Re: [Discuss-gnuradio] How do I capture of the time of USRP N210 samples with host computer system time?

[LD Zhang]

Hi Josh,

Thanks for replying. I have some thoughts on using the "set_start_time".
Please see my comments and questions  below:

=========================================================

There is a set_start_time() call. setting this will effect what time the
streaming begins when the flow graph starts

>>>
Once the set_time_now command is performed. I consider the USRP have the
same (or approximately the same) time as the host computer, correct?

The set_start_time() call looks nice, but it requires a time passed to it. I
currently don't know how to dynamically call the set_start_time() command
with a variable of system time in hour:min:sec.microsecond format. I found a
discussion a while ago on some problems with the set_start_time. Someone was
complaining that the time-out window in the cpp code is too short so a
future scheduled time did not work.

Thinking about what I need to achieve, the set_start_time command is
certainly good to make to work. But maybe I have an easier task here. Since
the time is already sync'd, and presuming that I can get the time tag of the
first sample, it is OK if the start time is off a bit(as long as it doesn't
jump around by more than 0.1 seconds each time I perform the same function),
all I need is to know the time of the start sample referenced to the host
system time. So I say all I need right now is to get the time tag of the
beginning sample and that would suffice, just to make it easier.

>>>

Also, as an alternative, there is access to the issue_stream_cmd(). You can
leave the flow graph running and issue commands to turn streaming on and
off, schedule bursts, etc...

>>>
I will try to make the previous approach to work before I mess with this
one.

LD