Using FPGA registers with custom Verilog code

I am running a custom feedback controller on the USRP1. So far I have
been content with hard coding parameters of the controller and
re-synthesizing the Verilog as needed. However I would like to explore
using the FPGA registers to set some parameter values using the python
function _write_fpga_reg(…).

What is the best way to go about setting up the Verilog to do this?
After looking at the usrp_std.v top level module, I included and setup
the serial_io and io_pins modules in my code and then used setting_reg
to read the register values. When I do this, the code synthesizes fine
but does not produce any output. Are there other modules that serial_io
and io_pins depend on? Or am I going about this the wrong way?