Octagon PC-500, User Manual

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22-1
PC-500 user’s manual CPU power management
Chapter 22:
CPU power management
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Description
The power demands of a system can severely limit an application due to
thermal constraints or the raw power usage in a battery-operated
application. In order to maintain speed and efficiency, a software-
controlled, power management system must be tailored to the applica-
tion. Even if your application is operating within specified limits, a
power management system may improve the life and reliability of your
system by reducing thermal stress to the CPU.
The advance power management functions include:
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SUSPEND/RESUME operation via SMI input and software
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Slowing down the CPU by dividing the clock
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Contextual Save to Disk
Power management can be enabled in the PC-500 SETUP program and
is adjusted with the PMISETUP program. DOS-supplied advanced
power management (APM) programs, such as POWER.EXE are also
supported. See the PC-500 utility disk for a list of example programs
located in the \EXAMPLES directory. For more information on using
the SETUP utility, refer to the SETUP programs chapter. For more
information on using the PMISETUP utility, see the PMISETUP
section later in this chapter.
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Power management overview
Power management is implemented via the software management
interface (SMI) function, and provides multiple levels of management.
The firmware is also capable of cooperative power management with an
APM compatible driver or application, such as POWER.EXE. Coopera-
tive power management allows power aware applications to control the
power state of the system without depending on interrupts or device
access to indicate that the CPU is actively executing application code.
At the hardware level, the power management system cannot detect
CPU activity except by monitoring bus activity such as interrupts or
access to specific memory or I/O address ranges.
The hardware is capable of minimal levels of power management with-
out interacting with the firmware at all. Once configured by the firm-
ware, the DOZE timer and the CPU activity monitor (cool-down clocking
mechanism) can slow the system clock to reduce power consumption.
The DOZE timer monitors specific bus activity and reduces the system
clock after periods of inactivity. The CDC mechanism simply guaran-
tees that the CPU spends some specified portion of time at a reduced
clock speed, either due to DOZE mode of firmware controlled reduced
clock mode, or by forcing cool-down periods if neither of these occur.