Question

I'm looking at the Analog_Output_Present_Value_Write function in src/bacnet/basic/object/ao.c and noticed a potential discrepancy between the documentation and implementation. I wanted to clarify the intended behavior.

Observation

Header documentation (ao.h:22-28)

/**
 * @brief Callback for gateway write present value request
 * @param  object_instance - object-instance number of the object
 * @param  old_value - floating point analog value prior to write
 * @param  value - floating point analog value of the write
 */
typedef void (*analog_output_write_present_value_callback)(
    uint32_t object_instance, float old_value, float value);

The documentation says value should be "floating point analog value of the write".

Implementation (ao.c:474-486)

old_value = Analog_Output_Present_Value(object_instance);
Analog_Output_Present_Value_Set(object_instance, value, priority);
// ...
} else if (Analog_Output_Write_Present_Value_Callback) {
    new_value = Analog_Output_Present_Value(object_instance);
    Analog_Output_Write_Present_Value_Callback(
        object_instance, old_value, new_value);
}

The implementation passes new_value (the resulting present value after priority resolution) rather than value (the value that was actually written).

Example scenario

• Priority 1 has value 100.0 (active)
• User writes 50.0 to Priority 8 (value = 50.0)
• old_value = 100.0 (from priority 1)
• new_value = 100.0 (priority 1 still active)
• Callback receives (100.0, 100.0) — the written value 50.0 is not passed

Question

Which behavior is intended?

1. Pass value — the value that was actually written (matches current documentation)
2. Pass new_value — the resulting present value after priority resolution (current implementation)

Both have valid use cases, so I wanted to confirm which one is the intended design before suggesting any changes.

Thank you!