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 if you have backups.

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

U-Boot features ability to detect transformer device model on which it is loaded. The list of supported devices include:

  • ASUS Transformer Prime TF201

  • ASUS Transformer Pad (3G/LTE) TF300T/TG/TL

  • ASUS Transformer Infinity TF700T

  • ASUS Portable AiO P1801-T

  • ASUS VivoTab RT TF600T

$ export CROSS_COMPILE=arm-none-eabi-
$ make transformer_t30_defconfig
$ 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 device individual SBK to continue.

$ 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> --split

where SBK has next form 0xXXXXXXXX 0xXXXXXXXX 0xXXXXXXXX 0xXXXXXXXX

The script will produce bct.img and ebt.img ready to flash.

NOTE! If you have TF700T it may have different sizes of boot0/boot1 partitions, re-crypt sets default boot partition size to 2MB and if you have different size add --bootsize key with yout boot partition size in bytes to the command.

Flashing U-Boot into the eMMC

DISCLAMER! All questions related to fusee-tools 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 by pre-loading just built U-Boot into RAM. Bct and bootloader will end up in boot0 and boot1 partitions of eMMC.

You have to clone and prepare fusee-tools from here: https://gitlab.com/grate-driver/fusee-tools according to fusee-tools README to continue.

Bootloader preloading is performed to device in APX/RCM mode connected to host PC. This mode can be entered by holding power and volume up buttons on turned off tablet connected to the host PC. Host PC should detect APX USB device in lsusb.

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. This is how U-Boot can be preloaded using fusee-tools:

$ ./run_bootloader.sh -s T30 -t ./bct/<dev>.bct --b u-boot-dtb-tegra.bin

Where <dev> is your devie codename (tf201, tf300t, tf700t etc.).

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.

Create repart-block.bin using re-crypt without --split key:

$ 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 tf600t --sbk <your sbk>

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.

Boot

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 bct.img and ebt.img 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.