UM0851 datasheet(225/245 Pages) STMICROELECTRONICS

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UM0851

Power management section

Doc ID 16604 Rev 2

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10.2.3

CPU frequency framework

Clock scaling allows you to change the clock speed of the CPUs on the fly. Cpufreq provides

a modularized set of interfaces to manage the CPU frequency changes.

Figure 66.

CPU freq kernel architectural blocks

●

CPUfreq core

The CPUfreq core offers a standardized interface for the CPUfreq architecture drivers.

CPUfreq notifiers conform to the standard kernel notifier interface. The device drivers

have to register themselves into these notifier lists to be informed of the events.

●

CPUfreq driver:

The architecture driver for the CPUfreq changes the registers into the CPUfreq

framework, and does the actual work of frequency transition. The details about this are

covered in the next section Architecture driver.

●

CPUfreq Governors:

The CPUfreq infrastructure allows for frequency-changing policy governors, which can

change the CPU frequency based on different criteria, such as CPU usage. Here is a

list of the governors which you can select.

–

Performance governor:

keeps the CPU at the highest possible frequency within

a user-specified range.

–

Powersave governor:

keeps the CPU at the lowest possible frequency within a

user-specified range.

–

Userspace governor:

exports the available frequency information to the user

level (through the sysfs) and permits user-space control of the CPU frequency. All

user-space dynamic CPU frequency governors use this governor as their proxy.

Clock framework low level

clock management

SPEAr Arch driver

(/arch/arm/plat-spear/cpu_spear.c)

CPU FREQ module (with /proc and /sys interfaces)

Performance

User space

Power save

OnDemand

Power saved

CPU speed

Governor

SPEAr architecture

User space

Governor

Kernel space

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