Forum: GNU Radio control FPGA new pin in N210

Dear all,    I am using N210, I wan to bring "AA17" pin of FPGA to up 
3.3v, and how can use UHD to do that?
    Josh replied me that make  a new settings register in u2plus_core.v 
and use set_user_register() to control it.    but I read the 
u2plus_core.v code, and try to add the setting_reg to control "AA17" 
pin, but how can I know the "addr" that multi_usrp.cpp can control it? 
could someone can give me an example? thanks a lot.Jack.