APPARATUS AND METHODS FOR SYNCHRONIZING A PLURALITY OF DOUBLE DATA RATE MEMORY RANKS

A shared data transfer clock is used among double data rate memory ranks. A memory controller processes incoming memory access commands destined for at least one of a plurality of double data rate memory ranks and determines when a target DDR memory rank is out of synchronization with respect to the shared data transfer clock and a memory clock. In response to determining that the target DDR memory rank is out of synchronization, the memory controller determines whether the non-target DDR memory rank is out-of-synchronization with respect to the shared data transfer clock and the memory clock, and issues a data transfer clock synchronization command to the target DDR memory rank in response to determining that the non-target DDR memory rank is out-of-synchronization with respect to the shared data transfer clock and the memory clock.