Re: [Discuss-gnuradio] UHD query PPS

[David Evans]

Maybe I misunderstand how to synchronise...

if I have two usrp2s, and I do a set_time_next_pps(), there is a chance that 
the pps could occur after the first call, so the second call will set the 
second usrp a second later. I would need to know when there is a pps or seconds 
transition prior to setup, then have one or two seconds to call 
set_time_next_pps(). Ok, I could read the system time, but I would need a gps 
with pps/ref out, and sync'd using ntpd or gpsd, and this may not be 
guaranteed. Or I could just monitor the pps level via the serial port (DCD, 
like ntpd does with nmea stream) to guarantee when the seconds tick over. If 
the pps state could be read back from the usrp (approx 80ns rtt) however, this 
would simplify the system and hardware requied (USB dongle, TTL to RS232 
convertor, extra wires, etc...). So...

while (get_pps_level() == 0); // wait for rising edge
while (get_pps_level() == 1);

u1->set_time_next_pps(...); // We are guaranteed at least one second to issue 
this to both usrp at once
u2->set_time_next_pps(...);

Cheers,
David


----- Original Message ----
From: Josh Blum <address@hidden>
To: David Evans <address@hidden>
Sent: Sat, 22 May, 2010 17:37:32
Subject: Re: [Discuss-gnuradio] UHD query PPS

Not sure what you mean. Perhaps readback the current time on the device?
-Josh

On 05/22/2010 07:23 AM, David Evans wrote:
> Is it, or could it be possible to add a query method to get the PPS state 
> (something like u2->get_pps())?
>
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