standardgalactic / ogma

OGMA

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.

Features

• Translating requirements defined in NASA requirements elicitation tool FRET into corresponding monitors in Copilot.

• Generating NASA Core Flight System applications that use Copilot for monitoring data received from the message bus.

• Generating message handlers for NASA Core Flight System applications to make external data in structs available to a Copilot monitor.

• Generating the glue code necessary to work with C structs in Copilot.

Table of Contents

• Installation
  • Pre-requisites
  • Compilation
• Usage
  • Language Transformations: FRET
  • cFS Application Generation
  • Struct Interface Generation
• Contributions
• Acknowledgements
• License

Installation

^{(Back to top)}

Pre-requisites

^{(Back to top)}

To install Ogma from source, users must have the tools GHC and Cabal installed. At this time, we recommend GHC 8.6 and a version of Cabal between 2.4 and 3.2 (however, these instructions have been tested with GHC 8.10 and Cabal to 3.6).

On Debian or Ubuntu Linux, both can be installed with:

$ apt-get install ghc cabal

On Mac, they can be installed with:

$ brew install ghc cabal

Compilation

^{(Back to top)}

Once 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-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.

Usage

^{(Back to top)}

The main invocation of ogma with --help lists sub-commands available:

$ ogma --help
ogma - an anything-to-Copilot application generator

Usage: ogma COMMAND
  Generate complete or partial Copilot applications from multiple languages

Available options:
  -h,--help                Show this help text

Available commands:
  structs                  Generate Copilot structs from C structs
  handlers                 Generate message handlers from C structs
  cfs                      Generate a complete cFS/Copilot application
  fret-component-spec      Generate a Copilot file from a FRET Component
                           Specification
  fret-reqs-db             Generate a Copilot file from a FRET Requirements
                           Database

Language transformations: FRET

^{(Back to top)}

Ogma can convert specifications written in other languages to Copilot monitors, such as the ones supported by NASA's requirements elicitation tool FRET. The commands fret-component-spec and fret-reqs-db allow users to interact with the different kinds of files produced by FRET.

FRET files include properties encoded using Temporal Logic, both in SMV and in CoCoSpec, the latter of which is based on Lustre. Ogma uses the SMV expressions by default, but the CLI flag --cocospec can be used to select the CoCoSpec variant of requirements instead.

For example, from the following FRET requirement:

test_component shall satisfy (input_signal <= 5)

Ogma generates the following Copilot specification:

import Copilot.Compile.C99
import Copilot.Language          hiding (prop)
import Copilot.Language.Prelude
import Copilot.Library.LTL       (next)
import Copilot.Library.MTL       hiding (since, alwaysBeen, trigger)
import Copilot.Library.PTLTL     (since, previous, alwaysBeen)
import Language.Copilot          (reify)
import Prelude                   hiding ((&&), (||), (++), not, (<=), (>=), (<), (>))

input_signal :: Stream Double
input_signal = extern "input_signal" Nothing

-- | propTestCopilot_001
--   @
--   test_component shall satisfy (input_signal <= 5)
--   @
propTestCopilot_001 :: Stream Bool
propTestCopilot_001 = ( alwaysBeen (( ( ( input_signal <= 5 ) ) )) )

-- | Complete specification. Calls the C function void  handler(); when
-- the property is violated.
spec :: Spec
spec = do
  trigger "handlerpropTestCopilot_001" (not propTestCopilot_001) []

main :: IO ()
main = reify spec >>= compile "fret"

This program can be compiled using Copilot to generate a fret.c file that includes a hard real-time C99 implementation of the monitor. The FRET specification example above is included with the Ogma distribution, and can be tested with:

$ ogma fret-component-spec --cocospec --fret-file-name examples/fret-reqs-small.json > FretCopilot.hs
$ runhaskell FretCopilot.hs

The first step executes ogma, generating a Copilot monitor in a file called FretCopilot.hs. The second step executes the Copilot compiler, generating a C implementation fret.c and C header file fret.h.

The resulting fret.c file can be tested with the main provided in examples/fret-reqs-small-main.c, which defines a handler for Copilot to call when the property monitored is violated, and a main function that steps through the execution, providing new data for the Copilot monitor:

#include <stdio.h>

double input_signal;  // Input data made available for the monitor
void step(void);      // Copilot monitor's main entry point

void handlerpropTestCopilot_001(void) {
  printf("Monitor condition violated\n");
}

int main (int argc, char** argv) {
  int i = 0;

  input_signal = 0;

  for (i=0; i<10; i++) {
    printf("Running step %d\n", i);
    input_signal += 1;
    step();
  }
  return 0;
}

To compile both files, run gcc examples/fret-reqs-small-main.c fret.c -o main. Executing the resulting main shows that the condition is violated after a number of steps:

Running step 0
Running step 1
Running step 2
Running step 3
Running step 4
Running step 5
Monitor condition violated
Running step 6
Monitor condition violated
Running step 7
Monitor condition violated
Running step 8
Monitor condition violated
Running step 9
Monitor condition violated

Take a peek inside the intermediate files FretCopilot.hs, fret.c and fret.h to see what is being generated by Ogma and by Copilot.

cFS Application Generation

Ogma includes multiple facilities to generate NASA's core Flight System (cFS) applications. The cFS applications generated by Ogma perform three simple steps to connect Copilot monitors to cFS:

• 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();
}

Struct Interface Generation

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 structure 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.

Contributions

^{(Back to top)}

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.

Acknowledgements

^{(Back to top)}

The Ogma team would like to thank Dimitra Giannakopoulou, Anastasia Mavridou, and Thomas Pressburger, from the FRET Team at NASA Ames, for the continued input during the development of Ogma.

We would also like to thank Cesar Munoz and Swee Balachandran, for their help with the cFS backend.

License

^{(Back to top)}

Copyright 2020 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.