[USRP-users] 2 B210 synchronous problem

Hideyuki Matsunaga hideyuki.matsunaga at gmail.com
Wed Oct 25 02:59:39 EDT 2017


Hi

I bought 2 B210s for testing direction of arrival estimation, like below.

=======================   Configuration =============================

Ch0 <--> | USRP0 Rx 0 |
         |            | <-- USB3.0 --> |       PC                        |
Ch1 <--> | USRP0 Rx 1 |                | Ubuntu 14.04                    |
                                       | GNU Radio Companion 3.7.11.1    |
Ch2 <--> | USRP1 Rx 0 |                | UHD_003.010.001.001-79-g7ac01c7f|
         |            | <-- USB3.0 --> |                                 |
Ch3 <--> | USRP1 Rx 1 |

- External 10MHz reference CLK & 1PPS are provided by function
generator(Tektronix AFG1012) to each B210
- center freq  2.4GHz
- samping rate 4MHz

In GRC
- 2 separate USRP Source for each B210, settings are below
 - Sync option   unknown pps
 - Clock Source  External
 - Time Source   External
 - Num Channels  2

I generated python code by GRC and then I added custom timing adjustment
code.
```
 self.uhd_usrp_source_0.set_time_next_pps(uhd.time_spec(0))
 self.uhd_usrp_source_1.set_time_next_pps(uhd.time_spec(0))
 time.sleep(1.0)

 start_time = uhd.time_spec(5.0)
 self.uhd_usrp_source_0.set_start_time(start_time)
 self.uhd_usrp_source_1.set_start_time(start_time)
```
===========================================================================

I believe that I am following all the instructions what I found in web.
but, when I tried to check that sampling timing is exactly matched or not
by dumping all the samples(connect File Sink), I found sampling gaps
between 2 B210.

While testing, I confirmed that
- there are no overflow,
- start timing would be exactly the same(using Tag Debug to confirm)

I observed that
- gaps looks fixed size during running
- gaps are slightly different every time


Please let me know what I am missing.


Thanks,
Matsu
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