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Parameter Management Functionality

References

Overview

Parameter management provides persistent storage and retrieval of configuration values used by components throughout the system. Parameters are named values defined in FPP models that can be loaded from a file at startup, queried by components during initialization, and updated by ground command during operation. The Parameter Database (PrmDb) is the central storage service.

Parameter Storage

The Parameter Database stores parameter values in serialized form in an internal table, indexed by parameter ID. At startup, it loads a set of parameter values from a file on the file system. This file contains the serialized state of all saved parameters from the last save operation.

Parameter Retrieval

During initialization, components request their parameter values from the Parameter Database. The request specifies a parameter ID, and the response includes the serialized value along with a validity status:

  • Valid — The parameter was found in the database and returned successfully.
  • Invalid — The parameter was not found or could not be retrieved.
  • Default — The parameter was not in the database, so the component uses its FPP-defined default value.
  • Uninitialized — The component has not yet called its parameter load function.

Parameter Updates

Parameters can be updated during operation via ground command. The command specifies the component, parameter name, and new value. When a parameter is updated:

  1. The new value is sent to the Parameter Database for storage.
  2. The component is notified of the update and can act on the new value immediately.

A separate save command writes all current parameter values back to the file system, persisting them for the next startup.

Off Nominal

  • If the parameter file is missing or corrupt at startup, the Parameter Database starts with an empty table and components fall back to their default values.
  • If a parameter value cannot be deserialized (e.g., type mismatch), the retrieval returns an invalid status.