[Halld-controls] PXI Time Stamps

[Mark Stevens]

Hi Brian,

I think "knowing of its existence" is good enough for now.

Best Regards,

Mark Stevens

----- Original Message -----
From: "Brian Eng" <beng at jlab.org>
To: "Hall D Controls" <halld-controls at jlab.org>
Sent: Thursday, August 30, 2018 1:46:47 PM
Subject: [Halld-controls] PXI Time Stamps

We recently discovered that the time used by the PLCs has a offset to it which causes them to use/provide an incorrect time.

It manifests itself in 2 ways:
1) If the CC server is the master the PLC will be 34 seconds fast
2) if the PLC is the master any devices on the same subnet will be 34 seconds fast

That 34 seconds is hard-coded in the PLC ethernet module and only changed by upgrading the firmware (but it still won't be user adjustable). It comes from the offset between UTC & TAI time when the module was purchased.

Currently we're operating in the second configuration.

There is an option to correct this offset with Linux based NI devices, but I haven't yet tested it with the other OSes (namely the PXI which uses Phar Lap).

Unfortunately even if I can remove this offset it will require rebooting the PXI, so my question is should I try pursuing fixing this or is knowing that there is a fixed & constant offset good enough for now?




P.S. This isn't like the earlier time problems we had where the time would slowly wander off, this is a fixed value with only the error of PTP coming into play which should be at the sub-ms level.
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