Timestamp is 0/NULL for all received messages

bistromath / gr-air-modes

Gnuradio Mode-S/ADS-B radio

This project implements a Mode S receiver for the Gnuradio software-defined radio project. It is designed to receive Mode S transmissions from aircraft and decode them to a human-readable format, including ADS-B information messages such as position and a

GNU General Public License v3.0

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Timestamp is 0/NULL for all received messages #18

Closed nervestaple closed 12 years ago

nervestaple commented 12 years ago

air_modes_preamble.cc doesn't seem to find any "rx_time" tags, ever, meaning all timestamps are set to 0. I'm not too familiar with any of the internals, so tracing it back to:

get_tags_in_range(tstamp_tags, 0, abs_sample_cnt, abs_sample_cnt + ninputs, pmt::pmt_string_to_symbol("rx_time"));

was about as far as I could take it.

I'm running an RTL dongle "ISDB-T". It seems to work fine otherwise. Grabbing the system time at this point would probably be good enough for my purposes, but I'm curious as to why the timestamp never comes through!

bistromath commented 12 years ago

Timestamp doesn't come through because the RTL dongles don't have hardware timestamp support. I can use a software timestamp to get "close enough" with the dongles, but the real reason timestamps are in there in the first place is for multilateration support -- and there's just no way a software timestamp is good enough to use for that.

nervestaple commented 12 years ago

I figured it was something to do with RTL dongles -- thanks for clearing that up!