloader in eMMC is to be kept, please copy the following file uEnv.txt to /media/rootfs/.

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##This will work with: Angstrom's 2013.06.20 u-boot.
 
loadaddr=0x82000000
fdtaddr=0x88000000
rdaddr=0x88080000
 
initrd_high=0xffffffff
fdt_high=0xffffffff
 
#for single partitions:
mmcroot=/dev/mmcblk0p1
 
loadximage=load mmc 0:1 ${loadaddr} /boot/vmlinuz-${uname_r}
loadxfdt=load mmc 0:1 ${fdtaddr} /boot/dtbs/${uname_r}/${fdtfile}
loadxrd=load mmc 0:1 ${rdaddr} /boot/initrd.img-${uname_r}; setenv rdsize ${filesize}
loaduEnvtxt=load mmc 0:1 ${loadaddr} /boot/uEnv.txt ; env import -t ${loadaddr} ${filesize};
loadall=run loaduEnvtxt; run loadximage; run loadxfdt;
 
mmcargs=setenv bootargs console=tty0 console=${console} ${optargs} ${cape_disable} ${cape_enable} root=${mmcroot} rootfstype=${mmcrootfstype} ${cmdline}
 
uenvcmd=run loadall; run mmcargs; bootz ${loadaddr} - ${fdtaddr};
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sudo cp -v ./uEnv.txt /media/rootfs/

6. Kernel Installation

1) Export MACRO kernel_version

Under the folder bb-kernel, a file named kernel_version was generated while building Linux kernel. In my case, I was building the NEWEST kernel 4.14.13-bone12. For convenience, we export a new MACRO kernel_version.

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$ cat kernel_version 
4.14.13-bone12
$ export kernel_version=4.14.13-bone12

2) Extract Debian Root File System onto TF Card

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$ sudo tar xfvp ./debian-9.3-minimal-armhf-2017-12-09/armhf-rootfs-debian-stretch.tar -C /media/rootfs/
$ sync
$ sudo chown root:root /media/rootfs/
$ sudo chmod 755 /media/rootfs/

3) Set uname_r in /boot/uEnv.txt

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$ sudo sh -c "echo 'uname_r=${kernel_version}' >> /media/rootfs/boot/uEnv.txt"

4) Copy Kernel Image

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$ sudo cp -v ./bb-kernel/deploy/${kernel_version}.zImage /media/rootfs/boot/vmlinuz-${kernel_version}

5) Copy Kernel Device Tree Binaries

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$ sudo mkdir -p /media/rootfs/boot/dtbs/${kernel_version}/
$ sudo tar xfv ./bb-kernel/deploy/${kernel_version}-dtbs.tar.gz -C /media/rootfs/boot/dtbs/${kernel_version}/

6) Copy Kernel Modules

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$ sudo tar xfv ./bb-kernel/deploy/${kernel_version}-modules.tar.gz -C /media/rootfs/

7) Set File Systems Table (/etc/fstab)

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$ sudo sh -c "echo '/dev/mmcblk0p1  /  auto  errors=remount-ro  0  1' >> /media/rootfs/etc/fstab"

8) Networking

To enable the Internet for the FIRST booting, we need to do the network configuration:

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$ sudo nano /media/rootfs/etc/network/interfaces

Add the following content:

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auto lo
iface lo inet loopback
 
auto eth0
iface eth0 inet dhcp

In order to use a shared SD card with multiple BeagleBones, and always enable the Ethernet interface as eth0, we need to add a particular udev rule as:

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$ sudo nano /media/rootfs/etc/udev/rules.d/70-persistent-net.rules

Add the following content:

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# BeagleBone: net device ()
SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{dev_id}=="0x0", ATTR{type}=="1", KERNEL=="eth*", NAME="eth0"

9) Remove TF Card

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$ sync
$ sudo umount /media/rootfs

PART C: Configurations after Booting from the SD Card

Insert TF card into a Beaglebone Black, connect BBB with an Internet cable, and connect a Micro HDMI cable on demand. After the flashing of on-board LEDs, you should be able to find the IP address of BBB via your router. All our future jobs are to be done via ssh command through this IP address. My personal preference is to set a static IP address for this particularly BBB in the router settings.