about sram and flash

If the SRAM is 32bit in your case, in my opinion, the A0 of SRAM should be connected to A2 of the Nios;

while, if your Flash is 8bit wide, then connect A0 to A0 will be OK. At least, the "avalon bus specification" says this.

thank you .

if my Flash is 16bit wide, the A0 of the flash should connect to" A0 OR A1" of the nios?

Table 15 Page 100 of Avalon Bus Specification:

in case of NIOSII: Master Width is always 32

native Alignement = Avalon Register Slave

dynamic Alignement = Avalon Memory Slave

Alignment | Master Width | Slave Width | A[0] of Slave is connected to Byte Address Bit Number

native | 32 | 32 | A2

native | 32 | 16 | A2

native | 32 | 8 | A2

dynamic | 32 | 32 | A2

dynamic | 32 | 16 | A1

dynamic | 32 | 8 | A0

so you have to connect A0 of your flash to A1 of nios address bus.