Data Sheet

Datasheet, Volume 1 of 2 81
Power Management
When entering the S3 – Suspend-to-RAM (STR) state or S0 conditional self-refresh, the
processor IA core flushes pending cycles and then enters SDRAM ranks that are not
used by the processor graphics into self-refresh. The CKE signals remain LOW so the
SDRAM devices perform self-refresh.
The target behavior is to enter self-refresh for package C3 or deeper power states as
long as there are no memory requests to service.
4.3.2.3 Dynamic Power-Down
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 IA 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.
4.3.2.4 DRAM I/O Power Management
Unused signals should be disabled to save power and reduce electromagnetic
interference. This includes all signals associated with an unused memory channel.
Clocks, CKE, ODT and CS signals are controlled per DIMM rank and will be powered
down for unused ranks.
The I/O buffer for an unused signal should be tri-stated (output driver disabled), the
input receiver (differential sense-amp) should be disabled, and any DLL circuitry
related ONLY to unused signals should be disabled. The input path should be gated to
prevent spurious results due to noise on the unused signals (typically handled
automatically when input receiver is disabled).
4.3.3 DDR Electrical Power Gating (EPG)
The DDR I/O of the processor supports Electrical Power Gating (DDR-EPG) while the
processor is at C3 or deeper power state.
In C3 or deeper power state, the processor internally gates VDDQ for the majority of
the logic to reduce idle power while keeping all critical DDR pins such as CKE and VREF
in the appropriate state.
Table 4-8. Targeted Memory State Conditions
State Memory State with Processor Graphics Memory State with External Graphics
C0, C1, C1E
Dynamic memory rank power-down based on
idle conditions.
Dynamic memory rank power-down based on
idle conditions.
C3, C6, C7 or
deeper
If the processor graphics engine is idle and
there are no pending display requests, then
enter self-refresh. Otherwise use 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.
S3 Self-Refresh Mode Self-Refresh Mode
S4 Memory power-down (contents lost) Memory power-down (contents lost)