SPRUI30H November 2015 – May 2024 DRA745 , DRA746 , DRA750 , DRA756
The EMIF uses two counters to schedule the Refresh (REF) commands: a 13-bit decrementing refresh interval counter and a 4-bit refresh backlog counter. The interval counter is used to define the rate at which connected SDRAM devices are refreshed. It is loaded with the value of the EMIF_SDRAM_REFRESH_CONTROL[15:0] REFRESH_RATE bit field at reset (only the 13 LSBs are taken). The interval counter decrements by 1 each cycle until it reaches 0x0, at which point it reloads from the EMIF_SDRAM_REFRESH_CONTROL[15:0] REFRESH_RATE bit field and restarts decrementing. The counter also reloads and restarts decrementing whenever the EMIF_SDRAM_REFRESH_CONTROL[15:0] REFRESH_RATE bit field is updated.
The refresh backlog counter records the number of the outstanding REF commands which the EMIF controller currently has. The backlog counter increments by 1 each time the interval counter reloads (unless it has reached its maximum value of 8). The backlog counter decrements by 1 each time the EMIF issues a REF command (unless it is already 0). For the range of values that the backlog counter can take, there are three levels of urgency with which the EMIF must perform refresh cycle in which it issues REF commands:
The two counters do not operate when SDRAM is in self-refresh mode. They start tracking the missed refreshes (the outstanding REF commands) only after initialization is complete.
The time between two REF commands is set through the EMIF_SDRAM_TIMING_3[12:4] T_RFC bit field.