Compaq 850 manual Rdram Power Management, Rdram CONFIGURATION/CONTROL, State Power Refresh

Chapter 3 Processor/Memory Subsystem

3.3.3 RDRAM POWER MANAGEMENT

The Rambus architecture provides for power management of each RDRAM device on a RIMM. RDRAM power management control is compatible with but may also work independently of ACPI. Power management of RDRAM is handled through control packets as well as the serial bus. Aside from complete “system off” state, an RDRAM may be placed in one of four basic power states:

♦Active

♦Standby

♦Nap

♦Powerdown

These states are characterized by parameters such as power consumed, refresh method, and the time required to resume full (Active state) operation. The following table defines the RDRAM power states.

State	Power	Refresh	RDRAM	Exit	RDRAM Functionality
	Consumed [1]	Method	CLK	Latency [2]
Powerdown	1 mW	Self	Stopped	12 ∝ s	Lowest power state and condition entered after
					initialization. Can remain in this state indefinitely.
					Brought out of Powerdown only by command
					over the SIO serial bus.
Nap	10 mW	MCH	On	90 ns	Low power state. Can remain in this state for up
					to 10 ∝ s. Brought out of Nap only by command
					over the SIO serial bus.
Standby	250 mW	MCH	On	20 ns	Idle power state automatically entered after a
					transaction. Available to receive row packets.
					Transitions to Active or Nap state upon receipt
					of specific command on ROW bus.
Active	500 mW	MCH	On	--	Full power state. Available to receive control
					packets and transmit or receive data packets.
NOTES:

[1]Per RDRAM device

[2]Transition to Active state

3.3.4RDRAM CONFIGURATION/CONTROL

The Rambus architecture employs a CMOS-level serial bus (SIO, SCK, CMD) similar to that used on SDRAM-equipped systems. This bus is used for status and control of RDRAM configuration parameters as well as bringing RDRAM devices out of Powerdown and Nap states. The SIO signal is bi-directional and daisy-chained through all RDRAM devices, alternating from SIO0 to SIO1 between devices . The SCK and CMD signals are applied in parallel to all RDRAM devices. The SCK signal operates at 1 MHz during configuration and at 100 MHz when commands are issued to switch RDRAM devices from Powerdown or Nap states.

3-8Compaq Deskpro EXS and Workstation 300 Personal Computers

Featuring the Intel Pentium 4 Processor

First Edition - December 2000