Adding a block in GRC

I ask how can i add a block in grc witch exist in gnuradio for example
the cyclic prefix exist in gnuradio but in grc it’s combined in OFDM
block and i want to use it as a block in grc , i know only that i  have
to configure an xml file of this block and rebuild gnuradio ( i’m using
gnuradio 3.2rc)
thanks

Take a look at this guide:

http://gnuradio.org/trac/wiki/GNURadioCompanion#CreatingtheXMLBlockDefinition
http://gnuradio.org/trac/wiki/GNURadioCompanion#InstallingtheXMLBlockDefinition

  1. create the xml file
  2. copy it into ~/.grc_gnuradio/
  3. run grc

-Josh