Wednesday, February 9, 2011

Firmware Loader for Gmini 402 CC too

Thanks to migge, a member of archosfans forums, I've been able to create a 402 CC version of the firmware loader.

However, I didn't release it until now because I didn't have a chance to test it. As I recently bought a Gmini 402 CC, I've been able to test it, so here it is.

Firmware loader is an utility which enables to temporarily load any firmware on Gmini 402 and 402 CC devices, from a firmware update file (.AOS). After a reboot, the device comes back to its original state.


Firmware upgrades files (AOS) for Gmini 402:

Firmware upgrades for Gmini 402 CC:

Note: these are links to archos site, so they may not work in the future.

Sunday, August 29, 2010

Gmini 402 firmware loader

The Gmini 402 firmware loader is an utility which allows to temporarily load any firmware on the device, without flashing it. This means that after a reboot, the original firmware will load as it would normally do.

This utility loads any firmware from an AOS (firmware upgrade) file provided by Archos. These files are normally used to upgrade the firmware, and usually don't allow to downgrade to an older firmware version. Thanks to a lot of reverse engineering, I have reversed the AOS1 file format, allowing the development of the firmware loader.

To use it, download the zip archive from the link given below. Then extract it to the root of your Gmini 402. It will create a file named "firmware-loader.avi", and a "firmwares" directory. Then, download and put some AOS files into this "firmwares" directory.

Launch firmware-loader.avi from your Gmini 402, it will show you the list of the AOS files present in the "firmwares" directory. Pick one, validate with the square button, and a few seconds after, the firmware you picked will be loaded. Reboot your device to get back to the original firmware.

This utility is compatible (for now) only with the Gmini 402 (not CC), with firmware 1.3.11 (like any MediOS app).

Download it here:

Download AOS upgrades here (these links link directly to, so they may not work in the future, but will still be available through

Note: I can make a Gmini 402cc version of the firmware loader, I just need someone with a Gmini 402cc to run a program on it and give me the output. Let me know if you want it.

Note 2: While reversing Archos firmware, I found that Archos implementation of RSA is very slow (mainly because they don't use any "mod" optimization). In half a day, I implemented from scratch an RSA implementation which uses Barrett reduction, which is about 1,000 times faster.

Note 3: I'll publish the details of the AOS1 file format soon.

Thursday, June 10, 2010

AOS1 file format reverse engineered

I've successfully reverse engineered the AOS1 file format. This means I can load any firmware on the Gmini 402 (or any device which uses the format) from an update file (*.AOS).

In a few days, I'll release an utility allowing to load any firmware from an AOS update file, without flashing the device. This means it'll be possible to temporarily use firmware 1.5.12 on a Gmini 402 1.3.11, and after a reboot, come back automatically to 1.3.11. This is useful for using USB Host mode with some cameras (like Canon ones) which were not detected by 1.3.11, and still use the 1.3.11 exploit to load mediOS and apps. Here is a piece of changelog of firmware 1.5.10:

USB Host: Cameras with proprietary protocols are detected and users are advised to switch it to a PTP or MSC protocol (notably Canon cameras)

Of course, temporarily loading a firmware was already possible, but releasing an utility to do so wasn't, because it implied releasing copyrighted code from Archos. The utility I'll release uses the AOS files provided by Archos, so there's no copyright problem anymore.

Along with releasing the utility, I'll detail the AOS1 file format.

The bootloader I aim to release will include this utility, to allow to boot on any firmware and mediOS and apps.

Monday, May 17, 2010

Placing breakpoints in the original firmware

When booting, the firmware erases IRAM and RAM.
However, it's easy to patch the code which erases IRAM. Then, by analyzing the firmware a little further, I noticed a safe location in IRAM to place my own code.

By digging a bit more in the firmware, I found the function that will show a messagebox, and a few other functions related to the UI (displaying bottom buttons, ...).

Using medios, I can reload the original firmware, patch it with a breakpoint (currently a very simple 8 bytes branch) and execute my code. Then, inside my code, I can show a message box with any value I want, including register values, memory, ... The only problem is that the device will crash after showing the message box because the breakpoint corrupts the stack. But it still enables to see some very interesting things.

Saturday, May 15, 2010

Gmini 402 bootloader

I'm starting to work on an Archos Gmini 402 bootloader (link to the FAQ page - the product page seems to have been removed... It is still present on the store though).

It's a pretty old device (released in 2005), but I find the challenge interesting. It has already been jailbroken, but the current exploit uses a malformed AVI file to execute arbitrary code. My goal is to replace the firmware with a bootloader, in order to allow to choose between MediOS and the original Archos firmware.

So I dumped the ROM, descrambled the firmware (the descrambling code can be found in MediOS). Let's get to work now.