Hi Mike,
1. making another identical object will just give you another copy of the same smart
pointer :)
1. & 2. & 3 are sadly all inadequate solutions, because you query the device time at some
randomly varying time after a sample has been produced.
The right approach is actually 4, but without you needing to copy the the UHD USRP Source:
The source already tags rx_time whenever the device sends time-containing metadata (which
it should do whenever you it sets the device time.
In your custom block, you just watch for these rx_time tags. When you find one, you save
the time (or better even, ticks) it contains, together with its sample offset. When you
later wonder what time a specific item was read, you just use nitems_read(0) of your block
to get the offset of the first item in your (general_)work() call, and calculate the time.
Best regards,
Marcus
On 13.01.22 23:24, Michael Bassi wrote:
Hi all,
I'm using GR3.9 with UHD4.1.0.1.
I have a flowgraph containing a UHD_USRP Source block, with Sync property set to "PC
Clock on Next PPS" so that the device time is synced to PC system time on the next PPS.
I want to then, somewhat frequently, access the usrp time from within downstream custom
C++ blocks.
Options that I've considered:
1. From the custom c++ block - make another UHD USRP device instance (though I don't
think this is possible, as the device has already been allocated to the source block):
uhd::device_addr_t deviceAddress("");
uhd::usrp::multi_usrp::sptr usrp =
uhd::usrp::multi_usrp::make(deviceAddress);
2. From the custom c++ block - Just retrieve clock info from the device a bit like this
(but it's too slow):
uhd::device_addr_t dev;
dev["addr"] = "192.168.XXX.XXX";
uhd::usrp_clock::multi_usrp_clock::sptr clock =
uhd::usrp_clock::multi_usrp_clock::make(dev);
std::cout << clock->get_time()
3. From the custom c++ block - Somehow access the already discovered usrp device from
the UHD_USRP source block (not sure how to do this)
4. Copy and modify the usrp source code to send time as a stream tag along with each
packet (seems like a lot of work!)
a. perhaps this could be achieved using the UHD_USRP Source block stream args property -
though would require mods to the .yml?
Thanks for your help!
Mike
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