cRIO andsbRIO PTP TimeSync

[TizianoTuccella]

Hello,

I'm tring to synchonize a sbRIO 9606 and a cRIO9076 using PTP time sync without success.

From MAX I have installed the following add-ons on the two real-time targets:

- NI 1588-2008 Network Management 14.0.0

- NI-TimeSync 14.0.0

-NI-TimeSync Plug-In for software based 1588 14.0.0

From the tab "Time Settings" the "Software 1588 time protocol (Ptp)" is enabled, but I can't get any kind of syncronization.

Can you explain to me the procedure you followed to synch your hardwares?

Thankyou very much!

[JKSH]

Hi TizianoTuccella,

I've never used an sbRIO before, but here's what I did to keep 2 cRIOs in sync.

1. Install "NI-TimeSync" and "NI-TimeSync Plug-In for software based 1588" on both targets
2. Make sure both targets are on the same subnet
3. Enable "Software 1588 time protocol (Ptp)" on both targets
4. Save the settings and reboot both targets at the same time

If you want more help, please describe what you mean by "I can't get any kind of syncronization" -- what do your clocks show?

[TizianoTuccella]

Hi JKSH!

Thanks a lot for your prompt answer. I followed your instructions. It works, but I had to set two different priorities to synchronize the sbRIO (master with priority=1) and the cRIO (slave with priority=20).

However after a certain time both the hardware became master and I must restart the cRIO to set it in slave mode again.

Do you know why a thing like this can happen?

[JKSH]

Hi TizianoTuccella,

PTP uses a "best master clock" algorithm to check the quality of the clocks in the network. The highest-quality clock will be chosen as the master. The priority is only a hint. See:

• http://en.wikipedia.org/wiki/Precision_Time_Protocol#Best_master_clock_algorithm

Perhaps the algorithm has determined that your cRIO has a better clock than your sbRIO?

[TizianoTuccella]

Hi JKSH,

no, I don't think this is the reason. After a certain amount of time both the device become Master and the syncronization get lost.

I have seen that this problem appears only when one of the two device is connected wireless to the network. If both the device are connected by ethernet everything works correctly. 

Have you got some expirience in using IEEE 1588 protocol in a WiFi network? Is there any limitation? 

Thankyou very much!

[JKSH]

Ooh, I've never tried PTP over WiFi before. This research article found that PTP can work over the old IEEE 802.11b WiFi standard.

I'm guessing that it depends on the reliability of your WiFi connection, and the traffic on your network. You said that both devices became Masters, which leads me to this hypothesis: The connection between your two devices got broken for some reason. The slave couldn't contact the master reliably, so it thinks that it's the only PTP-enabled device on the network. Thus, it promoted itself to Master. An Ethernet connection is much more stable than a WiFi connection, so your devices don't lose connection when wired over Ethernet.

(I'm not an expert on PTP; the above is just a guess)

Anyway,

1. Which WiFi standard does your router and WiFi receivers support?
2. What is the WiFi signal strength as seen by both RIO devices?
3. What other devices are connected to your WiFi network?

[TizianoTuccella]

These are the devices present in the network: 

- sbRIO-9606: https://www.ni.com/en-us/support/model.sbrio-9606.html
- cRIO-9076: https://www.ni.com/en-us/support/model.crio-9076.html
- Switch Catalyst 2960g:
http://www.cisco.com/c/en/us/products/switches/catalyst-2960-seriesswitches/
index.html#
- BAT-C:
http://www.hirschmann.com/en/Hirschmann_Produkte/Industrial_Ethe
rnet/news/New_BAT-C_from_HirschmannuE2u84uA2/index.phtml
- Open-BAT:
http://www.hirschmann.com/en/Hirschmann_Produkte/Industrial_Ethe
rnet/BAT-Family/open_BAT_wireless/index.phtml
- Desktop-PC with a network board, Realtek PCIe GBE Family Controller

I attached a block diagram that describes the Network Topology. The cRIO is connected by ethernet cable, while sbRIO is connected by WiFi. 

Both BAT-C and Open-BAT support WiFi 802.11 b/g/n.

I don't think that the problem could be that the WiFi connection get broken for some reason. Both the cRIO and the sbRIO send a continuous stream of the data to the PC. The stream (6 Mbit/s) coming from the sbRIO, that uses WiFi, arrives correctly without any lost in data also after the loss of PTP synchronization. If the connection was broken, I think that also this data stream would be corrupted.  

All the devices in the network are setted with a static IP address.