questions about flash in nios

You can get information about your configuration data addresses when you generate the .jic or .pof files with your hw and sw. It should be generated into an <output_name>.map file, which is simply a text file with the address ranges for you hw and sw.

You can write to flash from nios if you have the epcs_flash_controller module instantiated. You will need this module anyway b/c that is how you bootload the fpga from flash. (and this assume SPI flash).

I'm sure there are VHDL examples of r/w to flash.