Hi Leif and all,
- I would want a timestamp in there somewhere. It might be derived
from block_no, but why not make it explicit ?
I do not see what it would be good for. Why do you want the clock
from the master while there is another one in the slave?
Surely I could add this, but there is a cost to it.
The packages are sent out at maybe 1 kHz. The corresponding
time resolution is 1 ms. There is an appreciable time jitter
however and it is not obvious what time to put into
a specific package. Presumably it should be the time
when the first sample within the package was taken from
the hardware. What would it be good for? It is not trivial
to evaluate.
I agree that a timestamp will be useful. For what I am
thinking about, very high precision and high accuracy are
not required. JT65 wants to know the UTC of a data block to
within a second or so. (Relative timing among successive
blocks is of course maintained by the fixed and nominally
known sample rate.) Of course the slave computer could use
its own time, but that will add another level of jitter.
As a minimum, I suggest that each packet include as a 32-bit
integer the number of seconds since the Unix epoch,
according to the master computer's system clock. So much
the better if you include a number of milliseconds as a
second number, or combine both into a double.
Never mind about jitter; the receiving program would need to
know that jitter in the time values will exist, and behave
accordingly.
Together with the block number, these approaches will
suffice very nicely for JT65, anyway. They will work better
and more reliably than having the slave computer use its own
system clock.
Please let me know when a broadcast-enabled Linrad version
is available for testing with MAP65. And if you have some
example code for use by the receiving program -- or, say, a
stand-alone "dummy" receiving program that can receive
broadcast packets, I would be happy to see the code!
-- Joe, K1JT
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