AMD 8 manual AMD Athlon System Bus Specification, order#, SYSCLK/SYSCLK# to the processor

Preliminary Information

AMD Athlon™ XP Processor Model 8 Data Sheet 25175H— March 2003

	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

10 Power Management Chapter 4