Ogma is a tool to facilitate the integration of safe runtime monitors into other systems. Ogma extends Copilot, a high-level runtime verification framework that generates hard real-time C99 code.
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Generating NASA Core Flight System runtime monitoring applications that monitor data received from the message bus.
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Generating Robot Operating System runtime monitoring applications.
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Generating F' (FPrime) runtime monitoring components.
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Generating message handlers for NASA Core Flight System applications to make external data in structs available to a Copilot monitor.
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Generating the glue code necessary to work with C structs in Copilot.
Integration of monitors into larger applications (e.g., simulators).
To install Ogma from source, users must have the tools GHC and cabal-install. At this time, we recommend GHC 8.6 and a version of cabal-install between 2.4 and 3.2. (Ogma has been tested with GHC versions up to 9.2 and cabal-install versions up to 3.6, although the installation steps may vary slightly depending on the version of cabal-install being used.)
On Debian or Ubuntu Linux, both can be installed with:
$ apt-get install ghc cabal-installOn Mac, they can be installed with:
$ brew install ghc cabal-installOnce GHC and cabal are installed, the simplest way to install Ogma is with:
$ git clone https://github.com/nasa/ogma.git
$ cd ogma
$ export PATH="$HOME/.cabal/bin/:$PATH"
$ cabal v1-update
$ cabal v1-install alex happy
$ cabal v1-install BNFC copilot
$ cabal v1-install ogma-*/After that, the ogma executable will be placed in the directory
$HOME/.cabal/bin/, where $HOME represents your user's home directory.
The main invocation of ogma with --help lists sub-commands available. More
details are provided in the following sections.
NASA Core Flight System (cFS) is a flight software architecture to implement complex systems by combining multiple reusable applications that communicate to one another via a software bus. cFS has been used, among others, on spacecraft, cubesats, and drones.
Ogma includes multiple facilities to generate cFS applications. The cFS applications generated by Ogma perform three steps to connect Copilot monitors to the application:
- Subscribe to a message in the cFS communication bus.
- When a message of the desired kind arrives, copy the data to make it available to Copilot and call the monitor's main entry point.
- Declare handlers that are executed when the property being monitored is violated.
When using this facility, Ogma produces a Copilot file that the user is expected to modify to implement the property to monitor. To avoid having to modify the generated C files that implement the cFS app itself, Ogma gives the ability to state what information one is interested in monitoring. If the kind of information is known to Ogma, it will automatically subscribe to the necessary messages and make it available to Copilot. Ogma provides additional flags to customize the list of known variables, so that projects can maintain their own variable databases beyond what Ogma includes by default.
cFS applications are generated using the Ogma command cfs, which receives
three main arguments:
--app-target-dir DIR: location where the cFS application files must be stored.--variable-file FILENAME: a file containing a list of variables that must be made available to the monitor.--variable-db FILENAME: a file containing a database of known variables, and the message they are included with.
The following execution generates an initial cFS application for runtime monitoring using Copilot:
$ ogma cfs --variable-db examples/cfs-variable-db --variable-file examples/cfs-variables
The application generated by Ogma contains the following files:
copilot-cfs-demo/CMakeLists.txt
copilot-cfs-demo/fsw/for_build/Makefile
copilot-cfs-demo/fsw/mission_inc/copilot_cfs_perfids.h
copilot-cfs-demo/fsw/platform_inc/copilot_cfs_msgids.h
copilot-cfs-demo/fsw/src/copilot_cfs.c
copilot-cfs-demo/fsw/src/Properties.hs
copilot-cfs-demo/fsw/src/copilot_cfs_msg.h
copilot-cfs-demo/fsw/src/copilot_cfs_events.h
copilot-cfs-demo/fsw/src/copilot_cfs_version.h
copilot-cfs-demo/fsw/src/copilot_cfs.h
Users are expected to modify Properties.hs to adjust the property being
monitored. Although it is possible to adjust the file copilot_cfs.c to
include property violation handlers, we recommend adding them in a separate C
file and modifying the compilation scripts to include that additional file.
That way, invoking Ogma again will not overwrite the changes made to the cFS
application.
In this particular example, the C code generated contains the following
instruction to subscribe to an ICAROUS_POSITION_MID message to obtain
the vehicle position:
CFE_SB_Subscribe(ICAROUS_POSITION_MID, COPILOT_CommandPipe);The message dispatcher included in the application detects a message of this kind and calls a dedicated subroutine:
void COPILOT_ProcessCommandPacket(void)
{
CFE_SB_MsgId_t MsgId;
MsgId = CFE_SB_GetMsgId(COPILOTMsgPtr);
switch (MsgId)
{
case ICAROUS_POSITION_MID:
COPILOT_ProcessIcarousPosition();
break;
...Finally, the dedicated subroutine makes data available to the monitor
and calls the main Copilot entry point step:
void COPILOT_ProcessIcarousPosition(void)
{
position_t* msg;
msg = (position_t*) COPILOTMsgPtr;
position = *msg;
step();
}The Robot Operating System (ROS) is a framework to build robot applications.
Ogma is able to generate ROS monitoring applications that subscribe to obtain the data needed by the monitors and report any violations. At present, support for ROS app generation is considered preliminary.
ROS applications are generated using the Ogma command ros, which receives
four main arguments:
--app-target-dir DIR: location where the ROS application files must be stored.--variable-file FILENAME: a file containing a list of variables that must be made available to the monitor.--variable-db FILENAME: a file containing a database of known variables, and the topic they are included with.--handlers FILENAME: a file containing a list of handlers used in the specification.
The following execution generates an initial ROS application for runtime monitoring using Copilot:
$ ogma ros --handlers filename --variable-file variables --variable-db ros-variable-db --app-target-dir ros_demoThe application generated by Ogma contains the following files:
ros_demo/CMakeLists.txt
ros_demo/src/copilot_monitor.cpp
ros_demo/src/copilot_logger.cpp
ros_demo/src/.keep
ros_demo/package.xml
The user must place the code generated by Copilot monitors in two files,
ros_demo/src/monitor.h and ros_demo/src/monitor.c. No Copilot or C code for
the monitors is generated by default.
The code generated by default assumes that handlers receive no arguments. The user must modify the handlers accordingly if that is not the case.
Although the variable DB file is not mandatory, it is in practice required to monitor any requirement that uses any input data: no topic subscriptions will be generated for any variables for which a DB entry cannot be found. At present, Ogma will proceed without warnings if a variable is mentioned in a requirement or variables file but a matching entry is not found in the variable DB.
F' (FPrime) is a component-based framework for spaceflight applications.
Ogma is able to generate F' monitoring components that subscribe to obtain the data needed by the monitors and report any violations. At present, support for F' component generation is considered preliminary.
F' components are generated using the Ogma command fprime, which receives
five main arguments:
--app-target-dir DIR: location where the F' application files must be stored.--variable-file FILENAME: a file containing a list of variables that must be made available to the monitor.--variable-db FILENAME: a file containing a database of known variables, and their types.--handlers FILENAME: a file containing a list of handlers used in the specification.
The following execution generates an initial F' component for runtime monitoring using Copilot:
$ ogma fprime --handlers filename --variable-file filename --variable-db fprime-variable-db --app-target-dir fprime_demoThe component generated by Ogma contains the following files:
fprime_demo/CMakeLists.txt
fprime_demo/Copilot.fpp
fprime_demo/Copilot.cpp
fprime_demo/Copilot.hpp
fprime_demo/Dockerfile
fprime_demo/inline-copilot
The format of the variables, variable DB, and handlers file are as follows.
The variables file can contain a list of variables used in a specification, one
per line. For example, if we are working with a specification that uses three
boolean variables called autopilot, sensorLimitsExceeded, and pullup, we
can provide them to Ogma's fprime command in a file like the following:
$ cat variables
autopilot
sensorLimitsExceeded
pullupThe variables database file contains a list of known variables and their types. It does not matter if there are variables that are not used for one particular specification, or property/requirement/monitor. The only thing that matters is that the variables used, and their types, be listed in the file. Continuing with the same example, we could have:
$ cat fprime-variable-db
("temperature", "uint8_t")
("autopilot", "bool")
("sensorLimitsExceeded", "bool")
("pullup", "bool")
("current_consumption", "float")In our example, we only care about the boolean variables; it is sufficient that they be listed in the variable DB file.
Finally, the handlers file is a list of monitor handlers that the generated FPrime component should restrict to monitoring. They are listed one per line:
$ cat handlers
handlerpropREQ_001The user must place the code generated by Copilot monitors in three files,
fprime_demo/src/copilot.h, fprime_demo/src/copilot_types.h and
fprime_demo/src/copilot.c. No Copilot or C code for the monitors is generated
by default by the fprime command.
The code generated by default assumes that handlers receive no arguments. The user must modify the handlers accordingly if that is not the case.
A lot of the information that must be monitored in real-world C applications is packed in structs. Copilot allows accessing specific fields of C structs, but requires additional definitions in the Copilot language to make the shape of those structs known to the compiler.
Ogma is able to generate the boilerplate code needed to work with C structs in Copilot. For example, to use the following struct as the type of an extern stream in Copilot, the user is expected to define several Copilot (Haskell) types and type class instances:
typedef struct {
double x;
double y;
} point;Ogma can generate that code automatically with the structs subcommand:
$ ogma structs --header-file-name examples/point.h
data Point = Point
{ pX :: Field "x" Double
, pY :: Field "y" Double
}
instance Struct Point where
typename _ = "point"
toValues v = [ Value Double (pX v), Value Double (pY v) ]
instance Typed Point where
typeOf = Struct (Point (Field 0) (Field 0))
By including these definitions in a Copilot file, users can now access the
individual x and y fields of a Point in a stream.
The best way to contribute to Ogma is to report any issues you find via the issue tracker, and to use Ogma to build applications or in your own research and let us know about your results.
We kindly ask users not to send PRs to this project. Instead, please document the bugs you find or other suggestions as issues and we will make the necessary changes.
Ogma has been created by Ivan Perez and Alwyn Goodloe.
The Ogma team would like to thank Swee Balachandran, Dimitra Giannakopoulou, Anastasia Mavridou, Cesar Munoz and Thomas Pressburger, for the input during the development of Ogma.
X-Plane images obtained via the X-Plane 10 (Pro) flight simulator. Re-shared with permission.
Copyright 2020-2021 United States Government as represented by the Administrator of the National Aeronautics and Space Administration. All Rights Reserved.
See the file LICENSE.pdf for details.