Copilot is a realtime programming language and Runtime Verification framework. It allows users to write concise programs in a simple but powerful way using a stream-based approach.

Programs can be interpreted for testing, or translated C99 code to be incorporated in a project, or as a standalone application. The C99 backend ensures us that the output is constant in memory and time, making it suitable for systems with hard realtime requirements.

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-- Raw temperature from sensor, range -50.0C to 100.0C.
temp :: Stream Word8
temp = extern "temperature" Nothing

-- Transform the temperature to Celsius.
ctemp :: Stream Float
ctemp = (unsafeCast temp) * (150.0 / 255.0) - 50.0

-- Bind two triggers with a 3.0C hysteresis.
spec = do
  trigger "heaton"  (ctemp < 18.0) [arg ctemp]
  trigger "heatoff" (ctemp > 21.0) [arg ctemp]


Release 3.5 – 2021-09-07

We are pleased to announce the release of Copilot 3.5, a stream-based DSL for writing and monitoring embedded C programs, with an emphasis on correctness and hard realtime requirements. Copilot is typically used as a high-level runtime verification framework, and supports temporal logic (LTL, PTLTL and MTL), clocks and voting algorithms.

Among others, Copilot has been used at the Safety Critical Avionics Systems Branch of NASA Langley Research Center for monitoring test flights of drones.

This new release introduces a simple but important feature to make Copilot code more modular: the name of Copilot's main entry point in the generated C code, known as the step function, can now be customized. This will allow specifications to be defined in different modules, compiled separately, and linked as part of the same C executable. It will also facilitate interoperation with other systems that consider 'step' a reserved a global name. Additionally, this release introduces other fixes in the code and in the documentation, and deprecates definitions that have been superseded.

Current emphasis is on facilitating the use with other systems, and improving the codebase in terms of stability and test coverage. Users are encouraged to participate by opening issues and asking questions via our github repo.


Copilot is distributed under the BSD-3-Clause licence, which can be found here.


We are grateful for NASA Contract NNL08AD13T to Galois, Inc. and the National Institute of Aerospace, which partially supported this work.

Additionally NASA Langley contracts 80LARC17C0004 and NNL09AA00A supported further development of Copilot.

We would like to thank Kaveh Darafsheh (NASA Langley Research Center) for his help with testing Copilot. In addition numerous people have helped with smaller things, reporting bugs etc. Thanks to all of them!