DVFS User Guide

README.md

@@ -24,6 +24,8 @@
 
 [GPIO操作实例](./debug/platform_driver_test)
 
+[DVFS User Guide](./debug/misc)
+
 ## 应用开发
 
 [LCD应用编程](./apps)

debug/misc/README.md

@@ -0,0 +1,44 @@
+# DVFS Usser Guide
+
+[参考文章DVFS User Guide](http://processors.wiki.ti.com/index.php/DVFS_User_Guide)
+
+## What is DVFS
+
+```
+Dynamic Voltage and Frequency scaling is a framework to change the frequency
+and/or operating voltage of a processor(s) based on system performance
+requirements at the given point of time
+```
+
+## CPUFreq consists two elements
+
+- The Governor - that makes decisions
+- The Driver - acts based on the decisions made by the governor
+
+## Usage
+
+To list all available governors
+
+	cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_governors
+
+To see current active governor
+
+	cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
+
+To switch to a different governor(e.g. to switch to 'userspace' governor)
+
+	echo -n "userspace" > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
+
+Show current frequency of a cpu
+
+	cat /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_cur_freq
+
+Show All available frequencies
+
+	cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies
+
+when the frequency is changed, system voltage is also changed to meet the new
+requirements as part of scaling: This is done in two ways
+
+- when new frequency is higher (moving to high power state/opp) Voltage is increased first then the frequency,
+- when new frequency is lower (moving to low power state/opp) Frequency is reduced first then the voltage.