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ValueWrapper Template Class

ValueWrapper

Section titled “ValueWrapper”

Path: src/modbus/ValueWrapper.h

Revision History: Initial documentation

A template class that wraps values of any type with threshold-based update notifications through Modbus. This class monitors changes in a value and sends notifications to the owner component when changes exceed specified thresholds, using different comparison modes. It helps reduce network traffic by only sending updates when significant changes occur.

REQUIREMENTS

Section titled “REQUIREMENTS”
  • An owning Component instance that receives notifications
  • A Modbus address space for notifications
  • Function code configuration for the Modbus messages

PROVIDES

Section titled “PROVIDES”

  • ValueWrapper<T> - Template class for wrapping values of any type

  • ThresholdMode enumeration:

    • DIFFERENCE - Triggers when absolute difference between old and new values exceeds threshold
    • INTERVAL_STEP - Triggers when values cross step boundaries defined by the threshold

  • Macros:

    • DEFAULT_VW_POST_NOTIFY_LAMBDA - Helper for creating standard post-notification logging lambdas
    • INIT_COMPONENT_VALUE_WRAPPER - Simplifies ValueWrapper initialization

FEATURES

Section titled “FEATURES”
  • Wraps any data type, including enums, with transparent type conversion
  • Provides automatic threshold-based notifications through Modbus
  • Supports different threshold modes for different types of data
  • Handles both arithmetic types and enumerations correctly
  • Provides callbacks when notifications are sent
  • Automatic typecasting for Modbus message values

DEPENDENCIES

Section titled “DEPENDENCIES”

ValueWrapper

Component

ModbusTypes

enums

Logger

BEHAVIOUR

Section titled “BEHAVIOUR”

The ValueWrapper monitors changes to a value and sends notifications when thresholds are exceeded.

Constructor

update(newValue)

Below threshold

Above threshold

Update value without notification

Send Modbus update

Execute post-notification callback

Value updated

Ready for next update

Initialized

Comparing

ThresholdNotMet

ThresholdExceeded

ValueUpdated

NotifyOwner

CallbackExecution

TODOS

Section titled “TODOS”

PERFORMANCE

Section titled “PERFORMANCE”
  • Consider providing specialized implementations for common types to avoid template instantiation overhead
  • Investigate using std::variant for better type safety and potentially reduced memory footprint
  • Add an optional hysteresis parameter to prevent rapid oscillations around threshold values

SECURITY

Section titled “SECURITY”
  • Add bounds checking for Modbus addresses to prevent accidental overwrites
  • Consider adding validation callbacks to ensure values remain within acceptable ranges

COMPLIANCE

Section titled “COMPLIANCE”
  • Ensure all Modbus messages conform to the Modbus specification requirements
  • Consider adding support for additional Modbus function codes as needed

RECOMMENDATIONS

Section titled “RECOMMENDATIONS”
  • Use the INIT_COMPONENT_VALUE_WRAPPER macro to simplify instance creation
  • Choose appropriate threshold values to balance responsiveness and network traffic
  • For enum types, use threshold value of 1 to notify on any state change
  • For float values, consider the INTERVAL_STEP mode to create logical boundaries for notifications