So you’ve seen the available binary firmware and you’re not satisfied. You’re bored with OBD-II, your car’s automaker doesn’t support OpenXC yet, or want some data that’s not made available - you really need to know the engine oil pressure, and it’s not in any proprietary firmware. Maybe you work for a car company or an aftermarket supplier and you want to support some completely custom application, or you want to write some messages back to the bus.
You’re in luck - OpenXC can support all of these use cases. The core of the vehicle data translation resides in the firmware that runs on the vehicle interface. Besides knowing how to connect to the CAN bus and how to send data out over USB and Bluetooth, the firmware is also programmed with vehicle-specific knowledge that allows it to pick out the right messages from the car and translate the data into something you can use in your application.
The core of the firmware is open source - not the vehicle-specific parts, but the framework that makes it easy to do the translation once you understand the vehicle. When an automaker releases a binary firmware for an OpenXC VI, they’re probably taking the open source firmware, mixing in their proprietary vehicle knowledge, and send you the resulting compiled binary.
The OpenXC VI firmware is also increasingly capable of reading and writing raw CAN bus traffic, making it a low cost and extremely flexible version of some of the more expensive industry tools - and one that works on platforms besides Windows, too!
The firmware is written in C (with some minor C++ features like namespaces), but for most common reading and writing use cases, you don’t need to write any new code. The CAN signals to translate are configured with JSON files - simple, human readable files you can edit in any text editor.
Make sure you’ve gone through the VI Concepts page, to understand all of the various topics relating to OpenXC such as the communication architecture, the vehicle CAN bus, and vehicle diagnostics. The auto industry tends to be fairly jargon-laden, so even if you’re an expert it’s good to make sure we have the same understanding of the definitions.
Once you’ve read that (or if you’re feeling confident…) jump into the Advanced VI Firmware Docs for in-depth documentation to develop, compile and update your own OpenXC firmware to translate a new piece of data from the car.