fsfw/docs/README-localpools.md

Local Data Pools Developer Information

The following text is targeted towards mission software developers which would like to use the local data pools provided by the FSFW to store data like sensor values so they can be used by other software objects like controllers as well. If a custom class should have a local pool which can be used by other software objects as well, following steps have to be performed:

1. Create a LocalDataPoolManager member object in the custom class
2. Implement the HasLocalDataPoolIF with specifies the interface between the local pool manager and the class owning the local pool.

The local data pool manager is also able to process housekeeping service requests in form of messages, generate periodic housekeeping packet, generate notification and snapshots of changed variables and datasets and process notifications and snapshots coming from other objects. The two former tasks are related to the external interface using telemetry and telecommands (TMTC) while the later two are related to data consumers like controllers only acting on data change detected by the data creator instead of checking the data manually each cycle. Two important framework classes DeviceHandlerBase and ExtendedControllerBase already perform the two steps shown above so the steps required are altered slightly.

Storing and Accessing pool data

The pool manager is responsible for thread-safe access of the pool data, but the actual access to the pool data from the point of view of a mission software developer happens via proxy classes like pool variable classes. These classes store a copy of the pool variable with the matching datatype and copy the actual data from the local pool on a read call. Changed variables can then be written to the local pool with a commit call. The read and commit calls are thread-safe and can be called concurrently from data creators and data consumers. Generally, a user will create a dataset class which in turn groups all cohesive pool variables. These sets simply iterator over the list of variables and call the read and commit functions of each variable. The following diagram shows the high-level architecture of the local data pools.

.. image:: ../misc/logo/FSFW_Logo_V3_bw.png :alt: FSFW Logo

An example is shown for using the local data pools with a Gyroscope. For example, the following code shows an implementation to access data from a Gyroscope taken from the SOURCE CubeSat project:

class GyroPrimaryDataset: public StaticLocalDataSet<3 * sizeof(float)> {
public:
    /**
     * Constructor for data users
     * @param gyroId
     */
    GyroPrimaryDataset(object_id_t gyroId):
            StaticLocalDataSet(sid_t(gyroId, gyrodefs::GYRO_DATA_SET_ID)) {
        setAllVariablesReadOnly();
    }

    lp_var_t<float> angVelocityX = lp_var_t<float>(sid.objectId,
            gyrodefs::ANGULAR_VELOCITY_X, this);
    lp_var_t<float> angVelocityY = lp_var_t<float>(sid.objectId,
            gyrodefs::ANGULAR_VELOCITY_Y, this);
    lp_var_t<float> angVelocityZ = lp_var_t<float>(sid.objectId,
            gyrodefs::ANGULAR_VELOCITY_Z, this);
private:

    friend class GyroHandler;
    /**
     * Constructor for data creator
     * @param hkOwner
     */
    GyroPrimaryDataset(HasLocalDataPoolIF* hkOwner):
            StaticLocalDataSet(hkOwner, gyrodefs::GYRO_DATA_SET_ID) {}
};

There is a public constructor for users which sets all variables to read-only and there is a constructor for the GyroHandler data creator by marking it private and declaring the GyroHandler as a friend class. Both the atittude controller and the GyroHandler can now use the same class definition to access the pool variables with read and commit semantics in a thread-safe way. Generally, each class requiring access will have the set class as a member class. The data creator will also be generally a DeviceHandlerBase subclass and some additional steps are necessary to expose the set for housekeeping purposes.

Using the local data pools in a DeviceHandlerBase subclass

It is very common to store data generated by devices like a sensor into a pool which can then be used by other objects. Therefore, the DeviceHandlerBase already has a local pool. Using the aforementioned example, our GyroHandler will now have the set class as a member:

class GyroHandler: ... {

public:
	...
private:
	...
	GyroPrimaryDataset gyroData;
	...
};

The constructor used for the creators expects the owner class as a parameter, so we initialize the object in the GyroHandler constructor like this:

GyroHandler::GyroHandler(object_id_t objectId, object_id_t comIF,
        CookieIF *comCookie, uint8_t switchId):
        DeviceHandlerBase(objectId, comIF, comCookie), switchId(switchId),
		gyroData(this) {}

We need to assign the set to a reply ID used in the DeviceHandlerBase. The combination of the GyroHandler object ID and the reply ID will be the 64-bit structure ID sid_t and is used to globally identify the set, for example when requesting housekeeping data or generating update messages. We need to assign our custom set class in some way so that the local pool manager can access the custom data sets as well. By default, the getDataSetHandle will take care of this tasks. The default implementation for a DeviceHandlerBase subclass will use the internal command map to retrieve a handle to a dataset from a given reply ID. Therefore, we assign the set in the fillCommandAndReplyMap function:

void GyroHandler::fillCommandAndReplyMap() {
	...
	this->insertInCommandAndReplyMap(gyrodefs::GYRO_DATA, 3, &gyroData);
	...
}

Now, we need to create the actual pool entries as well, using the initializeLocalDataPool function. Here, we also immediately subscribe for periodic housekeeping packets with an interval of 4 seconds. They are still disabled in this example and can be enabled with a housekeeping service command.

ReturnValue_t GyroHandler::initializeLocalDataPool(localpool::DataPool &localDataPoolMap,
		LocalDataPoolManager &poolManager) {
	localDataPoolMap.emplace(gyrodefs::ANGULAR_VELOCITY_X,
			new PoolEntry<float>({0.0}));
	localDataPoolMap.emplace(gyrodefs::ANGULAR_VELOCITY_Y,
			new PoolEntry<float>({0.0}));
	localDataPoolMap.emplace(gyrodefs::ANGULAR_VELOCITY_Z,
			new PoolEntry<float>({0.0}));
	localDataPoolMap.emplace(gyrodefs::GENERAL_CONFIG_REG42,
			new PoolEntry<uint8_t>({0}));
	localDataPoolMap.emplace(gyrodefs::RANGE_CONFIG_REG43,
			new PoolEntry<uint8_t>({0}));

	poolManager.subscribeForPeriodicPacket(gyroData.getSid(), false, 4.0, false);
	return returnvalue::OK;
}

Now, if we receive some sensor data and converted them into the right format, we can write it into the pool like this, using a guard class to ensure the set is commited back in any case:

PoolReadGuard readHelper(&gyroData);
if(readHelper.getReadResult() == returnvalue::OK) {
	if(not gyroData.isValid()) {
		gyroData.setValidity(true, true);
	}

	gyroData.angVelocityX = angularVelocityX;
	gyroData.angVelocityY = angularVelocityY;
	gyroData.angVelocityZ = angularVelocityZ;
}

The guard class will commit the changed data on destruction automatically.

Using the local data pools in a ExtendedControllerBase subclass

Coming soon