how I can create a custom instruction to manage operations on vectors

hi,

I used Avalon MM Slave template, I put the file in QSYS slave_template.v and I connected it to NIOS

This template offers 16 registers

I can read write data from register with the operations of IORD_32DIRECT (), IOWR_32Direct ().

Now the problem is how do I create a component verilog / vhdl who make some operations with the values ​​loaded into the registers?

in the file .v I've seen that the following signals are available:

user_dataout_X

user_datain_X

how can I use them?

can you give me a link to some examples?