yotann/fernly

Fernvale research OS

Fernly - Fernvale Reversing OS

This is a project to reverse-engineer the MTK2502, MTK6260, MTK6261, and related SoCs from Mediatek. These chips are often found in cheap Chinese-brand dumbphones and smartwatches, and are also used in the Fernvale and LinkIt development boards. This project is not affiliated with Mediatek in any way.

This project primarily consists of the Fernly OS, a trivial operating system designed for experimentation and reverse engineering of these Mediatek chips. It also includes some documentation:

• Fernly FlashROM backup
• Memory map

Important links

• Original blog post
• Forums
• Port of NuttX OS to MTK6260
• Port of Fernly OS to MTK2502
• Port of Fernly OS to MTK6261

Setting up cross compilation

Linux

git clone https://github.com/robertfoss/setup_codesourcery.git
sudo setup_codesourcery/setup.sh
/usr/local/bin/codesourcery-arm-2014.05.sh

Building Fernly

To compile, simply run "make". If you're cross-compiling, set CROSS_COMPILE to the prefix of your cross compiler. This is very similar to how to compile for Linux.

For example:

make CROSS_COMPILE=arm-none-linux-gnueabi-

Running Fernly

To run, connect the target device and run the following command:

./build/fernly-usb-loader -s /dev/fernvale ./build/usb-loader.bin ./build/firmware.bin

This will open up /dev/fernvale, load usb-loader.bin as a stage 1 bootloader, and then load (and jump to) firmware.bin as stage 2. Optionally, you can add a stage 3 file by specifying it as an additional argument.

Many 3rd-party devices enter bootloader mode only for a short window (~1s) after being connected to USB. A device almost certainly should be "off". Some devices require that battery is removed, while some - don't. To accommodate such cases, there's -w (wait) option. Run fernly-usb-loader, and only then connect a device to USB. This will allow to try various combinations mentioned above with greater comfort (you need to disconnect and poweroff device after each try, and restart fernly-usb-loader).

./build/fernly-usb-loader -w -s /dev/ttyUSB0 ./build/usb-loader.bin ./build/firmware.bin

Linux Notes

Since Fernvale is based on a Mediatek chip, ModemManager will, by default, try to treat it as a modem and make it available for network connections. This is undesirable.

To work around this problem, create a udev rule under /etc/udev/rules.d/ called 98-fernvale.rules with the following contents:

SUBSYSTEM=="tty", ATTRS{idVendor}=="0e8d",\
    ATTRS{idProduct}=="0003",\
    MODE="0660", SYMLINK+="fernvale"

ACTION=="add|change", SUBSYSTEM=="usb",\
    ENV{DEVTYPE}=="usb_device", ATTRS{idVendor}=="0e8d",\
    ATTRS{idProduct}=="0003",\
    ENV{ID_MM_DEVICE_IGNORE}="1"

OSX Notes

The default OSX CDC matching seems to miss the Fernvale board. Use fernvale-osx-codeless to get a com port.

Licensing

Fernly is licensed under the BSD 2-clause license (see LICENSE).

Previous versions of fernly linked against division libraries taken from U-Boot, which were licensed under GPL-2. These files have been removed.

Instead, we supply a version of libgcc.a. This file was extracted from a standard gcc toolchain, specifically:

https://code.google.com/p/yus-repo/downloads/detail?name=arm-none-eabi-4.6-armv5.tar.gz

It has not been modified, and its distribution here should be covered under the "runtime exception".