
MOTOROLA
Chapter 10. Power Management
10-1
Chapter 10
Power Management
The G2 core is the first processor core specifically designed for low-power operation. It
provides both automatic and program-controllable power reduction modes for progressive
reduction of power consumption. This chapter describes the hardware support provided by
the G2 core for power management.
10.1 Overview
The G2 core has explicit power management features that are described in this chapter.
Note that the design of the G2 core is fully static, allowing the internal processor core state
to be preserved when no internal clock is present.
The device drivers must be modified for power management as operating systems service
I/O requests by system calls to the device drivers. When a device driver is called to reduce
the power of a device, it needs to be able to check the power state of the device, save the
device configuration parameters, and put the device into a power-saving mode.
Furthermore, every time the device driver is called, it needs to check the power status of the
device and restore the device to the full-on state, if the device is in a power-saving mode.
10.2 Dynamic Power Management
Dynamic power management (DPM) automatically powers up and down the individual
execution units of the G2 core, based on the contents of the instruction stream. For example,
if no floating-point instructions are being executed, the floating-point unit is automatically
powered down. Power is not actually removed from the execution unit; instead, each
execution unit has an independent clock input, which is automatically controlled on a
clock-by-clock basis. Because CMOS circuits consume negligible power when they are not
switching, stopping the clock to an execution unit effectively eliminates its power
consumption. The operation of DPM is completely transparent to software or any external
hardware. Dynamic power management is enabled by setting HID0[DPM] on power-up
following a hard reset sequence (core_hreset).
F
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
n
.