Proble opening the /dev/epcs_controller device

Kwok,

The next likely place to look is in the initialisation code for the EPCS device. I suggest you take a look at the function alt_epcs_flash_init which can be found in the file nios2\components\altera_avalon_epcs_flash_controller\Hal\src\altera_avalon_epcs_flash_controller.c

My guess is that this function is failing, which will cause the device not to be registerred and therefore you will get a null file pointer.