Dram Power Management And Initialization; Initialization Role Of Cke; Conditional Self-Refresh; Dynamic Power Down Operation - Intel BX80605X3430 - Xeon 2.4 GHz Processor Datasheet

4.3.2

DRAM Power Management and Initialization

The processor implements extensive support for power management on the SDRAM
interface. There are four SDRAM operations associated with the Clock Enable (CKE)
signals, which the SDRAM controller supports. The processor drives four CKE pins to
perform these operations.
4.3.2.1

Initialization Role of CKE

During power-up, CKE is the only input to the SDRAM that has its level recognized
(other than the DDR3 reset pin) once power is applied. It must be driven LOW by the
DDR controller to make sure the SDRAM components float DQ and DQS during power-
up. CKE signals remain LOW (while any reset is active) until the BIOS writes to a
configuration register. Using this method, CKE is ensured to remain inactive for much
longer than the specified 200 micro-seconds after power and clocks to SDRAM devices
are stable.
4.3.2.2

Conditional Self-Refresh

The processor conditionally places memory into self-refresh in the C3 and C6 low power
states.
When entering the Suspend-to-RAM (STR) state, the processor core flushes pending
cycles and then enters all SDRAM ranks into self refresh. In STR, the CKE signals
remain LOW so the SDRAM devices perform self refresh.
The target behavior is to enter self-refresh for the package C3 and C6 states as long as
there are no memory requests to service. The target usage is shown in
Table 4-6.

Targeted Memory State Conditions

Mode
C0, C1, C1E
C3, C6
S4
4.3.2.3

Dynamic Power Down Operation

Dynamic power-down of memory is employed during normal operation. Based on idle
conditions, a given memory rank may be powered down. The IMC implements
aggressive CKE control to dynamically put the DRAM devices in a power down state.
The processor core controller can be configured to put the devices in active power down
(CKE de-assertion with open pages) or precharge power down (CKE de-assertion with
all pages closed). Precharge power down provides greater power savings but has a
bigger performance impact, since all pages will first be closed before putting the
devices in power down mode.
If dynamic power-down is enabled, all ranks are powered up before doing a refresh
cycle and all ranks are powered down at the end of refresh.
44
Memory State with External Graphics
Dynamic memory rank power down based on idle conditions.
Dynamic memory rank power down based on idle conditions
If there are no memory requests, then enter self-refresh. Otherwise, use dynamic memory
rank power down based on idle conditions.
Memory power down (contents lost)
Power Management
Table 4-6.
Datasheet, Volume 1