Hi @Sindhu Vadde ,
As all HW related parameter this is managed through Device Tree.
So the DDR with 512MB you reported for your uboot is related to a specific board config/ device tree.
See DDRCTRL and DDRPHYC device tree configuration - stm32mpu
Pay attention that it should be handle in TF-A also and first.
You can refer to ST EV1 board configuration which as 1GB density.
STM32CubeMX also provide easy way to configure DDR size ( and all other design related aspect ) .
Hope it help,
Olivier
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