Chapter 1: Product Overview 1-25
ACPI Sleep States (S0 – S5)
Under the G1 sleeping state ACPI defines levels of system sleep state support. The
7409 supports the following sleeping states:
S0: Normal Powered
‐
On state
S1 (Standby): The S1 sleeping state is a low wake latency sleeping state. In this
state, no system context is lost (CPU or chip set) and hardware maintains all
system contexts.
Note:
The 7409 does not support S1 state. Turning off the backlight and hard
drives provides the equivalent power savings (due to Intel’s processor C
‐
states
feature) at nearly zero latency.
S3 (Suspend to Ram): The S3 sleeping state is a low wake latency sleeping state.
This state is similar to the S1 sleeping state except that the CPU and system cache
context is lost (the OS is responsible for maintaining the caches and CPU context).
Control starts from the processor’s reset vector after the wake event. In NCR
systems, during S3, power is only provided to the on
‐
board USB ports.
Note:
When the terminal resumes from an S3 state, all the USB devices re
‐
enumerate. This causes speaker tones as if they were disconnected and then
reconnected. This does not present a problem and the USB devices will continue
to operate correctly.
Requirements for S3 support:
–
O/S must be built on a system with S3 enabled in the BIOS
–
Some peripherals may not be S3 capable, which can prevent the system from
entering S3 state.
–
Currently, it is not recommended to use S3 on systems that are configured
with a Celeron 575 CPU if Intel
®
Active Management Technology (AMT) is
enabled. System lock ups can occur in this configuration.
S4 (Suspend to Disk): The S4 state is the lowest power, longest wake latency
sleeping state supported by ACPI. In order to reduce power to a minimum, it is
assumed that the hardware platform has powered off all devices. Platform context
is maintained.
Requirements for S4 support:
–
O/S must be built on a system with S3 enabled in the BIOS
–
Some peripherals may not be S4 capable, which can prevent the system from
entering S4 state.
Reference the
ACPI Specification
for details.
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