White Rabbit Calibration
Relative calibration
-
White Rabbit devices
calibration
- provides coarse calibration values for the official releases of WR Switch and WR PTP Core firmware. You can use them as defaults for matching hardware and gateware version. However, to achieve the best possible synchronization results you should perform the full calibration procedure for your WR hardware.
- WR Calibration Procedure
Absolute calibration
Overview
Absolute calibration enforces standardization since it enables
independent developers and/or vendors to exchange their WR gear while
achieving absolute sub ns timing. Absolute calibrated devices can be
used as "golden standards" for the relative calibration
procedure.
Absolute calibration is achieved by measuring the time relationship (Δ
TXcal, Δ RXcal) between the external electrical
phase planes of the PPS signal and the interface to the
Electrical-Optical / Optical-Electrical converter (EO/OE, usually the
electrical SFP connector) as shown in Figure
1.
Figure 1: White Rabbit link delay model for absolute calibration*
EO/OE converters have their own calibration parameters that define the
relationship between their electrical and optical phase planes.
For some WR applications the electrical system can be broken into
different parts (for example a DIO
FMC to be plugged
onto a SPEC board). When the
electrical phase plane of the PPS signal is defined on such an
exchangeable module and future exchange is foreseen then separate
calibration of each of these parts is necessary. The calibration
parameters for EO/OE converters and exchangeable modules are stored in
EPROM such that the system can automatically reach absolute calibration
during link initialization.
Last but not least, there is an asymmetry (WR alpha factor) between
forward and backward propagation delay over the fiber due to chromatic
dispersion. This can be measured and monitored in-situ.
To conclude:
Calibration of WR devices is spans three main calibration topics, each described on the following wiki pages:
- Absolute calibration
- Electrical-Optical / Optical Electrical
- In-situ determination of alpha
Contacts
Peter Jansweijer, Henk Peek, Tjeerd Pinkert, Guido Visser
Status
Date | Event |
24-02-16 | Start of project |
22-07-16 | added description of White Rabbit Absolute Calibration Procedure |
17-07-17 | divided calibration into three topics each described in sub-wiki pages |
Last updated: 17 Jul 2017