On 2022-01-13 18:56, Marcus Müller wrote:
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
As Mr. Mueller has indicated, UHD already inserts time tags into the
stream, and tags in general are fairly easy to deal with:
https://wiki.gnuradio.org/index.php/Stream_Tags
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