refer to the data sheet:
"The SRC_POR_B signal controls the processor POR and must be immediately asserted at
power-up and remain asserted until the VDD_ARM_CAP, VDD_SOC_CAP, and VDD_PU_CAP
supplies are stable. VDD_ARM_IN and VDD_SOC_IN may be applied in either order with no
restrictions."
for more detailed information, pls refer to the Power-Up Sequence of data sheet.