Information about HAL of device driver

Hi,

i would like to write a software for a Nios II. Where can i find more information about function of the device drivers expect for the header file. I will write a test for a CFI flash memory. I created my system in the SOPC Builder and use the altera_avalon_cfi_flash.h in the NIOS IDE. The description is not helpful in the altera_avalon_cfi_flash.h.

Thank you in advance!