MediaTek is a fabless semiconductor company that makes, among other things, smartphone SoCs with built-in LTE modems. These SoCs interest me for the following reasons:
- They're cheap.
- They're extremely popular.
- They're used in many inexpensive LTE smartphones.
- They primarily use off-the-shelf IP cores, which for the ARM cores means documentation is publicly available.
- Their Linux kernel sources are generally available, though not always buildable.
- While the BSPs for these SoCs usually support code signing/image verification/etc., most phones based on them either don't enable it or implement it incorrectly, enabling us to run our own code and build our own firmware.
- You can usually find their datasheets, TRMs, register manuals, functional specifications, and reference designs leaked online.
- Everyone else is interested in Qualcomm SoCs, so MediaTek SoCs are currently low-hanging fruit. :)
The LTE modem in these SoCs consists of two main components:
- A Cortex-R4 to handle the LTE protocol.
- A Coresonic DSP to hande the data-to-RF conversion.
The initial goals of this project are to reverse engineer the Coresonic DSP, its "SIMT" instruction set, the interface between the Cortex-R4 and the Coresonic DSP, and the interface between the Cortex-R4 and the SoC's applications processor. Doing this will empower users to build custom modems using inexpensive, off-the-shelf Android smartphones. Some examples of what would be possible:
- Over-engineered walkie-talkie.
- Smartphone DECT handset.
- Cognitive radio in TV whitespace.
- Dongle-free smartphone digital TV receiver.
- Dongle-free smartphone SDR/spectrum analyzer.
- Free Software LTE modem.
This repository will track the notes I write and the tools I build to do all of this.
The DSP firmware can be decoded. See the DSP directory for some scripts to do this and to read the notes on my findings.
My current task list is in Tasks.md.
See the General-Notes.adoc file in this directory for general information about MediaTek's LTE modems and SoCs. Information on each subsystem can be found in the "Notes.md" file in the directory for that subsystem.
The Documents.md file contains a list of research papers, presentations, patents, and other documents that are or might be relevant to this project.
Join us in the #postmarketos-lowlevel channel on
Matrix or
OFTC IRC
to discuss this and other low-level smartphone firmware projects.
Except where otherwise stated:
- All software in this repository (e.g., the serial monitor and the scripts and tools to build it, tools for unpacking and generating firmware, tools for building documentation, etc.) is made available under the GNU General Public License, version 3 or later.
- All copyrightable content that is not software (e.g., chip register and programming manuals, reverse engineering notes, this README file, etc.) is licensed under the Creative Commons Attribution-ShareAlike 4.0 International License.