Information

Building an old revision of Rockchip's U-Boot, I was able to obtain a binary very similar to the stock one.

Modifications

• Logs are printed on the LCD
• Removed read limit on LOADER mode
• Fastboot mode can be entered by pressing volume down
• Offline charging is now done in U-Boot instead of Android, this is useful because GSIs don't support offline charging.
  • U-Boot charging also has the advantage of showing battery percentage and information about the charging current & voltage.
• New fastboot commands:
  • oem rockusb: Reboots into LOADER (rockusb) mode

Known issues

• The LCD may not turn on as some tablets may come with different LCDs. If that's the case, let me know

Hotkeys

• With the tablet OFF:
  • With USB disconnected:
    • Enter Recovery: Power + Volume Up
    • Enter Fastboot: Power + Volume Down
  • With USB connected:
    • Enter LOADER mode: Volume Up
    • Enter Fastboot: Volume Down

Build process

• Download Linaro 6.3.1 toolchain
• make rk3368_defconfig
• make CROSS_COMPILE=<toolchain-path>/bin/aarch64-linux-gnu- -j$(nproc --all)
• Unpack stock uboot.img with imgRePackerRK
• Replace uboot.bin with the one you just built
• Repack uboot.img with imgRePackerRK
• Flash on your device