Data Sheet

Power Management
80 Datasheet, Volume 1 of 2
better than APD, but less than DLL-off. Power consumption is defined by IDD2P.
Exiting this mode is defined by tXP. The difference from APD mode is that when
waking-up, all page-buffers are empty.) The LPDDR does not have a DLL. As a
result, the power savings are as good as PPD/DDL-off but will have lower exit
latency and higher performance.
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 DDR
specification). This is significant when each channel is populated with more ranks.
Selection of power modes should be according to power-performance or thermal trade-
off of a given system:
When trying to achieve maximum performance and power or thermal consideration
is not an issue: use no power-down.
In a system which tries to minimize power-consumption, try using the deepest
power-down mode possible – PPD/DLL-off with a low idle timer value.
In high-performance systems with dense packaging (that is, tricky thermal design)
the power-down mode should be considered in order to reduce the heating and
avoid DDR throttling caused by the heating.
The default value that BIOS configures in PM PDWN configuration register is 6080 –
that is, PPD/DLL-off mode with idle timer of 0x80, or 128 DCLKs. This is a balanced
setting with deep power-down mode and moderate idle timer value.
The idle timer expiration count defines the # of DCLKs that a rank is idle that causes
entry to the selected power mode. As this timer is set to a shorter time the IMC will
have more opportunities to put the DDR in power-down. There is no BIOS hook to set
this register. Customers choosing to change the value of this register can do it by
changing it in the BIOS. For experiments, this register can be modified in real time if
BIOS does not lock the IMC registers.
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 reset pin) once power is applied. It should 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
During S0 idle state, system memory may be conditionally placed into self-refresh state
when the processor is in package C3 or deeper power state. Refer to Section 4.6.1.1 for
more details on conditional self-refresh with Intel HD Graphics enabled.