1. Precision Time Protocol IEEE1588
Klaus Mählert
Product Management Group Manager
Konstanz – April 17, 2012

2. Precision Time Protocol IEEE1588
with AVT GigE cameras
Presentation by courtesy of Allied Vision Technologies

3. What is Precision Time Protocol?
• An IEEE1588 networking standard
• Used to manage clock synchronization of
multiple devices across an Ethernet network
• Cameras can utilize the same time base and
relevance for the timestamp
• Adopted by machine vision with GigE Vision
2.0

4. Competing clock synchronization schemes
• Network time protocol (NTP)
• Offers poor accuracy ~ 10 ms
• Low cost, most common clock synchronization scheme in networking
• Global Positioning System (GPS)
• Provides excellent precision ~ ns
• An expensive component to incorporate into every
device
• Precision Time Protocol (PTP)
• Provides excellent precision ~ µs
• Low cost - can be incorporated into cameras using a
firmware change and without additional hardware

5. TimeStampValue represents camera clock
• The heart beat of the camera
• Drives signal timing including exposure start time
• Attached to every frame and used by the driver to
calculate frame rate

6. Enabling PTP Synchronization
• PtpMode = Off
• TimeStampValue is not synchronized with any other device.
• PtpMode = Master
• All Slave devices synchronize their clock to this camera's
TimeStampValue.
• PtpMode = Slave
• TimeStampValue is altered to align with a Master
TimeStampValue.
• PtpMode = Auto
• Uses the IEEE1588 best master clock algorithm to determine
which device is master.

7. Monitoring PTP Synchronization
• PtpStatus = Off (Read only)
• The device PtpMode is set to off.
• PtpStatus = Master (Read only)
• The device is configured and working as Master PTP device.
• PtpStatus = Error (Read only)
• The slave device is in the process of synchronizing with the master.
• PtpStatus = Slave (Read only)
• The device is acting as a slave and synchronized to within several
microseconds of the master.

8. How is PTP synchronization realized?
• Master PTP clock transmits a “Sync” telegram using
multicast messaging.
• Slave PTP clock cameras receive multicast and calculate
time difference between its own clock and the Master PTP
clock.
• Clock synchronization, using follow up and delay messages
is used to align the Slave PTP device clocks to the Master
PTP clock.

9. How is PTP synchronization realized?
• Once a Slave clock is within 2 µs of
the master, its PtpStatus is changed
from Error to Slave.
• If the timestamps are 2 seconds or
more apart, the Slave camera
overwrites its own timestamp with
the Master camera timestamp.

10. Implementing a scheduled software trigger
The PtpTriggerTime attribute is used to define
a future TimeStampValue for start of exposure.
1. Achieve clock synchronization. Set PtpMode =
Master, Slave or Auto.
2. Set camera FrameRate, FrameStartTriggerMode,
and AcquisitionMode as desired. Start an
acquisition stream using AcquisitionStart.
3. Determine the current camera TimeStampValue
using TimeStampValueLatch.
4. Set PtpTriggerTime to a value which sufficiently
exceeds the current camera TimeStampValue.
Allow several seconds for the camera to receive
PtpTriggerTime

11. PtpTriggerTime Notes
• Setting PtpTriggerTime will suspend all frame triggers in a camera’s current
AcquisitionStart stream while PtpTriggerTime >= TimeStampValue
• When TimeStampValue increases to reach PtpTriggerTime, frame triggers
resume
• To implement a scheduled (future) software trigger set
PtpTriggerTime = TimeStampValue + 
 = Time required to upload PtpTriggerTime to the camera
The PtpTriggerTime event does not start a new acquisition stream, it
simply resumes frame triggers on an existing stream.

12. Suggested PTP Camera Networks
• A switch is required for implementing a PTP network
• Cannot currently implement PTP synchronization
across multiple adapters
• LAG between host and switch has been tested and
shown poor results
• 10 GigE Uplink ports are being tested and have shown
good initial results

13. Comparing TimeStampValues between camera
events and frames
• Camera EventControls allow the host to receive a
TimeStampValue for a selected event, e.g.
EventSyncIn1Rise. Likewise all frames returned from
camera have a TimeStampValue associated with
them.
• Comparison of these TimeStampValues can give
valuable information, and with PTP synchronization,
allow for a common time base between cameras and
event sensors.

14. Thank you for your attention.
STEMMER IMAGING GmbH
Gutenbergstr. 9-13
82178 Puchheim
Germany
Phone: +49 89 80902-236
Fax: +49 89 80902-116
k.maehlert@stemmer-imaging.de
www.stemmer-imaging.de
Your contact: Klaus Mählert