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.
Over time, BeaglePlay images will include SystemReady support to provide for the most generic boot support allowing execution of
Distro Boot¶
For some background on distro boot, see the u-boot documentation on distro boot.
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 the kernel image we made in BeaglePlay Kernel Development. To do this, we need to have an uncompressed version of the kernel in the FAT32 file system and a ramdisk image we plan to use. The ramdisk image is utilized 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 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 Copy kernel to FAT32 filesystem, we perform a copy of the kernel that was installed via Install 6.6.0 kernel and reboot and then reverted with …
Todo
Put the step into play-kernel-development.rst to revert back to the Beagle kernel.
The contents of the initrd can be read using lsinitramfs /boot/firmware/initrd.img-6.6.0.
debian@BeaglePlay:~$ sudo cp /boot/vmlinuz-6.6.0 /boot/firmware/Image-6.6.gz
[sudo] password for debian:
debian@BeaglePlay:~$ sudo gunzip /boot/firmware/Image-6.6.gz
debian@BeaglePlay:~$ sudo cp /boot/initrd.img-6.6.0 /boot/firmware/
1menu title Select image to boot
2timeout 30
3default Linux 6.6
4
5label Linux default
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 Linux 6.6
13 kernel /Image-6.6
14 append root=/dev/mmcblk0p2 ro rootfstype=ext4 rootwait net.ifnames=0 quiet
15 fdtdir /
16 initrd /initrd.img-6.6.0
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:~$ ssh -Y debian@192.168.0.117
Debian GNU/Linux 11
BeagleBoard.org Debian Bullseye Xfce Image 2023-05-18
Support: https://bbb.io/debian
default username:password is [debian:temppwd]
debian@192.168.0.117's password:
The programs included with the Debian GNU/Linux system are free software;
the exact distribution terms for each program are described in the
individual files in /usr/share/doc/\*/copyright.
Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent
permitted by applicable law.
Last login: Tue Dec 12 15:33:21 2023 from 192.168.0.171
debian@BeaglePlay:~$ uname -a
Linux BeaglePlay 6.6.0 #4 SMP Tue Dec 5 13:50:59 UTC 2023 aarch64 GNU/Linux
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