Intel CW8064701487007 Datasheet download pdf (Page 57)

Datasheet, Volume 1 57

Power Management

4.2.4 Core C-states

The following are general rules for all core C-states, unless specified otherwise:

• A core C-State is determined by the lowest numerical thread state (such as Thread

0 requests C1E while Thread 1 requests C3, resulting in a core C1E state). See

Table 4-7.

• A core transitions to C0 state when:

— An interrupt occurs

— There is an access to the monitored address if the state was entered using an

MWAIT instruction

• For core C1/C1E, core C3, and core C6/C7, an interrupt directed toward a single

thread wakes only that thread. However, since both threads are no longer at the

same core C-state, the core resolves to C0.

• A system reset re-initializes all processor cores

4.2.4.1 Core C0 State

The normal operating state of a core where code is being executed.

4.2.4.2 Core C1 / C1E State

C1/C1E is a low power state entered when all threads within a core execute a HLT or

MWAIT(C1/C1E) instruction.

A System Management Interrupt (SMI) handler returns execution to either Normal

state or the C1/C1E state. See the Intel

64 and IA-32 Architecture Software

Developer’s Manual, Volume 3A/3B: System Programmer’s Guide for more information.

While a core is in C1/C1E state, it processes bus snoops and snoops from other

threads. For more information on C1E, see “Package C1/C1E”.

4.2.4.3 Core C3 State

Individual threads of a core can enter the C3 state by initiating a P_LVL2 I/O read to

the P_BLK or an MWAIT(C3) instruction. A core in C3 state flushes the contents of its

L1 instruction cache, L1 data cache, and L2 cache to the shared L3 cache, while

maintaining its architectural state. All core clocks are stopped at this point. Because the

core’s caches are flushed, the processor does not wake any core that is in the C3 state

when either a snoop is detected or when another core accesses cacheable memory.

4.2.4.4 Core C6 State

Individual threads of a core can enter the C6 state by initiating a P_LVL3 I/O read or an

MWAIT(C6) instruction. Before entering core C6, the core will save its architectural

state to a dedicated SRAM. Once complete, a core will have its voltage reduced to zero

volts. During exit, the core is powered on and its architectural state is restored.

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Intel CW8064701487007 Datasheet Page 57