Frequently Asked Questions
about the White Rabbit switch.
Connecting the switch to an external GPS receiver
Q: What are the advantages of using external GPS signals or are there any disadvantages of not using them and leave the connectors open?
A: You mainly get two things:
- A more stable oscillator for the master switch and therefore for all the network.
- A GPS/UTC/TAI-related time scale. This is important if you want to relate your events to official time or if you want to avoid re-starting your time scale at 1 Jan 1970 (or something like that) every time you reboot the switch. Two events seen in a WR network at very different times could have very similar time stamps in there was a switch reboot in between. Syncing to GPS time on reboot avoids that.
Q: When connecting the GPS-PPS or the 10 MHz GPS clock to the WhiteRabbit Switch, do I have to change/configure anything?
A: Yes, it is documented in the Note on using WR Switch in Grandmaster mode.
Q: The last paragraph of the Note on using WR Switch in Grandmaster mode mentions HAL messages and RT log. I find HAL messages but what is meant by RT log and where to find it?
A: By the RT (i.e. realtime) log mentioned in the Note on using WR Switch in Grandmaster mode we mean the messages generated by the LM32 CPU inside the Virtex FPGA. They may provide useful information for debugging the timing subsystem. They can be viewed by connecting a serial terminal to the the front left USB port (up to v. 3.2 switches) or the "FPGA test" USB port in the rear (newer switches). RS232 parameters are 115200, 8N1.
General questions
Q: Should green and orange LEDs be lit when copper SFP is used even without Ethernet cable plugged in ?
A: Yes, that is the normal behavior with most of the copper SFPs. Even after unplugging Ethernet cable the copper SFP fakes an active connection so green LED is ON and orange may be blinking.
Q: There are two fans. Is it correct that both of them push the air out of the box on backside?
A: Yes, it is correct that both fans push the air out of the box on backside. The idea is that the cold air is just sucked in at the SFP cages at the front. Tests have been made that shows that this is the best way of cooling that is also compatible to racks that have a front-to-back airflow. In the White Rabbit Switch Hardware project one can find the WRS - Stress Tests report.
Q: Does the switch comply to CE regulations (EMC)?
A: It is. The company Seven Solutions has performed extensive EMC tests on the switch.
Inter-operability
Q: Is the WR Switch inter-operable with standard PTP (IEEE1588-2008) gear ?
A: Yes, it is and it has been tested for inter-operability on ISCPS PlugFest, but
- currently, WR devices (Switch/nodes) do not support standard-PTP slave mode. This means that a standard PTP device can "slave" to WR device (being master) but a WR device cannot slave to standard PTP device (WR device cannot be standard PTP-slave)
- it is important to remember that WR devices use a very specific PTP
configuration (2-step, delay request-response mechanism, multicast,
Layer 2) which is not the most popular configuration and it is not
the default setting for standard-PTP devices (which use IP instead
of Layer 2). So it is not just plug&play, it's more like
1. buy PTP switch which supports fully the standard
2. configure it properly (change from IP to Layer 2)
3. plug & play
4 April 2013