How to call tightly couple module during C code for NIOS II

Any information passed to the software environment accessible from C that are generated from SOPC are stored in system.h. Most C files will# include system.h to get the definitions for all of the components in the SOPC design. What is in system.h for your peripheral depends completely on the design of the peripheral. At a minimum you will have the base address. I would think you need to write a HAL (API) layer to read/write the peripheral to get it to do something and maybe to return a result. This is probably done with IORD and IOWR C macros to make your peripheral functional.