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[Discuss-gnuradio] bug on get_mboard_sensor("gps_time") : may return old

From: Bastien Auneau
Subject: [Discuss-gnuradio] bug on get_mboard_sensor("gps_time") : may return old value
Date: Fri, 5 Aug 2011 12:50:21 +0200


Using USRP N210, UHD 3.2.1, windows7 (VC++ 9), GPSDO (Jackson Labs)

I first use :
  set_time_next_pps(0, 1, 54000000)

Since gps time returns soon after pps edge occurs, I know that time is set to 0 at a known GPS time called gps_t_0 (which is gps time returned by sensor + 1)
(this is based on previous comments of Nick http://lists.gnu.org/archive/html/discuss-gnuradio/2011-08/msg00097.html)

Then, I want to check that gps_t_0 is really my starting point, then I discovered the bug
Here is pseudo code (in real code I use get_full_secs())
        gps_now = get_mboard_sensor("gps_time")
        time_now = get_time_now()
        if ((gps_now - gps_t_0) != time_now){
            //NOT OK
            std::cout << (gps_now - gps_t_0) - time_now

If there is no Sleep(3000), results are OK
If I enable the Sleep(3000), it prints at every loop iteration either -2 or -3
If I change the sleep into Sleep(6000), it prints at every loop iteration -5 or -6

This means that query of gps_time is proportionally to Sleep(x) in the past
So I guess there is a problem of data flushing, the sensor query returning first gps phrase generated by GPSDO since last gps_time query
A way to solve this bug may be to flush previous gps_time phrase generated by GPSDO prior to get current time ??

Trying to dig into code (so far searching around get_nmea(...) in gps_ctrl.cpp l.148), but not sure this can be solved in host code ??


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