[Discuss-gnuradio] using PPS signal to trigger the received data storage in Pyton

[Yan Nie]

 Dear all,

I am using USRP N200 with LFRX +UHD to design a receiver, which works 
fine to continuously receive data. I need to use PPS signal to trigger 
the received data storing only for 1ms every second after detecting the 
edge of PPS signal every second. 

I tried the approach introduced in the gnuradio example, 
rx_timed_samples, detecting the PPS signal, then setup streaming, then 
fill out rx-meta-data by recv(). Eventually, I got to know the 
stream_cmd and recv are not swigged, which means I could use this method
 in Python.

>From previous email reply, the USRP source already tags the samples with
 a timestamp, I do not need to control when streaming begins, because 
the downstream block can determine the time of any samples using 
metadata. 

1. I am wondering how can I fill out meta-data by the received data if 
recv() cannot be used in Python,as I wish to set the time of samples as 
the time when PPS signal is detected every second and use the 
total_num_samps to control the number of data USRP received every second
 after triggering be PPS signal.
I am using the following method to detect PPS signal:

    self.clk_cfg = uhd.clock_config()
    self.clk_cfg.pps_source = uhd.clock_config.PPS_SMA
    self.clk_cfg.pps_polarity = uhd.clock_config.PPS_NEG
    self._usrp2.set_clock_config(self.clk_cfg, uhd.ALL_MBOARDS)
    self._usrp2.set_time_unknown_pps(uhd.time_spec(0.0))

2. The PPS setting is done right after the USRP device is created, hence
 the PPS signal could be detected when USRP device is setup. I am also 
wondering this PPS setting could let the USRP detect PPS signal every 
second, or only once when this setting is called? 

Any suggestion or idea will be really appreciated! 

Thanks,
Yan