C-States - Kontron COMe-cDC2 User Manual

4.15

C-States

New generation platforms include power saving features like SuperLFM, EIST (P-States) or C-States in O/S idle mode.
Activated C-States are able to dramatically decrease power consumption in idle mode by reducing the Core Voltage or
switching of parts of the CPU Core, the Core Clocks or the CPU Cache.
Following C-States are defined:
C-State Description
C0 Operating
C1 Halt State
C1E Enhanced Halt
C2 Stop Grant
C2E Extended Stop Grant
C3 Deep Sleep
C3E Extended Stop Grant
C4 Deeper Sleep
C4E Enhanced Deeper Sleep
C6 Deep Power Down
C7 Deep Power Down
C-States are usually enabled by default for low power consumption, but active C-States my influence performance
sensitive applications or real-time systems.
» Active C6-State may influence data transfer on external Serial Ports
» Active C7-State may cause lower CPU and Graphics performance
It's recommended to disable C-States / Enhanced C-States in BIOS Setup if any problems occur.
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Function
CPU fully turned on
Stops CPU main internal clocks via software
Similar to C1, additionally reduces CPU voltage
Stops CPU internal and external clocks via hardware
Similar to C2, additionally reduces CPU voltage
Stops all CPU internal and external clocks
Similar to C3, additionally reduces CPU voltage
Reduces CPU voltage
Reduces CPU voltage even more and turns off the memory cache
Reduces the CPU internal voltage to any value, including 0V
Similar to C6, additionally LLC (LastLevelCache) is switched off
COMe-cDC2 / Features and Interfaces