Audit Log

An Audit Log object stores a record of auditable actions, such as writes, creates and deletes, along with who did them and what they affected. It joins the notice from the actor with the notice from the target into one record. Clients retrieve the records for review and compliance.

Typical uses

• A trail of who changed a setpoint
• A record of object creation and deletion
• A history of configuration writes for an audit
• A central log that other devices send notices to

Key properties

Property	What it holds
Enable	Starts and stops the recording of new records.
Buffer_Size	How many records the log can hold before the oldest are overwritten.
Log_Buffer	The stored records. Clients read them with ReadRange or the audit log query service.
Total_Record_Count	How many records have ever been added. Each record’s sequence number comes from it.
Record_Count	How many records the log holds right now.

How it behaves

The log is a ring buffer: when it is full, new records replace the oldest. With intrinsic reporting, the standard applies no event algorithm to an Audit Log, and unlike the other log types it does not use BUFFER_READY.

With the CAS BACnet Stack

Enable it with the STACK_OPTION_OBJECT_TYPE_AUDIT_LOG build option. Add each object with BACnetStack_AddObject; the stack does not serve its property values on its own, so supply them through your property callbacks.

Related object types

Audit Reporter, Event Log, Trend Log

Properties

The properties ASHRAE 135-2024 clause 12.64 defines for this object type.

How to read the table:

• Conformance is what the standard asks of every object of this type: R is required, W is required and writable by a client, O is optional. A digit after the letter marks a condition in the standard that decides when the property is present or writable, such as support for intrinsic reporting.
• Present by default: yes means the stack presents the property as soon as you add the object; no means it is optional and you turn it on with BACnetStack_SetPropertyEnabled. This is the stack’s starting setup, so it can differ from the conformance code.
• Writable is whether a client can write the property by default. Change it with BACnetStack_SetPropertyWritable.
• not in profile means the stack does not offer this property for this object type.
• Value when your callback does not answer: “Held by the stack” means the stack stores and serves the value itself and does not ask your callbacks. Otherwise it is the value the stack answers when your callback declines or is not registered.

Property	Datatype	Conformance	Present by default	Writable	Value when your callback does not answer
Object_Identifier	BACnetObjectIdentifier	R	yes	no	Held by the stack.
Object_Name	CharacterString	R	yes	no	"Object <type>,<instance>", such as "Object 0,1" for Analog Input 1.
Object_Type	BACnetObjectType	R	yes	no	Held by the stack.
Description	CharacterString	O	no	no	""
Status_Flags	BACnetStatusFlags	R	yes	no	Built by the stack from your callbacks.
Event_State	BACnetEventState	R	yes	no	0
Reliability	BACnetReliability	O	no	no	0
Enable	Boolean	W	yes	yes	false
Buffer_Size	Unsigned32	R	yes	no	0
Log_Buffer	BACnetLIST of BACnetAuditLogRecord	R	yes	no	No default: the read fails.
Record_Count	Unsigned64	R	yes	no	0
Total_Record_Count	Unsigned64	R	yes	no	0
Member_Of	BACnetDeviceObjectReference	O1	no	no	No default: the read fails.
Delete_On_Forward	Boolean	O1,2	no	no	false
Issue_Confirmed_Notifications	Boolean	O1	no	no	false
Event_Detection_Enable	Boolean	O3,4	no	no	false
Notification_Class	Unsigned	O3,4	no	no	0
Event_Enable	BACnetEventTransitionBits	O3,4	no	no	An empty bit string.
Acked_Transitions	BACnetEventTransitionBits	O3,4	no	no	An empty bit string.
Notify_Type	BACnetNotifyType	O3,4	no	no	0
Event_Time_Stamps	BACnetARRAY[3] of BACnetTimeStamp	O3,4	no	no	No default: the read fails.
Event_Message_Texts	BACnetARRAY[3] of CharacterString	O4,5	no	no	""
Event_Message_Texts_Config	BACnetARRAY[3] of CharacterString	O4	no	no	""
Reliability_Evaluation_Inhibit	Boolean	O6	no	no	false
Audit_Level	BACnetAuditLevel	O7	no	no	0
Auditable_Operations	BACnetAuditOperationFlags	O7	no	no	An empty bit string.
Property_List	BACnetARRAY[N] of BACnetPropertyIdentifier	R	yes	no	Held by the stack.
Tags	BACnetARRAY[N] of BACnetNameValue	O	no	no	No default: the read fails.
Profile_Location	CharacterString	O	no	no	""
Profile_Name	CharacterString	O	no	no	""