Object Dictionary 1 Device Diagnostic Introduction The Device Diagnostic object supports various diagnostic functions of the device and monitors the device for an overload condition. This object allows a user to view diagnostic statistics of a device such as an N30 Supervisory Controller. May 1, 2002 Johnson Controls, Inc. www.johnsoncontrols.com Code No. LIT-694380 Software Release 5.1
2 Device Diagnostic Key Concepts Device Overload An overload condition indicates the device is not performing at a satisfactory level. hen an overload condition is detected, the device or the network of devices to which this device is connected may need to be re-engineered to reduce the load on this device. This may include reducing the number of objects contained by the device or adjusting attributes of objects within the device, or other devices, to reduce the burden on the device. It is possible that a device may be overloaded, but the Device Diagnostic object does not detect the condition. Alternatively, the Device Diagnostic object may report an overload condition on a device that is functioning at an acceptable level. The Device Diagnostic object only uses the following criteria for detecting an overload condition: If the lowest available size of the acquired memory pool (Acquired Pool Size attribute of the N30 Device object) drops to 35,000 bytes or less, the device begins to discard all incoming and outgoing communication messages and internally generated alarm messages until the available size of this pool increases. This check is made 15 minutes after a device startup or restart and every 30 minutes thereafter. The acquired memory pool is used for short-term use including communication messages. In this mode, the device may go offline or other devices may be reported offline, control may be lost, and alarm messages may be lost. An over-used network causes this overload condition most often.
Object Dictionary 3 If the average Central Processing Unit (CPU) idle time on the device is less than the Overload Threshold attribute of the device object, the default value is 50%, and the average CPU idle time is calculated every 8 seconds using a running average as follows: Average idle = Average idle + (Current Idle Average Idle) * 1% Using this formula, a device that runs at 0% idle time continuously is flagged as overloaded 9 minutes after restart or startup. A device that runs at 50% idle time is flagged as overloaded in about 90 minutes. The formula design allows high CPU usage for short periods of time. A low CPU idle time suggests the device is slow to respond to changing conditions. Note: Changing the Period attribute of this object from the default 8 seconds alters the timing of the overload calculation. An overload condition reports to the user through an alarm message on a device with the text CPU overload or Memory overload, an error log entry, and by the Device Overload attribute of this object. The device generates, at most, one message of each type after a startup or restart. There is no message to indicate a return to normal loading.
4 Device Diagnostic Attributes Specific Attributes Table 1: Attribute Properties Attribute Name Metasys Common Attributes Data Type Table 1 lists attributes specific to the Device Diagnostic object. The Device Diagnostic object also has the attributes of the Metasys Common object. Refer to Table 1 in the Metasys Common Object chapter (LIT-694020) for details. N30 Flags* N30 Default Value Options/Range See Table 1 in the Metasys Common Object chapter (LIT-694020). Average Idle Float Percent BACnet Object Type BACnet OID Allocated BACnet OID Used Enumerated BACnet Superclass of Object Type Comtest Dest String Maximum 32 characters Comtest orst Comtest Ave Device Overload Enable Diagnostic Error Log Last Idle Sample Last Method Message Receives Method to Stop Track Method To Track Object To Stop Track Float 0 Float Enumeration Normal Normal Memory Overload CPU Overload Boolean False Octet String Float Continued on next page... * - ritable Percent Milliseconds
Object Dictionary 5 Attribute Name (Cont.) Object To Track Other Message Count Peak Method Period Record Count Sign Pri Db Size Sign Pri Peak Sign Pri Used Surrogate Cache Cnt Surrogate Cache Max Task Exec Message Count r Db Size r Peak r Used Total Record Count * - ritable Data Type List of N30 Flags* N30 Default Value Options/Range 0 Milliseconds 8 Seconds List of Structures each containing: Task ID Runtime in milliseconds BACoid
6 Device Diagnostic Attribute Definitions Table 2: Attribute Definitions Attribute Name Metasys Common Attributes Average Idle BACnet Object Type BACnet OID Allocated BACnet OID Used Comtest Dest Comtest orst Comtest Ave Device Overload Enable Diagnostic Error Log Last Idle Sample Last Method Message Receives Method to Stop Track Method To Track Object To Stop Track Object To Track Table 2 lists the definitions of the attributes specific to Device Diagnostic object. Definition See Table 2 in the Metasys Common Object chapter (LIT-694020). Displays the average percent of the time the device is running in the idle task. Contains the generic BACnet base (super) class for the object. Displays the number of entries available in the BACnet Object Identifier (BACoid) table. This table maps external BACoid numbers to internal object identifiers. Every object available that communicates via BACnet requires a unique BACoid. Displays the number of entries currently in use in the BACoid table. Indicates the destination object for the communications test. Indicates the longest time for a message to complete during a communications test. Indicates the average time for a message to complete during a communications test. Indicates if a device overload condition has been detected since the last device startup or restart. hen this attribute is not Normal, refer to the device error log for additional information. The value can be reset to Normal only by a device restart or startup. The value reflects the last detected condition since the last restart or startup. Activates the method timing feature built into the Object Method (code execution). hen enabled, six other attributes provide a way to measure the duration of any method of any object or the start of the method of one object until the completion of the method of another object. The six attributes are Peak Method, Last Method, Method to Track, Object to Track, Method to Stop Track, Object to Stop Track. It should normally be disabled. Represents the error log as an octet string. Used for advanced troubleshooting. Displays the last sample of the processor idle time calculated. Displays the last measured time for the method sequence being timed. Indicates the total number of messages received as part of the communications test. Specifies the method number which, along with the Object to Stop Track, completes a timing sequence. To time a particular method of an object, this would normally be set to the same value as the Method to Track. Indicates the method number which, along with the Object to Track, defines when a new timing sequence starts. Timing begins any time this method of the specified object starts. Indicates the internal Object Identifier of the object whose method, when complete, completes a timing sequence. Upon completion, the Last Method is updated as well as the Peak Method if this is a new Peak Method. Indicates the internal Object Identifier of the object whose method the timing should start on. Other Message Count Displays the number of messages excluding periodic timer messages received by the object engine. This includes both offbox as well as onbox messages; Offbox meaning messages are not on (or off of) the local device, such as an N30 Supervisory Controller, and onbox meaning messages are on the local device. Continued on next page...
Object Dictionary 7 Attribute Name (Cont.) Peak Method Period Record Count Sign Pri Db Size Sign Pri Peak Sign Pri Used Surrogate Cache Cnt Surrogate Cache Max Task Exec Message Count r Db Size r Peak r Used Total Record Count Definition Resets to zero when any of the attributes of this feature are modified. It returns in milliseconds the worst case time measured for the method sequence being timed. This attribute supports triggering (automatically updating when a value changes). Defines in seconds how often this object will run and update the Average Idle and Last Idle Sample attributes as well as the Device Overload attribute. Displays the total number of entries currently used in the object database. Displays the total number of entries available in the signup/priority database for reading attribute signups and prioritized writes to attributes. Displays the largest number of entries ever used in the signup/priority. Displays the total number of entries currently used in the signup/priority database. Displays the current number of entries used in the surrogate cache. This is a cache of offbox references no longer used by the device, but kept in memory to optimize a future reference. Displays the maximum number of entries allowed in the surrogate cache. Contains task runtime information. Used for advanced troubleshooting. Displays the number of timer messages received by the object engine. Displays the total number of entries available in the timer database. This database is used to queue incoming messages to objects either from offbox or onbox. Displays the largest number of entries ever used in the timer database. Displays the total number of entries currently used in the timer database. Returns the number of entries currently available in the object database. This database will hold each object in the device as well as each string and list information. Controls Group 507 E. Michigan Street P.O. Box 423 Milwaukee, I 53201 www.johnsoncontrols.com Printed in U.S.A.