Information

DDR Memory Controller
MPC8308 PowerQUICC II Pro Processor Reference Manual, Rev. 1
Freescale Semiconductor 9-55
Table 9-43 summarizes the refresh types available in each power-saving mode.
Note that in the absence of refresh support, system software must preserve DDR SDRAM data (such as by
copying the data to disk) before entering the power-saving mode.
The dynamic power-saving mode uses the CKE DDR SDRAM pin to dynamically power down when there
is no system memory activity. The CKE pin is negated when both of the following conditions are met:
• No memory refreshes are scheduled
• No memory accesses are scheduled
CKE is reasserted when a new access or refresh is scheduled or the dynamic power mode is disabled. This
mode is controlled with DDR_SDRAM_CFG[DYN_PWR_MGMT].
Dynamic power management mode offers tight control of the memory system’s power consumption by
trading power for performance through the use of CKE. Powering up the DDR SDRAM when a new
memory reference is scheduled causes an access latency penalty, depending on whether active or precharge
powerdown is used, along with the settings of TIMING_CFG_0[ACT_PD_EXIT] and
TIMING_CFG_0[PRE_PD_EXIT]. A penalty of 1 cycle is shown in Figure 9-42.
Figure 9-42. DDR SDRAM Power-Down Mode
Table 9-43. DDR SDRAM Power-Saving Modes Refresh Configuration
Power Saving Mode Refresh Type SREN
Sleep Self 1
None —
Mem Bus Clock
NOP NOP
COMMAND
ACT
CKE