ENACOM Tablet Research

Caution

This document is not a guide of any kind. It's just a collection of personal notes I made while researching this tablet.
I'm NOT RESPONSIBLE for any damage that may be caused to your device.

Hardware Info

As far as I know, there are two rk3368 tablets distributed by ENACOM:

• TBT8A10 (also known as i-Buddie TG08RK1)
• M1045W

Both are built by Incartech and are pretty much the same, except for some differences (LCD, camera...). This research is mainly focused on my tablet (TBT8A10) but most of the information should be applicable to the other one too.

Hardware and blobs/drivers information can be found on the TBT8A10 branch and M1045W branch of the vendor repo.

Special Modes

• MASKROM/BootROM Mode: Can flash the firmware and partitions.
• Uboot: One of the bootloaders. Handles pretty much the whole boot process.
  • LOADER/Rockusb Mode: Can flash and dump partitions, and reboot into MASKROM.
  • fastboot: Useful to disable Android Verified Boot (AVB) and flash boot/recovery/uboot partitions. Can't flash super. The only way to access this mode is with adb reboot-bootloader or through the Reboot to bootloader option in recovery.
• Recovery:
  • fastbootd: Useful to check whether AVB is unlocked and flash boot/recovery/super (system, vendor, odm, product) partitions

Tools

Rockchip Tools

Use the following versions unless specified otherwise. Newer or older ones may not work properly.

• DriverAssitant_v4.5: Drivers required to interact with the device while on LOADER/MASKROM mode.
• AndroidTool_Release_v2.71 (aka RKDevTool): Can flash firmware (LOADER/MASKROM mode), flash partitions (LOADER mode) and dump firmware (LOADER mode).
  • WARNING: Before flashing partitions, load the partition table of this device (right click -> Load Config) or create it yourself with the output of Dev Partition.
• FactoryTool_v1.45_bnd: Can flash firmware. I've never needed to use it.
• SD_Firmware_Tool._v1.46: Can flash firmware to an SD Card.

Other Tools

• imgRePackerRK: Unpack/repack Rockchip firmware and partition images.
• rkDumper: Dump firmware through LOADER mode
• adbDumper: Dump firmware through ADB (root required)

Key combinations

• With the tablet OFF:
  • Enter Loader Mode: Hold volume Up/Down and connect USB cable
  • Enter Recovery: Hold Volume Up/Down + Power
• With the tablet ON:
  • Reboot: Hold either Volume down + Power or just the power button
    • An alternative is to use a toothpick to press the button under the power button.
  • Shutdown: Hold Volume up + Power

Boot Sequence

Wiki Page|Wiki Page

1. BootROM (Hard-coded, can't be modified)
   • Searches bootable firmware on the eMMC and maybe on the SD Card too.
   • If none is found, enters MASKROM mode.
     • According to Rockchip, we can force enter it by "shorting the eMMC clock to GND" (basically, prevent eMMC from being read so no firmware can be found and loaded)
     • Some devices include two testpoints next to the eMMC that can be used to do this. I disassembled mine and it doesn't seem to have them.
2. miniloader/idbloader (MiniLoaderAll.bin in firmware)
   • "Usbplug" Mode (rk3368_usbplug_v2.6 inside MiniLoaderAll.bin)
     • Helper of MASKROM mode. This mode is entered when flashing firmware or partitions in MASKROM.
   • Finds and loads Uboot. It's likely it may first search for it on the SD Card
3. Uboot
   • If the respective key combination is pressed, enters Uboot's LOADER mode or Android's recovery.
   • Finds a bootable boot image in the following order:
     • SD Card
     • eMMC
     • USB Device (untested)
   • Loads resources from boot image (DTB, logo...)
   • Initializes some hardware like the display
   • Displays ENACOM logo
   • Boots the image
4. Linux Kernel (boot or recovery)

Unbrick

1. Open AndroidTool and load the partition table of our device
2. If your device can't enter LOADER or MASKROM mode you have two options:
   • Force MASKROM Mode by shorting the eMMC (no idea on how to do this)
   • Try to enter MASKROM/LOADER by booting from an SD Card.
     • If your uboot is broken for some reason, this can perfectly unbrick your device
     1. Connect SD Card to the computer & flash stock firmware to it using Rockchip's SD_Firmware_Tool
     2. Insert card into Tablet
     3. Try to reboot into LOADER mode. Device should enter it or enter MASKROM.
3. Once in MASKROM or LOADER, either:
   • Flash the corrupted partition(s)
     • If you are on MASKROM mode, you'll also need to flash the miniloader into the first partition (Loader) so the device can boot into Usbplug Mode.
   • Reflash stock firmware (Upgrade firmware tab)

Firmware

Official TBT8A10 firmware is available on Google Drive (September 13, 2021 build).

For information on how to search for OTA updates and download them, go to this repo.

Dump firmware

Out of the box, only the first 32 MB of the eMMC can be read through LOADER Mode. Additionally, LOADER mode can't access anything before uboot, so we can't dump the miniloader.
Thus, only the following partitions can be dumped:

• uboot (start=16384 count=8192)
• trust (start=24576 count=8192)
• misc (start=32768 count=8192)
• dtb (start=40960 count=8192)
• dtbo (start=49152 count=8192)
• vbmeta (start=57344 count=2048)

However, we can easily patch uboot to allow us to dump up to 4 GB of the eMMC:

1. Grab uboot.img from firmware or dump uboot from device (recommended)
2. Unpack uboot.img with imgRePackerRK
3. Open uboot.bin with an hex editor and search for 81 00 01 8B 24 00 02 8B 9F 40 40 F1 49 01 00 54
4. Replace 40 40 with 00 60 and save it
5. Repack uboot.img & flash it

To dump, use AndroidTool_Release_v2.38 as newer versions don't allow to dump after 32 MB. Now we can also dump these partitions:

• boot (start=59392 count=65536)
• security (start=124928 count=8192)
• recovery (start=133120 count=196608)
• backup (start=329728 count=229376)
• cache (start=559104 count=786432)
• metadata (start=1345536 count=32768)
• frp (start=1378304 count=1024)
• super (start=1379328 count=6373376)

Unlock bootloader

I'm 90% sure the bootloader comes unlocked out of the box, but we can't flash boot and partitions inside super unless we disable AVB.

1. Enable OEM Unlock in Android developer settings (probably not required, but do it just in case)
2. Reboot into uboot's fastboot (adb reboot-bootloader)
3. fastboot oem at-unlock-vboot (this will unlock verified boot, allowing to flash any recovery/boot/super (system, vendor, odm, product)
4. fastboot flashing unlock (Probably irrelevant) (unlocks flashing boot/recovery and maybe other partitions through uboot's fastboot)
5. fastboot flashing unlock_critical (Probably irrelevant) (not sure what it unlocks or if it does anything)
6. Now recovery's fastbootd should report device's unlocked when executing fastboot getvar unlocked

To re-enable AVB, fastboot oem at-lock-vboot may do the trick (untested).

---

Customizing the tablet

I asked Incar for the kernel and U-Boot's source code, but sadly they can't share it.

Building U-Boot

Information available on the U-Boot repo.

Building Android Kernel

As of now, I wasn't able to boot a kernel built by me; it freezes at an early stage. This may not be feasible due to all the changes Incar has made to Rockchip's kernel.

DTB & Enacom Logo

The boot image contains a DTB just like most Android devices. However, that one is not used.
Additionally, it contains a "second" file (unpack with AIK and it will be inside the split_img folder) which can be unpacked/repacked with imgRePackerRK. Inside it is the real DTB and the ENACOM splash screen bitmap.

I've extracted the DTS from both devices and cleaned it using my Python script to make it more readable. They are available on the resources folder.

Building TWRP

Information available on the device tree repo (twrp-11 branch).

Building AOSP

This should be possible using Rockchip's device trees. However, the tablet supports Project Treble and GSIs work fine.

Flashing a GSI

The kernel is built for arm64, but the vendor uses 32-bit binaries. Thus, only arm32_binder64 variants of GSIs will work. I recommend to try TrebleDroid or phhusson's GSIs first.

Known issues on TrebleDroid/PHH or GSIs based on them:

• Android 12 or higher doesn't boot due to issues with the GPU Driver and SkiaGL
  • This can be easily fixed by updating the GPU driver blobs, particularly two of them (the other ones are already up to date).
  • You can find them here. Their version is UM S 5.59 and were grabbed from this repo.
• Headphone jack doesn't work properly on old PHH GSIs. This is fixed on TrebleDroid 13.
• Bluetooth doesn't work on TrebleDroid 14.
• Boot animation doesn't work. This is fixed on TrebleDroid 14.
• WiFi may not work on the first boot. If that's the case, try rebooting a few times and turning it on and off.
• HDMI may not work (never tested it)
• Performance is terrible. The UI is very laggy and unresponsive. The stock ROM also suffers from this but it's less noticeable there.
  • It's suggested to disable animations in Developer Settings (set all animation scales to zero). Decreasing the DPI also seems to help