Re: LXI, IEEE1588 and TTP


Paul E. Bennett wrote:
> Does anyone on here have any experiences to relate about implementing any
> of the above protocols. How much effort did it take, how much processor and
> memory resource and how accurate a timing correlation can be achieved
> across nodes on the network. I would also be interested in knowing if some
> of the schemes used other timing synchronisation distribution schemes in
> addition to these protocols.
>
> I am looking at a situation with approximately 50,000 sensors, some time
> critical control requirements and and a need to ensure that all the data is
> on a closely relateable timebase.

For an accurate time synchronisation, the method I have used
on party line protocols was based on measuring the time with the
following procedure:

A sends a synchronisation frame to B and starts a timer (1) when
a specific character is sent
B reads the time at wich it receives the character and starts
a timer (2)
B sends a reply frame, reads the timer (2) when the equivalent
character is sent and writes its value in the frame as it goes.
A reads the timer (1) when it receives the reply, substracts the time
value (2) in the frame and divides the result by two in order
to compute the time it takes to send a frame.

The timers should be started in an ISR upon transmit interrupt

When you send a time synchronisation frame you add the time it takes
to send a frame to your local time. You read the time when you send
the specific character, in the ISR.

I could achieve 80us accuracy on a fieldbus with this method and 1ms
accuracy on long distances at 1200bds

.

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