Understanding Boot#
There are several phases to BeaglePlay boot. The simplest place to take control of the system is using Distro Boot. It is simplest because it is very generic, not at all specific to BeaglePlay or AM62, and was included in the earliest BeagleBoard.org Debian images shipping pre-installed in the on-board flash.
Distro Boot#
For some background on distro boot, see the u-boot documentation on distro boot. There is also BeaglePlay specific u-boot documentation.
In Typical /boot/firmware/extlinux/extlinux.conf file, you can see line 1 provides a label and subsequent indented lines provide parameters for that boot option.
1label Linux eMMC
2 kernel /Image
3 append root=/dev/mmcblk0p2 ro rootfstype=ext4 rootwait net.ifnames=0 quiet
4 fdtdir /
5 #fdtoverlays /overlays/<file>.dtbo
6 initrd /initrd.img
It is important to note that this file is not on the root file system of BeaglePlay. It
is sitting on a separate FAT32 partition that is mounted at /boot/firmware. You can
see the mounted file systems and their formats in List of mounted file systems.
The FAT32 partition in this setup is often referred to as the boot file system.
debian@BeaglePlay:~$ df
Filesystem 1K-blocks Used Available Use% Mounted on
udev 903276 0 903276 0% /dev
tmpfs 197324 1524 195800 1% /run
/dev/mmcblk0p2 14833640 12144024 1914296 87% /
tmpfs 986608 0 986608 0% /dev/shm
tmpfs 5120 4 5116 1% /run/lock
/dev/mmcblk0p1 130798 53214 77584 41% /boot/firmware
tmpfs 197320 32 197288 1% /run/user/1000
debian@BeaglePlay:~$ lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
mmcblk0 179:0 0 14.6G 0 disk
├─mmcblk0p1 179:1 0 128M 0 part /boot/firmware
└─mmcblk0p2 179:2 0 14.5G 0 part /
mmcblk0boot0 179:256 0 4M 1 disk
mmcblk0boot1 179:512 0 4M 1 disk
debian@BeaglePlay:~$ sudo sfdisk -l /dev/mmcblk0
Disk /dev/mmcblk0: 14.6 GiB, 15678308352 bytes, 30621696 sectors
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: 0xba67172a
Device Boot Start End Sectors Size Id Type
/dev/mmcblk0p1 * 2048 264191 262144 128M c W95 FAT32 (LBA)
/dev/mmcblk0p2 264192 30621695 30357504 14.5G 83 Linux
To better understand BeaglePlay’s U-Boot Distro Boot, let’s install a Linux kernel and initramfs from the Buildroot project. There is a pre-built image release at https://git.beagleboard.org/beagleboard/buildroot/-/releases/2023.11-beagle1.
Currently, the Linux kernel image needs to be uncompressed and stored in the FAT32 file system. An initramfs image is a simple way to provide a starting root file system. When running Linux, some kind of root file system is required.
An initramfs image is utilized on Debian systems to make sure any kernel modules needed are available and to provide a bit of a recovery opportunity in case the root file system is corrupted. You can learn more about initramfs and initrd on the Debian Initrd Wiki page <https://wiki.debian.org/Initrd> and the Linux kernel documentation admin guide initrd entry <https://docs.kernel.org/admin-guide/initrd.html>.
In the case of utilizing Buildroot, the entire Linux distribution is incorporated into the initramfs root file system image.
The contents of the initrd can be read using lsinitramfs /boot/firmware/initrd.img.
debian@BeaglePlay:~$ wget https://git.beagleboard.org/beagleboard/buildroot/-/jobs/19194/artifacts/raw/public/beagleplay/images/Image
--2023-12-19 22:17:54-- https://git.beagleboard.org/beagleboard/buildroot/-/jobs/19194/artifacts/raw/public/beagleplay/images/Image
Resolving git.beagleboard.org (git.beagleboard.org)... 44.226.162.25
Connecting to git.beagleboard.org (git.beagleboard.org)|44.226.162.25|:443... connected.
HTTP request sent, awaiting response... 200 OK
Length: 32172544 (31M) [application/octet-stream]
Saving to: ‘Image’
Image 100%[===================>] 30.68M 1.78MB/s in 18s
2023-12-19 22:18:13 (1.74 MB/s) - ‘Image’ saved [32172544/32172544]
debian@BeaglePlay:~$ sudo cp Image /boot/firmware/Image-buildroot
[sudo] password for debian:
debian@BeaglePlay:~$ wget https://git.beagleboard.org/beagleboard/buildroot/-/jobs/19194/artifacts/raw/public/beagleplay/images/rootfs.cpio.gz
--2023-12-19 22:16:44-- https://git.beagleboard.org/beagleboard/buildroot/-/jobs/19194/artifacts/raw/public/beagleplay/images/rootfs.cpio.gz
Resolving git.beagleboard.org (git.beagleboard.org)... 44.226.162.25
Connecting to git.beagleboard.org (git.beagleboard.org)|44.226.162.25|:443... connected.
HTTP request sent, awaiting response... 200 OK
Length: 30111086 (29M) [application/octet-stream]
Saving to: ‘rootfs.cpio.gz’
rootfs.cpio.gz 100%[===================>] 28.72M 21.5MB/s in 1.3s
2023-12-19 22:16:46 (21.5 MB/s) - ‘rootfs.cpio.gz’ saved [30111086/30111086]
debian@BeaglePlay:~$ sudo cp rootfs.cpio.gz /boot/firmware/rootfs.cpio.gz-buildroot
1menu title Select image to boot
2timeout 10
3default Buildroot
4
5label Debian
6 kernel /Image
7 append root=/dev/mmcblk0p2 ro rootfstype=ext4 rootwait net.ifnames=0 quiet
8 fdtdir /
9 #fdtoverlays /overlays/<file>.dtbo
10 initrd /initrd.img
11
12label Buildroot
13 kernel /Image-buildroot
14 append rootwait net.ifnames=0 quiet
15 fdtdir /
16 initrd /rootfs.cpio.gz-buildroot
debian@BeaglePlay:~$ sudo shutdown -r now
Connection to 192.168.0.117 closed by remote host.
Connection to 192.168.0.117 closed.
jkridner@slotcar:~$ sudo nmap -n -p 22 192.168.0.0/24
Starting Nmap 7.94SVN ( https://nmap.org ) at 2023-12-19 17:32 EST
...
PORT STATE SERVICE
22/tcp open ssh
MAC Address: 50:3E:AA:AD:78:06 (TP-Link Technologies)
Nmap scan report for 192.168.0.112
Host is up (0.00020s latency).
...
jkridner@slotcar:~$ ssh root@192.168.0.112
The authenticity of host '192.168.0.112 (192.168.0.112)' can't be established.
ED25519 key fingerprint is SHA256:EZdvLkCNMyhy4RhvseUSC5EwaJR5Kgpk8JZG9kF+pmk.
This key is not known by any other names.
Are you sure you want to continue connecting (yes/no/[fingerprint])? yes
Warning: Permanently added '192.168.0.112' (ED25519) to the list of known hosts.
root@192.168.0.112's password:
# uname -a
Linux BeaglePlay 6.6.3 #1 SMP Tue Dec 19 21:32:06 UTC 2023 aarch64 GNU/Linux
# cat /etc/os-release
NAME=Buildroot
VERSION=2023.11-beagle1
ID=buildroot
VERSION_ID=2023.11
PRETTY_NAME="Buildroot 2023.11"
Booting U-Boot#
#!/bin/bash
if ! id | grep -q root; then
echo "must be run as root"
exit
fi
wdir="/opt/u-boot/bb-u-boot-beagleplay"
if [ -b /dev/mmcblk0 ] ; then
#mmc extcsd read /dev/mmcblk0
mmc bootpart enable 1 2 /dev/mmcblk0
mmc bootbus set single_backward x1 x8 /dev/mmcblk0
mmc hwreset enable /dev/mmcblk0
echo "Clearing eMMC boot0"
echo '0' >> /sys/class/block/mmcblk0boot0/force_ro
echo "dd if=/dev/zero of=/dev/mmcblk0boot0 count=32 bs=128k"
dd if=/dev/zero of=/dev/mmcblk0boot0 count=32 bs=128k
echo "dd if=${wdir}/tiboot3.bin of=/dev/mmcblk0boot0 bs=128k"
dd if=${wdir}/tiboot3.bin of=/dev/mmcblk0boot0 bs=128k
fi
