Overview - Motorola MPC8240 User Manual

Chapter 14
Power Management
A key feature of the MPC8240 and its predecessor, the MPC603e microprocessor, is that
they are designed for low-power operation. The MPC8240 provides both automatic and
program-controllable power reduction modes for progressive reduction of power
consumption. This chapter describes the support features provided by the MPC8240 for
power management of both the processor core and the peripheral logic.

14.1 Overview

The MPC8240 has explicit power management features for both the processor core and the
peripheral logic, both of which are described in this chapter. Note that the design of the
MPC8240 is fully static, allowing the internal logic states to be preserved during power
management. The MPC8240 implementation offers the following enhancements to the
original MPC603e family:
• Lower-power design
• 2.5-volt core and 3.3-volt I/O
Because operating systems service I/O requests by system calls to the device drivers, the
device drivers must be modified for power management. 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.
14.2 Processor Core Power Management
The processor core has various types of power management features. Dynamic power
management occurs automatically (if enabled), depending on the activity of the execution
units. The programmable doze, nap, and sleep modes provide further power savings. The
power management features in the processor core are very similar to that in the MPC603e
device.
Chapter 14. Power Management 14-1