questions about flash in nios

thanks!

1. i think both the hardware image and the software image can not be changed, i think the configure data contains hardware image, software image and the bootloader. i want to know the size of the configure data( hardware image, software image and the bootloader) or where the configure data ends.

2. i can not find the rbf file, can your give me more details?

3. i do not want to W/R the flash in flash programmer, i want to W/R the flash in the main.c,

4. i do not want to W/R the flash in Quartus II programmer, i want to W/R the flash in vhdl.

i want to tread the unused flash space like a flash device that i can W/R in my code when the fpga is running, not just once.