Some of the variants support the fabric DDR (FDDR) and microcontroller subsystem DDR (MDDR) and some variants support only FDDR in SmartFusion2. See datasheet to know the bank on which the DDR is supported on each particular device. The layout guidelines of the respective VDDIO should be followed. It also needs VREF voltage for an internal reference. Noise on VREF impacts the read performance of SmartFusion2/IGLOO2 devices. VREF lines must not be routed near the aggressive nets or switching power supplies. For more information about DDR memory layout guidelines, see the Micron DDR3 Memory Layout Guidelines. The VDDIO guidelines should be followed for DDR bank VDDIO. This section explains the guidelines to be used for VREF.