Acpi Processor C-States - NCR RealPOS XR6 User Manual

Product Overview 1-13

ACPI Processor C-States

ACPI defines the power state of system processors while in the G0 working state as
being either active (executing) or sleeping (not executing). Processor power states are
designated C0, C1, C2, C3, ...Cn.
The C0 power state is an active power state where the CPU executes instructions. The C1
through Cn power states are processor sleeping states where the processor consumes
less power and dissipates less heat than leaving the processor in the C0 state.
While in a sleeping state, the processor does not execute any instructions. Each
processor sleeping state has a latency associated with entering and exiting that
corresponds to the power savings. In general, the longer the entry/exit latency, the
greater the power savings when in the state.
To conserve power, OSPM places the processor into one of its supported sleeping states
when idle. While in the C0 state, ACPI allows the performance of the processor to be
altered through a defined "throttling" process and through transitions into multiple
performance states (P-states).
Note:
The 7603 Atom D2550 Processor supports C0 and C1 states. Support of deeper
sleep states is not required due to its inherently low power consumption.