Posted on April 11, 2018 at 08:38The 512 MBit flash chips are still somewhat rare, indeed. But as long as you don't need some fancy special features of a particular chip, almost any vendor's chip will do: ISSI, Micron, Macronix, Winbond, Cypress. Although there are minor differences (IDs, configuration register settings for dual/quad mode, drive strength), firmware changes should be rather limited.
And, I'd suggest to be prepared to use different chips in your final product anyway ...
