Resolved! On the STM32H745 platform,When I use the memcpy or memset function to access external SDRAM(0xC0000000),If the address is not double byte aligned, the program enters harddefault.I tested the same situation on M4 platform without any problems.
memcpy(0xc0000000,buffer,2) this is okmemcpy(0xc0000001,buffer,2) this is error