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tmlind Updated images for WLAN and to developer option to download kernels
Fixed WLAN timeouts and added support for using device MAC address
from nvs_map.bin file.

Also adds an optional developer option to automatically download a
test kernel from specified location if /etc/wpa_supplicant.conf and
/etc/kernel and /etc/preinit are configured. For more information,
see droid4-kexecboot-2017.11 commit 38dfae22ed4d ("Add support for
downloading an updated test kernel over WLAN") that these images are
built with.

Signed-off-by: Tony Lindgren <>
Latest commit 2350249 May 6, 2018


Kexecboot based bootloader images for droid 4

These images can be flashed to the 4MB mmcblk1p13 "bpsw" on droid 4 eMMC for a
kexec based bootloader. We can now configure the stock bootloader to boot to
mmcblk1p13 partition using utagboot bootloader configurator. And then we can
use kexecboot for a GUI to boot a newer kernel to the selected distro. We can
now also boot to the stock Android and SafeStrap using pivot_root.


To install, use fastboot to unlock the utags and bpsw partition. Then flash
current droid4-kexecboot image and utags to boot to it:

$ fastboot flash mbm allow-mbmloader-flashing-mbm.bin
$ fastboot reboot bootloader
$ fastboot flash bpsw current/droid4-kexecboot.img
$ fastboot flash utags utags-mmcblk1p13.bin

And then you may want to lock the utags and bpsw partitions later on after
things are working again with:

$ fastboot flash mbm mbm.bin

You can get the mbm.bin from the droid 4 stock kernel firmware. And you should
have droid 4 updated to VRZ_XT894_9.8.2O-72_VZW-18-8_CFC version first.

And then you have to configure kexecboot, see CONFIGURATION below.


$ fastboot flash mbm allow-mbmloader-flashing-mbm.bin
$ fastboot reboot bootloader
$ fastboot erase utags
$ fastboot flash mbm mbm.bin


Kexecboot will try to mount all usable partitions and look for boot/boot.cfg
file on them. The stock Android distro is the only one configured by default,
and then you can add addtional boot.cfg files.

So you could have the following boot.cfg on mmcblk0p1:

LABEL=SafeStrap rom-slot1

LABEL=SafeStrap rom-slot2

LABEL=Linux on mmcblk0p1
CMDLINE=console=tty0 console=ttyS2,115200 fbcon=rotate:1 debug earlycon ro \
rootwait rootfstype=ext4 root=/dev/mmcblk0p1

Note that there is currently nothing updating the kernels extracted from
rom slots if those kernels get updated and you have to update the kernels

For booting v3.0.8 legacy kernels, also SafeStrap atags file is needed in
the same directory with devtree file above. It can be found on the device
in /system/etc/kexec/atags and should be the same for all v3.0.8 based

And please note that any partition kexecboot tries to use must be unmounted
or else kexecboot can't use it. See kexecboot documentation for more
information on boot.cfg file:


Use the buildroot git tree for most recent droid4 work branch at:

Then just do:

$ git checkout droid4-kexecboot-2017.11
$ make droid4_kexecboot_defconfig
$ make
$ sudo dd if=/dev/zero of=/tmp/boot.img bs=1M count=4
$ sudo mkfs.ext2 /tmp/boot.img
$ sudo mount -o loop /tmp/boot.img /mnt
$ sudo tar xf output/images/rootfs.tar -C /mnt
$ sudo umount /mnt

And then you should be able to flash /tmp/boot.img to mmcblk1p13 bpsw
partition on droid 4 as described in INSTALL above. The binary for
utags-mmcblk1p13.bin is generated with utagboot at:

And probably does not need to be changed unless you want some custom
kernel cmdline options for the stock kernel when booting to buildroot.


You can build a USB to serial adapter for droid 4 using the instructions at:

And then you need to configure droid4-kexecboot image to set proper user and
password or at least a root password. Or rebuild the image with Kconfig option


Current v3.0.8 based Android images depend on SafeStrap configuration being on
mmcblk1p25 vfat partition. If somebody fixes the Android images for their
initramfs to use the root partition based on kernel command line, we should be
able to also boot Android images. And then mmcblk1p25 can be formatted as ext4
and is usable for distros.

Note that the stock v3.0.8 kernel does not seem to survive kexec boot at all.
To boot to the stock v3.0.8 kernel, we start kexecboot as pid 1 so we can
pivot_root to the stock Android distro if selected in kexecboot.