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10 Power Management Chapter 4
AMD Athlon™ XP Processor Model 8 Data Sheet 25175H—March 2003
Preliminary Information
The following sections provide an overview of the power
management states. For more details, refer to the
AMD Athlon™ System Bus Specification, order# 21902.
Note: In all power management states that the processor is
powered, the system must not stop the system clock
(SYSCLK/SYSCLK#) to the processor.
Working State The Working state is the state in which the processor is
executing instructions.
Halt State When the processor executes the HLT instruction, the processor
enters the Halt state and issues a Halt special cycle to the
AMD Athlon system bus. The processor only enters the low
power state dictated by the CLK_Ctl MSR if the system
controller (Northbridge) disconnects the AMD Athlon system
bus in response to the Halt special cycle.
If STPCLK# is asserted, the processor will exit the Halt state
and enter the Stop Grant state. The processor will initiate a
system bus connect, if it is disconnected, then issue a Stop
Grant special cycle. When STPCLK# is deasserted, the
processor will exit the Stop Grant state and re-enter the Halt
state. The processor will issue a Halt special cycle when
re-entering the Halt state.
The Halt state is exited when the processor detects the
assertion of INIT#, RESET#, SMI#, or an interrupt via the INTR
or NMI pins, or via a local APIC interrupt message. When the
Halt state is exited, the processor will initiate an AMD Athlon
system bus connect if it is disconnected.
Stop Grant States The processor enters the Stop Grant state upon recognition of
assertion of STPCLK# input. After entering the Stop Grant
state, the processor issues a Stop Grant special bus cycle on the
AMD Athlon system bus. The processor is not in a low-power
state at this time, because the AMD Athlon system bus is still
connected. After the Northbridge disconnects the AMD Athlon
system bus in response to the Stop Grant special bus cycle, the
processor enters a low-power state dictated by the CLK_Ctl
MSR. If the Northbridge needs to probe the processor during
the Stop Grant state while the system bus is disconnected, it
must first connect the system bus. Connecting the system bus