21264/EV68A Hardware Reference Manual
Initialization and Configuration 7–9

Energy Star Certificationand Sleep Mode Flow

Figure 7–2 Fault Reset Sequence of Operation
7.3 Energy Star Certi fication and Sleep Mode Flow
The 21264/EV68Ais Energy Star compliant. Energy Star is a program administeredby
the EnvironmentalProtection Agency to reduce energy consumption. For compliance,
a computerm ustautomatically enter a low power sleep mode using 30 watts or less
aftera specified period of inactivity. When the system is awakened,the user shall be
returnedautomatically to the same situation that existed priorto entering sleep mode.
During normaloperation, the 21264/EV68A encounters inactive periods and enters a
mode thatsaves the entire active processor state to memory.
The PALcodeis responsible for saving all necessary state to DRAM and flushing the
caches.
Thesleep mode sequence of operations is triggered by the PALcode twice performinga
HW_MTPR to the Ibox SLEEP IPR. The first write prevents the assertion of
ClkFwdRst_H fromfault-resetting the chip.
The PALcodethen informs the system, in an implementation-dependent way,that it
may assert ClkFwdRst_H.
On the second HW_MTPR to the SLEEP IPR, the PLL begins to ramp down and the
21264/EV68Acan then respond to the ClkFwdRst_H that was asserted by the system,
causingthe outgoing clocks from the 21264/EV68A to stop.
The PLL ramp-downsequence takes exactly the same amount of time as the ramp up
sequencedescribed in Section 7.1.3. The same internal duration counter is used and the
reset statemachine transitions through the DOWN1, DOWN2, and DOWN3 states
which have similarPLL divisor ratios and clock speeds to the RAMP2, RAMP1, and
WAIT_NOMINALstates.
state
SromOE_L
ClkFwdRst_H
internal ClkFwdRst
RUN WAIT_FAULT_RESET
internal clks aligned
external Clks
WAIT_ClkFwdRst0 WAIT_ClkFwdRst1
no min no min
bc
A
e
f
g
a
FM-06488B.AI4
RUN