A10 DRAM Controller Calibration

The DRAM controller supports setting quite a number of various delays and phase shifts to improve signal integrity. Some calibration may be necessary for getting the best results out of it. Allwinner offers the dram_tpr3 parameter for such tuning. And it can be already used to improve dram overclocking potential quite significantly. For example, setting dram_tpr3=0x72222 for the Cubietruck allows to clock DRAM nearly up to 600MHz on some devices.

Some links, which are not directly describing sunxi hardware, but may be useful for grasping the general concept:
 * Altera - Utilizing Leveling Techniques in DDR3 SDRAM Memory Interfaces
 * Freescale - i.MX 6 Series DDR Calibration