Re: USRP N200

On 05/31/2021 06:23 AM, Skyvalakis Konstantinos wrote:

Hi,

I have 2 USRP N200 devices equipped with an SBX daughterboard each.

I want to build a 1 Tx, 2 Rx system, where everything is synchronized.

​I have an external generator to provide 10MHz ref clock and PPS input for both USRP devices with equal length cables.

The 1st USRP, with the SBX daughterboard, is both Tx and Rx.

The 2nd USRP, with the SBX daughterboard, is just Rx.

Phase synchronization is crucial to my application and thus I really need to know if I am doing it right or not.

Therefore, I am attaching the following code in Python, that I use to synchronize the devices and I would like to know if it's correct or not.

  def usrp_init(self):

    self.source = [None, None]

    self.source[0] = uhd.usrp_source(

    device_addr=self.usrp_address_source[0],

    stream_args=uhd.stream_args(

    cpu_format="fc32",

    channels=range(1),

    ),

    )

    self.source[1] = uhd.usrp_source(

    device_addr=self.usrp_address_source[1],

    stream_args=uhd.stream_args(

    cpu_format="fc32",

    channels=range(1),

    ),

    )

    self.sink = uhd.usrp_sink(

    device_addr=self.usrp_address_sink,

    stream_args=uhd.stream_args(

    cpu_format="fc32",

    channels=range(1),

    ),

    )

    self.source[0].set_clock_source('external', 0);

    self.source[0].set_time_source('external', 0);

    self.source[0].set_time_unknown_pps(uhd.time_spec())

    self.source[0].set_samp_rate(self.adc_rate)

    self.source[0].set_gain(self.rx_gain0, 0)

    self.source[0].set_antenna("RX2", 0)

    self.source[1].set_clock_source('external', 0)

    self.source[1].set_time_source('external', 0)

    self.source[1].set_time_unknown_pps(uhd.time_spec())

    self.source[1].set_samp_rate(self.adc_rate)

    self.source[1].set_gain(self.rx_gain1, 0)

    self.source[1].set_antenna("RX2", 0)

    self.sink.set_clock_source('external', 0);

    self.sink.set_time_source('external', 0);

    self.sink.set_time_unknown_pps(uhd.time_spec())

    self.sink.set_samp_rate(self.dac_rate)

    self.sink.set_gain(self.tx_gain, 0)

    self.sink.set_antenna("TX/RX", 0)

    time.sleep(1)

    cmd_time0 = self.source[0].get_time_last_pps()

    cmd_time1 = self.source[1].get_time_last_pps()

    cmd_time2 = self.sink.get_time_last_pps()

    real_seconds0 = uhd.time_spec_t.get_real_secs(cmd_time0)

    real_seconds1 = uhd.time_spec_t.get_real_secs(cmd_time1)

    real_seconds2 = uhd.time_spec_t.get_real_secs(cmd_time2)

    future_real_seconds0 = real_seconds0 + 1

    future_real_seconds1 = real_seconds1 + 1

    future_real_seconds2 = real_seconds2 + 1

    future_cmd_time0 = uhd.time_spec_t(future_real_seconds0)

    future_cmd_time1 = uhd.time_spec_t(future_real_seconds1)

    future_cmd_time2 = uhd.time_spec_t(future_real_seconds2)

    self.source[0].set_command_time(future_cmd_time0)

    self.source[1].set_command_time(future_cmd_time1)

    self.sink.set_command_time(future_cmd_time2)

    self.source[0].set_center_freq(uhd.tune_request(self.freq,0), 0)

    self.source[1].set_center_freq(uhd.tune_request(self.freq,0), 0)

    self.sink.set_center_freq(uhd.tune_request(self.freq,0), 0)

    self.source[0].clear_command_time()

    self.source[1].clear_command_time()

    self.sink.clear_command_time()

Thanks in advance.

Konstantinos

Your RX streams need to be coming from a SINGLE multi_usrp object, not separate objects.

Please see the rx_multi_samples example code.

Also there's a good knowledge-base article about synchronization:

https://kb.ettus.com/Synchronization_and_MIMO_Capability_with_USRP_Devices