Initial TSN Setup Questions

[mcduff]

For the end goal, I want to connect some TSN FieldDAQs and cDAQ chassis together through a TSN switch. Unfortunately, switches have a long lead time. NI has started to deliver the products I ordered and I would like to start programming and testing if possible before the switch arrives.

The instruments will be controlled by a Windows computer, no cRIO, no Linux RT.

1. Can I daisy chain devices together for testing until switch arrives, with the Windows Host computer? Will their clocks synchronize?
2. Do you know the difference between Host Time and I/O Device time, that is, how to convert between them? The Help states I/O Device Time is better, but what is its form?
3. Any ideas about how to test before the switch arrives?

Thanks

[vacharya · Accepted solution]

Can I daisy chain devices together for testing until switch arrives, with the Windows Host computer? Will their clocks synchronize?

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The TSN-based ethernet cDAQs and FieldDAQs support daisy chaining without the need for a TSN switch. When an external 802.1as GM is not present, one of the devices in the daisy chain will be selected as the GM, and all the remaining devices will synchronize the clocks to that GM.

Note: None of the devices in the daisy chain will be synchronized to the Windows Host computer, since it is on a different timescale (or time domain).

Do you know the difference between Host Time and I/O Device time, that is, how to convert between them? The Help states I/O Device Time is better, but what is its form?

The host time is the time on the Windows host computer. e.g. the host time would be some time in 4/13/2022.

The I/O Device time is the time on the devices in the daisy chain. The time on the cDAQ chassis starts at 1/1/1970 (the linux time epoch) when powered on. Since there is no external GM, the time on all devices in the daisy chain would be some time in 1/1/1970.

The user can acquire measurements via the DAQmx API using either host time or I/O device time.

• When a user selects I/O device time, the time on the device (I/O device time) is used without any modifications.
• When a user selects host time, the I/O device time is converted to the approximate time on the host when the measurement was acquired.

Any ideas about how to test before the switch arrives?

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You could test the devices in a single daisy chain topology without a TSN switch. But for any other topologies (star, multiple daisy chains etc), you would probably need a TSN switch.