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README.md
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README.md
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Flight Software Framework (FSFW)
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======
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I want to be written!
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The Flight Software Framework is a C++ Object Oriented Framework for unmanned,
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automated systems like Satellites.
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The initial version of the Flight Software Framework was developed during
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the Flying Laptop Project by the University of Stuttgart in cooperation
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with Airbus Defence and Space GmbH.
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## Intended Use
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The framework is designed for systems which communicate with external devices, perform control loops, receive telecommands and send telemetry, and need to maintain a high level of availability. Therefore, a mode and health system provides control over the states of the software and the controlled devices. In addition, a simple mechanism of event based fault detection, isolation and recovery is implemented as well.
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## Structure
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The general structure is driven by the usage of interfaces provided by objects. The FSFW uses C++11 as baseline. The intention behind this is that this C++ Standard should be widely available, even with older compilers.
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The FSFW uses dynamic allocation during the initialization but provides static containers during runtime.
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This simplifies the instantiation of objects and allows the usage of some standard containers.
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Dynamic Allocation after initialization is discouraged and different solutions are provided in the FSFW to achieve that.
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The fsfw uses Run-time type information.
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Exceptions are not allowed.
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### Failure Handling
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Functions should return a defined ReturnValue_t to signal to the caller that something is gone wrong.
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Returnvalues must be unique. For this the function HasReturnvaluesIF::makeReturnCode or the Macro MAKE_RETURN can be used.
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The CLASS_ID is a unique id for that type of object. See returnvalues/FwClassIds.
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### OSAL
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The FSFW provides operation system abstraction layers for Linux, FreeRTOS and RTEMS. A independent OSAL called "host" is currently not finished. This aims to be running on windows as well.
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The OSAL provides periodic tasks, message queues, clocks and Semaphores as well as Mutexes.
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### Core Components
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Clock:
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* This is a class of static functions that can be used at anytime
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* Leap Seconds must be set if any time conversions from UTC to other times is used
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ObjectManager (must be created):
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* The component which handles all references. All SystemObjects register at this component.
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* Any SystemObject needs to have a unique ObjectId. Those can be managed like objects::framework_objects.
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* A reference to an object can be get by calling the following function. T must be the specific Interface you want to call.
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A nullptr check of the returning Pointer must be done. This function is based on Run-time type information.
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``` c++
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template <typename T> T* ObjectManagerIF::get( object_id_t id )
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```
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* A typical way to create all objects on startup is a handing a static produce function to the ObjectManager on creation.
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By calling objectManager->initialize() the produce function will be called and all SystemObjects will be initialized afterwards.
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Event Manager:
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* Component which allows routing of events
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* Other objects can subscribe to specific events, ranges of events or all events of an object.
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* Subscriptions can be done during runtime but should be done during initialization
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* Amounts of allowed subscriptions must be configured by setting this parameters:
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``` c++
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namespace fsfwconfig {
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//! Configure the allocated pool sizes for the event manager.
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static constexpr size_t FSFW_EVENTMGMR_MATCHTREE_NODES = 240;
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static constexpr size_t FSFW_EVENTMGMT_EVENTIDMATCHERS = 120;
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static constexpr size_t FSFW_EVENTMGMR_RANGEMATCHERS = 120;
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}
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```
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Health Table:
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* A component which holds every health state
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* Provides a thread safe way to access all health states without the need of message exchanges
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Stores
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* The message based communication can only exchange a few bytes of information inside the message itself. Therefore, additional information can be exchanged with Stores. With this, only the store address must be exchanged in the message.
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* Internally, the FSFW uses an IPC Store to exchange data between processes. For incoming TCs a TC Store is used. For outgoing TM a TM store is used.
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* All of them should use the Thread Safe Class storagemanager/PoolManager
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Tasks
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* There are two different types of tasks
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** The PeriodicTask just executes objects that are of type ExecutableObjectIF in the order of the insertion to the Tasks.
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** FixedTimeslotTask executes a list of calls in the order of the given list. This is intended for DeviceHandlers, where polling should be in a defined order. An example can be found in defaultcfg/fsfwconfig/pollingSequence
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### Static Ids in the framework
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Some parts of the framework use a static routing address for communication.
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An example setup of ids can be found in the example config in "defaultcft/fsfwconfig/objects/Factory::setStaticFrameworkObjectIds()".
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### Events
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Events are tied to objects. EventIds can be generated by calling the Macro MAKE_EVENT. This works analog to the returnvalues.
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Every object that needs own EventIds has to get a unique SUBSYSTEM_ID.
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Every SystemObject can call triggerEvent from the parent class.
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Therefore, event messages contain the specific EventId and the objectId of the object that has triggered.
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### Internal Communication
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Components communicate mostly over Message through Queues.
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Those queues are created by calling the singleton QueueFactory::instance()->create().
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### External Communication
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The external communication with the mission control system is mostly up to the user implementation.
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The FSFW provides PUS Services which can be used to but don't need to be used.
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The services can be seen as a conversion from a TC to a message based communication and back.
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#### CCSDS Frames, CCSDS Space Packets and PUS
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If the communication is based on CCSDS Frames and Space Packets, several classes can be used to distributed the packets to the corresponding services. Those can be found in tcdistribution.
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If Space Packets are used, a timestamper must be created.
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An example can be found in the timemanager folder, this uses CCSDSTime::CDS_short.
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#### DeviceHandling
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DeviceHandlers are a core component of the FSFW.
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The idea is, to have a software counterpart of every physical device to provide a simple mode, health and commanding interface.
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By separating the underlying Communication Interface with DeviceCommunicationIF, a DH can be tested on different hardware.
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The DH has mechanisms to monitor the communication with the physical device which allow for FDIR reaction.
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A standard FDIR component for the DH will be created automatically but can be overwritten by the user.
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#### Modes, Health
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The two interfaces HasModesIF and HasHealthIF provide access for commanding and monitoring of components.
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On-board Modemangement is implement in hierarchy system.
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DeviceHandlers and Controllers are the lowest part of the hierarchy.
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The next layer are Assemblies. Those assemblies act as a component which handle redunandcies of handlers.
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Assemblies share a common core with the next level which are the Subsystems.
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Those are intended to act as auto-generated components from a database which describes the subsystem modes.
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The definitions contain transition and target tables which contain the DH, Assembly and Controller Modes to be commanded.
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Transition tables contain as many steps as needed to reach the mode from any other mode, e.g. a switch into any higher AOCS mode might first turn on the sensors, than the actuators and the controller as last component.
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The target table is used to describe the state that is check continuously by the subsystem.
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All of this allows System Modes to be generated as Subsystem object as well from the same database.
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This System contains list of subsystem modes in the transition and target tables.
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Therefore, it allows a modular system to create system modes and easy commanding of those, because only the highest components must be command.
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The health state represents if the component is able to perform its tasks.
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This can be used to signal the system to avoid using this component instead of a redundant one.
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The on-board FDIR uses the health state for isolation and recovery.
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## Example config
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A example config can be found in defaultcfg/fsfwconfig.
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## Unit Tests
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Unit Tests are provided in the unittest folder. Those use the catch2 framework but do not include catch2 itself.
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See README.md in the unittest Folder.
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