C-States - Kontron nanoETXexpress-SP User Manual

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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 Function
C0 Operating CPU fully turned on
C1 Halt State Stops CPU main internal clocks via software
C1E Enhanced Halt Similar to C1, additionally reduces CPU voltage
C2 Stop Grant Stops CPU internal and external clocks via hardware
C2E Extended Stop Grant Similar to C2, additionally reduces CPU voltage
C3 Deep Sleep Stops all CPU internal and external clocks
C3E Extended Stop Grant Similar to C3, additionally reduces CPU voltage
C4 Deeper Sleep Reduces CPU voltage
C4E Enhanced Deeper Sleep Reduces CPU voltage even more and turns off the memory cache
C6 Deep Power Down Reduces the CPU internal voltage to any value, including 0V
C7 Deep Power Down Similar to C6, additionally LLC (LastLevelCache) is switched off
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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