U-Boot for the ASUS Transformer device family

DISCLAMER! Moving your ASUS Transformer to use U-Boot assumes replacement of the vendor ASUS bootloader. Vendor Android firmwares will no longer be able to run on the device. This replacement IS reversible.

Quick Start

  • Build U-Boot

  • Process U-Boot

  • Flashing U-Boot into the eMMC

  • Flashing U-Boot into the SPI flash

  • Boot

  • Self Upgrading

Build U-Boot

Device support is implemented by applying a config fragment to a generic board defconfig. Valid fragments are tf201.config, tf300t.config, tf300tg.config, tf300tl.config, tf700t.config, tf600t.config and p1801-t.config.

$ export CROSS_COMPILE=arm-linux-gnueabi-
$ make transformer_t30_defconfig tf201.config # For TF201
$ make

After the build succeeds, you will obtain the final u-boot-dtb-tegra.bin image, ready for further processing.

Process U-Boot

DISCLAMER! All questions related to the re-crypt work should be asked in re-crypt repo issues. NOT HERE!

re-crypt is a tool that processes the u-boot-dtb-tegra.bin binary into form usable by device. This process is required only on the first installation or to recover the device in case of a failed update. You need to know your tablet’s individual SBK to continue.

Permanent installation can be performed either by using the nv3p protocol or by pre-loading just built U-Boot into RAM.

Processing for the NV3P protocol

$ git clone https://gitlab.com/grate-driver/re-crypt.git
$ cd re-crypt # place your u-boot-dtb-tegra.bin here
$ ./re-crypt.py --dev tf201 --sbk <your sbk>


The script will produce a repart-block.bin ready to flash.

Processing for pre-loaded U-Boot

The procedure is the same, but the --split argument is used with the re-crypt.py. The script will produce bct.img and ebt.img ready to flash.

Flashing U-Boot into the eMMC

DISCLAMER! All questions related to NvFlash should be asked in the proper place. NOT HERE! Flashing U-Boot will erase all eMMC, so make a backup before!

Permanent installation can be performed either by using the nv3p protocol or by pre-loading just built U-Boot into RAM.

Flashing with the NV3P protocol

Nv3p is a custom Nvidia protocol used to recover bricked devices. Devices can enter it either by using wheelie with the correct blob.bin file or by pre-loading vendor bootloader with the Fusée Gelée.

With nv3p, repart-block.bin is used. It contains BCT and a bootloader in encrypted state in form, which can just be written RAW at the start of eMMC.

$ wheelie --blob blob.bin
$ nvflash --resume --rawdevicewrite 0 1024 repart-block.bin

When flashing is done, reboot the device.

Flashing with a pre-loaded U-Boot

U-Boot pre-loaded into RAM acts the same as when it was booted “cold”. Currently U-Boot supports bootmenu entry fastboot, which allows to write a processed copy of U-Boot permanently into eMMC.

While pre-loading U-Boot, hold the volume down button which will trigger the bootmenu. There, select fastboot using the volume and power buttons. After, on host PC, do:

$ fastboot flash 0.1 bct.img
$ fastboot flash 0.2 ebt.img
$ fastboot reboot

Device will reboot.

Flashing U-Boot into the SPI Flash

Some of Transformers use a separate 4 MB SPI flash, which contains all data required for boot. It is flashed from within U-Boot itself, preloaded into RAM using Fusée Gelée.

After creating your repart-block.bin you have to place it on a 1st partition of microSD card formated in fat. Then insert this microSD card into your tablet and boot it using Fusée Gelée and U-Boot, which was included into repart-block.bin, while booting you must hold the volume down button.

The process should take less than a minute, if everything goes correctly, on microSD will appear spi-flash-backup.bin file, which is the dump of your SPI Flash content and can be used to restore UEFI, do not lose it, tablet will power itself off.

Self-updating of U-Boot is performed by placing u-boot-dtb-tegra.bin on 1st partition of microSD, inserting it into the tablet and booting with a pressed volume down button.


To boot Linux, U-Boot will look for an extlinux.conf on MicroSD and then on eMMC. Additionally, if the Volume Down button is pressed while booting, the device will enter bootmenu. Bootmenu contains entries to mount MicroSD and eMMC as mass storage, fastboot, reboot, reboot RCM, poweroff, enter U-Boot console and update bootloader (check the next chapter).

Flashing repart-block.bin eliminates vendor restrictions on eMMC and allows the user to use/partition it in any way the user desires.

Self Upgrading

Place your u-boot-dtb-tegra.bin on the first partition of the MicroSD card and insert it into the tablet. Enter bootmenu, choose update the bootloader option with the Power button and U-Boot should update itself. Once the process is completed, U-Boot will ask to press any button to reboot.