Flash Device Access

Hej

I am using my custom board where I have an external flash device attached..I want to read and write the flash device..I read the manual Nios II Software Developer's Handbook...and acording to the instructions given there..i tried to use HAL functions to open the flash drive..but i could not open the flash drive..I found tht when i tried to debug my code..and the pointer gets the value NULL even i am giving the name of flash device...correctly as I check that out in system.h file as well..i wrote like this..

alt_flash_fd* fd;

fd= alt_flash_open_dev("/dev/cfi_flash");

but after the execution of statement..fd gets 0.i.e; NULL...so the flash device doesnt opens...Can any1 please help me in this regard...