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+     CPU frequency and voltage scaling code in the Linux(TM) kernel
+
+
+                         L i n u x    C P U F r e q
+
+                             U S E R   G U I D E
+
+
+                    Dominik Brodowski  <linux@brodo.de>
+
+
+
+   Clock scaling allows you to change the clock speed of the CPUs on the
+    fly. This is a nice method to save battery power, because the lower
+            the clock speed, the less power the CPU consumes.
+
+
+Contents:
+---------
+1. Supported Architectures and Processors
+1.1 ARM
+1.2 x86
+1.3 sparc64
+1.4 ppc
+1.5 SuperH
+
+2. "Policy" / "Governor"?
+2.1 Policy
+2.2 Governor
+
+3. How to change the CPU cpufreq policy and/or speed
+3.1 Preferred interface: sysfs
+3.2 Deprecated interfaces
+
+
+
+1. Supported Architectures and Processors
+=========================================
+
+1.1 ARM
+-------
+
+The following ARM processors are supported by cpufreq:
+
+ARM Integrator
+ARM-SA1100
+ARM-SA1110
+
+
+1.2 x86
+-------
+
+The following processors for the x86 architecture are supported by cpufreq:
+
+AMD Elan - SC400, SC410
+AMD mobile K6-2+
+AMD mobile K6-3+
+AMD mobile Duron
+AMD mobile Athlon
+AMD Opteron
+AMD Athlon 64
+Cyrix Media GXm
+Intel mobile PIII and Intel mobile PIII-M on certain chipsets
+Intel Pentium 4, Intel Xeon
+Intel Pentium M (Centrino)
+National Semiconductors Geode GX
+Transmeta Crusoe
+Transmeta Efficeon
+VIA Cyrix 3 / C3
+various processors on some ACPI 2.0-compatible systems [*]
+
+[*] Only if "ACPI Processor Performance States" are available
+to the ACPI<->BIOS interface.
+
+
+1.3 sparc64
+-----------
+
+The following processors for the sparc64 architecture are supported by
+cpufreq:
+
+UltraSPARC-III
+
+
+1.4 ppc
+-------
+
+Several "PowerBook" and "iBook2" notebooks are supported.
+
+
+1.5 SuperH
+----------
+
+The following SuperH processors are supported by cpufreq:
+
+SH-3
+SH-4
+
+
+2. "Policy" / "Governor" ?
+==========================
+
+Some CPU frequency scaling-capable processor switch between various
+frequencies and operating voltages "on the fly" without any kernel or
+user involvement. This guarantees very fast switching to a frequency
+which is high enough to serve the user's needs, but low enough to save
+power.
+
+
+2.1 Policy
+----------
+
+On these systems, all you can do is select the lower and upper
+frequency limit as well as whether you want more aggressive
+power-saving or more instantly available processing power.
+
+
+2.2 Governor
+------------
+
+On all other cpufreq implementations, these boundaries still need to
+be set. Then, a "governor" must be selected. Such a "governor" decides
+what speed the processor shall run within the boundaries. One such
+"governor" is the "userspace" governor. This one allows the user - or
+a yet-to-implement userspace program - to decide what specific speed
+the processor shall run at.
+
+
+3. How to change the CPU cpufreq policy and/or speed
+====================================================
+
+3.1 Preferred Interface: sysfs
+------------------------------
+
+The preferred interface is located in the sysfs filesystem. If you
+mounted it at /sys, the cpufreq interface is located in a subdirectory
+"cpufreq" within the cpu-device directory
+(e.g. /sys/devices/system/cpu/cpu0/cpufreq/ for the first CPU).
+
+cpuinfo_min_freq :              this file shows the minimum operating
+                                frequency the processor can run at(in kHz) 
+cpuinfo_max_freq :              this file shows the maximum operating
+                                frequency the processor can run at(in kHz) 
+scaling_driver :                this file shows what cpufreq driver is
+                                used to set the frequency on this CPU
+
+scaling_available_governors :   this file shows the CPUfreq governors
+                                available in this kernel. You can see the
+                                currently activated governor in
+
+scaling_governor,               and by "echoing" the name of another
+                                governor you can change it. Please note
+                                that some governors won't load - they only
+                                work on some specific architectures or
+                                processors.
+scaling_min_freq and 
+scaling_max_freq                show the current "policy limits" (in
+                                kHz). By echoing new values into these
+                                files, you can change these limits.
+
+
+If you have selected the "userspace" governor which allows you to
+set the CPU operating frequency to a specific value, you can read out
+the current frequency in
+
+scaling_setspeed.               By "echoing" a new frequency into this
+                                you can change the speed of the CPU,
+                                but only within the limits of
+                                scaling_min_freq and scaling_max_freq.
+                                
+
+3.2 Deprecated Interfaces
+-------------------------
+
+Depending on your kernel configuration, you might find the following 
+cpufreq-related files:
+/proc/cpufreq
+/proc/sys/cpu/*/speed
+/proc/sys/cpu/*/speed-min
+/proc/sys/cpu/*/speed-max
+
+These are files for deprecated interfaces to cpufreq, which offer far
+less functionality. Because of this, these interfaces aren't described
+here.
+