# Help to get control over USRP from custom block

**URL:** <https://www.ruby-forum.com/t/help-to-get-control-over-usrp-from-custom-block/233961>\
**Category:** GNU Radio\
**Created:** [January 26, 2015, 12:55pm UTC](https://www.ruby-forum.com/t/help-to-get-control-over-usrp-from-custom-block/233961 "2015-01-26T12:55:34Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![addis\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c4cdca/32.png) [@addis\_a](https://www.ruby-forum.com/u/addis_a)\
**Post date:** [January 26, 2015, 12:55pm UTC](https://www.ruby-forum.com/t/help-to-get-control-over-usrp-from-custom-block/233961/1 "2015-01-26T12:55:34Z")

</div>

Hi all,

A last attempt this time, after struggling already several months with  
this subject…

From within my custom (out-of-tree) C++ block I need full control over  
USRP sink/source. According to the documentation, the command interface  
only implements three functions (gain, center frequency and LO\_offset ).  
I need much more functionality however (sensors, IQ-imbalance, etc…),  
so I looked at another solution.

In my custom block class I added a method that takes 2 pointers:

```
boost::shared_prt<gr::uhd::usrp_sink>
boost::shared_prt<gr::uhd::usrp_source>

```

In the Python top\_block.py code I add a call to this method in order to  
pass the USRP pointers from Python to my C++ custom block.

The pointers seem to be valid in C++, but apparently the corresponding  
classes have empty virtual methods, so if I want to use the pointers  
nothing happens or Python crashes.

Does anybody know how to get pointers that have all functionality  
implemented from the original Ettus library? I am completely stuck… It  
may be an ugly hack, but I just need to get things done now.

Regards,

```
   Jeroen

```

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