Octagon 6000 Series, User Manual

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18-3
6000 Series user’s manual CPU power management
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System power management
At the system level, power management is very similar to the device
level management, with a few exceptions. Cooperative management is
supported, allowing an APM driver, such as POWER.EXE, to control the
actual power state transitions. This is done by identifying power man-
agement events and reporting them to the APM driver via a polling
mechanism. Power state transitions then occur at the request of the
APM driver.
The IDLE timer can be reset by numerous sources, including device
accesses and interrupts. Note that it is possible for the IDLE timer
configuration to be of shorter duration than the device timers. This
means that the system can be deemed IDLE even though some of the
devices are still active. When this occurs, the device power states are
set according to their configuration in CMOS.
Note that the APM interface prevents the system from entering
SUSPEND mode directly. These modes are entered, but that occurs
through the APM interface (INT15h) at the request of the APM driver.
SUSPEND mode is the lowest power state that the system can attain
while still powered. The system enters the SUSPEND state when the
RESUME switch is turned off. All controllable devices are powered
down and the CPU halts. In the SUSPEND state, an IRQ event includ-
ing a timer tick will cause the CPU to resume from halt. If the CPU
determines that the only cause of resume was the IRQ event from the
timer tick, then the CPU halts again. Otherwise, the CPU resumes
from the SUSPEND state. The devices which are powered ON when the
system RESUMEs are specified in CMOS, loaded from the .PMI file.
Devices which do not have associated access SMIs, must be powered up.
In addition, since the CPU was stopped, the system time must be up-
dated. If an APM driver is operating, it has the responsibility of updat-
ing the time when notified to do so. Otherwise, the firmware will up-
date the DOS compatible system time if configured to do so. For operat-
ing systems with DOS compatible system clocks, this function should be
disabled in CMOS. Since the clock does not run in SUSPEND mode and
the system is not restarted by IRQ0 to maintain the time of day, the
time must be reset when the system resumes. The BIOS can read the
actual time from the real time clock and restore the operating system’s
timer from that value. The time update can be enabled or disabled
using the SETUP program. In SETUP, the option initiating the
SUSPEND/RESUME with system activities, is available.