Intel BX80646I74770K manual DRAM Power Management and Initialization, No power-down CKE disable

Power Management—Processor

•Reduced possible overshoot/undershoot signal quality issues seen by the processor I/O buffer receivers caused by reflections from potentially un- terminated transmission lines.

When a given rank is not populated, the corresponding chip select and CKE signals are not driven.

At reset, all rows must be assumed to be populated, until it can be determined that the rows are not populated. This is due to the fact that when CKE is tri-stated with an SO-DIMM present, the SO-DIMM is not ensured to maintain data integrity.

CKE tristate should be enabled by BIOS where appropriate, since at reset all rows must be assumed to be populated.

4.3.2DRAM 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.

The CKE is one of the power-save means. When CKE is off, the internal DDR clock is disabled and the DDR power is reduced. The power-saving differs according to the selected mode and the DDR type used. For more information, refer to the IDD table in the DDR specification.

The processor supports three different types of power-down modes in package C0. The different power-down modes can be enabled through configuring "PM_PDWN_config_0_0_0_MCHBAR". The type of CKE power-down can be configured through PDWN_mode (bits 15:12) and the idle timer can be configured through PDWN_idle_counter (bits 11:0). The different power-down modes supported are:

•No power-down (CKE disable)

•Active power-down (APD): This mode is entered if there are open pages when de-asserting CKE. In this mode the open pages are retained. Power-saving in this mode is the lowest. Power consumption of DDR is defined by IDD3P. Exiting this mode is defined by tXP – small number of cycles. For this mode, DRAM DLL must be on.

•PPD/DLL-off:In this mode the data-in DLLs on DDR are off. Power-saving in this mode is the best among all power modes. Power consumption is defined by IDD2P1. Exiting this mode is defined by tXP, but also tXPDLL (10–20 according to DDR type) cycles until first data transfer is allowed. For this mode, DRAM DLL must be off.

The CKE is determined per rank, whenever it is inactive. Each rank has an idle- counter. The idle-counter starts counting as soon as the rank has no accesses, and if it expires, the rank may enter power-down while no new transactions to the rank arrives to queues. The idle-counter begins counting at the last incoming transaction arrival.

It is important to understand that since the power-down decision is per rank, the IMC can find many opportunities to power down ranks, even while running memory intensive applications; the savings are significant (may be few Watts, according to the DDR specification). This is significant when each channel is populated with more ranks.

Desktop 4th Generation Intel® Core™ Processor Family, Desktop Intel® Pentium® Processor Family, and Desktop Intel® Celeron® Processor Family

December 2013	Datasheet – Volume 1 of 2
Order No.: 328897-004	61