Thanks for your replay!
when i flow the "iMX 8M Mini Register Programming Aid DRAM PLL setting", It says :
2. Next, in the RPA DDR stress test file worksheet tab search for “memory set 0x30360054”. The address “0x30360054” is for the DRAM PLL register address and its setting needs to be updated to the desired frequency.
But I can't find the "memory set 0x30360054"