Hi Fabio,
Is this board confirmed to be working properly? Have you done the procedures described here: http://processors.wiki.ti.com/index.php/AM335x_EMIF_Configuration_tipshttp://processors.wiki.ti.com/index.php/AM335x_DDR_PHY_register_configuration_for_DDR3
There is also a tutorial about these procedures here: http://processors.wiki.ti.com/index.php/Sitara_Linux_Training:_Tuning_the_DDR3_Timings_on_BeagleBoneBlack