Dynamic power management for embedded system

Ø This dynamic power management refers to power management schemes implemented while programs are running.

Ø This architecture is based on the capabilities of current and next-generation processors and their application requirements.

REQUIREMENTS

Ø The overriding power management goal in portable system is to reduce system-wide energy consumption.

Ø Dynamic power management is only concerned with voltage and frequency.

Ø Dynamic power management architecture supports the ability of processors and external bus frequencies, in concerned with or even independent of the CPU frequency.

Ø The low-level implementation of the dynamic power management architecture (DPM) is resident in the kernel of the operating system.

Ø DPM is not a self-contained device driver.

Ø Complete power management strategy is communicated to DPM in to ways: as an predefined set of policies and as an application/policy-set specific manager that manages them.

Ø Policies specify the component and device-state transitions that ensure reliable operation in line with the power management strategy.

Ø DPM policy managers are executable programs that activate policies by name.

Ø Policy managers implement user defined and/or application-specific power management strategies. They can execute either as part of the kernel or in user space (or both) as required by the strategy.

POLICY ARCHITECTURE

OPERATING POINTS

ü Operating point may be described different parameters such as core voltage, CPU bus frequencies and states of peripheral devices.

ü Operating points for the IBM PowerPC 405LP specify a core voltage level, CPU and bus frequencies, memory timing parameters and other clocking related data.

Ø OPERATING STATES

ü In dynamic power management policy, operating state associated with an operating point specific to the requirements of that state.

ü Operating state was the observation that includes the system-wide energy savings, it can be done by reducing CPU and bus frequency and core voltage while the system is in ideal state.

DEVICE CONSTRAINT MANAGER

Ø Automatic selection of operating points as devices change states is a central feature of DPM.

Ø Embedded systems may not have a BIOS or machine abstraction layer to insulate the operating system from low-level device and power management.

Ø The most aggressive power management strategies will also require the system designer to carefully consider the influence of attached devices on the strategy.

Implementation and Effects Of task_specific Operating States

Ø task-specific operating points,implemented by assigning different task operating states to different tasks.

Ø The task state of a task is changed by the set_task_state () entry point, which may be exported to the user level as a system call.
Thus a system can be constructed where a single intelligent policy manager controlled the task states of critical programs for improved power/performance efficiency.